Development of highly active and robust Cu-Co–rGO electro-catalytic electrode for OER

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Manu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4589766/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In the present work a facile method was adopted for the fabrication of highly active and dimensionally stable cobalt-reduced graphene oxide (rGO) based composite electrode for OER process. The metal loading and the amount of graphene was optimized for better performance of the electrode. The development of these type of electrodes is noteworthy taking the advantage of the method and the materials used. The morphology and the composition were analyzed through scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and X-ray photo electron spectroscopy (XPS). Spectroscopic characterization was done using Fourier transform infrared (FTIR) analysis. Electrochemical characterization revealed excellent electro-catalytic activity of the prepared electrode and strongly suggest synergistic reaction between Co 3 O 4 and rGO. The developed electrode can realize excellent Oxygen Evolution Reaction (OER) activity in alkaline media with low over potential and low tafel slope with long-term stability as evidenced from various analysis. Electrodeposition Nano Composite electrode rGO OER Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. INTRODUCTION Energy security has been a major concern to world since the beginning of 21st century. With the increase in human population there is manifold surge in the energy demand for various application, considering the per capita consumption of energy. More over the source for fossil fuel is fast dwindling unless new excavation results in their production. Also, fossil fuel combustion leads to several environmental impacts that resulted in new forms of energy which are widely researched to make it more acceptable [ 1 , 2 ]. Therefore, increasing attention has been paid to develop clean energy which are a sustainable and renewable alternative to fossil fuel [ 3 ]. In the last decades numerous studies were carried out to establish better energy storage technologies, metal-air batteries, fuel cells and energy conversion processes [ 4 ]. The quest to develop new techniques to produce clean and sustainable energy is in the path of continues evolution. The idea of water splitting technology has given much attention over the years, since it plays a pivotal role in the production of hydrogen, which is a superior alternative to fossil fuels [ 5 ]. However, oxygen evolution reaction [OER] is a high energy process with a higher kinetic barrier [ 6 ]. In this regard the design and development of an efficient electrocatalyst with superior catalytic activity will be always in demand [ 7 ]. Transition metal-based compounds (especially Fe, Co, Ni) have inevitably become a hot research topic as they hold advantages like low price, abundant resources and environmental friendliness [ 8 , 9 ]. So recently many reports demonstrated these metals as a promising candidate for most accepted noble metal catalyst (Pt, Ir, Ru based compounds) which possess high cost and less abundance [ 10 , 11 ]. Among the various transition metal compounds, cobalt is of particular interest to the researcher for application in alkaline OER activity due to its low cost, mixed oxidation state, and the comparative performance when compared with other metals [ 12 – 14 ]. Recent advances in the field of composite coating have opened new possibilities for graphene oxide as an ideal catalyst support because of its fast electron transfer, large surface area, wide potential window, excellent biocompatibility, good chemical and environmental stability [ 15 , 16 ]. Vapor deposition, hydro, solvo-thermal, sol-gel method etc. are concomitantly employed for fabrication of metal-based electrode. In contrast, electrodeposition is a unique technology with a number of advantages which is economical and easy to apply [ 17 , 18 ]. Fabrication of self-standing electrodes can be easily attained through electrodeposition process as the deposits rigidly attached to the substrate. When compared to conventional drop cast method electrodes made through deposition technique have the advantage of active site utilization, good stability and simple process fabrication. By varying concentration of different components in precursor solution the electrode composition can be suitably modified [ 19 ]. Considering the above advantages the present work envisages on the development of electrocatalyst based on Co 3 O 4 -rGO composite for oxygen evolution reaction. The modified electrode was characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy to know physicochemical and surface morphology characteristics of the electrode. Elemental profile and its percentage abundance was determined using energy dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS) techniques. Electrochemical