Enhanced hydrogen evolution by nanostructures CuO composites

Enhanced hydrogen evolution by nanostructures CuO composites | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhanced hydrogen evolution by nanostructures CuO composites Bharat Kumar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7626843/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Herein, I report nano size effect on electrocatalytic hydrogen evolution reaction (HER) by using nano-micron (n-µ) composites of CuO. These n-µ CuO composites were synthesized by mixing copper oxalate nanorods and CuO in different (20 to 80 weight percentage) ratios followed by heating at 350 °C in air. As the amount of copper oxalate increases in the in the mixture of nano-micron composites, there is a decrease in the particle size (50–20 nm) of the composites. The pure nano and micron-sized CuO particles was found to be the size of ~ 15 nm and ~ 110 nm respectively. On the electrochemical HER study the highest (272 mA/cm 2 mg) and lowest (3.8 mA/cm 2 mg) current density (hydrogen evolution) was observed for pure nano and micron-sized particles respectively at -1.3 V potential for Ag/AgCl working electrode (-0.293 V vs RHE) on electroactive surface area. In case of n-µ composites, it is found that as the amount of nano sized particles increases there is increase in current density due to increase in surface area and interconnectivity of the nanoparticles. The CuO nanoparticles are very stable over 500 cycles. The present study of nano–micron composites show the combined effect of nanoscale advantages (high activity) with microscale advantages (conductivity and mechanical stability) for different potential applications. Composites electrocatalysts HER electroactive surface area nano-sized Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Hydrogen 1 , 2 is known as future generation fuel due to the increasing energy demand and depletion of fossil fuels. Environment problems can also be overcome by using the hydrogen as clean fuel (by product is H 2 O) because of their higher energy and low pollution content. Hydrogen fuel has various potential applications in the energy as well as in other sector such as engine fuel, power generation, fuel cell and battery devices 3 , 4 . Hence, the efficient production of hydrogen using cheap and present renewable resources is a key factor for the development of future energy storage technologies. The major challenge for scientists is to develop a low cost-based technology to address this issue. Hydrogen can be produced through the splitting of water either by solar hydrogen generation 5 or electrochemical reaction 6 , 7 or by photochemical 8 , 9 or by hydrolysis of ammonia borane 10 . The main problems in the hydrogen production are the inefficiency of available catalysts. Pt-group metals are well known for hydrogen evolution reaction (HER) but they are in less quantity in earth crust and very expensive, hence developments of cost-effective, efficient and easily available catalysts are highly desirable. Among various 3D transition metals oxides and their derivatives, cupric oxide (CuO), a p-type semiconductor is an important material with a narrow band gap ( E g ) of 1.4 eV 11 . Due to the dual magnetic – semiconducting properties 12 and high solar absorbance, low thermal emittance, good electrical property and high carrier concentration, it has been widely relevant for number of interesting applications. It forms the basis of several high temperature superconductors (YBCO) 13 and giant magnetoresistance materials 14 . Due to the large surface to volume ratio, CuO nanostructures have size effects on physical and chemical properties compared to their bulk counterparts 15 . It has various potential applications as electrode in rechargeable lithium ion batteries 16 , 17 due to high capacity, eco-friendly nature and safe disposal. It is also used in gas sensors 18 , bio sensors 19 nanofluids 20 in heat-transfer applications, photodetectors 2 1 , photovoltaic 22 , supercapacitors 23 , energetic materials 24 , catalysis 25 , solar cell 26 and magnetic storage media 27 . But, to the best of our knowledge, HER studies and nano-sized effect have not been investigated using CuO as an electrocatalysts. Due to importance of CuO nanostructured materials, there are several reports on the synthesis with different morphologies such as nanoparticles 28 , nanowires 29 , nanorods 30 , nanoribbons 31 and nanoflowers 32 from different routes such as hydrothermal 33 , thermal reduction 34 , solvothermal 35 , modified rivers micellar 36 , sol-gel 37 and sonochemical 38 . Earlier our own group 36 has synthesized CuO nanoparticles and studied for their magnetic properties. There is report recent report on for HER studies using Cu 39 , Cu 2 O 40 , Cu-Co 41 , Fe-Co 42 Cu/Cu 2 O 43, 44 , graphene/CuO hybrid 45 materials and CuO immobilized stainless-steel electrode 46 , however no report using pure CuO nanostructures as an electrocatalysts. In this paper I had discussed the effect of nano-sized particles on hydrogen evolution reaction and compared with micron-sized particles. I synthesized n-µ composites of CuO by mixing of CuO and copper oxalate nanorods by varying weight percent (20 to 80%) of copper oxalate (Table S1 ) followed by heating at 350 °C for 6 h in air atmospheres. Pure nano and micron sized CuO were also synthesized by heating of copper oxalate and CuO under similar condition respectively. The copper oxalate nanorods were obtained using a microemulsion method 36 , 39 . These materials were fully characterized using powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and BET surface area analyzer. The hydrogen evolution reaction (HER) of these materials was investigated which show significantly high catalytic activity compared to earlier Cu based nanostructured materials. Synthesis and characterization The following commercial reagents, cetyltrimethylammonium bromide (CTAB) (Spectrochem, AR, 99%), n-butanol (Qualigens, 99.5%), isooctane (Spectrochem, 98%), copper nitrate (CDH, 98%), ammonium oxalate (CDH, 99%), CuO (Aldrich, 99.99%), ethanol (Merck), KOH (Fisher Scientific), methanol (Fisher Scientific) and chloroform (Fisher Scientific) have been used for the synthesis. Copper oxalate nanorods were synthesized by the reverse micellar route 36 , 39 . Nano-micron composites of CuO were synthesized by mixing copper oxalate nanorods and CuO in weight ratio of 20 to 80% (varied the weight of micron sized CuO and copper oxalate) followed by heating at 350 °C for 6 h in air. At this temperature nanorods of copper oxalate were decomposed to yield nanocrystalline CuO. Pure micron sized CuO was synthesized by heating micron size CuO at 350 °C for 6 h in air atmosphere whereas pure nano sized CuO was synthesized by heating of copper oxalate nanorods under the similar condition as above. The weight fraction of micron sized particles of CuO and copper oxalate nanorods for the entire series of CuO are given in Table S1 . Powder X-ray diffraction studies (PXRD) were carried out using Ni filtered Cu-Kα radiation. Normal scans were recorded with a step size of 0.02° and step time of 1 s. The K α2 reflections were removed to obtain accurate lattice constants. The crystallite size of the particles were determined from x-ray line broadening studies using Scherrer’s formula (t = 0.9λ/ B cosθ) where t is crystallite size, λ is the wavelength (for CuKα, λ = 1.5418 Å) and B = √(B M 2 – B S 2 ) (B M is the full width at half maximum for a particular reflection of the sample and B S is that of standard (with crystallite size of around 2 µm). A quartz standard was chosen such that at least one reflection of the sample and the standard have similar 2θ values. Field emission scanning electron microscopy (FESEM) of the entire series of CuO were carried out on FEI quanta 3D FEG – FESEM by coating the powder samples with silver. Transmission Electron Microscope (TEM) studies were carried out using a Tecnai G 2 20 electron microscope operated at 200 KV. TEM specimens were prepared by dispersing the n-µ composites of CuO in ethanol by ultrasonic treatment, dropping onto a porous carbon film supported on a copper grid, and then drying in air. Nitrogen adsorption–desorption isotherms were recorded at liquid nitrogen temperature (77 K) using a Nova 2000e (Quantachrome Corp.) equipment and the specific area was determined by the Brunauer–Emmett–Teller (BET) method. The compounds were degassed at 150 ºC for 4 h prior to the surface area measurements. Density of each composite of CuO was measured by using Micromeritics AccuPyc II 1340 gas pycnometer by applying 19.5 psi pressure of helium gas. Diffuse-reflectance spectra (DR) spectra were recorded on Shimadzu UV-2450 spectrophotometer where the baseline was fixed using a barium sulfate reference. Cyclic voltammetry (CV) was carried out with a computer controlled electrochemical workstation (Autolab PGSTAT 302N). Hydrogen evolution reactions were studied by using Ag/AgCl as reference electrode while Pt was used as counter electrode. A Pt disk electrode with a geometric surface area of 0.03 cm² served as the working electrode. The working electrodes were polished using (0.05 µm) alumina paste, ultrasonicated in distilled water and then in ethanol for HER studies. 1 mg of electrocatalysts were sonicated in 20 µL of isopropanol and then 10 µL of Nafion was added. This paste was placed on the working electrode and dried for half an hour. All the three electrodes were placed in a freshly prepared 0.5 M KOH (potassium hydroxide solution). For each experiment freshly prepared KOH solution was used. Cyclic voltammetry was carried out at a scan rate of 0.025 V/s in the potential range of -1.3 to 0 V in HER studies. The electroactive surface areas of the catalyst on the working electrode were measured by CV in 0.5 M KOH. Results and discussion In this study, I determine the nano-sized effect (size and interconnectivity of the nanoparticles) on the electrocatalytic process for hydrogen evolution using ambient stable CuO. Pure micron and nano-sized particles along with their nano-micron composites were synthesized for comparative study. Nano-micron composites of CuO as well as pure nano-sized CuO were synthesized using copper oxalate nanorods obtained by reverse micelle route. All the details about copper oxalate nanorods are given in our previous paper 39 . Figure 1 shows the powder X-ray diffraction patterns of pure nano and micron sized CuO as well as n-µ composites of CuO with different weight ratio. All these compounds crystallize in monoclinic (C2/c) crystal system and all their reflection patterns were indexed on basis of this crystal system. The crystallite size of the particles was calculated from x-ray line broadening using Scherrer’s formula. These calculated crystallite sizes are given in Table 1. The highest and lowest crystallite size was found to be 87 and 16 nm for pure micron & pure nano size CuO respectively. The crystallite sized of nano-micron composites of CuO are in between the pure nano and micron sized particles. As the weight percentage of nano sized particles increases, there is decrease in the average crystallite size. The crystallite size of 20% and 80% nano-micron composites is found to be 56 and 29 nm respectively. Figure S1 shows the field emission scanning electron micrograph of pure micron and nano sized copper oxide (CuO). Pure micron-sized CuO show large agglomerated particles whereas nano-sized CuO form corn type (rod shape) morphology with assemblies of spherical particles. The pure nanoparticles of CuO are very uniform in nature. In 20% nano-micron composite it was observed (Figure S2 a) that the nano sized particles are embedded in between the micron sized CuO to form dense structures (less voids). The nano-sized particles fill the void created between the micron-sized particles. This is the reason for the enhancement of the density (discussed later) in the nano-micron composites. In case of 40% nano-micron composites of CuO (Figure S2 b), more nano-sized particles are observed on the surface of micron-sized CuO which leads to decrease in the density (further confirmed by density measurement) because nanoparticles have lesser density as compared to micron-sized particles of the same compounds. In 50% nano-micron composites (Figure S2 c) it was observed that both the nano and micron-sized CuO particles were uniformly fused to each other and form cage-like morphology. Further increase of nanoparticles in the nano-micron composites leads to formation of agglomerated particles (Figure S2 d) which are spherical in nature. In case of 80% nano-micron composites, particles start assembling to form rod-like structure (morphology) which is clearly observed in pure nano-sized CuO particles where corn type morphology was observed. The FESEM microstructures patterns of these nano-micron composites also follow the variation of density of these materials which discussed latter. Transmission electron microscopy was also carried out to calculate the average particle size of all nano-micron composites of CuO as well as pure nano and micron-sized particles of CuO. Figure 2 shows the transmission electron micrograph (TEM) of pure micron and nano sized CuO. Pure micron-sized particles are large in particles size which are agglomerated whereas pure-nano sized CuO particles are uniform and spherical in shape which assemble to form aligned rod-like (corn type) morphology. The particles size of pure micron and nano CuO was found to be ~ 160 & ~ 15 nm respectively. The high-resolution TEM micrograph (Fig. 3 b) of the pure-nano sized CuO particles shows the presence of (111) lattice fringes which confirms the single crystalline nature of the nanoparticles. The interplanar distance (d-spacing) for (111) plane is calculated by HETEM and found to be 0.2387 nm. The above d-spacing values (obtained from TEM) are compared from the d-spacing value obtained from PXRD (d CuO111 = 0.23212 nm). Both the d-spacing values (TEM and PXRD) correlated to each other (Fig. 3 b). Figure 4 shows the TEM micrograph of nano – micron composites of CuO. As the amount of amount of copper oxalate increase in nano-micron composites there is decrease in average particle size due to more percentage of nano-sized CuO as compare to micron-sized CuO. The average particle size of all the nano-micron composites is given in Table 1. In 20% nano-micron composite we observed that nano-sized CuO particles are embedded with the micron-sized CuO particles. In case of 50% nano-micron composites it is clearly observed that micron and nano-sized particles and fused to each other and uniformly distributed in nano-micron CuO structure (Fig. 4 c). 