Phytochemical mediated Synthesis and Characterization of Copper Oxide Nanoparticles and Its Oxygen Reduction Reaction Activity

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( C. roxburghii Spreng.) and its application towards oxygen reduction reaction (ORR) are reported here. The synthesized CuONPs were characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transforms infrared (FTIR) spectroscopy, X‑ray diffraction (XRD), Scanning electron microscope (SEM), high reosolution-transmission electron microscopy (HR-TEM), Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and thermogravimetric analysis (TGA). ICP-AES and SEM mapping confirmed the presence of Cu in synthesised NPs. The size of synthesized CuONPs had been found in the range of 2.06 to 6.20 nm with distorted spherical shape by HR-TEM. Both PE and CuONPs were coated on glassy carbon (GC) electrode to form modified electrodes, designated as GC/PE and GC/CuONPs respectively. These GC/PE and GC/CuONPs electrodes were subjected to cyclic voltammetry (CV) characterizations. It was found that GC/CuONPs displays good electrocatalytic activity for ORR. GC/CuONPs also exhibits outstanding operational stability up to 1000 CV cycles. Oxygen reduction reaction Electrocatalytic activity Fuel cells Copper oxide nanoparticles Impedance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Introduction Currently worldwide energy crunch as well as enormous environmental pollution has become an obstacle for the growth and subsistence of humanity. To counter this issue we require energy sources that are viable, efficient and environment friendly. The development of oxygen reduction reaction (ORR) based electrochemical devices such as fuel cells, metal-air batteries etc. play an important role in generation of these energy sources [ 1 , 2 ]. Therefore, the development of an efficient catalyst for cathodic ORR has become center of attraction among researchers globally. Theoretically, best suited catalyst for ORR need to have the potential to effectively break the high enthalpy O = O bond. Regarding this concern platinum (Pt) is most utilized metal [ 3 ]. However, high price, CO poisoning and less stability are the key difficulties for the commercial viability of platinum associated electrodes [ 4 ]. To address these difficulties numerous researches are going on to find an alternate material to Pt for the purpose of ORR [ 5 – 8 ]. Among various available alternate materials to substitute Pt based electrodes, Cu have been found as a promising material related ORR due to its easy availability, low price and variable oxidation state having varied structures [ 9 , 10 ]. Ongoing research reports reveal that various physical as well as chemical methods have been employed successfully for the synthesis of CuONPs [ 11 – 13 ]. But the green approaches for the synthesis of CuONPs having advantage of being environment friendly, avoiding hazardous and expensive chemical entities. In addition to these advantages, this approach also utilises renewable plant materials as a reagent for the synthesis of CuONPs. Biomolecules present in these plant materials reduce the Cu ions and also stabilize the synthesized CuONPs via complexation [ 14 ]. Present research work consists of phytochemical mediated, green, simplistic and commercially sustainable approach for the synthesis of CuONPs utilising leaves extract of plant C. roxburghii Spreng.. Further these NPs have been analysed for its activity towards ORR. Experimental Chemicals and reagents Cupric sulphate (CuSO 4 .5H 2 O), N, N'-dimethylformamide (DMF) and potassium hydroxide (KOH) were purchased from Sd-fine Chem., India. Preparation of the CuONPs and all the electrochemical tests were performed in triple distilled water. Preparation of plant leaves extract Leaves of the C. roxburghii Spreng. were washed three times by using double distilled water and dried at room temperature under shaded environment for two weeks. These dried leaves were again washed with double distilled water and chopped into small pieces. 30 grams of these chopped leaves were added in 100 mL of water and further, this mixture was heated at 45°C for 40 min. Temperature of the mixture was lowered to room temperature and it was subjected to filteration using Whatman (grade − 1) filter paper to obtain a brownish aqueous leaves extract. This aqueous leaves extract was further utilized for the synthesis of desired CuONPs. Synthesis of plant derived CuONPs Filtered aqueous leaves extract (50 mL) was added drop wise into an aqueous stirred solution of CuSO 4 .5H 2 O (10 mM, 50 mL) at room temperature. Reaction mixture was initially turned to light brown which became dark brown later. Further, reaction mixture was stirred for 12 h at room temperature and formation of suspended particles was observed that showed formation of CuONPs. A brownish black precipitate of CuONPs was obtained after centrifugation of reaction mixture at 3500 rpm for 15 min. These CuONPs precipitate was washed thrice with triple distilled water to remove associated water soluble impurities. CuONPs were dried at 60°C for 6 h and used for characterization and ORR activity. Preparation of modified electrode A suspension (1% w/v) of PE and CuONPs was prepared in DMF. A 5µL suspension of PE was fabricated on GC electrode, kept for 3 hours to dry and represented as GC/PE. Likewise, modified GC/CuONPs electrode also prepared. Characterization techniques of CuONPs UV–vis spectra spectra were recorded with Systronics Double Beam Spectrophotometer (AU 2703) over the wavelength range of 200 to 800 nm. FTIR spectrum was obtained from PerkinElmer (spectrum 2, UK) by using KBr pellets over the range of 400–4000 cm − 1 . Powder X-ray diffraction (XRD) measurements were performed using CuKα1, 2 radiation on a Bruker D8, Germany advance reflection diffractometer equipped with a LynxEye energy-discriminating position-sensitive detector and samples were scanned over a range of 2θ values, 5–80°. High-resolution transmission electron microscopy (HR-TEM) was performed on the samples using a Titan 80–300 ST microscope from Thermo-Fisher Scientific. The microscope had a spherical aberration corrector for the electron beam and an energy filter of GIF Quantum 966. The microscope was operated at an accelerating voltage of 300 kV. Scanning electron microscope (SEM) was performed on Quattro FEG SEM from Thermo Fisher. Samples were deposited on carbon film before measurement. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) for evaluating metals loading amounts was conducted on a Thermo-Electron 3580 instrument after acid digestion. Thermogravimetric Analysis (TGA) was performed on TGA-50 from Shimadzu Ltd. Electrochemical tests were executed by using an electrochemical workstation (CHI-760E, make USA). A three electrode system namely Ag/AgCl, glassy carbon (GC) and platinum wire were used as a reference, working and counter electrode, respectively. Nitrogen and oxygen gas was purged in the electrolytes for 15 minutes to make inert and oxygen saturated, solution respectively. Results and discussion Synthesis of plant derived CuONPs Change of initial blue color of CuSO 4 .5H 2 O solution to a prominent light brown color and formation of suspended particles in the reaction mixture after addition of aqueous plant extract (Fig. 1 ) indicated formation of the CuONPs [ 15 ]. UV-vis spectroscopy analysis of synthesized CuONPs During the course of reaction, a change of colour from blue to brown was observed with the wavelength of maximum absorbance near to 405 nm (Fig. 2 ). This absorbance infers the formation of CuONPs [ 15 ]. FTIR Spectroscopy analysis FTIR spectrum of the synthesized CuONPs is shown in Fig. 3 . This spectrum displays various peaks formed due to interaction of copper ions and different functional groups present in molecules of PE. A broad peak at 3364 cm − 1 is obtained because of hydrogen bonded O-H stretching vibration of the hydroxyl group. An absorption band at 2932 cm − 1 is attributed to C-H stretching vibration. The absorption bands at 1730 cm − 1 may be assigned to carbonyl C = O of either aldehyde, ketone or acid and 1617 cm − 1 correspond to amide (CONH–) group [ 16 ]. 1442 cm − 1 correspond to aromatic C = C stretching vibration [ 17 ]. An absorption peak at 1524 cm − 1 and 1360 cm − 1 correspond to asymmetric and symmetric N-O stretching vibration respectively [ 16 ]. An absorption peak at 1196 cm − 1 infers to the presence of aliphatic C–N stretching vibration [ 18 ]. The absorption band at 1083 cm − 1 corresponds to the C–O stretching vibration [ 16 ]. The absorption bands at 826 cm − 1 and 764 cm − 1 due to the out of plane C-H bending vibrations [ 16 ]. Two absorption peaks present at 505 cm − 1 and 464 cm − 1 infers the presence of Cu-O [ 9 , 19 ]. These two specific peaks are absent in FTIR spectrum of PE (Fig. 3 ) further depicting the formation of Cu-O bond in CuONPs. Analysis of FTIR spectrum data reveals that electron donating functional groups (-OH, -NH 2 ) may be playing an important role in formation as well as stabilization of CuONPs. Thermogravimetric Analysis (TGA) TGA of the synthesized CuONPs was done to assess its thermal stability in the temperature range of 30°C to 800°C. TGA curve depicts a two-step continuous weight loss of CuONPs between 30°C to 123°C and 225°C to 800°C. First step weight loss is may be due to loss of associated moisture and second weight loss may be attributed to decomposition of capped phytochemicals of CuONPs [ 20 ]. Moreover, the weight loss of the synthesized CuONPs has been found nearly constant in the temperature range of 123°C to 225°C, inferring thermal stability in this range. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis The amount of copper atom present in the synthesized nanoparticles estimated by using ICP-AES was found to be 6.1 wt %. This analysis further confirms the formation of targeted CuONPs. Powder XRD analysis Figure 5 shows the XRD pattern of the synthesized CuONPs. The crystalline diffraction intensities were taken from 10 to 80 at 2θ angles. Five characteristic Bragg’s reflection peaks were obtained at 2θ angles of 23.8°, 32.4°, 36.9°, 51.4° and 56.3° corresponding to the (021), (110), (130), (020) and (202) set of lattice planes [ 21 , 22 ]. XRD data indicates that the nature of the synthesized CuONPs is monoclinic with low crystallinity [ 23 ]. We have calculated lattice constant values and these values are a = 4.3876 Å, b = 3.5526 Å, and c = 4.8891 Å. These values have been found close to the reported literature values [ 20 ]. Average crystallite size of the CuONPs was determined by using Debye-Scherrer formula, D = 0.94 λ/β cosθ, where D = average crystallite size, λ = X-ray wavelength of 1.54 Å, β = full wavelength half maximum (FWHM) and θ = Bragg diffraction angle. The average crystallite size of the synthesized CuONPs was calculated to be ∼6.3 nm corresponding to (110) plane. This calculated crystallite size is close to the average size (4.23 nm) of CuONPs determined by TEM analysis. On other hand, no peaks are found in XRD spectrum of PE, indicating its amorphous nature. SEM and TEM analysis of synthesized CuONPs The SEM images show that morphology of the synthesized CuONPs is irregular (Fig. 6 a). EDAX mapping shows the presence of C, O and Cu atoms in synthesized sample, confirming the formation of CuONPs (Fig. 6 b). Moreover, this mapping also depicts the homogeneous elemental distribution of C, O and Cu all over the surface. According to the TEM image (Fig. 7 a) shape of the synthesized CuONPs are distorted spherical. The range of particle size of the partially agglomerated synthesized CuONPs is between 2.06 to 6.20 nm and size distribution histogram curve infers that the average size of the CuONPs is ∼4.23 nm (Fig. 7 b). Electrochemical characterization Electrochemical characterization of the modified electrode GC/PE and GC/CuONPs was tested