analysis of the electrode was performed by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electronic impedance spectroscopy (EIS) analysis. In the present work Cu-Co 3 O 4 -rGO electrode was synthesized by simple electrodeposition technique from cobalt-rGO precursor solution on to copper foil. The morphology, structure and electrochemical performance of the modified electrode were studied and compared with other reported work. The developed Cu-Co 3 O 4 -rGO composite electrode has uniform morphology and the electrode was stable after OER process as revealed from SEM and XPS studies. Effect of concentration of reduced graphene oxide was studied by adding different amount of rGO to the standardized bath solution. The inference from electrochemical analysis showed better activity towards OER process and the electrode was stable after repeated cycles of operation. The result of the electrochemical analysis reveals better performance and dimensional stability to the fabricated electrode. 2. EXPERIMENTAL METHODS 2.1 Materials : All the chemicals used for the present work are of analytical grade and used as such. Cobalt sulphate, sulphuric acid (98%) and other reagents were purchased from Merck, India Ltd. Deionized water was used as a solvent for the synthesis of various solutions as well as for the electrochemical studies. 2.2 Synthesis of Graphene Oxide : Graphene oxide (GO) was prepared using modified Hummer’s method by the oxidation of graphite flake [ 20 , 21 ]. Graphite rod purchased from Graphite India Ltd., was powdered and sieved through sieving mesh having specific pore size. 1 g of graphite powder of purity 99.8% was accurately weighed and stirred in 98% H 2 SO 4 for 30 minutes. 3 g KMnO 4 crystal was added to the solution with continuous stirring. The beaker containing graphite powder dispersed in acidic solution was maintained below 20 0 C temperature by keeping it in an ice bath. The resulting mixture was stirred for 48 hours by keeping the temperature at 35 0 C. Then the reaction mixture was allowed to cool at room temperature and 45 ml deionized water was added to it with vigorous stirring. The obtained mixture was then treated with 5 ml of 30% H 2 0 2 and added 75 ml deionized water. Supernatant solution was filled in small vials and then centrifuged for 15 minutes at 5000 rpm using refrigerated micro centrifuge RC 4815 F. The filtered product is washed with 5% HCl and further with deionized water until the P H of the solution becomes 6–7. The obtained residue was dried by keeping it in an oven at 60 0 C for 24 hours. The fine powder of graphene oxide synthesized was used as such for further studies. 2.3 Fabrication of Cu-Co 3 O4-rGO electrode Prior to electrodeposition, copper foil was polished with different grades of emery paper (grade − 80, 120, 220) to make the surface homogeneous and moderately rough to enhance the nucleation during electrodeposition process. The sample was then cleaned with acetone and dilute HCl and finally with plenty of water and dried in room temperature. 1 cm 2 of the substrate surface was exposed for electrodeposition. The deposition was carried out by using platinum as positive electrode (anode) and copper foil as negative electrode (cathode). Current density was set at 0.5 mA and deposition was done for 30 minutes. The deposition bath was prepared by accurately weighing different amount of graphene oxide. 0.1 g to 0.3 g of graphene oxide was dispersed in 10 ml of deionized water under ultra-sonication and then magnetically stirred for 15 minutes at 500 rpm. To this solution, 0.2 g of CoSO 4 .7H 2 O, dissolved in 10 ml of deionized water is added and stirred continuously for 15 minutes. Graphene oxide was added to this solution of cobalt and was stirred using magnetic stirrer for 30 minutes at 500 rpm at a temperature of 40 0 C. The solution mixture was kept under agitating condition during electrodeposition. After electrodeposition, the coated electrode was washed with water and dried. Electrodeposition was performed using APLAB L 3205 regulated dual DC power supply rectifier. Effect of different concentration of rGO during deposition was also studied. Along with that Deposition was performed without addition of rGO. 3. RESULTS AND DISCUSSION 3.1 FTIR-ATR analysis of Cu-Co 3 O 4 -rGO electrode FTIR-ATR spectra of the Cu-Co 3 O 4 -rGO electrode are shown in Fig. 1 . The spectra reveals that the major peak obtained at 517.2 cm − 1 in the low frequency can be assigned to metal oxygen bond stretching vibrations in Co 3 O 4 [ 22 ]. Absorption band at 1354.06 cm − 1 is attributed to C-OH stretching vibrations in graphene oxide and the appearance of a strong peak at 1087.6 cm − 1 belonging to the stretching vibration mode of C-O corresponding to carbonyl group present in graphene [ 23 ]. The broad peak appeared at 3324 cm − 1 in the high frequency area attributed to the O-H bending mode of water molecule. The presence of these types of groups reveals that functionalization was effective as evidenced from the stretching frequency in the FTIR spectrum. 