60% (Fig. 4 d) onward the nano sized spherical particles start assembled and aligning to rod morphology which is clearly seen in 80% nano-micron composites and pure nano-sized CuO. Theoretical density of CuO was found to be 6.53 g/cm 3 . The density of pure micron and nano-sized CuO were found to be 6.3 and 5.43 g/cm 3 respectively. As we increase the nano-sized CuO by 20%, there is increase in density of nano-micron composites (6.43 g/cm 3 ) this suggests that the addition of nanoparticles fills the void space available between two-micron sized particles in the composites which may result in the increase in density of the composite. Further increase in the amount of nano-sized CuO leads to decrease in the density due to a greater number of nano sized CuO particles on the surface of micron-sized particles (discussed in FESEM microstructural analysis). The density of pure nano and micron-sized CuO particles as well nano-micron composites of CuO are given in Table 1. Figure S3 shows the diffuse reflectance spectra of the CuO composites materials. It was observed that pure micron sized and 20–60% nano-micron had very slight change in the band gap and it was found ~ 1.42 eV. The band gap of 80% nano-micron composites was found to be 1.45 eV and for pure-nano sized CuO it was found to be 1.49 eV. The optical properties (band gap) of nanomaterials are size and morphology dependent 46 , 47 . For several cases, it is observed that a change in size and morphology can alter the band gap. The detailed analysis of N 2 adsorption-desorption measurement has been carried out to find surface area of pure nano and micron-sized particles as well nano-micron composites. It was found that as the amount of copper oxalate increases there is increase in surface area of the nano-micron composites due to increase in the number of nano-sized particles in the nano-micron composites. The Fig. 5 show N 2 adsorption-desorption measurement for pure micron and nano size and it was found to be the highest and lowest surface area 9 and 63 m 2 /g (Figure S5) respectively. This measurement is further given in details with average pore size and total pore volume (Figure S6 and Figure S7). The surface area of nano-micron composites is in between the pure micron and nano sized CuO and given in Table 1. I have investigated the electrochemical properties (hydrogen evolution reaction) of the entire series of CuO nano-micron composites as well as pure nano and micron sized CuO (electrocatalysts) using cyclic voltammetry on platinum (Pt) disc as working electrode. A platinum (Pt) disc electrode was used because it exhibits superior efficiency and kinetics for reactions such as HER, ORR, and HOR due to its fast electron transfer and optimal hydrogen adsorption energy (ΔG_H* ≈ 0 eV). Its smooth, crystalline surface ensures reproducible electrochemical behavior, unlike the amorphous glassy carbon electrode (GCE), which is prone to surface variation. Therefore, the Pt disc was used as the working electrode for its reliable performance. These electrocatalysts were used for hydrogen evolution reaction (HER) by applying a negative potential from − 1.3 to 0 V (Ag/AgCl as reference electrode) in 0.5 M KOH solution at the scan rate of 0.025 Vs − 1 . All the parameters were kept constant for the electrochemical measurements. The equations given below explain the hydrogen generation mechanism. Figure 6 shows the cyclic voltammograms of CuO materials for HER activity. The reduction (cathodic) and oxidation (anodic) peaks are observed in the cyclic voltammogram in the entire CuO. The observed reduction peak at -0.842 V is due to Cu ++ to Cu 0 and oxidation peak at -0.364 V is due to Cu 0 to Cu ++ respectively. There is a slight variation in these peaks due to nano-sized effect because as the particle size reduces peak separation between cathodic and anodic peak increased. From Fig. 6 it is observed that as weight % of nano-sized CuO increases, there is an increase in current during the hydrogen evolution reaction. As the weight percentage of nano-sized CuO increases, more exposed catalytic sites become available for proton (H⁺) adsorption and subsequent reduction, thereby enhancing the hydrogen evolution reaction (HER) current density. The higher nanoparticle content increases the electrochemically active surface area (ECSA), allowing more electrons to participate in the Volmer–Heyrovsky or Volmer–Tafel steps. With increased loading, nano-CuO particles form interconnected networks that improve charge transport, reduce electron path length, and minimize charge-transfer resistance. Moreover, nano-CuO contains abundant surface defects, edges, and oxygen vacancies that act as active centers for water dissociation and hydrogen adsorption, lowering the activation energy for the Volmer step and accelerating HER kinetics. The higher nanoparticle fraction also produces a rough, porous morphology, improving electrolyte diffusion and gas desorption while maintaining a stable reaction interface. At higher nano size CuO loadings, a percolation network forms, creating continuous pathways for electron and ion transport, enhancing conductivity, catalyst stability, and overall, HER activity. The highest (18 mA) and lowest (0.1 mA) currents are observed for pure nano and pure micron-sized particles respectively at -1.3 V potential for Ag/AgCl working electrode. The Ag/AgCl potential can be converted with comparison to Reversible Hygrogen Electrode (RHE) by following given formulae: The RHE potentials was found to be − 0.293 V. The detail calculation is given in supporting information. From the above data it is clearly observed that there is strong nano-sized effect on hydrogen evolution reaction. The current generation for nano-micron composites is in between those observed for the pure nano and pure micron-sized particles. Current was found to be highest for 80% and lowest for 20% nano-micron composites of CuO. The onset potential for the hydrogen evolution reaction (HER) was observed at − 0.28 V vs. Ag/AgCl for pure nano-sized CuO, which is significantly lower than that reported for other Cu-based nanostructured materials (refs. 39–41, 43, 44), indicating superior catalytic activity. Furthermore, the overpotential required to achieve a current density of 10 mA cm⁻² (corresponding to the benchmark value for approximately 10% solar-to-fuel conversion efficiency) was found to be − 0.301 V vs. Ag/AgCl for pure nano-sized CuO, confirming its high electrocatalytic efficiency toward hydrogen generation. Q H is calculated by extrapolating the curve obtained from the cyclic voltammetry. The Q ref for Cu materials is 420 µC/cm 2 48 . The electroactive surface area of the various composites is given in Table 2. It is highest for pure nano sized CuO and lowest for pure micron sized CuO particles. As the weight % of nano-sized CuO increases in the nano-micron composites, there is an increase in electroactive surface area. By applying the above electroactive surface area, the current density (Fig. 7 ) was calculated for pure nano (272 mA/cm 2 mg) and micron sized (3.8 mA/cm 2 mg) CuO as well as for the nano-micron composites of CuO. The highest current density (pure nano-sized CuO) at geometric surface area of the electrode as found to be 596 mA/cm 2 mg. In nano-micron composites, the current density increases with the weight % of nano-sized CuO particles. All the current density values (Table 2) of nano-micron composites are in between pure nano and micron-sized CuO. There are reports by our group on Cu based 39 – 41 , 43 , 44 and other nanostructures 42 materials. Recently Muralikrishna et al studied and reported pH dependent electrocatalysis using graphene/Cu ++ hybrid 45 materials and observed 46 mA/cm 2 current density. Islam et al 46 also recently reported for CuO Immobilized Stainless-Steel Electrode Prepared by the SILAR Method where onset potential was low 0.154 V but their catalyst produces only 0.5 mA/cm 2 current density (less than 10 mA cm⁻² corresponding to the benchmark value for approximately 10% solar-to-fuel conversion efficiency) at − 0.35 V potential. There are also some recent reports on HER by other groups 49 – 55 . Compared to the above reported values it was observed that the CuO nanostructured produced much higher current. The current density is very stable in nature over the 500th cycle (Figure S7) due to the stability of CuO nanoparticles in ambient condition for long time. Stability is also confirmed by the monophasic nature of CuO nanoparticles shown by the X-ray diffraction pattern (Fig. 8 and Figure S8) after the hydrogen evolution reaction. The slight noise in PXRD is due to the low amount of sample on glass sample holder. The particles remained spherical in nature as they were before electrocatalysis, having average diameters of 15–20 nm (Fig. 8 ) which is same as earlier. The alignment and interconnectivity of the nanoparticles still remain after the electrocatalysis which support that no further surface oxidation is possible and materials and very stable at ambient condition. This type of ideas shows the different aspect such as surface area, charge transport, structure stability, catalyst accessibility, scalability and handling for new catalyst where some properties are better for nano size and micron size for industrial applications. Conclusions Nano-micron composites of CuO were synthesized in air by mixing the micron-sized CuO and copper oxalate heated at 350 °C (resulting in mixture of micron and nano-sized CuO). We investigated the hydrogen evolution reaction by using these materials as electrocatalysts. It was observed that pure nano sized particles of CuO shows highest current density (272 mA/cm 2 ) indicative of more production of hydrogen in this chosen system as compared to pure micron sized particles and nano-micron composites due to high surface area and alignment of the nanoparticles. The electrocatalyst is highly stable in ambient condition and retain their catalytic efficiency over 500 cycles. From this study we can clearly state that there is strong nano-sized effect on hydrogen evolution. This study may be expanded to obtaining other electrocatalysts with increased activity. This study also shows the effect of combination of nano–micron and opens the door for technology. Declarations Acknowledgments BK thanks ANRF for providing support through the grant no SUR/2022/004717. The author also thanks Prof Ashok K Ganguli and IIT Delhi India for reaction and characterization facility. Author contributions: Bharat Kumar: Concept, synthesis modification, final draft writing and final submission. Funding: Funding is not applicable Clinical trial: Clinical trial is not applicable in the manuscript. Consent to Publish declaration: Not applicable Ethics and Consent to Participate declarations: Not applicable Competing interests: The authors declare no competing interests . Data availability: The authors declare that the data supporting the findings of this study are available within the paper file. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request. References Turner JA. Science. 2004;305:972. Dresselhaus MS, Thomas IL. Nature. 2001;414:332. Lewis NS, Nocera DG. Proc. Natl. Acad. Sci , 2005, 43, 15729. Armaroli N, Balzani V. Angew Chem Int Ed. 2007;46:52. Hensel J, Wang G, Li Y, Zhang JZ. Nano Lett. 2010;10:478. Doyle RL, Godwin IG, Brandon MP, Lyons MEG. Phys Chem Chem Phys. 2013;15:13737. Kong D, Cha JJ, Wang H, Lee HR, Cui Y. Energ Environ Sci. 2013;6:3553. Zou Z, Ye J, Sayama K, Arakawa H. Nature. 2001;414:625. Bard AJ, Fox MA. Acc Chem Res. 1995;28:141. Yamada Y, Miyahigashi T, Kotani H, Ohkubo K, Fukuzumi S. Energ Environ Sci. 2012;5:5356. Heinemann M, Eifert B, Heiliger C. Phys Rev B. 2013;87:115111. Reitz JB, Solomon EI. J Am Chem Soc. 1998;120:11467. He Z, Lin C, Cheng W, Okazawa A, Kojima N, Yamaura J, Ueda Y. J Am Chem Soc. 2011;133:1298. Zeng Z, Greenblatt M, Subramanian MA, Croft M. Phys Rev Lett. 1999;82:3164. Wang H, Xu JZ, Zhu JJ, Chen HY. J Cryst Growth. 2002;244:88. Taberna PL, Mitra S, Poizot P, Simon P, Tarascon JM. Nat Mater. 2006;5:567. Hu Y, Huang X, Wang K, Liu J, Jiang J, Ding R, Ji X, Li X. J Solid State Chem. 2010;183:662. Zhang J, Liu J, Peng Q, Wang X, Li Y. Chem Mater. 2006;18:867. Reitz E, Jia W, Gentile M, Wang Y, Lei Y. Electroanalysis. 2008;20:2482. Loa CH, Tsunga TT, Chen LC. J Cryst Grow. 2005;277:636. Rahman MM, Jamal A, Khan SB, Faisal M. ACS Appl Mater Interfaces. 2011;3:1346. Bao Q, Li CM, Liao L, Yang H, Wang W, Ke C, Song Q, Bao H, Yu T, Loh KP, Guo J. Nanotechnology. 2009;20:065203. Shaikh JS, Pawar RC, Devan RS, Ma YR, Salvi PP, Kolekar SS, Patil PS. Electrochim Acta. 2011;56:2127. Leventis N, Chandrasekaran N, Sadekar AG, Leventis CS, Lu H. J Am Chem Soc. 2009;131:4576. Kauffman DR, Ohodnicki PR, Kail BW, Matranga C. J. Phys. Chem. Lett. , 2011, 2, 2038. Anandan S, Wen X, Yang S. Mater Chem Phys. 2005;93:35. Junod A, Eckert D, Triscone G, Muller J, Reichardt W. J Phys Condens Matter. 