in 0.1M KOH at different scan rate from 20–500 mVs − 1 (Fig. 8 ). The modified electrode GC/ CuONPs does not represent any redox signal with CV scan in 0.1M KOH. It may be possible may be due to very weak redox process of CuONPs in the aqueous medium (Fig. 8 ) [ 24 ]. On increasing the scan rate from 20 to 500 mV − 1 , oxygen reduction current (ORR) current of CuONPs increases as expected [ 25 ]. The electrocatalytic activity of GC/ CuONPs is further tested for ORR. Electrochemical Oxygen Reduction Reaction To understand the electrochemical characteristics of the materials, cyclic voltammetry (CV) response of the two electrodes, GC/PE and GC/CuONPs are recorded in 0.1 M KOH at the scan rate of 20 mVs − 1 (Fig. 9 ). In nitrogen saturated condition show no redox signals are observed for GC/PE (a) and GC/CuONPs (b) electrodes in aqueous medium. However, in oxygen saturated condition GC/PE (a’) and GC/CuONPs (b’) show sufficient reduction current at onset potential − 0.3V and − 0.2V, respectively. Reduction current at GC/PE (a’) and GC/CuONPs (b’) are − 15 µA and − 20 µA respectively. A low ORR onset potential signifies efficient ORR activity at GC/CuONPs, demonstrating that GC/CuONPs possess strong electrocatalytic properties for ORR. However, the ORR current for GC/CuONPs is lower when compared to commercial catalysts. The effectiveness of the system can be improved by utilizing appropriate transducers such as graphene, carbon nanotubes, mesoporous carbon, etc [ 25 ]. Electrochemical Impedance spectroscopy Electrochemical Impedance spectroscopy ( EIS) is a technique used to investigate the interfacial properties of electrochemical sensor platforms. Figure 10 shows the Nyquist plot for GC, GC/PE and GC/CuONPs Composite in 0.1M Fe(CN) 6 3− / Fe(CN) 6 4– (1:1 molar ratio) as a redox probe containing 0.1 M KCl [ 26 ]. In this circuit, R s and R ct indicate solution resistance and charge transfer resistance, respectively. The constant phase element is linked to the parameter O, which is the Warburg impedance due to mass diffusion and capacitance of the double layer (interface between the polarised electrode and the electrolytic solution) [ 27 , 28 ]. The solution resistance (R s ) of the GC, GC/PE and GC/CuONPs are nearly identical at room temperature. In addition, the capacitive resistances (R ct ) of GC (3921 Ω), GC/PE (3647 Ω), GC/CuONPs (2059 Ω) has quite variation. The R ct values for GC/CuONPs are lower compared to GC and GC/CuONPs. It indicates the high electrical conductivity of GC/CuONPs. The lower Rct values of the composite materials indicate their greater electrochemical conductivity. Stability of the modified electrode for ORR To test the operational stability of modified electrode GC/CuONPs, with 1000 CV cycles were tested in 0.1 M KOH (Fig. 11 ). The 1st (a) and 1001th (b) CV cycle of GC/CuONPs are representing very small variations in ORR current. GC/CuONPs retain more than 90% ORR current even after 1000 CV scan. It is indicating the high operational stability of the modified electrode at GC/CuONPs for ORR. Conclusions Present research work comprises a facile, commercially feasible and a green method, utilizing nontoxic renewable biomass (leaves extract of plant C. roxburghii Spreng.) based synthesis of CuONPs. These NPs have been synthesised first time by using leaves extract of plant C. roxburghii Spreng. as reducing as well as stabilizing agent. The CuONPs have been characterized by UV-vis spectroscopy, FTIR, HR-TEM, SEM, ICP-AES, TGA and XRD. TEM infers the size of synthesized CuONPs in the range of 2.06 to 6.20 nm with distorted spherical shape. Further, the CuONPs based modified electrode show the efficient electrochemical activity for ORR. GC/CuONPs has remarkable conductivity compare to bare electrodes GC/PE and GC electrodes. It shows the high operational stability upto 1000 CV cycles. It is clear from the above studies that GC/CuONPs could be a remarkable cathode material for development of low cost fuel cells. Declarations Conflict of interest The authors declare no competing interests. Author Contribution Manisha Kumari and Kumari Rinki did the synthesis of nanoparticles. Piyush Kumar Sonkar, and Narvadeshwar Kumar did the electrochemical characterization and ORR analysis. Shyam Raj Yadav and Jai Prakash wrote the main manuscript text . Acknowledgements The authors (JP and SRY) are thankful to the Principal, S P Jain College, Sasaram for providing all required amenities and infrastructure to carry out this research. PKS acknowledges Institute of Eminence, Banaras Hindu University (IoE, BHU), India for Transdisciplinary research project for funding support. References Chen Q, Zhang Z, Zhang R, Hu M, Shi L, Yao Z (2023) Recent Progress of Non-Pt Catalysts for Oxygen Reduction Reaction in Fuel Cells. Processes 11:361. https:// doi.org/10.3390/pr11020361 Li Y, Lu J (2017) Metal–Air Batteries: Will They Be the Future Electrochemical Energy Storage Device of Choice. 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Cite Share Download PDF Status: Under Review Version 1 posted Editor assigned by journal 29 Jul, 2024 Submission checks completed at journal 29 Jul, 2024 First submitted to journal 26 Jul, 2024 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-4807046","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":333400872,"identity":"0a553b4b-22eb-4197-aeb5-e12d0cac0993","order_by":0,"name":"Shyam Raj Yadav","email":"","orcid":"","institution":"S P Jain College, Veer Kunwar Singh University","correspondingAuthor":false,"prefix":"","firstName":"Shyam","middleName":"Raj","lastName":"Yadav","suffix":""},{"id":333400873,"identity":"3961ffe0-2324-4ee0-a425-31ae19c668df","order_by":1,"name":"Jai 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University","correspondingAuthor":false,"prefix":"","firstName":"Narvadeshwar","middleName":"","lastName":"Kumar","suffix":""}],"badges":[],"createdAt":"2024-07-26 09:36:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4807046/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4807046/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":63250916,"identity":"dcd7f661-55e4-4ff3-b78d-68bf44b9681b","added_by":"auto","created_at":"2024-08-26 07:06:00","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":51620,"visible":true,"origin":"","legend":"\u003cp\u003eSynthesis of plant derived CuONPs.