3.2 SEM-EDAX analysis of the Cu-Co 3 O 4 -rGO deposit The result of EDAX analysis is consistent with the formation of Cu-Co 3 O 4 -rGO composite electrode as revealed by the presence of distinct peaks for cobalt, carbon and oxygen as shown in Fig. 2 . SEM image of Cu-Co 3 O 4 -rGO2 electrode surface resembled cauliflower-like pattern, characteristic for Co deposits as shown in Fig. 3 . The morphology reveals that the flowers are made up of agglomerates and few porous islands which in turns build a porous surface feature. The flower like pattern observed in Fig. 3 a and 3 b ascribed to the Co deposits within the graphene layer structure and its distribution on the graphene sheet tends to be uniform. Optimizing the deposition time could control the grain growth size and morphology of Co 3 O 4 nanoparticles forming a uniform morphology. The more or less porous morphology observed enacts larger surface area for the deposit. Small nanoparticles and large specific surface area can shorten the transmission path of charge, which is believed to be beneficial to increase specific capacitance and multiplier capacity. This could result in increased specific surface area there by number of active sites is increased, and the Faraday redox reaction is more active, which may influence the electrochemical performance of the deposit [39]. The Fig. 3 c and d shows the surface topography of the Cu-Co 3 O 4 -rGO2 electrode after OER. The morphology shows not much difference from the earlier fresh sample revealing that the electrode surface is stable and more adherent to the substrate. The plate like morphology seen in Fig. 3 c exposes the graphene layered surface laced within the composite matrix during OER. Table 1 Elemental percentage analysis of the deposit of Cu-Co 3 O 4 -rGO2 electrode. Element Weight % C K 21.81 O K 27.66 Co K 50.53 3.3 XPS analysis of the Cu-Co 3 O 4 -rGOelectrode Elemental composition and oxidation state of C, Co and O in the electrode were determined using XPS technique. As shown in Fig. 4 a, XPS survey spectrum revealed the presence of core level signals for Co 2p, O 1s, C 1s. This is clear from intense peak observed for specific oxidation state of the elements and also reveals the absence of other impurities. Gaussian fitting method was adopted for high magnification XPS studies of C 1s, Co 2p, O 1S spectrum. XPS spectrum of Co-reduced graphene composites exhibited peaks for Co, O, and C elements, that reveals cobalt nanoparticles get co-deposited on the graphene sheets during electrodeposition. In Fig. 4 b, four component peaks ascribed to C 1s attributed to C-C bond at 283 eV and energy peak at 284 eV is associated with C = C. The other two component peaks at 287 eV and 288 eV were assigned to C-O and O-C = O groups respectively [ 24 ]. The peaks reveals that the process of functionalization was effective for graphene. High-resolution Co 2p spectrum can be deconvoluted in to two distinct peaks centered with the binding energies (BEs) of 780.0 eV and 795.0 eV, which attributed to the spin orbit peaks of Co 2p 3/2 and Co 2p 1/2 because of the spin orbit coupling as shown in Fig. 4 c [ 25 ]. The BEs of 2p 3/2 and 2p 1/2 spin orbitals of Co 3+ and Co 2+ was observed at 779.6 eV / 795 eV and 781 eV / 796.7 eV respectively. 2 Satellite peaks are related to the formation of CoO in the deposit [ 26 ]. Figure 4 d clearly reveals the three distinct peaks at 529.8 eV, 531 eV, and 532.5 eV for O 1s associated to Co-O bond in Co 3 O 4 -rGo, C-O, and chemisorbed and physiosorbed water molecule on the electrode surface. XPS analysis of the sample after OER was performed and it shown in Fig. 5 . The spectrum showed no major shift in binding energies of the components reported earlier when compared with the fresh sample. It is observed that even after OER studies the Cu-Co 3 O 4 -rGO2 electrode was stable as revealed from XPS analysis. C 1s and O 1s peak do not have any significant changes in BE when compared with fresh sample, that strongly supports that graphene oxide which act as catalyst support is having a stable microstructure even after OER activity. This was supplemented by SEM analysis where the surface was intact after OER activity. 