1989;1:8021. Rout L, Sen TK, Punniyamurthy T. Angew Chem Int Ed. 2007;46:5583. Jiang X, Herricks T, Xia Y. Nano Lett. 2002;2:1333. Yao WT, Yu SH, Zhou Y, Jiang J, Wu QS, Zhang L, Jiang J. J Phys Chem B. 2005;109:14011–6. Ke FS, Huang L, Wei GZ, Xue LJ, Li JT, Zhang B, Chen SR, Fan XY, Sun SG. Electrochim Acta. 2009;54:5825. Duan Y, Liu X, Han L, Asahina S, Xu D, Cao Y, Yao Y, Che S. J Am Chem Soc. 2014;136:719. Outokesh M, Hosseinpour M, Ahmadi SJ, Mousavand T, Sadjadi S, Soltanian W. Ind Eng Chem Res. 2011;50:3540. Chen L, Li L, Li G. J Alloys Comp. 2008;464:532. Ghosh M, Rao CNR. Chem Phys Lett. 2004;393:493. Ahmad T, Chopra R, Ramanujachary KV, Lofland SE, Ganguli AK. Solid State Sci. 2005;7:891. Wang ZM, Lin YS. J Catal. 1998;174:43. Anandan S, Lee GJ, Wu JJ. Ultrason Sonochem. 2012;19:682. Kumar B, Saha S, Basu M, Ganguli AK. J Mater Chem A. 2013;1:4728. Kumar B, Saha S, Ganguly A, Ganguli AK. RSC Adv. 2014;4:12043. Ahmed J, Ganguly A, Saha S, Gupta G, Trinh P, Mugweru AM, Lofland SE, Ramanujachary KV, Ganguli AK. J Phys Chem C. 2011;115:14526. Ahmed J, Kumar B, Mugweru AM, Trinh P, Ramanujachary KV, Lofland SE, Govind AK, Ganguli. J Phys Chem C. 2010;114:18779. Kumar B, Saha S, Ojha K. K Ganguli Mater Res Bull. 2015;64:283. Kumar B, Rao GK, Saha S, Ganguli AK. ChemPhysChem. 2016;17:155. Muralikrishna S, Ravishankar TN, Ramakrishnappa T, Nagaraju DH, Pai RK. Environmen Prog Sustain Energy, 10.1002/ep.12238 Islam MN, Ahmed J, Faisal M, Algethami JS, Aoki K, Nagao Y, Harraz FA, Hasnat MA. ChemistrySelect. 2023;8. 10.1002/slct.202301077 . Kuo CH, Chen CH, Huang MH. Adv Funct Mater. 2007;17:3773. Deori K, Deka S. CrystEngComm. 2013;15:8465. Green CL, Kucernak A. J Phys Chem B. 2002;106:1036. Majumdar S, Sharma IG, Bidaye AC, Suri AK. Thermochimica acta. 2008;473:45. Crespo MAD, Meneses ER, Palma VM, Huerta AMT, Rosales HD. Int J Hydrogen Ener. 2009;34:1664. Muler CI, Rauscher T, Schmidt A, Schubert T, Weibgarber T, Kieback B, Rontzsch L. Int J Hydrogen Energy. 2014;39:8926–37. Zeng M, Li Y. J Mater Chem A. 2015;3:14942–62. Lu X, Ng YH, Zhao C. Chemsuschem. 2014;7:82. Cherevko S, Kulyk N, Chung CH. Langmuir. 2012;28:3306. Suryanto BHR, Lu X, Zhao C. J Mater Chem A. 2013;1:12726. Tables Table 1: Crystallite size, particles size, density and surface area nano-micron CuO composites S. No. Compounds Crystallite Size (nm) Particles Size (nm) Density (g/cm 3 ) Surface area (m 2 /g) 1 Pure Micron 64 160 6.30 9 2 20% 47 50- 20 6.43 15 3 40% 44 15- 35 6.23 16 4 50% 42 18- 35 6.15 17 5 60% 41 12 - 30 6.03 24 6 80% 29 15- 25 5.84 54 7 Pure nano 18 ~ 15 5.43 62.5 Table 2: Electroactive surface area, current and current density of nano-micron composites of CuO vs Ag/AgCl reference electrode S. No. Compounds ESA (cm 2 /mg) Current (mA) Current density (mA/cm 2 ) ESA -1.3 V potential Current density (mA/cm 2 ) GEO -1.3 V potential 1 Pure Micron 0.026 0.1 3.8 3.2 2 20% 0.028 0.9 32 27 3 40% 0.044 3.6 81 128 4 50% 0.050 5.0 100 163 5 60% 0.052 7.5 145 208 6 80% 0.056 11.1 198 372 7 Pure nano 0.067 18.2 272 596 Additional Declarations No competing interests reported. Supplementary Files ReviseSupportinginformation.docx TableofContent.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 28 Dec, 2025 Reviewers agreed at journal 16 Dec, 2025 Editor assigned by journal 29 Nov, 2025 Reviews received at journal 03 Nov, 2025 Reviewers agreed at journal 02 Nov, 2025 Reviewers agreed at journal 31 Oct, 2025 Reviewers invited by journal 31 Oct, 2025 Submission checks completed at journal 28 Oct, 2025 First submitted to journal 28 Oct, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7626843","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":538144493,"identity":"e356b114-1fe6-41c9-8ab4-a19f27c45500","order_by":0,"name":"Bharat Kumar","email":"data:image/png;base64,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","orcid":"","institution":"M V College Buxar (Constituent unit of Veer Kunwar Singh University Ara)","correspondingAuthor":true,"prefix":"","firstName":"Bharat","middleName":"","lastName":"Kumar","suffix":""}],"badges":[],"createdAt":"2025-09-16 06:53:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7626843/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7626843/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":95007181,"identity":"4c4073c0-9d6b-4172-a23b-7341e188a410","added_by":"auto","created_at":"2025-11-03 09:39:06","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6678635,"visible":true,"origin":"","legend":"","description":"","filename":"RevisedManuscript.docx","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/b8be93d44aacb01f36a089ee.docx"},{"id":95007165,"identity":"2075b17e-02b5-4cec-993f-23192e24baa9","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"json","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":3530,"visible":true,"origin":"","legend":"","description":"","filename":"b3d14719e1ce48568a86ca495fb83285.json","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/fe6530780dced13c8969c8de.json"},{"id":95007148,"identity":"60c98880-e4c6-4543-8eb1-2dd1786dfb49","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":10352638,"visible":true,"origin":"","legend":"","description":"","filename":"ReviseSupportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/806fb7553ee8377c1b36519b.docx"},{"id":95007166,"identity":"b13ebcd1-a38e-4e7b-aa66-2aa1ec3eaf46","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"xml","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":103484,"visible":true,"origin":"","legend":"","description":"","filename":"b3d14719e1ce48568a86ca495fb832851enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/940210b12a378e46c445d21d.xml"},{"id":95007136,"identity":"6b8f87b6-432d-4b0c-89ae-899e63f8f5dd","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"eps","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":105058,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage2.eps","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/6c6c00780a87c56a429a7fba.eps"},{"id":95007169,"identity":"0eb0a0b0-995b-466a-a3f7-69d20600f242","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"eps","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":58084,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage3.eps","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/49c253931dd5fc6a8304c369.eps"},{"id":95007133,"identity":"384143be-1c7b-479b-b62a-1a9933e886fa","added_by":"auto","created_at":"2025-11-03 09:39:04","extension":"eps","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":214,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage4.eps","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/ca81ac2a32e646c54d043ce9.eps"},{"id":95221202,"identity":"a6b45f36-7221-40ba-b61b-52228bd2522c","added_by":"auto","created_at":"2025-11-05 16:18:35","extension":"eps","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":63380,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage5.eps","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/fedc80079df6795f9c296509.eps"},{"id":95007132,"identity":"93bf186f-8e36-4cb5-b27f-1965fb16043b","added_by":"auto","created_at":"2025-11-03 09:39:04","extension":"jpeg","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":554558,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/a8c7b019e6e37cf0985812ac.jpeg"},{"id":95007180,"identity":"5fc969d0-6379-4395-86ef-eccd8b5a7c1e","added_by":"auto","created_at":"2025-11-03 09:39:06","extension":"jpeg","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":817993,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/39bd9d5a57c306a85bec3519.jpeg"},{"id":95007164,"identity":"03bad476-dc96-49a9-a8e5-af5caa7799a4","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"jpeg","order_by":11,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":924698,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/0f61852e5f9ed3c9434c021a.jpeg"},{"id":95221399,"identity":"b5ba94b7-bb96-44eb-9cd8-6348cdc5f8e9","added_by":"auto","created_at":"2025-11-05 16:18:55","extension":"jpeg","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1139965,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/af892a19088a195c1e53da1f.jpeg"},{"id":95220847,"identity":"57b3c8f2-6a08-450d-a915-05f75db0f7c6","added_by":"auto","created_at":"2025-11-05 16:16:02","extension":"jpeg","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1167200,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/b2d5bd013c3335860ebbc25f.jpeg"},{"id":95221075,"identity":"d21b8e90-1179-40a0-81ae-57b0fc8f2e96","added_by":"auto","created_at":"2025-11-05 16:18:11","extension":"jpeg","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1825110,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/37c804cced2b2e584b0b0701.jpeg"},{"id":95007176,"identity":"d7f83f94-08b1-4cf4-a488-47f29185ad99","added_by":"auto","created_at":"2025-11-03 09:39:06","extension":"emf","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":36872,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage6.emf","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/67572e4c7e0bbc481e36e70d.emf"},{"id":95007138,"identity":"2953127a-bccc-4903-af9d-a88dab863e5b","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"jpeg","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":649594,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/213e331d6194ecab3ce91a69.jpeg"},{"id":95007142,"identity":"01afb048-6f23-4675-ba9c-9c7778f9d3c9","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"jpeg","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":239294,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/a274d0984ad878b267f37088.jpeg"},{"id":95221155,"identity":"8cb8e5ff-fabe-4c0f-92cc-ee5f9175c394","added_by":"auto","created_at":"2025-11-05 16:18:30","extension":"jpeg","order_by":18,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":814812,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/fbfa391d77ef130ea3d77cc5.jpeg"},{"id":95221369,"identity":"d069c8b1-a9a7-40ad-a926-ae7e5b38168f","added_by":"auto","created_at":"2025-11-05 16:18:51","extension":"jpeg","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":9700,"visible":true,"origin":"","legend":"","description":"","filename":"groupimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/8a9760d784f4a3cdcb35f940.jpeg"},{"id":95221064,"identity":"e472701c-6262-4242-8799-01246b77564d","added_by":"auto","created_at":"2025-11-05 16:18:09","extension":"jpeg","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":3146,"visible":true,"origin":"","legend":"","description":"","filename":"groupimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/dbc9fd43cc23f3d705a5397a.jpeg"},{"id":95221125,"identity":"0a9c0028-4ff2-48a0-b441-4f17bc2cfce8","added_by":"auto","created_at":"2025-11-05 16:18:24","extension":"png","order_by":21,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":90782,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/8fa51f1339d282d4966593b2.png"},{"id":95007145,"identity":"6ecdc824-a5ea-477c-b69e-493ebcd5d6d2","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"png","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":192735,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/80d862c1f32d7fe89108b7a1.png"},{"id":95007150,"identity":"dda8822d-1243-4807-abd6-2e6a6855fe50","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"png","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":161428,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/9ef3fdfa93b147fd7bb6c467.png"},{"id":95221186,"identity":"340cc0ea-ceb0-49b8-97a0-beec9ed20622","added_by":"auto","created_at":"2025-11-05 16:18:34","extension":"png","order_by":24,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":418909,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/46f5ff853eeaa371132ef3ec.png"},{"id":95007179,"identity":"78715d11-5d03-442e-951d-68ec306147c8","added_by":"auto","created_at":"2025-11-03 09:39:06","extension":"png","order_by":25,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":270958,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/dc862a06f52a618757cb57e4.png"},{"id":95007140,"identity":"b626b402-66e2-4d60-953a-57fe57ffec41","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"png","order_by":26,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":623449,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/c1b8986ab78b28b4ca9341d9.png"},{"id":95007183,"identity":"13138b76-a50c-482b-9f39-92dee7737539","added_by":"auto","created_at":"2025-11-03 09:39:06","extension":"png","order_by":27,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":73126,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/fbac798bbed8ad6f4e6fa55b.png"},{"id":95007172,"identity":"12978834-7f0a-4bc5-bca6-c2296399be0c","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"png","order_by":28,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":100199,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/3b784f3a2a9cf3c4353ac8a1.png"},{"id":95221319,"identity":"82c798ef-3126-4102-8dc0-85987e56c659","added_by":"auto","created_at":"2025-11-05 16:18:49","extension":"png","order_by":29,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":35548,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/cee551a83e822a96b04a706c.png"},{"id":95220958,"identity":"194c9aa0-03c8-4670-84b8-10fe1d2e4957","added_by":"auto","created_at":"2025-11-05 16:17:24","extension":"png","order_by":30,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":226491,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/761a6de48519ab7f53ffd512.png"},{"id":95007184,"identity":"ce2f55df-68ca-487d-8dc4-c6ab7f457197","added_by":"auto","created_at":"2025-11-03 09:39:06","extension":"png","order_by":31,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6130,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinegroupimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/d87dcaf8b1f7b7bfb3b249b7.png"},{"id":95007131,"identity":"a1859cbe-3cd0-448c-baa2-3728b65d2072","added_by":"auto","created_at":"2025-11-03 09:39:04","extension":"png","order_by":32,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":2122,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinegroupimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/cfe37ae80d76f93eaa52cf65.png"},{"id":95221397,"identity":"3b7b6f08-825a-49fa-bb62-96e7d1c41736","added_by":"auto","created_at":"2025-11-05 16:18:55","extension":"xml","order_by":33,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":100435,"visible":true,"origin":"","legend":"","description":"","filename":"b3d14719e1ce48568a86ca495fb832851structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/aed7e3eee96a2573b9b31c46.xml"},{"id":95221190,"identity":"51e55df0-a9b5-4804-a3b2-03be108eb5aa","added_by":"auto","created_at":"2025-11-05 16:18:35","extension":"html","order_by":34,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":110014,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/674254f0955fd3241b353175.html"},{"id":95221070,"identity":"b7a29b3e-873f-48a7-9a22-42fdc73d2d36","added_by":"auto","created_at":"2025-11-05 16:18:11","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":89349,"visible":true,"origin":"","legend":"\u003cp\u003ePowder X-ray diffraction pattern of CuO.