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/87e1650f4e7a0847695a2bd2.jpg"},{"id":63250926,"identity":"91f273c3-3bbb-45f4-9dd3-f5e5fc9b28a1","added_by":"auto","created_at":"2024-08-26 07:06:00","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":28746,"visible":true,"origin":"","legend":"\u003cp\u003eUV-vis absorbance of reaction mixture, PE and CuSO\u003csub\u003e4\u003c/sub\u003e.5H\u003csub\u003e2\u003c/sub\u003eO solution.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/568d8212e7db142677feed61.jpg"},{"id":63250925,"identity":"337637d2-3e20-4f27-8513-7b0200c7cf8c","added_by":"auto","created_at":"2024-08-26 07:06:00","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":34530,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR Spectrum of PE and CuONPs.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/ee3cc74acfeb2885450b59a6.jpg"},{"id":63250924,"identity":"b73939ff-0636-4f16-b01f-e80c07abfeb3","added_by":"auto","created_at":"2024-08-26 07:06:00","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":25971,"visible":true,"origin":"","legend":"\u003cp\u003eTGA of CuONPs.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/5f5a98df94d14c297c8ee2ce.jpg"},{"id":63250927,"identity":"18758a75-6f2f-4ebb-82db-94e9b94c129b","added_by":"auto","created_at":"2024-08-26 07:06:00","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":30633,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of PE and CuONPs.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/f9a03a99a82cff8f979e83c1.jpg"},{"id":63250918,"identity":"0e44e9d1-0543-4c01-a38c-7e7a73b7e130","added_by":"auto","created_at":"2024-08-26 07:06:00","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":101884,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea) \u003c/strong\u003eSEM image of CuONPs \u003cstrong\u003eb)\u003c/strong\u003e EDAX mapping of CuONPs.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/6c37b56170c8117c72ed5a2c.jpg"},{"id":63250922,"identity":"3bffcb37-d42b-4651-9821-ef8ad3a761d2","added_by":"auto","created_at":"2024-08-26 07:06:00","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":62612,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e) HR-TEM of CuONPs \u003cstrong\u003eb\u003c/strong\u003e) Size distribution histogram curve of CuONPs.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/58f8f6cb101e6e8006543ed4.jpg"},{"id":63251525,"identity":"639bac05-eec0-41d0-8a74-f029412180ab","added_by":"auto","created_at":"2024-08-26 07:14:00","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":60855,"visible":true,"origin":"","legend":"\u003cp\u003eShow the CV scan at modified electrode GC/ CuONPs with different scan rate (20, 50, 100, 200, 300, 400, 500 mV s\u003csup\u003e-1\u003c/sup\u003e in electrolyte 0.1 M KOH.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/f9791e0d377bcd80b89d7d3f.jpg"},{"id":63250920,"identity":"4db2dfbc-e77d-41bc-acd3-03615941648e","added_by":"auto","created_at":"2024-08-26 07:06:00","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":30208,"visible":true,"origin":"","legend":"\u003cp\u003eShow the CV of GC/PE (a,a’) and GC/CuONPs (b,b’)\u0026nbsp; in nitrogen (a,b) and oxygen (a’,b’) saturated condition with the scan rate 20mV\u003csup\u003e-1\u003c/sup\u003e in 0.1M KOH.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/997549bafe2c110284b58e76.jpg"},{"id":63251526,"identity":"c205eb1a-87df-4704-81d7-110ee9c96433","added_by":"auto","created_at":"2024-08-26 07:14:00","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":43149,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plot for (a) GC/CuONPs, (b) GC, and (c) GC/PE in 0.1M Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4– \u0026nbsp;\u003c/sup\u003e(1:1 molar ratio) containing 0.1M KCl.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/68b99427f620e762ba8a68ba.jpg"},{"id":63251528,"identity":"354f4a1c-cfa0-41d8-ae2a-8d0dbb73cfde","added_by":"auto","created_at":"2024-08-26 07:14:00","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":44733,"visible":true,"origin":"","legend":"\u003cp\u003eShows the 1\u003csup\u003est\u003c/sup\u003e (a) 1001\u003csup\u003eth\u003c/sup\u003e (b) CV scan of GC/CuONPs in oxygen saturated condition 0.1M KOH, scan rate 20 mV s\u003csup\u003e-1\u003c/sup\u003e . Inset represents 1000 CV cycles at GC/CuONPs under similar condition at a scan rate of 200 mV s\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/912275253af5c1048efaec5c.jpg"},{"id":63252096,"identity":"7933b8b4-ea96-41db-930f-34b704ab7185","added_by":"auto","created_at":"2024-08-26 07:22:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1024751,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4807046/v1/3292f07c-3c0f-448b-9cb9-6af9cc7cab76.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Phytochemical mediated Synthesis and Characterization of Copper Oxide Nanoparticles and Its Oxygen Reduction Reaction Activity","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCurrently worldwide energy crunch as well as enormous environmental pollution has become an obstacle for the growth and subsistence of humanity. To counter this issue we require energy sources that are viable, efficient and environment friendly. The development of oxygen reduction reaction (ORR) based electrochemical devices such as fuel cells, metal-air batteries etc. play an important role in generation of these energy sources [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Therefore, the development of an efficient catalyst for cathodic ORR has become center of attraction among researchers globally.