3.4 Electrocatalytic Studies towards Oxygen Evolution Reactions (OER) Tafel plot reflects the electrochemical kinetics of OER activity of the electrode that reveals the key parameters usually used to characterize the catalytic activity of an electrocatalyst [ 27 – 28 ]. In this work, linear sweep voltammogram (LSV), tafel and cyclic voltammetry method were carried out to assess the electro-catalytic activity of the electrode with a typical three-electrode system. In accordance with the Nernst equation ( E RHE = E (vs. SCE) + E SCE (0.241) + 0.0591 × pH), the measured values of potential Vs SCE (Saturated Calomel Electrode) were converted into a reversible hydrogen electrode (RHE). It is important that the supporting electrolyte 1 M KOH solution should be saturated with N 2 so as to fix the O 2 / H 2 O equilibrium potential at 1.23 V vs. RHE. Electrochemical activity of as-synthesized Cu-Co 3 O 4 -rGO2 exhibits the lowest onset potential of 1.48 V vs. RHE among all the other electrodes. The working potential at a current density of 10 mA cm − 2 is an essential parameter to evaluate OER activity. Cu-Co 3 O 4 -rGo2 shows relatively low working potential of 1.48 V (over potential of 259 mV) at 10 mA cm − 2 , compared to Cu-Co 3 O 4 -rGO1(1.52 V, 301 mV), Cu-Co 3 O 4 -rGo3 (1.506 V, 276 mV), and Cu-Co 3 O 4 (1.65 V, 422 mV) electrodes. From this it is assumed that there should be some optimum concentration of rGO in the metal composite in order to achieve better OER activity as revealed from the LSV analysis. In practical application, the electrochemical kinetics of OER can be judged based on the magnitude of Tafel slope. Tafel plots derived from the LSV curves are shown in Figure 6 . These plots are based on the Tafel formula of η = a + b log( j ), in which η refers to the overpotential ‘ a ’ represents the intercept on the Y axis, ‘ b ’ indicates the Tafel slope, and j refers to the current density. The Tafel graphs were plotted through the corresponding polarization curves. The value of Tafel slope can be considered as a prime factor for evaluating OER activity. Specifically, higher OER activity is clearly evident from the smaller value of tafel slope which in turn increase the rate of reaction [ 29 ]. The results show that the Tafel slope for Cu-Co 3 O 4 -rGO2 (116 mV dec − 1 ) is lower than that of Cu-Co 3 O 4 -rGO1 (122 mV dec − 1 ) and Cu-Co 3 O 4 -rGo3 (119 mV dec − 1 ) denoted as b,c and d in Fig. 7 . The Tafel slope for Cu-Co 3 O 4 -rGO2 electrodes was low when compared with Cu-Co 3 O 4 electrode as shown in Fig. 7 and it shows a Tafel value of 167 mV dec − 1 . The excellent electrochemical performance can be ascribed to the fact that incorporation of rGO, reduces the resistance of the catalyst there by improving its catalytic nature. The excellent electrochemical performance can be ascribed to the fact that the catalytic activity is greatly enhanced due to addition of conductive rGO. The results strongly reveal the synergistic effect of catalysis between Co 3 O 4 and rGO which is responsible for the highest performance attained by the Cu-Co 3 O 4 -rGO2 electrode. The homogeneous distribution of Co 3 O 4 along the defective plane of rGO improve the catalytic activity that could influence electrochemical performance of the electrode. Further enhanced OER activity and long-term stability of Cu-Co 3 O 4 -rGO2 suggests that incorporation of rGO provides conducting platform along with large number of active sites for water oxidation reaction. Both bare rGO and pure Co 3 O 4 exhibited lower catalytic activity as revealed by higher Tafel slope and the over potential observed for the OER confirmed the effective interaction between Co 3 O 4 and electron rich rGO in the developed electrode and these findings are in good agreement with literature reports. Further a detailed study was conducted on the effect of concentration of rGO in the electrode towards OER. As the concentration of rGO in the deposit continued to increase from 0.01 gml − 1 to 0.03 gml − 1 , it is observed that the values of over potential and tafel slope shows a negative gradation despite an increase in rGO concentration beyond 0.02 gml − 1 . As per reaction mechanism of OER, the metal cations are the reaction centres for redox reaction. In addition, the metal cations in octahedral site place an efficient role in OER. Therefore, superior electrochemical activity can be achieved through fine tuning the concentration of various components in the electrode matrix. By increasing the concentration of rGO to 0.03 gml − 1 (Cu-Co 3 O 4 -rGO3) the number of metal active centres present within the graphene layer decreased due to agglomeration of rGO that has an adverse effect on the over potential and Tafel slope as revealed from the analysis. Thus, higher electrocatalytic activity of Cu-Co 3 O 4 -rGO2 sample compared to other samples confirmed that there should be some optimum concentration of rGO and cobalt in the electrode to show greater OER activity. Comparison of LSV data for water oxidation in 1 M KOH at different concentration of rGO are listed in the Table 1 . Table 2 Comparisons of LSV data for water oxidation in 1 M KOH with different concentration of rGO Sl.NO Electrocatalyst Concentration of cobalt ions (gml − 1 ) Concentration of rGO (gml − 1 ) Working potential (V) Overpotential (mV) Tafel slope (mV dec − 1) 1 Cu-Co 3 O 4 0.02 0 1.65 422 167 2 Cu-Co3O4-rGO1 0.02 0.01 1.52 301 122 3 Cu-Co3O4-rGO2 0.02 0.02 1.48 259 116 4 Cu-Co3O4-rGO3 0.02 0.03 1.50 276 119 Figure 8 