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/4c083ad3bb36bd1b0c97e227.jpg"},{"id":95007128,"identity":"8f5e14b2-41a8-4efa-8537-f59ca3146bc7","added_by":"auto","created_at":"2025-11-03 09:39:04","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":158347,"visible":true,"origin":"","legend":"\u003cp\u003eTEM micrograph of (a) pure micron (b) pure nano-sized CuO\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/bd6c3bc05decfb955db6f7d3.jpg"},{"id":95007171,"identity":"e9a4268e-5da9-43e2-830a-c334f9d956d3","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":156484,"visible":true,"origin":"","legend":"\u003cp\u003e(a) TEM (b) HRTEM micrograph of pure nano-sized CuO particles\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/74f2f5c0d0d46cf9f1d048a7.jpg"},{"id":95220889,"identity":"3eb44c87-5ef0-43f9-9d2d-6d69224cbebf","added_by":"auto","created_at":"2025-11-05 16:16:46","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":209418,"visible":true,"origin":"","legend":"\u003cp\u003eTEM micrograph of nano-micron composites of CuO (a) 20 % (b) 40 % (c) 50 % (d) 80 %\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/c487972e70b27f1cbd643c25.jpg"},{"id":95007149,"identity":"f8d8a82c-5864-4f76-b85a-306639d0b46a","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":77120,"visible":true,"origin":"","legend":"\u003cp\u003eBET analysis of N2 adsorption-desorption isotherm of pure micron and pure nano CuO particles.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/b9cf82efda1da47ec9e8006b.jpg"},{"id":95007129,"identity":"b017160a-30b8-4393-bab6-bfa44a3c5a99","added_by":"auto","created_at":"2025-11-03 09:39:04","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":53212,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammogram of CuO nanocomposites.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/2814bfc01aebbe65797a69d1.jpg"},{"id":95221100,"identity":"13d5f53c-36fc-498b-a68e-53777d74ee2b","added_by":"auto","created_at":"2025-11-05 16:18:16","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":87686,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammogram of CuO nanocomposites (current density on ESA and geometric surface area of electrode)\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/bb47fb538af8c9c7ca141b64.jpg"},{"id":95221370,"identity":"d309ef07-9d5f-4129-99f8-37971695ce4a","added_by":"auto","created_at":"2025-11-05 16:18:51","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":81702,"visible":true,"origin":"","legend":"\u003cp\u003ePXRD and TEM micrograph of nano-sized CuO particles after HER.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/2b3c34eda7d048eaacb3e9a0.jpg"},{"id":95229755,"identity":"875d9eca-720d-41b2-ab48-c5f12d4e862c","added_by":"auto","created_at":"2025-11-05 16:36:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1609729,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/3072a841-a54f-47ec-96a5-9305e27713eb.pdf"},{"id":95007152,"identity":"48e95026-77b3-48fd-8f8b-85ad8cd100f8","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":10352638,"visible":true,"origin":"","legend":"","description":"","filename":"ReviseSupportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/b7b2f1e5f427b85b3583ef65.docx"},{"id":95007167,"identity":"5f04837c-7f97-4af7-a994-b381273a3f31","added_by":"auto","created_at":"2025-11-03 09:39:05","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1060120,"visible":true,"origin":"","legend":"","description":"","filename":"TableofContent.docx","url":"https://assets-eu.researchsquare.com/files/rs-7626843/v1/4f0045d9133a745955d29dda.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Enhanced hydrogen evolution by nanostructures CuO composites","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHydrogen\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e is known as future generation fuel due to the increasing energy demand and depletion of fossil fuels. Environment problems can also be overcome by using the hydrogen as clean fuel (by product is H\u003csub\u003e2\u003c/sub\u003eO) because of their higher energy and low pollution content. Hydrogen fuel has various potential applications in the energy as well as in other sector such as engine fuel, power generation, fuel cell and battery devices\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Hence, the efficient production of hydrogen using cheap and present renewable resources is a key factor for the development of future energy storage technologies. The major challenge for scientists is to develop a low cost-based technology to address this issue. Hydrogen can be produced through the splitting of water either by solar hydrogen generation\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003eor electrochemical reaction\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e or by photochemical\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e or by hydrolysis of ammonia borane\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. The main problems in the hydrogen production are the inefficiency of available catalysts. Pt-group metals are well known for hydrogen evolution reaction (HER) but they are in less quantity in earth crust and very expensive, hence developments of cost-effective, efficient and easily available catalysts are highly desirable.\u003c/p\u003e\u003cp\u003eAmong various 3D transition metals oxides and their derivatives, cupric oxide (CuO), a p-type semiconductor is an important material with a narrow band gap (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e) of 1.4 eV\u003csup\u003e11\u003c/sup\u003e. Due to the dual magnetic \u0026ndash; semiconducting properties\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e and high solar absorbance, low thermal emittance, good electrical property and high carrier concentration, it has been widely relevant for number of interesting applications. It forms the basis of several high temperature superconductors (YBCO) \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e and giant magnetoresistance materials\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Due to the large surface to volume ratio, CuO nanostructures have size effects on physical and chemical properties compared to their bulk counterparts\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. It has various potential applications as electrode in rechargeable lithium ion batteries\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e due to high capacity, eco-friendly nature and safe disposal. It is also used in gas sensors\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, bio sensors\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e nanofluids\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e in heat-transfer applications, photodetectors\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, photovoltaic\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, supercapacitors\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, energetic materials\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, catalysis\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, solar cell\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e and magnetic storage media\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. But, to the best of our knowledge, HER studies and nano-sized effect have not been investigated using CuO as an electrocatalysts. Due to importance of CuO nanostructured materials, there are several reports on the synthesis with different morphologies such as nanoparticles\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, nanowires\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, nanorods\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e, nanoribbons\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e and nanoflowers\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e from different routes such as hydrothermal\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e, thermal reduction \u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e, solvothermal\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e, modified rivers micellar\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, sol-gel\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e and sonochemical\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. Earlier our own group\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e has synthesized CuO nanoparticles and studied for their magnetic properties. There is report recent report on for HER studies using Cu\u003csup\u003e39\u003c/sup\u003e, Cu\u003csub\u003e2\u003c/sub\u003eO\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e, Cu-Co\u003csup\u003e41\u003c/sup\u003e, Fe-Co\u003csup\u003e42\u003c/sup\u003e Cu/Cu\u003csub\u003e2\u003c/sub\u003eO\u003csup\u003e43, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e, graphene/CuO hybrid\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e materials and CuO immobilized stainless-steel electrode\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e, however no report using pure CuO nanostructures as an electrocatalysts.\u003c/p\u003e\u003cp\u003eIn this paper I had discussed the effect of nano-sized particles on hydrogen evolution reaction and compared with micron-sized particles. I synthesized n-\u0026micro; composites of CuO by mixing of CuO and copper oxalate nanorods by varying weight percent (20 to 80%) of copper oxalate (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) followed by heating at 350 \u0026deg;C for 6 h in air atmospheres. Pure nano and micron sized CuO were also synthesized by heating of copper oxalate and CuO under similar condition respectively. The copper oxalate nanorods were obtained using a microemulsion method\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. These materials were fully characterized using powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and BET surface area analyzer. The \u003cb\u003ehydrogen evolution reaction (HER)\u003c/b\u003e of these materials was investigated which show significantly high catalytic activity compared to earlier Cu based nanostructured materials.\u003c/p\u003e"},{"header":"Synthesis and characterization","content":"\u003cp\u003eThe following commercial reagents, cetyltrimethylammonium bromide (CTAB) (Spectrochem, AR, 99%), n-butanol (Qualigens, 99.5%), isooctane (Spectrochem, 98%), copper nitrate (CDH, 98%), ammonium oxalate (CDH, 99%), CuO (Aldrich, 99.99%), ethanol (Merck), KOH (Fisher Scientific), methanol (Fisher Scientific) and chloroform (Fisher Scientific) have been used for the synthesis.\u003c/p\u003e\u003cp\u003eCopper oxalate nanorods were synthesized by the reverse micellar route\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. Nano-micron composites of CuO were synthesized by mixing copper oxalate nanorods and CuO in weight ratio of 20 to 80% (varied the weight of micron sized CuO and copper oxalate) followed by heating at 350 \u0026deg;C for 6 h in air. At this temperature nanorods of copper oxalate were decomposed to yield nanocrystalline CuO. Pure micron sized CuO was synthesized by heating micron size CuO at 350 \u0026deg;C for 6 h in air atmosphere whereas pure nano sized CuO was synthesized by heating of copper oxalate nanorods under the similar condition as above. The weight fraction of micron sized particles of CuO and copper oxalate nanorods for the entire series of CuO are given in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003ePowder X-ray diffraction studies (PXRD) were carried out using Ni filtered Cu-Kα radiation. Normal scans were recorded with a step size of 0.02\u0026deg; and step time of 1 s. The K\u003csub\u003eα2\u003c/sub\u003e reflections were removed to obtain accurate lattice constants. The crystallite size of the particles were determined from x-ray line broadening studies using Scherrer\u0026rsquo;s formula (t\u0026thinsp;=\u0026thinsp;0.9λ/ B cosθ) where t is crystallite size, λ is the wavelength (for CuKα, λ\u0026thinsp;=\u0026thinsp;1.5418 \u0026Aring;) and B = \u0026radic;(B\u003csub\u003eM\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e \u0026ndash; B\u003csub\u003eS\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e) (B\u003csub\u003eM\u003c/sub\u003e is the full width at half maximum for a particular reflection of the sample and B\u003csub\u003eS\u003c/sub\u003e is that of standard (with crystallite size of around 2 \u0026micro;m). A quartz standard was chosen such that at least one reflection of the sample and the standard have similar 2θ values. Field emission scanning electron microscopy (FESEM) of the entire series of CuO were carried out on FEI quanta 3D FEG \u0026ndash; FESEM by coating the powder samples with silver. Transmission Electron Microscope (TEM) studies were carried out using a Tecnai G\u003csup\u003e2\u003c/sup\u003e 20 electron microscope operated at 200 KV. TEM specimens were prepared by dispersing the n-\u0026micro; composites of CuO in ethanol by ultrasonic treatment, dropping onto a porous carbon film supported on a copper grid, and then drying in air. Nitrogen adsorption\u0026ndash;desorption isotherms were recorded at liquid nitrogen temperature (77 K) using a Nova 2000e (Quantachrome Corp.) equipment and the specific area was determined by the Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) method. The compounds were degassed at 150 \u0026ordm;C for 4 h prior to the surface area measurements. Density of each composite of CuO was measured by using Micromeritics AccuPyc II 1340 gas pycnometer by applying 19.5 psi pressure of helium gas. Diffuse-reflectance spectra (DR) spectra were recorded on Shimadzu UV-2450 spectrophotometer where the baseline was fixed using a barium sulfate reference.