\u003c/p\u003e \u003cp\u003eTheoretically, best suited catalyst for ORR need to have the potential to effectively break the high enthalpy O\u0026thinsp;=\u0026thinsp;O bond. Regarding this concern platinum (Pt) is most utilized metal [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, high price, CO poisoning and less stability are the key difficulties for the commercial viability of platinum associated electrodes [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. To address these difficulties numerous researches are going on to find an alternate material to Pt for the purpose of ORR [\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAmong various available alternate materials to substitute Pt based electrodes, Cu have been found as a promising material related ORR due to its easy availability, low price and variable oxidation state having varied structures [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Ongoing research reports reveal that various physical as well as chemical methods have been employed successfully for the synthesis of CuONPs [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. But the green approaches for the synthesis of CuONPs having advantage of being environment friendly, avoiding hazardous and expensive chemical entities. In addition to these advantages, this approach also utilises renewable plant materials as a reagent for the synthesis of CuONPs. Biomolecules present in these plant materials reduce the Cu ions and also stabilize the synthesized CuONPs via complexation [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePresent research work consists of phytochemical mediated, green, simplistic and commercially sustainable approach for the synthesis of CuONPs utilising leaves extract of plant \u003cem\u003eC. roxburghii\u003c/em\u003e Spreng.. Further these NPs have been analysed for its activity towards ORR.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eChemicals and reagents\u003c/h2\u003e \u003cp\u003eCupric sulphate (CuSO\u003csub\u003e4\u003c/sub\u003e.5H\u003csub\u003e2\u003c/sub\u003eO), N, N'-dimethylformamide (DMF) and potassium hydroxide (KOH) were purchased from Sd-fine Chem., India. Preparation of the CuONPs and all the electrochemical tests were performed in triple distilled water.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of plant leaves extract\u003c/h2\u003e \u003cp\u003eLeaves of the \u003cem\u003eC. roxburghii\u003c/em\u003e Spreng. were washed three times by using double distilled water and dried at room temperature under shaded environment for two weeks. These dried leaves were again washed with double distilled water and chopped into small pieces. 30 grams of these chopped leaves were added in 100 mL of water and further, this mixture was heated at 45\u0026deg;C for 40 min. Temperature of the mixture was lowered to room temperature and it was subjected to filteration using Whatman (grade \u0026minus;\u0026thinsp;1) filter paper to obtain a brownish aqueous leaves extract. This aqueous leaves extract was further utilized for the synthesis of desired CuONPs.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of plant derived CuONPs\u003c/h2\u003e \u003cp\u003eFiltered aqueous leaves extract (50 mL) was added drop wise into an aqueous stirred solution of CuSO\u003csub\u003e4\u003c/sub\u003e.5H\u003csub\u003e2\u003c/sub\u003eO (10 mM, 50 mL) at room temperature. Reaction mixture was initially turned to light brown which became dark brown later. Further, reaction mixture was stirred for 12 h at room temperature and formation of suspended particles was observed that showed formation of CuONPs. A brownish black precipitate of CuONPs was obtained after centrifugation of reaction mixture at 3500 rpm for 15 min. These CuONPs precipitate was washed thrice with triple distilled water to remove associated water soluble impurities. CuONPs were dried at 60\u0026deg;C for 6 h and used for characterization and ORR activity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of modified electrode\u003c/h2\u003e \u003cp\u003eA suspension (1% w/v) of PE and CuONPs was prepared in DMF. A 5\u0026micro;L suspension of PE was fabricated on GC electrode, kept for 3 hours to dry and represented as GC/PE. Likewise, modified GC/CuONPs electrode also prepared.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization techniques of CuONPs\u003c/h2\u003e \u003cp\u003eUV\u0026ndash;vis spectra spectra were recorded with Systronics Double Beam Spectrophotometer (AU 2703) over the wavelength range of 200 to 800 nm. FTIR spectrum was obtained from PerkinElmer (spectrum 2, UK) by using KBr pellets over the range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003ePowder X-ray diffraction (XRD) measurements were performed using CuKα1, 2 radiation on a Bruker D8, Germany advance reflection diffractometer equipped with a LynxEye energy-discriminating position-sensitive detector and samples were scanned over a range of 2θ values, 5\u0026ndash;80\u0026deg;. High-resolution transmission electron microscopy (HR-TEM) was performed on the samples using a Titan 80\u0026ndash;300 ST microscope from Thermo-Fisher Scientific. The microscope had a spherical aberration corrector for the electron beam and an energy filter of GIF Quantum 966. The microscope was operated at an accelerating voltage of 300 kV. Scanning electron microscope (SEM) was performed on Quattro FEG SEM from Thermo Fisher. Samples were deposited on carbon film before measurement. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) for evaluating metals loading amounts was conducted on a Thermo-Electron 3580 instrument after acid digestion. Thermogravimetric Analysis (TGA) was performed on TGA-50 from Shimadzu Ltd. Electrochemical tests were executed by using an electrochemical workstation (CHI-760E, make USA). A three electrode system namely Ag/AgCl, glassy carbon (GC) and platinum wire were used as a reference, working and counter electrode, respectively. Nitrogen and oxygen gas was purged in the electrolytes for 15 minutes to make inert and oxygen saturated, solution respectively.