shows the nature of LSV curve for the electro catalyst during the first and 1000th cycle in 1 M KOH solution. It is clear from the figure that, after 1000th CV cycle, the working potential of Cu-Co 3 O 4 -rGO2 shows a slight shift in potential as revealed from analysis. It is indicated that presence of rGO enhances easy electron transfer through high specific surface area and superior chemical stability towards water oxidation. The stability testing methods mentioned above demonstrate that this catalyst has a reasonably good durability and is a good candidate to use as OER catalysts [ 30 ]. Presence of more active sites on the catalyst surface can rapidly enhance OER activity. On the other hand, higher the conductivity of the catalyst, the more favourable the electron transfer that leads to higher catalytic activity for corresponding OER performance. All these observations suggests that electrocatalytic activity of as-synthesized Cu-Co 3 O 4 -rGO2 modified electrodes towards OER performance was superior to those with higher stability performance The CV measurements were conducted within the potential range of -1 V to + 1 V (vs. Ag/AgCl). The analysis revealed the super capacitor behaviour of Cu-Co 3 O 4 -rGO electrodes as shown in Fig. 9 . The CV curves of the Cu-Co 3 O 4 -rGO2 measured at typical scan rates from 30 mVs − 1 to 200 mVs − 1 is shown in Fig. 9 . In addition, these were found that the obtained CV curves are highly symmetrical. The peak current remarkably increases along with the increase in scan rates, peak position also changes accompanied by the increase of scan rates. The peaks obtained in the anodic sweep shifted to a higher potential value, while the peaks which originated from the cathodic sweep moved towards a lower potential value and no significant distortion was observed with respect to CV curves obtained at 30 mVs − 1 and 200 mVs − 1 . It has also been confirmed that with increase in scan rate the current density increase and the potential shifts towards more positive confirms that the OER on Cu-Co 3 O 4 -rGO2 electrocatalytic systems is diffusion-controlled process towards water oxidation. All these factors suggest that the Cu-Co 3 O 4 -rGO2 electrode developed shows quasi reversibility and the pseudo capacitive behaviour [ 33 ] Figure 10 shows the Electrochemical impedance spectroscopic studies of bare Cu, Cu-Co 3 O 4 -, Cu-Co 3 O 4 -rGO1, Cu-Co 3 O 4 -rGO2 and Cu-Co 3 O 4 -rGO3. The impedance results were simulated using Z-view software and the fitted equivalent circuit model is shown as an inset in Fig. 10 . Circuit consisting of solution resistance ( R1 ) in series with one constant phase element-resistance ( Q2 ) and in parallel with charge transfer resistance ( R2 ) and Warburg resistance ( Wd2 ) fits the experimental data well at all the electrodes tested. Significant difference in the EIS spectra of modified electrodes with respect to bare copper clearly indicate the surface modification of developed electrodes. The diameter of semicircle is equivalent to charge transfer resistance ( R c t ) and it corresponds to electron transfer process. The R ct values calculated from EIS spectrum of each material as for bare Cu was about 922 Ω, for Cu-Co 3 O 4 was about 262.1 Ω, for Cu-Co 3 O 4 -rGO1, Cu-Co 3 O 4 -rGO2 and Cu-Co 3 O 4 -rGO3 were about 33.96 Ω,62.42 Ω and 76.21 Ω respectively. The substantially reduced charge transfer resistance achieved for Cu-Co 3 O 4 -rGO2 in comparison to others is clearly evident from its smallest semicircle diameter. All these suggests optimum value of rGO enhances rapid charge transfer kinetics between the Cu-Co 3 O 4 -rGO2 and electrolyte during the OER process among all samples. 4. Conclusions The present work investigates on the fabrication of Cu-Co 3 O 4 -rGO composite electrodes which has been synthesized by simple electro deposition method. The physico chemical analysis of the Cu-Co 3 O 4 -rGO composite electrode revealed characteristic surface topography and superior coting strength. The EDAX and FTIR analysis showed characteristic peaks and percentage abundance of different elements in the electrode. XPS study confirms the oxidation state of composite elements and the mechanism take place during OER activity. The results of electrochemical analysis such as Cyclic voltammetry, LSV curves, Tafel plots and EIS studies strongly suggests that Cu-Co 3 O 4 -rGO composite electrode can be used as an electrocatalyst for OER. The results demonstrates that synergistic interaction between Co 3 O 4 and rGO is responsible for the high performance attained by the Cu-Co 3 O 4 -rGO2 catalyst toward OER. From the results it was confirmed that there should be some optimum concentration of rGO and Cobalt oxide inorder to show OER activity. The fabrication of these type of electrocatalytic electrode can be applied as low-cost substitutes for noble metal OER catalysts. Development of these types of electrocatalytic