\u003c/p\u003e\u003cp\u003eCyclic voltammetry (CV) was carried out with a computer controlled electrochemical workstation (Autolab PGSTAT 302N). Hydrogen evolution reactions were studied by using Ag/AgCl as reference electrode while Pt was used as counter electrode. A Pt disk electrode with a geometric surface area of 0.03 cm\u0026sup2; served as the working electrode. The working electrodes were polished using (0.05 \u0026micro;m) alumina paste, ultrasonicated in distilled water and then in ethanol for HER studies. 1 mg of electrocatalysts were sonicated in 20 \u0026micro;L of isopropanol and then 10 \u0026micro;L of Nafion was added. This paste was placed on the working electrode and dried for half an hour. All the three electrodes were placed in a freshly prepared 0.5 M KOH (potassium hydroxide solution). For each experiment freshly prepared KOH solution was used. Cyclic voltammetry was carried out at a scan rate of 0.025 V/s in the potential range of -1.3 to 0 V in HER studies. The electroactive surface areas of the catalyst on the working electrode were measured by CV in 0.5 M KOH.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eIn this study, I determine the nano-sized effect (size and interconnectivity of the nanoparticles) on the electrocatalytic process for hydrogen evolution using ambient stable CuO. Pure micron and nano-sized particles along with their nano-micron composites were synthesized for comparative study. Nano-micron composites of CuO as well as pure nano-sized CuO were synthesized using copper oxalate nanorods obtained by reverse micelle route. All the details about copper oxalate nanorods are given in our previous paper\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the powder X-ray diffraction patterns of pure nano and micron sized CuO as well as n-\u0026micro; composites of CuO with different weight ratio. All these compounds crystallize in monoclinic (C2/c) crystal system and all their reflection patterns were indexed on basis of this crystal system. The crystallite size of the particles was calculated from x-ray line broadening using Scherrer\u0026rsquo;s formula. These calculated crystallite sizes are given in Table\u0026nbsp;1. The highest and lowest crystallite size was found to be 87 and 16 nm for pure micron \u0026amp; pure nano size CuO respectively. The crystallite sized of nano-micron composites of CuO are in between the pure nano and micron sized particles. As the weight percentage of nano sized particles increases, there is decrease in the average crystallite size. The crystallite size of 20% and 80% nano-micron composites is found to be 56 and 29 nm respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e shows the field emission scanning electron micrograph of pure micron and nano sized copper oxide (CuO). Pure micron-sized CuO show large agglomerated particles whereas nano-sized CuO form corn type (rod shape) morphology with assemblies of spherical particles. The pure nanoparticles of CuO are very uniform in nature. In 20% nano-micron composite it was observed (Figure S2 a) that the nano sized particles are embedded in between the micron sized CuO to form dense structures (less voids). The nano-sized particles fill the void created between the micron-sized particles. This is the reason for the enhancement of the density (discussed later) in the nano-micron composites. In case of 40% nano-micron composites of CuO (Figure S2 b), more nano-sized particles are observed on the surface of micron-sized CuO which leads to decrease in the density (further confirmed by density measurement) because nanoparticles have lesser density as compared to micron-sized particles of the same compounds. In 50% nano-micron composites (Figure S2 c) it was observed that both the nano and micron-sized CuO particles were uniformly fused to each other and form cage-like morphology. Further increase of nanoparticles in the nano-micron composites leads to formation of agglomerated particles (Figure S2 d) which are spherical in nature. In case of 80% nano-micron composites, particles start assembling to form rod-like structure (morphology) which is clearly observed in pure nano-sized CuO particles where corn type morphology was observed. The FESEM microstructures patterns of these nano-micron composites also follow the variation of density of these materials which discussed latter.\u003c/p\u003e\u003cp\u003eTransmission electron microscopy was also carried out to calculate the average particle size of all nano-micron composites of CuO as well as pure nano and micron-sized particles of CuO. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the transmission electron micrograph (TEM) of pure micron and nano sized CuO. Pure micron-sized particles are large in particles size which are agglomerated whereas pure-nano sized CuO particles are uniform and spherical in shape which assemble to form aligned rod-like (corn type) morphology. The particles size of pure micron and nano CuO was found to be ~\u0026thinsp;160 \u0026amp; ~ 15 nm respectively. The high-resolution TEM micrograph (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) of the pure-nano sized CuO particles shows the presence of (111) lattice fringes which confirms the single crystalline nature of the nanoparticles. The interplanar distance (d-spacing) for (111) plane is calculated by HETEM and found to be 0.2387 nm. The above d-spacing values (obtained from TEM) are compared from the d-spacing value obtained from PXRD (d\u003csub\u003eCuO111\u003c/sub\u003e = 0.23212 nm). Both the d-spacing values (TEM and PXRD) correlated to each other (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the TEM micrograph of nano \u0026ndash; micron composites of CuO. As the amount of amount of copper oxalate increase in nano-micron composites there is decrease in average particle size due to more percentage of nano-sized CuO as compare to micron-sized CuO. The average particle size of all the nano-micron composites is given in Table\u0026nbsp;1. In 20% nano-micron composite we observed that nano-sized CuO particles are embedded with the micron-sized CuO particles. In case of 50% nano-micron composites it is clearly observed that micron and nano-sized particles and fused to each other and uniformly distributed in nano-micron CuO structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). 60% (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) onward the nano sized spherical particles start assembled and aligning to rod morphology which is clearly seen in 80% nano-micron composites and pure nano-sized CuO.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTheoretical density of CuO was found to be 6.53 g/cm\u003csup\u003e3\u003c/sup\u003e. The density of pure micron and nano-sized CuO were found to be 6.3 and 5.43 g/cm\u003csup\u003e3\u003c/sup\u003e respectively. As we increase the nano-sized CuO by 20%, there is increase in density of nano-micron composites (6.43 g/cm\u003csup\u003e3\u003c/sup\u003e) this suggests that the addition of nanoparticles fills the void space available between two-micron sized particles in the composites which may result in the increase in density of the composite. Further increase in the amount of nano-sized CuO leads to decrease in the density due to a greater number of nano sized CuO particles on the surface of micron-sized particles (discussed in FESEM microstructural analysis). The density of pure nano and micron-sized CuO particles as well nano-micron composites of CuO are given in Table\u0026nbsp;1.\u003c/p\u003e\u003cp\u003eFigure S3 shows the diffuse reflectance spectra of the CuO composites materials. It was observed that pure micron sized and 20\u0026ndash;60% nano-micron had very slight change in the band gap and it was found\u0026thinsp;~\u0026thinsp;1.42 eV. The band gap of 80% nano-micron composites was found to be 1.45 eV and for pure-nano sized CuO it was found to be 1.49 eV. The optical properties (band gap) of nanomaterials are size and morphology dependent\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. For several cases, it is observed that a change in size and morphology can alter the band gap.\u003c/p\u003e\u003cp\u003eThe detailed analysis of N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption measurement has been carried out to find surface area of pure nano and micron-sized particles as well nano-micron composites. It was found that as the amount of copper oxalate increases there is increase in surface area of the nano-micron composites due to increase in the number of nano-sized particles in the nano-micron composites. The Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e show N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption measurement for pure micron and nano size and it was found to be the highest and lowest surface area 9 and 63 m\u003csup\u003e2\u003c/sup\u003e/g (Figure S5) respectively. This measurement is further given in details with average pore size and total pore volume (Figure S6 and Figure S7). The surface area of nano-micron composites is in between the pure micron and nano sized CuO and given in Table\u0026nbsp;1.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eI have investigated the electrochemical properties (hydrogen evolution reaction) of the entire series of CuO nano-micron composites as well as pure nano and micron sized CuO (electrocatalysts) using cyclic voltammetry on platinum (Pt) disc as working electrode. A platinum (Pt) disc electrode was used because it exhibits superior efficiency and kinetics for reactions such as HER, ORR, and HOR due to its fast electron transfer and optimal hydrogen adsorption energy (ΔG_H* \u0026asymp; 0 eV). Its smooth, crystalline surface ensures reproducible electrochemical behavior, unlike the amorphous glassy carbon electrode (GCE), which is prone to surface variation. Therefore, the Pt disc was used as the working electrode for its reliable performance. These electrocatalysts were used for hydrogen evolution reaction (HER) by applying a negative potential from \u0026minus;\u0026thinsp;1.3 to 0 V (Ag/AgCl as reference electrode) in 0.5 M KOH solution at the scan rate of 0.025 Vs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. All the parameters were kept constant for the electrochemical measurements. The equations given below explain the hydrogen generation mechanism.\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAxgAAAD3CAYAAACeh/KuAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAAFiUAABYlAUlSJPAAADN2SURBVHhe7d1PbCNlmvjxJ79Tn2ArngNCDAJXOKAFZZZxundRMlKPBGU1CPVIDXZYCfUKRGMP2oWFTiA9iMN2Q9uAmEVs/iDQIrTbdqBHoJWcSboPjNbeWYYOO7ZmViBNV0AtxHIoYxCH5fb+Drhq631dTpykkjjJ9yOV5Hrft8rlqvJb9VS99daAUkoJAAAAAMTg/5kJAAAAALBRBBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAgL71+OOPS71eN5MBAH2MAGMNxWJRBgYGOobBwUFpNptmcc3c3FzHdP5Qq9XM4uhBrVbblvXnf89qg4hIOp3uSA8PxWLRnHVParWaZLNZGRwc1OY3MjIip06dkpWVFXOSvrNd2wp723vvvSd/8Rd/IT/72c8INHqwWt211n+x0Wh0TBOuy7odD/0hnU6LiHSkm8Nay7Eb9WN912w2pVgsysjIiLb+BwcHJZvNSrlcNicRWeW8xx/283bGOiisyfM8lclklIhoQ6lUMotqbNtWqVRKm6ZSqZjFsA7ValWJiKpWq2bWligUCtr2syxL1et1rYzrusq2ba1cLpfTyvTK8zzlOE4wn0KhoFzXVUopVa/Xtf1wamrKnLyvbPe2wt50ww03aP+to0ePqt///vdmMRjMuquXeimXy3Ucs8x6Jup4mEqllOd5Wjn//x8e1jpm7mb9Vt+VSiVlWVawffxzD8/ztDzbtjuOaX45tjM2gwCjR9VqNfLP1k21WlW5XE47WRTiuU3biUo8vP0cxzGzlYo4mG9k+TzP0w7uhULBLKKUUto+tdYJw07aiW2FvccMMPyBQGNtjuMEJ5L+YJ4g+vz6p5e6zDyp7KWukj1+/Oun+q5UKgXr3LKsyG0e3oZRF87MMmxnrNeA+v4ECmuo1Wry29/+Vt555x1ZXl4O0qvVqoyOjmplRUTy+bzcfffd8sorr8jS0lKQzurenFqtJmNjY13X+1YYaDeHEhFxHEcWFxe1fGnfUp6cnAzGN7J86XQ62Fcsy5KvvvrKLCLSbsbwox/9KBgvFAoyMTGhlekHO7Gt9qt6vS7vvfeembwn/OM//qN8/fXXZnLg6NGj8uyzz2r/CXwvnU7Lj3/8Y3nuueeCtG71Rblclj/84Q9y9dVXr1mX+f9tX7d5hus02ePHv36p78xtMzs7KydOnNDK+LLZrMzPz4u0jzl/+tOfJJFIBPnmvNjOWBcz4kC0arWqCoWCdmVAulxB9q8EKSL72O3EVaLw9tuqOxjmlaKo/Sos3CSr2xWqnbYT22q/+ud//mdt/9mPA3c0OjmOo1zX1daTbdtmMaVCZXupy8z6iivb/VPfmevcb2IbxTyfMbcj2xmbwUPe65TNZsWyrGB8Zmam42Hvixcvyr333qulAat59dVXtfHh4WFt3DQ0NBR8brVacvHiRS0fukajIdlsVntIMfwAYj6f1x5ODK9f7A4ffPCB/OY3v5HvvvvOzNrXksmkZDKZYNx1XVlYWNDK+J1GJJNJLR27S6PR0O4kWJa16ja97rrrtPHXXntNG4/D0NCQVrfm83mzCPYomkj1yG8iNTExIadOndJuOZu3IEdGRmR+fl6SySS3DjfBXHdr6dZ8abPiaiI1NDQkruuKiEipVJJsNhuZJ12mDzP3wampKTlz5oxWZjv1y7aK0mg05PDhw9JqtaRer8t1110nhw4dEtd111zPu8V+biJ1zTXXyOTkpDzyyCNy4MABM3tfS6fTsri4KAsLC3LXXXcF6ZlMRutB6NSpU3LrrbdKNpvtqS7biaYz4XrYrD+3m/m71rJd9V25XJbx8fFgfK3vbTab8oMf/EBL8zwvaCa1E9sZe4h5SwPR/CZSqt1rUPh2YPiWs9/Tj49bhxtnrru1hm7NlzbL/J5eBvM2udnLlFlmtbwoZjOGrfrtveqXbWXyPC94yDX8v5yamlKySnMR9I9uD3lfc8016uWXX1b/+7//a06CtvD/zKyDwk1nwv8Ds26JqovMpjO9Dpvlz2eneynq1/rO3Ha9fK+5rOHtvVPbGXsDTaQ2YLVbzm+//bYcPXo0VBobtbi4KO2ezoKhWq2KtK+qmXmrXamJi+M4Hd+rlJJCoWAWDZTLZXn44YdFKaXdpTh37pxWbjfrx20lInL+/HlptVoiInLbbbcF6VdffbVI+7/baDSCdPS/a665Rl5++WX59NNP5bHHHuOuRY9Onjypjb/xxhsiIrKwsCB33nmnlrdehUKh4z+ulBLHccyie0K/1ndbbb9tZ2wOAcYGPfDAA9r4W2+9JSIi8/PzO3rrFv3n4MGDwW3lZDIpuVxORERuuOGGoIxt28HnXnzzzTfa+E9/+lNtHN97//33g8+Tk5NBO+BwE5Bvv/02+Iz+RWCxOceOHdPGZ2ZmRNrHrm69DGF3uf76682kVZnPj4pIR3M4YKMIMDboyJEj2knh/Py8FItF7c4GIKs8OHn77bcHn80riP/93/+tjZs++ugjbfyWW27RxvG9cNv9bnefOKD2NwKLeCQSieDihrQ7hygWi+K67pqdSmyVdDq96