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of plant derived CuONPs\u003c/h2\u003e \u003cp\u003eChange of initial blue color of CuSO\u003csub\u003e4\u003c/sub\u003e.5H\u003csub\u003e2\u003c/sub\u003eO solution to a prominent light brown color and formation of suspended particles in the reaction mixture after addition of aqueous plant extract (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) indicated formation of the CuONPs [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eUV-vis spectroscopy analysis of synthesized CuONPs\u003c/h2\u003e \u003cp\u003eDuring the course of reaction, a change of colour from blue to brown was observed with the wavelength of maximum absorbance near to 405 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This absorbance infers the formation of CuONPs [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eFTIR Spectroscopy analysis\u003c/h2\u003e \u003cp\u003eFTIR spectrum of the synthesized CuONPs is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. This spectrum displays various peaks formed due to interaction of copper ions and different functional groups present in molecules of PE. A broad peak at 3364 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is obtained because of hydrogen bonded O-H stretching vibration of the hydroxyl group. An absorption band at 2932 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to C-H stretching vibration. The absorption bands at 1730 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e may be assigned to carbonyl C\u0026thinsp;=\u0026thinsp;O of either aldehyde, ketone or acid and 1617 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to amide (CONH\u0026ndash;) group [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. 1442 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to aromatic C\u0026thinsp;=\u0026thinsp;C stretching vibration [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. An absorption peak at 1524 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1360 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to asymmetric and symmetric N-O stretching vibration respectively [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. An absorption peak at 1196 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e infers to the presence of aliphatic C\u0026ndash;N stretching vibration [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The absorption band at 1083 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the C\u0026ndash;O stretching vibration [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The absorption bands at 826 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 764 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e due to the out of plane C-H bending vibrations [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Two absorption peaks present at 505 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 464 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e infers the presence of Cu-O [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. These two specific peaks are absent in FTIR spectrum of PE (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) further depicting the formation of Cu-O bond in CuONPs. Analysis of FTIR spectrum data reveals that electron donating functional groups (-OH, -NH\u003csub\u003e2\u003c/sub\u003e) may be playing an important role in formation as well as stabilization of CuONPs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eThermogravimetric Analysis (TGA)\u003c/h2\u003e \u003cp\u003eTGA of the synthesized CuONPs was done to assess its thermal stability in the temperature range of 30\u0026deg;C to 800\u0026deg;C. TGA curve depicts a two-step continuous weight loss of CuONPs between 30\u0026deg;C to 123\u0026deg;C and 225\u0026deg;C to 800\u0026deg;C. First step weight loss is may be due to loss of associated moisture and second weight loss may be attributed to decomposition of capped phytochemicals of CuONPs [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Moreover, the weight loss of the synthesized CuONPs has been found nearly constant in the temperature range of 123\u0026deg;C to 225\u0026deg;C, inferring thermal stability in this range.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eInductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis\u003c/h2\u003e \u003cp\u003eThe amount of copper atom present in the synthesized nanoparticles estimated by using ICP-AES was found to be 6.1 wt %. This analysis further confirms the formation of targeted CuONPs.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003ePowder XRD analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the XRD pattern of the synthesized CuONPs. The crystalline diffraction intensities were taken from 10 to 80 at 2θ angles. Five characteristic Bragg\u0026rsquo;s reflection peaks were obtained at 2θ angles of 23.8\u0026deg;, 32.4\u0026deg;, 36.9\u0026deg;, 51.4\u0026deg; and 56.3\u0026deg; corresponding to the (021), (110), (130), (020) and (202) set of lattice planes [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. XRD data indicates that the nature of the synthesized CuONPs is monoclinic with low crystallinity [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. We have calculated lattice constant values and these values are a\u0026thinsp;=\u0026thinsp;4.3876 \u0026Aring;, b\u0026thinsp;=\u0026thinsp;3.5526 \u0026Aring;, and c\u0026thinsp;=\u0026thinsp;4.8891 \u0026Aring;. These values have been found close to the reported literature values [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Average crystallite size of the CuONPs was determined by using Debye-Scherrer formula, D\u0026thinsp;=\u0026thinsp;0.94 λ/β cosθ, where D\u0026thinsp;=\u0026thinsp;average crystallite size, λ\u0026thinsp;=\u0026thinsp;X-ray wavelength of 1.54 \u0026Aring;, β\u0026thinsp;=\u0026thinsp;full wavelength half maximum (FWHM) and θ\u0026thinsp;=\u0026thinsp;Bragg diffraction angle. The average crystallite size of the synthesized CuONPs was calculated to be \u0026sim;6.3 nm corresponding to (110) plane. This calculated crystallite size is close to the average size (4.23 nm) of CuONPs determined by TEM analysis. On other hand, no peaks are found in XRD spectrum of PE, indicating its amorphous nature.