electrodes is noteworthy considering the simplicity of the process and the materials used. Declarations Author Contribution The two authors listed for the manuscript have equal contribution and the complete report is prepared with mutual discussion taking full confidence Acknowledgement Author Ms. Aiswarya. P acknowledges CSIR-UGC for the award of junior research fellowship to carry out the present work. Authors are thankful to the financial assistance received from DST-FIST, New Delhi, for the instruments purchased with the assistance. Authors also thankful to technical officers at CMET, University of Kerala, and University of Calicut for extending help in doing analysis. References Wu L-K, Wu W-Y, Xia J, Cao H-Z, Hou G-Y, Tang Y-P, Zheng G-Q (2017) A nanostructured nickel–cobalt alloy with an oxide layer for an efficient oxygen evolution reaction. 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New J Chem 44:15776–15784. https://doi.org/10.1039/d0nj02598d Shi P, Dai X, Zheng H et al (2014) Synergistic catalysis of Co 3 O 4 and graphene oxide on Co 3 O 4 /GO catalysts for degradation of Orange II in water by advanced oxidation technology based on sulfate radicals. Chem Eng J 240:264–270. https://doi.org/10.1016/j.cej.2013.11.089 Gong X, Li A, Wu J et al (2020) Graphene-cobalt based oxygen electrocatalysts. Catal Today 358:184–195. https://doi.org/10.1016/j.cattod.2019.10.027 Fan X, Ohlckers P, Chen X (2020) Tunable synthesis of hollow Co 3 O 4 nanoboxes and their application in supercapacitors. Appl Sci (Switzerland) 10:1–12. https://doi.org/10.3390/app10041208 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. 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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-4589766","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":321498063,"identity":"189ee9ca-62e2-4a28-a697-8dbc5005781f","order_by":0,"name":"P Aiswarya","email":"","orcid":"","institution":"Sri Vyasa N. S. S. College","correspondingAuthor":false,"prefix":"","firstName":"P","middleName":"","lastName":"Aiswarya","suffix":""},{"id":321498064,"identity":"31fdca17-bd94-4688-b0c6-6d4520e14e21","order_by":1,"name":"R. Manu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA60lEQVRIiWNgGAWjYBADHgkeIPkBiNnYSdHCOAOkhZlYa0BamEE2MRDSott+9ph0Qc0dGcmew8c+2/zaJs/HzMD44WMObi1mZ/LSpGcce8YjzduWPDu377ZhGzMDs+TMbXi0HMgxk+ZhO8wjx89jzJzbc5sRqIWNmReflvNvgFr+gbTwf2a27LltT1jLDaAtvG2HgQ7rYWZm+HE7kQgtb4ytZ/Yd5pHsOWbM2NtwO7mNmbEZv1/O5xjeLvh22F7iTPJjhh9/btvOb28++OEjHi0ggIgIxjYw2YBfPYoWhj8EFY+CUTAKRsEIBADGG0nwTwpkWAAAAABJRU5ErkJggg==","orcid":"","institution":"Sri Vyasa N. S. S. College","correspondingAuthor":true,"prefix":"","firstName":"R.","middleName":"","lastName":"Manu","suffix":""}],"badges":[],"createdAt":"2024-06-16 12:54:52","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4589766/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4589766/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":60338971,"identity":"5beea9a0-28b1-4ba4-a070-a954111b730e","added_by":"auto","created_at":"2024-07-15 17:51:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":15577,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR-ATR spectra of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrode.\u003c/p\u003e","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/620f99ba8c3e93fa933b38eb.png"},{"id":60338965,"identity":"60330935-6615-4cfa-b10c-16576b6f43ed","added_by":"auto","created_at":"2024-07-15 17:51:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":51064,"visible":true,"origin":"","legend":"\u003cp\u003eEDAX spectrum of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrode.\u003c/p\u003e","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/c7a06701dda8a34ec392d708.png"},{"id":60339424,"identity":"2b90ab4e-69ed-431b-931e-6be25cdf9276","added_by":"auto","created_at":"2024-07-15 17:59:58","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":95370,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO\u003cstrong\u003e \u003c/strong\u003eelectrode a \u0026amp; b before OER and c \u0026amp; d after OER\u003c/p\u003e","description":"","filename":"groupimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/80e2b0425dc532e6dff929c0.jpeg"},{"id":60338972,"identity":"c923bc46-2114-4091-b18f-99265a0daee7","added_by":"auto","created_at":"2024-07-15 17:51:58","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":247449,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XPS survey scan of freshly prepared Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 (b-d) High resolution XPS spectra of C 1s, Co 2p, O 1s regions respectively\u003c/p\u003e","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/b44fe90b13207d5fb056dbdf.png"},{"id":60339423,"identity":"d542e928-a939-4981-bb69-0c490091d5e8","added_by":"auto","created_at":"2024-07-15 17:59:58","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":246728,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XPS