gPA5XK5a55EvLU8qsx+cvDgQW38ww8/1MZNH3/8sTaeSqW0cWAzCDA2wbzlfPbsWbnvvvu0NMB04cIFyeVy2ont/fffr5VZq9nO5cuXg8+2bcuRI0e0fHQKrzPsHv/5n/9JYBET807F2bNn5aGHHtLStku5XJalpSXJ5XKi2g8Fz8zMBL271Wo1GR8fF9u2RSklP/nJT4w5iBw/fjyY3m+itJ8lk0mtuVKr1Qp6CIvy+eefa+NPPPGENg5sBgHGJhw7dkzrsta27R27EoTdoVwui+u6Mj09raWPjo5qd7/CPbyYarWa9izHK6+8ouXj/4Sbjrmuq3VNKyIyNze36gEY2EuGh4c7TkDNplPbJZvNilKqoy70+c+oPfzwwyLt8qahoSGZmZmRfD4vo6OjXee1n5jPA67Whfmbb74ZfE6lUpHrGNgoAoxNSCQS2h8yKvqPauOI/WllZUXGx8e14CDsn/7pn4Jb1H7zhSinT58OPudyOe5erMI8ebrnnnu0K6RXrlzp2oQN2IuOHz8efM7lctqbmyXi+a6t5jdz8vlX1XsJ/BcXF8VxHJmZmZGBgYGOCwj70fDwsJRKpWD86aefjjwPqdVqQdeylmXJ66+/bhYBNsfsVgqdXNdVmUxGpVKpjrdi1ut1JV3ephzVxVulUtHKoL+Z3f5ZlqXq9bpWxnXdji4go97Ebdu2tv+USqWO/cnzPJXJZIL5FAqFYL/y90M/b3Z2VpsW0fwuac0h6j8L7AWe56lCoaAsy4rsZtbvutnMi6rLpqamtDJmHSUiKpVKdfyXoo5/ZveyEuoq2iyTy+WUGHWpWSbMzzPr1P2qUqkE2zmVSmnbulQqaXlR6yzO7Yz9iQBjDeYJpkT0Le04TscJpTmNOZgVO/pLVKVpDqqH/tD9d6f4B8vwsNo7GKrVqsrlciqVSmnTOI6jpqamIg8I6K5UKmnrMpfLsQ6xJ3Wru8IKhUJH/dNLXRZ1PAwP/rHRTDcHv36T0H/Rz/NPTkulkpJQPRn+XX4Zx3GCY6lfnv/1//E8T83OzirHcYKAwl+nmUymayAQ53bG/sWbvIEtls/ngy4hw3K5HG2GAexL4bdO27YtQ0NDQZMd13UlmUxqbxV3HEd7W7TruvLiiy/KyspKkL7Tb/gG8H8IMAAAAADEhoe8AQAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAAAAMSGAAMAAABAbAgwAAB9q1wuy3fffWcmAwD62IBSSpmJAAD0gxtvvFG+++47mZyclEceeUQOHDhgFgEA9BnuYAAA+tqXX34pjz/+uNx4443yy1/+kjsaANDnCDAAALsCgQYA7A40kQKAXe7LL7+UTz75xEzeE8bHx+XLL780k0VE5JprrqHpFAD0IQIMANjl3nzzTfmbv/kbM3nfINAAgP5CEykAwK7mN516/PHHaTYFAH2AOxgAsMstLi5KoVAwk/eEDz74YM2g4ejRo/Lss8/Kj370IzMLALADCDAAAH3rxhtvlM8++8xMFiGwAIC+RRMpAMCucvToUfn9738v7777LsEFAPQhAgwAwK5AYAEAuwMBxhqKxaIMDAx0DIODg9JsNs3imrm5uY7p/KFWq0k6ne5IDw/FYlFqtVpHujnsJ/722Grdtrs/pNNpEZGOdHOo1WrmrHtSLpcj9490Oi1zc3Nr7ntbYbvWPWDaj4HFTtdB+41/rO2n9dVsNqVYLMrIyIi2TQcHByWbzUq5XDYnEQn9ltUGEYk8xoSHYrFoznpP2K7f1m39+v/d1WSz2Y7p/GHXUFiT53kqk8koEdGGUqlkFtXYtq1SqZQ2TaVS0cq4rqts29bK5HI5rYxSShUKBa2MZVmqXq+bxfY8fz1sh6jtnkqllOd5WrlqtaqVkR72jW7q9XqwP1iWpUqlUvB9lUol2J/8vO20nese8H366adm0r6xE3XQfuWvw2q1ambtiFKppCzLCra5f+7geZ6WZ9t213OBXs4bej0H2UtERBUKBTN5S0StXxFRruuaRQOu63acO1qWteo0/YizhR5Vq9XIir6barWqcrmcchxHmyaKWQl0q+DCZRzHMbP3he0+yTUP3N0qpV6281rq9Xpw0Oi2H3iep5XZzpOI7V73ALa3DtrP+inAKJVKwXa0LKsjoFTGfhEVOPjC+0S384Zez0H2itX+R1uhUCh0nD9OTU2ZxQKFQkHbB1bbdv2MJlLrcNttt0kqlQrGl5eXu95OPXfunNx9991mMhCp2WzK4cOHpdVqiYhIJpOR0dFRs5gkEgl5/vnng/Hx8fGu+yAAYHep1WoyPj4ejD///POSSCS0MiIio6OjkslkRESk1WrJ4cOHd6TpLHrzwAMPaOMzMzNdt9drr70md9xxh5m86xBgrNMTTzyhjZ87d04bl/bJ4qVLl+TIkSNmFhDpjTfeCIILabc578aseE6fPq2NAwB2J7M+N+v7sPBxotVqyRtvvKHlo39cddVVksvlgvFWqyUXL17Uykg7wLzzzjsjg8rdhgBjnbLZrFiWFYxHRaEXL16Ue++9V0sDVnP27Flt/Oabb9bGw5LJpDa+tLQkKysrWtpe12g0tIfg0um0didnaGhIeygun89r0wNAv2k0GrK0tBSMW5bVUd+HXXfdddr4a6+9po3Hgbo0PidOnNDGX3rpJW1c2het77//fjN5VyLA2IBwFCoicv78eW38pZdekmPHjmlp/cTsYaJfT07NnhMGBgZkcnKya9529AqxUSsrK13X+crKinb3QkRkeHhYGzeFm+qJiHzyySfa+GaZ67af1n2j0ZDDhw/L/Py81Ot18TxPLl++LGNjY0GQcfnyZWk/YyZKKZmenjZnA+wrq9VB+01U7z5jY2MiIjI2NtaR10uvP3H4+OOPtfGDBw9q4ybzQpTruh0XPDdrN9el3XpiExGZnJzsSPfztsrw8HBHM/tGoxGMN5tNuXDhQmTz6N2IAGMDHnzwQW38hRdeCD43Gg2xbXvVqw5riarg4tzxR0dHpVqtmsnoQbdKKXzVybSysiK2bWtp4fEvvvhCy+uFefv0j3/8oza+V4WfVclkMjI8PCyJRCJoi3z8+HFzEmBP2Yo6CP3hypUrZtKqzOOARAQpYUtLSx37zUDo4hG2ntnMfm5uLvh8/vx5OXnypJa/mxFgbEAymQxOaKR91WBhYUFERN5+++1V28/3olqtalcM/GG/MX+/UkoKhULXvImJCXMWsSsUCh3fq5QSx3HMooEXX3wx2KalUilI79aHeT8wf18/rHtpV8D+3Z7bbrstSL/66qtF2v/F8BUhYK/ZL3XQVlpcXOxYf/5Ft6jj7+LiojmLXclxnI7fpkJ1+14zMTHR8VtV+1yq2/9oq63WzP71119f9Zmb3YYAY4PMHgHeeustERGZn5+XbDar5WF/e/LJJ4NbntlsNrhy6Lefvfbaa7XyvTBvg99+++3a+F71/vvvB5/DV3LDV+C+/fbb4DOAtesg9Ifrr7/eTFqVeRyQdgsF9LeoZvZxtH7pNwQYG3TkyBHtFvP8/LwUi0XtzsZ2M297mlen8vl8kBfV+5XZXtGcHhvTrcLwDwTJZLKjucJaV+GXl5e1cbMt7l719ddfB5+7XY3jAAvo1qqD0B/MZy4+/PBDbdxkNocyn81Df4pqZj83N9dx4Xq3I8DYBLOt3NmzZ+W+++7T0raL37NDqVQKbvWG+9IuFosyMzMjuVwu8jbgysqKTE5OSqlUErWHb5nutJWVFXFdV2umICLy8MMPa+PmgSPMfDgzl8tFtsXd6y5fvmwmAVhDtzoIOy+ZTGpN3VqtVkd9H/b5559r42b7fvSnqGb2Fy5c2HOvNiDA2IRjx45pbels216z95+tMj09LUqprs2z/O7r/O7PzG7Q/Ctc4+PjUi6XZWJiouu8sHEvvviiOI7TsW4ffPBB7S7Ge++9p+WHhXstsyxLnnzySS1/L/vpT38afHZdt+Mlg3Nzc6sekIH9rlsdhP5gXtyLeleC78033ww+p1Iptuku8uijj2rjO9n6ZasQYGxCIpHQ/tBRVw+i2khupWKxGHS3J6Gr3a7rhkpF8+9sjI+Py0CMvVbhe+VyWS5cuBD5wGAikZBf/epXQcA6Pz/fcfIs7f0p/M6M6enprs0f9iKz++d77rknWE+1Wk2uXLmyr9YHsB6r1UHoD8PDw9rdpaeffjryPKJWqwU9h1mWJa+//rpZBH1sdHRUu6hoNpuK2ua7jsKaXNdVmUxGpVIp5bqullev15WIKMuylOd5Wl61WlUiog2VSkUr47qusm1bK5PL5bQySilVKBS0MpZlqXq9HuT735XL5bTv9ZfX/45SqaSVD5cx52Xbtpa+33iepzKZjLbeU6lUT9vZX88+fzuHFQoFbVy196dUKhVs4/B8qtWqlletVrVp94upqamO9e2vE3PbALvZTtRB6A+VSkVZlhVs83B9XyqVtDzzGO5b67xBreMcBBtTr9eVbdsql8t1/G9nZ2eViCjHcbR01WXbddvO/YoAYw3mRo7aGRzH6fhDmtOYQ7VaVY7jdKSHh0KhEHngMAdlBBClUinI83fIXC6nJFRxhH+XX8afl1/ePBjtJ1HbPTz4+4CZbg7+QcGswGWNSrxUKqlMJqNNZ1mWchxHzc7OdlRU+02pVAqCLX9d7rbKF1jNTtdB2Hme56nZ2VnlOE4QUEj74l8mk+kIIn29njf0cg6CjYtav+F16nle5IVEcxpz2C0GVNQTv9h18vm8zMzMiLQf+vU/27YdPAybTqeDW6qO4wSf/TLheUi7WRXNTTZvaGgosolaqVSizSyALUcdBGC7EWAAAAAAiA0PeQMAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYAAAAACIDQEGAAAAgNgQYKCvFYtFyefzUiwWZWBgoGMYHByUZrNpTqaZm5vrmM4farWaWXxL1Gq1ju/uZQgz84rFopaP7ZdOp7Vtkk6nzSJ9x/8/AQCwVQgw0JcajYaMjIzIO++8IydOnJCJiQnxPE8ymYxWrtVqycWLF7U00wsvvCCpVEpLq1QqopSS0dFRLX2rjI6OilJKKpWKlu44jiilgsF1XSkUCloZn+d5ZtK2WVlZkWw2aybveiMjI2bSuiwuLnbsW9tpI8t/4sQJeeedd2RkZERWVlbMbAAANo0AA31nZWVFDh8+LNI+gRseHhYRkUQiIY8++mhHkPHSSy9p42G1Wk3uvPNOSSQSWvqRI0e08e2y1vcmk0mZmJiQ2dlZM6vjN2ynTCYjX3/9tZm8q506dUqWl5fN5HXbqe2y0eUfHh6WxcVFabVakkql1rwDCADAehFgoO9kMhlptVry8ssvR5683XbbbdpV4+Xl5a5Nnc6dOyd33323mdy3/CY2J06cENu2zewdkc/nN3Qi28/K5bI899xzZvKusdnlTyQS8uabb0qr1doVzboAALsLAQb6SrFYlOXlZUmlUqs2X3riiSe08XPnzmnjIiLNZlMuXbq05l2DfmE2V7nzzju18e3WbDYlm83KzMyMmbWrFYtFGR8fN5N3jbiWf3R0VGzbluXlZZ7JAADEigADfaPZbMrZs2dFROTee+81szXZbFYsywrGZ2ZmOpp6XLx4cc35rMZ8gLeXYTPOnz+vjU9PT2vjvVhYWJCRkZFgefL5fEfg4iuXy1rZkZERKZfLIu1g59ChQzI/Px+UX1pa0n5n1IP30l6GoaEhGRgYkLm5uWB6Py/8nel0WhYWFrQyYbVaTbLZbFB+aGhIisVix7b2yw0ODgZls9msNBoNrVw6nZbJyUktzS8fvgvW6/y66bbvdMv3lcvlYN2l02lpNpsyNDSkTbfW8vvPLw2011ej0ZB8Ph95l89vbnj27NmOdQoAwIYpoE/Mzs4qEVEioiqVipmtlFKqWq2qQqGglFJqamoqKC8ianZ2ViubSqWU67pKKaUcx9HK9sKcppehF+HyjuMopZSqVCrKsqxgvJvwtP568JVKJSUiyrZt5XmeqtfrSkSUZVnK8zytbC6XC77f8zxtXYbXY3gdRC2buQ38ZYiaxi9r27ZyXVd5nqds21YionK5nDZfFfo9lmUp13VVpVIJ5pvJZIJy/nz99eH/bn/aer0emqtShUJBW0bTeucXtY48zwvWsT9EbQP/t6n2PhD+ba7rqlQq1bGMqy2/67rKsqxgHwgvR7Va1cqq0HdKe9sBABAH7mCgb7z77rvB56uuukrLi/Lggw9q4y+88ELwudFoiG3bkkwmtTLrsbi4qPXw1MuwXv5dgbvuuktarZaZ3bNarRY0mzl58qQkEgkZHh6WVColrVZLnnnmmaDs3Nxc0Ozpb//2byWRSMh9990X3BH64Q9/GJRdy9VXX62Nv/nmm+J5nkxNTYmIyM9+9jOR9vL5zwxkMhlJJpOSSCTk4YcfFmnfgQpfYW80GsHvyeVykkwm5dChQ8GzN/7zKSsrK8F833nnHZH2Q8yO44i0exlbWlpqz3Vtcc0vkUjIP/zDP2h32aJ6O5ueng720bfeekvLSyaTsri4uK5ncS5evKjtR4lEQqanpzs6RvCF/2fvvfeelgcAwEYRYKBvfPjhh8Hna6+9VsuLkkwmtRMn13WD5jZvv/22HD16NFS6P/nd1JZKJTNrXV599dXg85//+Z8Hn/2H5P2mT2IEYv4J5vDwsHz11VeilNrUMyt+wHLmzBlRSsmJEydEjOUzgxJfuEy4aZVfPpFIyKVLl0QpJWfOnAny/JN413WDaTYqzvn5J/e+X/ziF8HnlZUVuXDhgtb1r99L1/z8fNCFbCKRkMuXLwdl1vLNN9+ItJf9pptuCoK2crkc+UzTzTffHHy+cOGClgcAwEYRYKBvhK+89nrn4YEHHtDG/avA8/Pzm35vg9lOvpdho7LZbNf3X/QifHI4NjYWLI9/td1ft41GY9MnzqvpFpz0cvIaLhMOiFaTSCRkeXlZqtWqLC8vS7PZlGKxuK6T8rC453fHHXdoAYt/wn/+/Png7o3v+PHjwWe/owPzGZa1HDt2LPjcarVkbGxMTp061fX5inAvbZu5gwYAQBgBBna1I0eOaE1I5ufnpVgsdm0S0s/CJ4frFT45LBQKHU23/OZb3377bWiq7dPLyWu4TC/lfclkUm6++WY5f/68HDp0SG655Rbtwej1inN+iURCnnrqqWD89OnTIiLy2muvdTTxy2azQdMyaa+DRx55RPL5vFZuNclkUkqlktY067nnngseGAcAYDsQYGDXO3nypDZ+9uxZue+++7S0jdiOZzDCou7azM3Nde0FqpvPPvvMTOrq17/+tZm0JcInvOvlPwvRTaPRkEOHDsnk5KS88sorXe+i9Cru+T344IPB719aWpJisRj58kcRkTNnzkilUunoIa3XOzrSDlTef//9jnfFhJ/DAQBgKxFgoG+ET6rWc7X12LFj2rS2bQdv/95tFhcXtfEXXnghMvAw+Q8hS7t5kbn+Tp06JdJ+94F58mqW7bUr1vXo5Z0e4btO4c9RL1L0l9F/67vf7GuzwUDc85P2XYxwc73JyUm5//77tTJhR44ckT/96U/aNr1y5YpWZi3Dw8Ny6dIl7Y5IVKAaTttMEAgAQBgBBvpG+CT0448/1vJWY57AmS/hk3UGLP0in8/3fNIXbr/vv53ZP3mcm5uTW2+9NcjP5XJdyxaLRXn77beD/LBmsynNZjMIVtbj0UcfDT77DyKbn8NlzGdr7rnnniDIWFhYCN4Fcf78ea05VaPRkFqtpvX0FP6OKM1mM2iGFMf8ojz55JPBZ9u2Ix+4TqfTQeCUSCQ6gs1uwstfLBa15zbOnDmjBSqmL774Ivh88OBBLQ8AgA0z+60Fdkr4HQpR78FwXVdlMhnt/Ra+1d75UK1WtfcGdJv/dgi/d8Afwr/F8zxVqVSCdyuE3yPheZ423dTUVJCn2u/9MOdtzkO159OtbCqV0taf+c4FMdad+R4Mc7uE+e9j8N+D4bruqu/BMN8j4Q/hd1GE353iD7lcTmUyGS0tvK6i9gc/fyPzC6/LVCoVpJv832O+r8XnOI6yLCt4H0V4nw6v19WW399ehUIheA+Gv46j9vnw/thtuQAAWC8CDPQNz/OUZVkdJ3Cqy4mueeLsOE7Hiao5jTlEvXxsK0SdFPYyhF+mZ+ZJRABSKBSCE0rLsoITTZP/cj1/fdu23fHiPp8fRPjz80VtE3OZTaVSqeOEfLUXvM3Ozmq/J5fLab/H87wgGLNtWzs5Dwcv5joolUrBbw/nr3d+4ZfshYco/j5gLovPcRzluq4qFArBsmUymY4X+6lVlr9QKKhKpaJKpVKwvKlUKjK4UKFtGBWYAwCwUQNqs0+mAjEqFosyOTkptm1vuGtQoB+Vy2X593//d+3dGDttZGRElpeXpVAoyMTEhJkNAMCGEGCg7/gnPdVqNbKtOrAbZbNZefTRR/tmn67VajI2NiapVEouXbpkZgMAsGEEGOg7zWZTbrrpJhkcHJTf/e53kd15Av3OD5QrlYocOnRIDh061Dd35ZrNphw6dEi++uorWV5e7qmnMgAAekWAAQAAACA2dFMLAAAAIDYEGAAAAABiQ4ABAAAAIDYEGAAAAABiQ4ABAAAAIDYEGAAAAABiQ4ABAAAAIDYEGAAAAABiQ4ABAAAAIDYEGAAAAABiQ4ABAAAAIDYEGAAAAABiQ4ABAAAAIDYEGAAAAABiQ4ABAAAAIDYEGAAAAABiQ4ABAAAAIDYEGAAAAABiQ4ABAAAAIDYEGLvAwsKCDA4OSjabNbMAAACAvrKpAKNWq8nAwIA2lMtls1igWCx2lB8YGDCLAQAAANilBpRSykxcj2azKRcvXpR8Pi+tVktEROr1ugwPD5tFRdrlf/7zn8uFCxfk/fff71quF9lsdtWAZrdpNBqytLQkExMTZhYAAACwK2zqDoaISCKRkGw2K//yL/8SpB0+fFhWVla0cr5EIiGPPvqoHDx4cFPBxcrKiszPz5vJu9rc3JyZBAAAAOwqmw4wfFdddZXYti2WZUmr1ZJMJiPNZtMsFpupqSkzaVdrNBoyMzNjJgMAAAC7SmwBhojI0NCQvP/++yIisry8LM8884xZJBblcnlP3b1oNpvy0EMPmckAAADArhNrgCEiMjw8LKVSSUREZmZm1t3sp1arSTabDR4AT6fT0mg0gvxisSjj4+PBuF+uWCwGaaZmsynlclnS6bSk02lpNpuSTqc7pms2m1IsFmVoaEgGBgZkcHAwcr4rKyuSzWZlcHAwKJfP57vesSmXyzIyMhIs68jIiCwsLIi053Xo0CFZXl4WEZHJycmOh9/Dyx5lYWEh+D3+/KOeTVlYWJB8Ph/Mu1arBcs1MjKirWcAAABgQ1RMqtWqchwnGJ+amlIiokREVavVVcv6SqWSsiwrKF+tVpVlWcqyLFWv17Wy/rx7MTs7q1KplBIR5TiOyuVyKpfLKRFRtm0rpZTyPE+lUimVy+WU53nK87ygTC6XC+bleZ6yLEulUinleZ5SSqlCoRDM25TL5VQqlQp+U71eV5ZlKRFRlUolKOfPo1AohKb+Pt1xnFXnb1lWMC/XdYPy4eWuVCoqk8kE661UKinHcbT5++sCAAAA2KjeztB7EBU0+CeuZoAQVdZ13chgpNvJ+3oCDNX+Tn9ZXNdVqn2y73/O5XId3+EHE+Hlmp2djQwEopanVCpF/iY/+CqVSkFatwBDhZbdXL5KpdIxH9Vebtu2O/I8zwuW05zGL28GcgAAAMB6xN5EKuxf//VfJZVKSavVkoceeqhrEyIRkTfeeENs25bR0VEt/fbbbxcRkaWlpVWn79XBgwclmUyKtJtzJZNJaTabMjMzI8ePH9fKJhIJOXjwoIiI/PrXvxYRkR/+8IciInLLLbdoZaP84he/kFQq1fGbzpw5I0qpTb8479lnnxURkTvuuENLTyQScvLkSZH2MoTTfeZ3Dw0NiYjIt99+q6UDAAAA67GlAUYikZDXX39dLMuS5eVl+fnPf24WCXz00Ufium7wHIE/jI2NBWU+/vhjbZq4+PMdHx/v+P6lpSWR9vKJiBw5ckSUUnLkyJHg2Y6RkRFtftJ+nsN1Xe2kPk7NZjN4biPqO/7yL/9SRERc1+3aZTAAAAAQty0NMKR9l+Df/u3fRERkfn4+8qFpXyqVknazrcjBvBMQt0ql0vGd/rC4uBiUazabcurUKTl06JD84Q9/kNdff12bj2xhMORba/7hd4x88cUXWh4AAACwVbY8wBARGR0dDXqWmpycDJobmZaXl2NpBrVR//Ef/2EmdWg0GnLTTTfJRx99JL/73e/kzJkzkS8MvPbaa0VibNpl8ucv7WVazVYHZgAAAIBvWwIMabf5z+VyIiLy3HPPmdnBcxHd3p0xNze3ZU19/JP1mZmZyJN1v/taEZHnn39eWq2WTE9PRzZN8iWTSbEsS0REzp8/b2aLtLvc3ahkMim2bYuIyAcffGBmB+vKcRwzCwAAANgysQYYly9fNpM009PTXU9477//fpH2SX42mw1O9JvNpszNzcm7774bBCFRarWamdSzZDIpjuNIq9WSw4cPS7lcDu46NBoNSafTwcPmFy5cEDGaHZmBjz/tU089JSIiTz/9tLZ8zWZT8vm8XH/99UGaqdForHnn4/Tp0yLt+ZtlP/zwQxHjIe/1WlhYkMHBQRkZGemYPwAAABDJ7FZqo/yuV80uWU3++ybMLleV8e6M8GB2c6uUCrqPzWQyKpPJrPm9/rzD3dSGua4bzNMcwu+T8N8lYVmWKhQKKpfLqUwmE0yby+WCrmb93+rPx//dlmVp81Sh7m/9+WYymSDP78LWtu3g3Rs+/10dqVQq+F3++0Ompqa0sn63uWJ0Rxvu1jY8jd/NsLkOAAAAgG42HWD4J7/msJp6va6dQIdVKhXtpDyTyUQGBP5L+SzL6ning8lcNunyvgn/5Xp+sGDbtpqdne0oE34xnZ/vBzDmSb3neapQKGjz7Pbd4Rfq+YGEudwSEcSVSqWOdRZ+iZ8yggV/8F+0Z6ZLe/v5AUm3gBAAAAAwDajvT2KBrmq1mrz66qtSLpfNLAAAAEAT6zMY2Jt++9vfytGjR81kAAAAoAMBBlbVaDTkm2++6XjzNwAAABCFJlLoqlwuy5UrV2RiYsLMAgAAACIRYAAAAACIDU2kAAAAAMSGAAMAAABAbAgwAAAAAMSGAAPYBsViUYaGhmRgYEAGBwcln89Ls9nsKDMwMNB1SKfTIiId6eZQq9W0+faqXC5LOp3umF86nZa5ubmO5d1J6XQ6WB87rZdtC+ykna5bdkqtVuv75V5YWJCRkZFgHWezWWk0Gmaxnq2srEg+nw/qJH8YGhqSfD7fdV3s130EW8h88x6AeIXfsh4eLMsK3tju8zxPZTIZrVwqleooV61WO+a31hvtu6nX68q27WCZSqVS8H2VSiVYfj+vHziO0xdvl1/PtgV20k7ULTvN/y3VatXM6gtTU1Md69ofNrLM4fllMhlVr9eVUkq5rqsKhUKQ5zhOx3ZX+3QfwdYhwAC2ULhSjxpyuZw5SUflXSgUzCJKtU+yw+U2ol6vK8uygnlEHdQ8z9PK9MOBpB8CjI1sW2AnbWfd0g/6OcAwt4U52LZtTrKqXC4XTNutbgzXWVGBg4pYrr2+j2Dr0EQK2EKvvfaazM7OilJKPM+TQqGg5c/MzGjj26nZbMrhw4el1WqJiEgmk5HR0VGzmCQSCXn++eeD8fHxcW6D9/m2xe7z9ddfm0nYw1599VWZmpoSz/NEKSWlUkksywryXdftuZ4tFotafWPWRb6JiYngO5aXl+Wv//qvzSJAbAgwgC3SaDTk9OnTcuLECZH2ifrExITkcjmz6I544403guBCROTo0aNaftgdd9yhjZ8+fVob32/6fdti9/mrv/orefzxx+XLL780s7AH2bYtZ86ckUQiISIi2WxWpqenzWJrajabcvbs2WDctm0ZHh7WyoRls9ng89LSUs9BDLBeBBjAFhkeHtYqc98NN9wQfHYcR8vbTuGDkojIzTffrI2HJZNJbXxpaUlWVla0tP1kM9vWfKgzn89r69J8aLJYLGrTY2/67rvv5Je//KXceOONBBr7wJkzZ8wkue6667TxqDvKpvPnz2sXilKplJZvCtdRIiLnzp3TxuNAHQYhwAB21vHjx82k2Pg9qPhD2MrKinZQkvZJ82rMA9cnn3yijW8F8zf4w9LSkiwtLXWkD/RRLyZR27ZcLstdd90lrVZLPM+Ter0uMzMzkkqlgp6n2s/GBcPExIQ5G+xhuyHQMP+X/SCqB7yxsTERERkbG+vI65de6Lrp9W6o2ePUbbfdpo2bbrnlFm380qVL2ngcqMMgBBjA9vvss89E2ifsUVfBTZOTkx0Hx4H2SXY3tVotOLj6hoaGgs9ffPGFltcL/1a+749//KM2jtW3ba1Wk/HxcREROXnypCQSCRkeHpZUKiWtVkueeeYZrTz2t+0INLaibsHGff755yIiYlmWPPnkk2Z2pPXeSb7qqqu08eXlZW3ctJF9BBARGVBKKTMRwNZoNpty0003SavVknq9HnnXwDyAFwqFyCtA6XRaq+TDf+V0Oi3T09OSTCalWCzK5OSkiIhUq1UZHR3t+A4xpo9ifl+35doO/tXHxcVFM2vHrLVts9mszM/Pi4S2g4TWq2VZ8tVXX2nT7DWHDx82k9D2wQcfyHfffWcmBw4cOCCPPPKITE5OyjXXXGNm98T833f7D5v/9fXULf3E/739uGxR/PU+OzsbPN+1FnNbddumPnMfEGP7mvnd5md+71rHD+xDZrdSALaO303gal29xtFNoOu62rhfxk93XVeb1pw+ivnOh53s+rEfuqk1rbVtw139dhv2OvP3Mqx/OHDggHrqqafMVduT7ahb+kk/d1Nr8pd1vd1bh7unXW2b+iqVilberEfj2EcARTe1wPZpNBoyOTkps7OzHc1n4mY+lC3t3kX89GQyKbZta/lmW16TeSt9tYfC95tetm34mZdCodDRTpkrgFiLfxfj7/7u78ysbbNW3YL1azabcvz4cclkMuvuSeonP/mJNv5f//Vf2rjJbNr64x//WBsH4kITKWAb+M1neumKMO5b1N2aCYSbN4iIlEqlrifHKysrWkCSy+XW/B1bqZ+aSPW6bQdCD8Pu9PrbKb/5zW/MJLSNj493fc4ijuZRso11S7/o9+XzpdNpaTabsri42PGs21rCTTOlHexdvnzZLBbI5/PaOzNc19WCw7j3Eexj5i0NAPFLpVKRt76r1WpHety3qB3H6fgO1X5Dt23bwfSZTMYsEgi/AdayrB1vDtFPTaR63bbh7WVZVsdbdKemprRx7C833HCD9n+WdnOoxx57TP3P//yPWXxDtqtu6Re7oYnU1NRU5Fu1XdftuY6bnZ3Vtle9XjeLKNWu88NNNaPqnLj3EexfNJECtlg+n5fl5WWZmZnp6IljbGys42HgOPn9j0ddLU8kEvKrX/0qeLPr/Py81CK6eDVf5OQ/4In1bdtwt7WtVkvS6XTQA8zc3JzceuutQT72twMHDshjjz0mn376qbz88subumuxVVarW9Cbcrkszz33nCwvL8sPfvADrf6wbVv+7M/+zJwk0okTJ7RubcN3psPCL1dNpVLy93//92YRID5mxAEgPuEr/92G8NUmz/NUJpPR8qOubplXmSTi4eJqtdpxBSzqalS9Xg8e4LYsS5tPtVrV8vr5SuB2W++2VREPyvuDuZ2w/9xwww2x37EI24m6Bd1FrWdzmJ2dNSdbVbhOymQywZ1mz/O0vFwu17Hd/XJx7SMAAQawRUqlUkclbA6WZQXl1zph9Q/oZro5+EGAmS6r3O5W7eXNZDJasynLspTjOGp2drbjILOfrXfb+vwDvb+OLctShUKBdQv1/PPPb0lgofqgboGuXq/31KuceYGiF67rqqmpqY4mTH5Tzm4XieLeRwAe8gb2oPADxWH9/rAjgP5G3QKgFwQYAAAAAGLDQ94AAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYkOAAQAAACA2BBgAAAAAYvP/AYjOWVYuiBNiAAAAAElFTkSuQmCC\" style=\"width: 