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eSEM and TEM analysis of synthesized CuONPs\u003c/h2\u003e \u003cp\u003eThe SEM images show that morphology of the synthesized CuONPs is irregular (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). EDAX mapping shows the presence of C, O and Cu atoms in synthesized sample, confirming the formation of CuONPs (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). Moreover, this mapping also depicts the homogeneous elemental distribution of C, O and Cu all over the surface.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAccording to the TEM image (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea) shape of the synthesized CuONPs are distorted spherical. The range of particle size of the partially agglomerated synthesized CuONPs is between 2.06 to 6.20 nm and size distribution histogram curve infers that the average size of the CuONPs is \u0026sim;4.23 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical characterization\u003c/h2\u003e \u003cp\u003eElectrochemical characterization of the modified electrode GC/PE and GC/CuONPs was tested in 0.1M KOH at different scan rate from 20\u0026ndash;500 mVs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). The modified electrode GC/ CuONPs does not represent any redox signal with CV scan in 0.1M KOH. It may be possible may be due to very weak redox process of CuONPs in the aqueous medium (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. On increasing the scan rate from 20 to 500 mV\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, oxygen reduction current (ORR) current of CuONPs increases as expected [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The electrocatalytic activity of GC/ CuONPs is further tested for ORR.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical Oxygen Reduction Reaction\u003c/h2\u003e \u003cp\u003eTo understand the electrochemical characteristics of the materials, cyclic voltammetry (CV) response of the two electrodes, GC/PE and GC/CuONPs are recorded in 0.1 M KOH at the scan rate of 20 mVs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). In nitrogen saturated condition show no redox signals are observed for GC/PE (a) and GC/CuONPs (b) electrodes in aqueous medium. However, in oxygen saturated condition GC/PE (a\u0026rsquo;) and GC/CuONPs (b\u0026rsquo;) show sufficient reduction current at onset potential \u0026minus;\u0026thinsp;0.3V and \u0026minus;\u0026thinsp;0.2V, respectively. Reduction current at GC/PE (a\u0026rsquo;) and GC/CuONPs (b\u0026rsquo;) are \u0026minus;\u0026thinsp;15 \u0026micro;A and \u0026minus;\u0026thinsp;20 \u0026micro;A respectively. A low ORR onset potential signifies efficient ORR activity at GC/CuONPs, demonstrating that GC/CuONPs possess strong electrocatalytic properties for ORR. However, the ORR current for GC/CuONPs is lower when compared to commercial catalysts. The effectiveness of the system can be improved by utilizing appropriate transducers such as graphene, carbon nanotubes, mesoporous carbon, etc [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical Impedance spectroscopy\u003c/h2\u003e \u003cp\u003eElectrochemical Impedance spectroscopy \u003cb\u003e(\u003c/b\u003eEIS) is a technique used to investigate the interfacial properties of electrochemical sensor platforms. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the Nyquist plot for GC, GC/PE and GC/CuONPs Composite in 0.1M Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026ndash;\u003c/sup\u003e (1:1 molar ratio) as a redox probe containing 0.1 M KCl [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. In this circuit, R\u003csub\u003es\u003c/sub\u003e and R\u003csub\u003ect\u003c/sub\u003e indicate solution resistance and charge transfer resistance, respectively. The constant phase element is linked to the parameter O, which is the Warburg impedance due to mass diffusion and capacitance of the double layer (interface between the polarised electrode and the electrolytic solution) [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The solution resistance (R\u003csub\u003es\u003c/sub\u003e) of the GC, GC/PE and GC/CuONPs are nearly identical at room temperature. In addition, the capacitive resistances (R\u003csub\u003ect\u003c/sub\u003e) of GC (3921 Ω), GC/PE (3647 Ω), GC/CuONPs (2059 Ω) has quite variation. The R\u003csub\u003ect\u003c/sub\u003e values for GC/CuONPs are lower compared to GC and GC/CuONPs. It indicates the high electrical conductivity of GC/CuONPs. The lower Rct values of the composite materials indicate their greater electrochemical conductivity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eStability of the modified electrode for ORR\u003c/h2\u003e \u003cp\u003eTo test the operational stability of modified electrode GC/CuONPs, with 1000 CV cycles were tested in 0.1 M KOH (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e). The 1st (a) and 1001th (b) CV cycle of GC/CuONPs are representing very small variations in ORR current. GC/CuONPs retain more than 90% ORR current even after 1000 CV scan. It is indicating the high operational stability of the modified electrode at GC/CuONPs for ORR.