survey scan of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2\u003cstrong\u003e \u003c/strong\u003eelectrode after OER activity (b-d) High resolution XPS spectra of C 1s, Co 2p, O 1s regions respectively\u003c/p\u003e","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/8fa7e121cc4a4833f5ad956c.png"},{"id":60338967,"identity":"329ed761-87f7-42e9-a21a-3911f0b38d10","added_by":"auto","created_at":"2024-07-15 17:51:58","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":13859,"visible":true,"origin":"","legend":"\u003cp\u003eLSV curves of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 (a), Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO3 (b) Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO1 (c),\u003cstrong\u003e \u003c/strong\u003eCu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (d) and bare Cu (e) in 1 M KOH solution\u003c/p\u003e","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/45a915e04c46085e8c60c3fe.png"},{"id":60338969,"identity":"a7d417b6-023d-4db2-9171-5919e5bcbbec","added_by":"auto","created_at":"2024-07-15 17:51:58","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":12007,"visible":true,"origin":"","legend":"\u003cp\u003eTafel plots for Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (a), Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO1 (b), Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO3 (c) and Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003e-rGO2 (d) in 1M KOH solution\u003c/p\u003e","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/66401cdcffb22a70cd3d6218.png"},{"id":60338970,"identity":"8d30b45d-f958-45cd-b4e5-205956f67499","added_by":"auto","created_at":"2024-07-15 17:51:58","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":14704,"visible":true,"origin":"","legend":"\u003cp\u003eOER Durability test for Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2\u003c/p\u003e","description":"","filename":"Onlinefloatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/5811c17a1f29b49ebf1e07d7.png"},{"id":60338991,"identity":"8217f175-29da-42f4-8690-95fc44a632e1","added_by":"auto","created_at":"2024-07-15 17:51:59","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":6007,"visible":true,"origin":"","legend":"\u003cp\u003eSuperimposed cyclic voltammogram of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 in 0.5 M KOH solution using Pt and SCE as counter and reference electrodes respectively at different scan rates.\u003c/p\u003e","description":"","filename":"Onlinefloatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/2074169fe0af26f6aa17e6fb.png"},{"id":60339425,"identity":"f9d8aa39-821a-4291-9935-22c0c845f033","added_by":"auto","created_at":"2024-07-15 17:59:58","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":4694,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plots of bare Cu (a) Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e(b) Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO1 (c) Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO3 (d) and Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 (e) in 1 M KOH solution. Inset figure shows corresponding equivalent circuit.\u003c/p\u003e","description":"","filename":"Onlinefloatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/55abfe754b9f88cb329d351d.png"},{"id":60340017,"identity":"dbf026ed-fee6-4f41-ae3c-7a554b4f9dff","added_by":"auto","created_at":"2024-07-15 18:16:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1583049,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4589766/v1/40c2c882-14af-4365-8713-ec8a46b0b771.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Development of highly active and robust Cu-Co–rGO electro-catalytic electrode for OER","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eEnergy security has been a major concern to world since the beginning of 21st century. With the increase in human population there is manifold surge in the energy demand for various application, considering the per capita consumption of energy. More over the source for fossil fuel is fast dwindling unless new excavation results in their production. Also, fossil fuel combustion leads to several environmental impacts that resulted in new forms of energy which are widely researched to make it more acceptable [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Therefore, increasing attention has been paid to develop clean energy which are a sustainable and renewable alternative to fossil fuel [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In the last decades numerous studies were carried out to establish better energy storage technologies, metal-air batteries, fuel cells and energy conversion processes [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe quest to develop new techniques to produce clean and sustainable energy is in the path of continues evolution. The idea of water splitting technology has given much attention over the