580px; height: 180.884px;\" width=\"580\" height=\"180.884\"\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the cyclic voltammograms of CuO materials for HER activity. The reduction (cathodic) and oxidation (anodic) peaks are observed in the cyclic voltammogram in the entire CuO. The observed reduction peak at -0.842 V is due to Cu\u003csup\u003e++\u003c/sup\u003e to Cu\u003csup\u003e0\u003c/sup\u003e and oxidation peak at -0.364 V is due to Cu\u003csup\u003e0\u003c/sup\u003e to Cu\u003csup\u003e++\u003c/sup\u003e respectively. There is a slight variation in these peaks due to nano-sized effect because as the particle size reduces peak separation between cathodic and anodic peak increased. From Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e it is observed that as weight % of nano-sized CuO increases, there is an increase in current during the hydrogen evolution reaction. As the weight percentage of nano-sized CuO increases, more exposed catalytic sites become available for proton (H⁺) adsorption and subsequent reduction, thereby enhancing the hydrogen evolution reaction (HER) current density. The higher nanoparticle content increases the electrochemically active surface area (ECSA), allowing more electrons to participate in the Volmer\u0026ndash;Heyrovsky or Volmer\u0026ndash;Tafel steps. With increased loading, nano-CuO particles form interconnected networks that improve charge transport, reduce electron path length, and minimize charge-transfer resistance. Moreover, nano-CuO contains abundant surface defects, edges, and oxygen vacancies that act as active centers for water dissociation and hydrogen adsorption, lowering the activation energy for the Volmer step and accelerating HER kinetics. The higher nanoparticle fraction also produces a rough, porous morphology, improving electrolyte diffusion and gas desorption while maintaining a stable reaction interface. At higher nano size CuO loadings, a percolation network forms, creating continuous pathways for electron and ion transport, enhancing conductivity, catalyst stability, and overall, HER activity. The highest (18 mA) and lowest (0.1 mA) currents are observed for pure nano and pure micron-sized particles respectively at -1.3 V potential for Ag/AgCl working electrode. The Ag/AgCl potential can be converted with comparison to Reversible Hygrogen Electrode (RHE) by following given formulae:\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" style=\"width: 402px; height: 47.9883px;\" width=\"402\" height=\"47.9883\"\u003e\u003c/p\u003e\n\u003cp\u003eThe RHE potentials was found to be \u0026minus;\u0026thinsp;0.293 V. The detail calculation is given in supporting information. \u003cb\u003eFrom the above data it is clearly observed that there is strong nano-sized effect on hydrogen evolution reaction.\u003c/b\u003e The current generation for nano-micron composites is in between those observed for the pure nano and pure micron-sized particles. Current was found to be highest for 80% and lowest for 20% nano-micron composites of CuO. The onset potential for the hydrogen evolution reaction (HER) was observed at \u0026minus;\u0026thinsp;0.28 V vs. Ag/AgCl for pure nano-sized CuO, which is significantly lower than that reported for other Cu-based nanostructured materials (refs. 39\u0026ndash;41, 43, 44), indicating superior catalytic activity. Furthermore, the overpotential required to achieve a current density of 10 mA cm⁻\u0026sup2; (corresponding to the benchmark value for approximately 10% solar-to-fuel conversion efficiency) was found to be \u0026minus;\u0026thinsp;0.301 V vs. Ag/AgCl for pure nano-sized CuO, confirming its high electrocatalytic efficiency toward hydrogen generation.\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" style=\"width: 320px; height: 74.2584px;\" width=\"320\" height=\"74.2584\"\u003e\u003c/p\u003e\u003cp\u003eQ\u003csub\u003eH\u003c/sub\u003e is calculated by extrapolating the curve obtained from the cyclic voltammetry. The Q\u003csub\u003eref\u003c/sub\u003e for Cu materials is 420 \u0026micro;C/cm\u003csup\u003e2 48\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe electroactive surface area of the various composites is given in Table\u0026nbsp;2. It is highest for pure nano sized CuO and lowest for pure micron sized CuO particles. As the weight % of nano-sized CuO increases in the nano-micron composites, there is an increase in electroactive surface area. By applying the above electroactive surface area, the current density (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e) was calculated for pure nano (272 mA/cm\u003csup\u003e2\u003c/sup\u003emg) and micron sized (3.8 mA/cm\u003csup\u003e2\u003c/sup\u003emg) CuO as well as for the nano-micron composites of CuO. The highest current density (pure nano-sized CuO) at geometric surface area of the electrode as found to be 596 mA/cm\u003csup\u003e2\u003c/sup\u003emg. In nano-micron composites, the current density increases with the weight % of nano-sized CuO particles. All the current density values (Table\u0026nbsp;2) of nano-micron composites are in between pure nano and micron-sized CuO. There are reports by our group on Cu based\u003csup\u003e\u003cspan additionalcitationids=\"CR40\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e and other nanostructures\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e materials. Recently Muralikrishna et al studied and reported pH dependent electrocatalysis using graphene/Cu\u003csup\u003e++\u003c/sup\u003e hybrid\u003csup\u003e45\u003c/sup\u003e materials and observed 46 mA/cm\u003csup\u003e2\u003c/sup\u003e current density. Islam et al\u003csup\u003e46\u003c/sup\u003e also recently reported for CuO Immobilized Stainless-Steel Electrode Prepared by the SILAR Method where onset potential was low 0.154 V but their catalyst produces only 0.5 mA/cm\u003csup\u003e2\u003c/sup\u003e current density (less than 10 mA cm⁻\u0026sup2; corresponding to the benchmark value for approximately 10% solar-to-fuel conversion efficiency) at \u0026minus;\u0026thinsp;0.35 V potential. There are also some recent reports on HER by other groups \u003csup\u003e\u003cspan additionalcitationids=\"CR50 CR51 CR52 CR53 CR54\" citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e. Compared to the above reported values it was observed that the CuO nanostructured produced much higher current. \u003cb\u003eThe current density is very stable in nature over the 500th cycle\u003c/b\u003e (Figure S7) due to the stability of CuO nanoparticles in ambient condition for long time. Stability is also confirmed by the monophasic nature of CuO nanoparticles shown by the X-ray diffraction pattern (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003e and Figure S8) after the hydrogen evolution reaction. The slight noise in PXRD is due to the low amount of sample on glass sample holder. The particles remained spherical in nature as they were before electrocatalysis, having average diameters of 15\u0026ndash;20 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003e) which is same as earlier. The alignment and interconnectivity of the nanoparticles still remain after the electrocatalysis which support that no further surface oxidation is possible and materials and very stable at ambient condition. This type of ideas shows the different aspect such as surface area, charge transport, structure stability, catalyst accessibility, scalability and handling for new catalyst where some properties are better for nano size and micron size for industrial applications.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eNano-micron composites of CuO were synthesized in air by mixing the micron-sized CuO and copper oxalate heated at 350 \u0026deg;C (resulting in mixture of micron and nano-sized CuO). We investigated the hydrogen evolution reaction by using these materials as electrocatalysts. It was observed that pure nano sized particles of CuO shows highest current density (272 mA/cm\u003csup\u003e2\u003c/sup\u003e) indicative of more production of hydrogen in this chosen system as compared to pure micron sized particles and nano-micron composites due to high surface area and alignment of the nanoparticles. The electrocatalyst is highly stable in ambient condition and retain their catalytic efficiency over 500 cycles. From this study we can clearly state that there is strong nano-sized effect on hydrogen evolution. This study may be expanded to obtaining other electrocatalysts with increased activity. This study also shows the effect of combination of nano\u0026ndash;micron and opens the door for technology.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBK thanks ANRF for providing support through the grant no SUR/2022/004717. The author also thanks Prof Ashok K Ganguli and IIT Delhi India for reaction and characterization facility.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u0026nbsp;\u003c/strong\u003eBharat Kumar: Concept, synthesis modification, final draft writing and final submission.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003eFunding is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial:\u0026nbsp;\u003c/strong\u003eClinical trial is not applicable in the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish declaration:\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics and Consent to Participate declarations:\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u0026nbsp;\u003c/strong\u003eThe authors declare that the data supporting the findings of this study are available within the paper file. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTurner JA. Science. 2004;305:972.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDresselhaus MS, Thomas IL. Nature. 2001;414:332.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLewis NS, Nocera DG. \u003cem\u003eProc. Natl. Acad. Sci\u003c/em\u003e, 2005, 43, 15729.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eArmaroli N, Balzani V. Angew Chem Int Ed. 2007;46:52.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHensel J, Wang G, Li Y, Zhang JZ. Nano Lett. 2010;10:478.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDoyle RL, Godwin IG, Brandon MP, Lyons MEG. Phys Chem Chem Phys. 2013;15:13737.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKong D, Cha JJ, Wang H, Lee HR, Cui Y. Energ Environ Sci. 2013;6:3553.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZou Z, Ye J, Sayama K, Arakawa H. Nature. 2001;414:625.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBard AJ, Fox MA. Acc Chem Res. 1995;28:141.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYamada Y, Miyahigashi T, Kotani H, Ohkubo K, Fukuzumi S. Energ Environ Sci. 2012;5:5356.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHeinemann M, Eifert B, Heiliger C. Phys Rev B. 2013;87:115111.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eReitz JB, Solomon EI. J Am Chem Soc. 1998;120:11467.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHe Z, Lin C, Cheng W, Okazawa A, Kojima N, Yamaura J, Ueda Y. J Am Chem Soc. 2011;133:1298.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZeng Z, Greenblatt M, Subramanian MA, Croft M. Phys Rev Lett. 1999;82:3164.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang H, Xu JZ, Zhu JJ, Chen HY. J Cryst Growth. 2002;244:88.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTaberna PL, Mitra S, Poizot P, Simon P, Tarascon JM. Nat Mater. 2006;5:567.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHu Y, Huang X, Wang K, Liu J, Jiang J, Ding R, Ji X, Li X. J Solid State Chem. 2010;183:662.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhang J, Liu J, Peng Q, Wang X, Li Y. Chem Mater. 2006;18:867.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eReitz E, Jia W, Gentile M, Wang Y, Lei Y. Electroanalysis. 2008;20:2482.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLoa CH, Tsunga TT, Chen LC. J Cryst Grow. 2005;277:636.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRahman MM, Jamal A, Khan SB, Faisal M. ACS Appl Mater Interfaces. 2011;3:1346.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBao Q, Li CM, Liao L, Yang H, Wang W, Ke C, Song Q, Bao H, Yu T, Loh KP, Guo J. Nanotechnology. 2009;20:065203.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShaikh JS, Pawar RC, Devan RS, Ma YR, Salvi PP, Kolekar SS, Patil PS. Electrochim Acta. 2011;56:2127.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLeventis N, Chandrasekaran N, Sadekar AG, Leventis CS, Lu H. J Am Chem Soc. 2009;131:4576.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKauffman DR, Ohodnicki PR, Kail BW, Matranga C. \u003cem\u003eJ. Phys. Chem. Lett.\u003c/em\u003e, 2011, 2, 2038.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAnandan S, Wen X, Yang S. Mater Chem Phys. 2005;93:35.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJunod A, Eckert D, Triscone G, Muller J, Reichardt W. J Phys Condens Matter. 1989;1:8021.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRout L, Sen TK, Punniyamurthy T. Angew Chem Int Ed. 2007;46:5583.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJiang X, Herricks T, Xia Y. Nano Lett. 2002;2:1333.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYao WT, Yu SH, Zhou Y, Jiang J, Wu QS, Zhang L, Jiang J. J Phys Chem B. 2005;109:14011\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKe FS, Huang L, Wei GZ, Xue LJ, Li JT, Zhang B, Chen SR, Fan XY, Sun SG. Electrochim Acta. 2009;54:5825.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDuan Y, Liu X, Han L, Asahina S, Xu D, Cao Y, Yao Y, Che S. J Am Chem Soc. 2014;136:719.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOutokesh M, Hosseinpour M, Ahmadi SJ, Mousavand T, Sadjadi S, Soltanian W. Ind Eng Chem Res. 2011;50:3540.