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003ePresent research work comprises a facile, commercially feasible and a green method, utilizing nontoxic renewable biomass (leaves extract of plant \u003cem\u003eC. roxburghii\u003c/em\u003e Spreng.) based synthesis of CuONPs. These NPs have been synthesised first time by using leaves extract of plant \u003cem\u003eC. roxburghii\u003c/em\u003e Spreng. as reducing as well as stabilizing agent. The CuONPs have been characterized by UV-vis spectroscopy, FTIR, HR-TEM, SEM, ICP-AES, TGA and XRD. TEM infers the size of synthesized CuONPs in the range of 2.06 to 6.20 nm with distorted spherical shape. Further, the CuONPs based modified electrode show the efficient electrochemical activity for ORR. GC/CuONPs has remarkable conductivity compare to bare electrodes GC/PE and GC electrodes. It shows the high operational stability upto 1000 CV cycles. It is clear from the above studies that GC/CuONPs could be a remarkable cathode material for development of low cost fuel cells.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of interest\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eManisha Kumari and Kumari Rinki did the synthesis of nanoparticles. Piyush Kumar Sonkar, and Narvadeshwar Kumar did the electrochemical characterization and ORR analysis. Shyam Raj Yadav and Jai Prakash wrote the main manuscript text .\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors (JP and SRY) are thankful to the Principal, S P Jain College, Sasaram for providing all required amenities and infrastructure to carry out this research. PKS acknowledges Institute of Eminence, Banaras Hindu University (IoE, BHU), India for Transdisciplinary research project for funding support.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eChen Q, Zhang Z, Zhang R, Hu M, Shi L, Yao Z (2023) Recent Progress of Non-Pt Catalysts for Oxygen Reduction Reaction in Fuel Cells. Processes 11:361. https:// doi.org/10.3390/pr11020361\u003c/li\u003e\n\u003cli\u003eLi Y, Lu J (2017) Metal\u0026ndash;Air Batteries: Will They Be the Future Electrochemical Energy Storage Device of Choice. ACS Energy Lett 2:1370\u0026ndash;1377. https://doi.org/10.1021/acsenergylett.7b00119\u003c/li\u003e\n\u003cli\u003eWang J, Wang K, Wang FB et al. (2014) Bioinspired copper catalyst effective for both reduction and evolution of oxygen. 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RSC Advances 4:27591-27596. https://doi.org/10.1039/C4RA02691H\u003c/li\u003e\n\u003cli\u003eMatemadombo F, Nyokong T (2007) Characterization of self-assembled monolayers of iron and cobalt octaalkylthiosubstituted phthalocyanines and their use in nitrite electrocatalytic oxidation. ElectrochimActa 52:6856. https://doi.org/10.1016/j.electacta.2007.05.002\u003c/li\u003e\n\u003cli\u003eRastogi P K, Ganesan V, Krishnamoorthi S (2014) A promising electrochemical sensing platform based on a silver nanoparticles decorated copolymer for sensitive nitrite determination J Mater Chem\u003cem\u003e \u003c/em\u003eA 2:933\u0026ndash;943. https://doi.org/10.1039/C3TA13794E\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-nanoparticle-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"nano","sideBox":"Learn more about [Journal of Nanoparticle Research](http://link.springer.com/journal/11051)","snPcode":"11051","submissionUrl":"https://submission.nature.com/new-submission/11051/3","title":"Journal of Nanoparticle Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Oxygen reduction reaction, Electrocatalytic activity, Fuel cells, Copper oxide nanoparticles, Impedance","lastPublishedDoi":"10.21203/rs.3.rs-4807046/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4807046/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA successful preparation of copper oxide nanoparticles (CuONPs) by using leaves extract (PE) of plant \u003cem\u003eCombretum roxburghii\u003c/em\u003e Spreng. (\u003cem\u003eC. roxburghii\u003c/em\u003e Spreng.) and its application towards oxygen reduction reaction (ORR) are reported here. The synthesized CuONPs were characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transforms infrared (FTIR) spectroscopy, X‑ray diffraction (XRD), Scanning electron microscope (SEM), high reosolution-transmission electron microscopy (HR-TEM), Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and thermogravimetric analysis (TGA). ICP-AES and SEM mapping confirmed the presence of Cu in synthesised NPs. The size of synthesized CuONPs had been found in the range of 2.06 to 6.20 nm with distorted spherical shape by HR-TEM. Both PE and CuONPs were coated on glassy carbon (GC) electrode to form modified electrodes, designated as GC/PE and GC/CuONPs respectively. These GC/PE and GC/CuONPs electrodes were subjected to cyclic voltammetry (CV) characterizations. It was found that GC/CuONPs displays good electrocatalytic activity for ORR. GC/CuONPs also exhibits outstanding operational stability up to 1000 CV cycles.\u003c/p\u003e","manuscriptTitle":"Phytochemical mediated Synthesis and Characterization of Copper Oxide Nanoparticles and Its Oxygen Reduction Reaction Activity","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-26 07:05:55","doi":"10.21203/rs.3.rs-4807046/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorAssigned","content":"","date":"2024-07-29T20:32:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-29T04:00:36+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Nanoparticle Research","date":"2024-07-26T09:32:35+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-nanoparticle-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"nano","sideBox":"Learn more about [Journal of Nanoparticle Research](http://link.springer.com/journal/11051)","snPcode":"11051","submissionUrl":"https://submission.nature.com/new-submission/11051/3","title":"Journal of Nanoparticle Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"9b76e309-3712-4685-b605-f8205b01eec8","owner":[],"postedDate":"August 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-08-26T07:05:55+00:00","versionOfRecord":[],"versionCreatedAt":"2024-08-26 07:05:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4807046","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4807046","identity":"rs-4807046","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}