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChen L, Li L, Li G. J Alloys Comp. 2008;464:532.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGhosh M, Rao CNR. Chem Phys Lett. 2004;393:493.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAhmad T, Chopra R, Ramanujachary KV, Lofland SE, Ganguli AK. Solid State Sci. 2005;7:891.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang ZM, Lin YS. J Catal. 1998;174:43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAnandan S, Lee GJ, Wu JJ. Ultrason Sonochem. 2012;19:682.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKumar B, Saha S, Basu M, Ganguli AK. J Mater Chem A. 2013;1:4728.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKumar B, Saha S, Ganguly A, Ganguli AK. RSC Adv. 2014;4:12043.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAhmed J, Ganguly A, Saha S, Gupta G, Trinh P, Mugweru AM, Lofland SE, Ramanujachary KV, Ganguli AK. J Phys Chem C. 2011;115:14526.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAhmed J, Kumar B, Mugweru AM, Trinh P, Ramanujachary KV, Lofland SE, Govind AK, Ganguli. J Phys Chem C. 2010;114:18779.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKumar B, Saha S, Ojha K. K Ganguli Mater Res Bull. 2015;64:283.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKumar B, Rao GK, Saha S, Ganguli AK. ChemPhysChem. 2016;17:155.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMuralikrishna S, Ravishankar TN, Ramakrishnappa T, Nagaraju DH, Pai RK. Environmen Prog Sustain Energy, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/ep.12238\u003c/span\u003e\u003cspan address=\"10.1002/ep.12238\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIslam MN, Ahmed J, Faisal M, Algethami JS, Aoki K, Nagao Y, Harraz FA, Hasnat MA. ChemistrySelect. 2023;8. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/slct.202301077\u003c/span\u003e\u003cspan address=\"10.1002/slct.202301077\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKuo CH, Chen CH, Huang MH. Adv Funct Mater. 2007;17:3773.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDeori K, Deka S. CrystEngComm. 2013;15:8465.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGreen CL, Kucernak A. J Phys Chem B. 2002;106:1036.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMajumdar S, Sharma IG, Bidaye AC, Suri AK. Thermochimica acta. 2008;473:45.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCrespo MAD, Meneses ER, Palma VM, Huerta AMT, Rosales HD. Int J Hydrogen Ener. 2009;34:1664.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMuler CI, Rauscher T, Schmidt A, Schubert T, Weibgarber T, Kieback B, Rontzsch L. Int J Hydrogen Energy. 2014;39:8926\u0026ndash;37.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZeng M, Li Y. J Mater Chem A. 2015;3:14942\u0026ndash;62.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLu X, Ng YH, Zhao C. Chemsuschem. 2014;7:82.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCherevko S, Kulyk N, Chung CH. Langmuir. 2012;28:3306.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSuryanto BHR, Lu X, Zhao C. J Mater Chem A. 2013;1:12726.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1: Crystallite size, particles size, density and surface area nano-micron CuO composites\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"511\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 11.9374%;\"\u003e\n \u003cp\u003eS. No.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.7867%;\"\u003e\n \u003cp\u003eCompounds\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003eCrystallite Size (nm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003eParticles Size (nm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003eDensity \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9609%;\"\u003e\n \u003cp\u003eSurface area (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 11.9374%;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.7867%;\"\u003e\n \u003cp\u003ePure Micron\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e160\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e6.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9609%;\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 11.9374%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.7867%;\"\u003e\n \u003cp\u003e20%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e50- 20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e6.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9609%;\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 11.9374%;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.7867%;\"\u003e\n \u003cp\u003e40%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e15- 35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e6.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9609%;\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 11.9374%;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.7867%;\"\u003e\n \u003cp\u003e50%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e18- 35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e6.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9609%;\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 11.9374%;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.7867%;\"\u003e\n \u003cp\u003e60%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e12 - 30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e6.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9609%;\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 11.9374%;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.7867%;\"\u003e\n \u003cp\u003e80%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e15- 25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e5.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9609%;\"\u003e\n \u003cp\u003e54\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 11.9374%;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.7867%;\"\u003e\n \u003cp\u003ePure nano\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e~ 15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.4384%;\"\u003e\n \u003cp\u003e5.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.9609%;\"\u003e\n \u003cp\u003e62.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2: \u0026nbsp;Electroactive surface area, current and current density of nano-micron composites of CuO vs Ag/AgCl reference electrode\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"685\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 6.27737%;\"\u003e\n \u003cp\u003eS. No.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.0146%;\"\u003e\n \u003cp\u003eCompounds\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003eESA (cm\u003csup\u003e2\u003c/sup\u003e/mg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003eCurrent (mA)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.781%;\"\u003e\n \u003cp\u003eCurrent density \u0026nbsp;(mA/cm\u003csup\u003e2\u003c/sup\u003e)\u003csub\u003eESA\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp;-1.3 V potential\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30.6569%;\"\u003e\n \u003cp\u003eCurrent density \u0026nbsp;(mA/cm\u003csup\u003e2\u003c/sup\u003e)\u003csub\u003eGEO\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp;-1.3 V potential\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 6.27737%;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.0146%;\"\u003e\n \u003cp\u003ePure Micron\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.026\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.781%;\"\u003e\n \u003cp\u003e3.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30.6569%;\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 6.27737%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.0146%;\"\u003e\n \u003cp\u003e20%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.028\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.781%;\"\u003e\n \u003cp\u003e32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30.6569%;\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 6.27737%;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.0146%;\"\u003e\n \u003cp\u003e40%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.044\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e3.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.781%;\"\u003e\n \u003cp\u003e81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30.6569%;\"\u003e\n \u003cp\u003e128\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 6.27737%;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.0146%;\"\u003e\n \u003cp\u003e50%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.050\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e5.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.781%;\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30.6569%;\"\u003e\n \u003cp\u003e163\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 6.27737%;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.0146%;\"\u003e\n \u003cp\u003e60%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.052\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.781%;\"\u003e\n \u003cp\u003e145\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30.6569%;\"\u003e\n \u003cp\u003e208\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 6.27737%;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.0146%;\"\u003e\n \u003cp\u003e80%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.056\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e11.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.781%;\"\u003e\n \u003cp\u003e198\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30.6569%;\"\u003e\n \u003cp\u003e372\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 6.27737%;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.0146%;\"\u003e\n \u003cp\u003ePure nano\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e0.067\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.63504%;\"\u003e\n \u003cp\u003e18.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.781%;\"\u003e\n \u003cp\u003e272\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30.6569%;\"\u003e\n \u003cp\u003e596\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-electrochemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Electrochemistry](https://link.springer.com/journal/44373)","snPcode":"44373","submissionUrl":"https://submission.nature.com/new-submission/44373/3","title":"Discover Electrochemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Composites, electrocatalysts, HER, electroactive surface area, nano-sized","lastPublishedDoi":"10.21203/rs.3.rs-7626843/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7626843/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHerein, I report nano size effect on electrocatalytic hydrogen evolution reaction (HER) by using nano-micron (n-\u0026micro;) composites of CuO. These n-\u0026micro; CuO composites were synthesized by mixing copper oxalate nanorods and CuO in different (20 to 80 weight percentage) ratios followed by heating at 350 \u0026deg;C in air. As the amount of copper oxalate increases in the in the mixture of nano-micron composites, there is a decrease in the particle size (50\u0026ndash;20 nm) of the composites. The pure nano and micron-sized CuO particles was found to be the size of ~\u0026thinsp;15 nm and ~\u0026thinsp;110 nm respectively. On the electrochemical HER study the highest (272 mA/cm\u003csup\u003e2\u003c/sup\u003emg) and lowest (3.8 mA/cm\u003csup\u003e2\u003c/sup\u003emg) current density (hydrogen evolution) was observed for pure nano and micron-sized particles respectively at -1.3 V potential for Ag/AgCl working electrode (-0.293 V vs RHE) on electroactive surface area. In case of n-\u0026micro; composites, it is found that as the amount of nano sized particles increases there is increase in current density due to increase in surface area and interconnectivity of the nanoparticles. The CuO nanoparticles are very stable over 500 cycles. The present study of nano\u0026ndash;micron composites show the combined effect of nanoscale advantages (high activity) with microscale advantages (conductivity and mechanical stability) for different potential applications.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e","manuscriptTitle":"Enhanced hydrogen evolution by nanostructures CuO composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-03 09:38:57","doi":"10.21203/rs.3.rs-7626843/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2025-12-28T05:45:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"36835506326634579392707551116824117023","date":"2025-12-17T02:14:33+00:00","index":"hide","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-29T16:25:07+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-03T19:56:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"69072326014675947551492652070566650761","date":"2025-11-02T14:32:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"79596467157804922538017220825473447910","date":"2025-10-31T15:09:28+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-31T12:46:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-10-28T06:24:33+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Electrochemistry","date":"2025-10-28T05:13:27+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-electrochemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Electrochemistry](https://link.springer.com/journal/44373)","snPcode":"44373","submissionUrl":"https://submission.nature.com/new-submission/44373/3","title":"Discover Electrochemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7034bbb0-d33e-4bbb-b7cb-27b66b72d45e","owner":[],"postedDate":"November 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-01-16T05:08:52+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-03 09:38:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7626843","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7626843","identity":"rs-7626843","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}