years, since it plays a pivotal role in the production of hydrogen, which is a superior alternative to fossil fuels [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. However, oxygen evolution reaction [OER] is a high energy process with a higher kinetic barrier [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. In this regard the design and development of an efficient electrocatalyst with superior catalytic activity will be always in demand [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Transition metal-based compounds (especially Fe, Co, Ni) have inevitably become a hot research topic as they hold advantages like low price, abundant resources and environmental friendliness [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. So recently many reports demonstrated these metals as a promising candidate for most accepted noble metal catalyst (Pt, Ir, Ru based compounds) which possess high cost and less abundance [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAmong the various transition metal compounds, cobalt is of particular interest to the researcher for application in alkaline OER activity due to its low cost, mixed oxidation state, and the comparative performance when compared with other metals [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Recent advances in the field of composite coating have opened new possibilities for graphene oxide as an ideal catalyst support because of its fast electron transfer, large surface area, wide potential window, excellent biocompatibility, good chemical and environmental stability [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Vapor deposition, hydro, solvo-thermal, sol-gel method etc. are concomitantly employed for fabrication of metal-based electrode. In contrast, electrodeposition is a unique technology with a number of advantages which is economical and easy to apply [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Fabrication of self-standing electrodes can be easily attained through electrodeposition process as the deposits rigidly attached to the substrate. When compared to conventional drop cast method electrodes made through deposition technique have the advantage of active site utilization, good stability and simple process fabrication. By varying concentration of different components in precursor solution the electrode composition can be suitably modified [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eConsidering the above advantages the present work envisages on the development of electrocatalyst based on Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO composite for oxygen evolution reaction. The modified electrode was characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy to know physicochemical and surface morphology characteristics of the electrode. Elemental profile and its percentage abundance was determined using energy dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS) techniques. Electrochemical analysis of the electrode was performed by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electronic impedance spectroscopy (EIS) analysis. In the present work Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO electrode was synthesized by simple electrodeposition technique from cobalt-rGO precursor solution on to copper foil. The morphology, structure and electrochemical performance of the modified electrode were studied and compared with other reported work. The developed Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO composite electrode has uniform morphology and the electrode was stable after OER process as revealed from SEM and XPS studies. Effect of concentration of reduced graphene oxide was studied by adding different amount of rGO to the standardized bath solution. The inference from electrochemical analysis showed better activity towards OER process and the electrode was stable after repeated cycles of operation. The result of the electrochemical analysis reveals better performance and dimensional stability to the fabricated electrode.\u003c/p\u003e"},{"header":"2. EXPERIMENTAL METHODS","content":"\u003cp\u003e\u003cspan\u003e\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.1 Materials\u003c/strong\u003e: All the chemicals used for the present work are of analytical grade and used as such. Cobalt sulphate, sulphuric acid (98%) and other reagents were purchased from Merck, India Ltd. Deionized water was used as a solvent for the synthesis of various solutions as well as for the electrochemical studies.\u003c/p\u003e\u003cspan\u003e\n \u003cp\u003e\u003cstrong\u003e2.2 Synthesis of Graphene Oxide\u003c/strong\u003e: Graphene oxide (GO) was prepared using modified Hummer\u0026rsquo;s method by the oxidation of graphite flake [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. Graphite rod purchased from Graphite India Ltd., was powdered and sieved through sieving mesh having specific pore size. 1 g of graphite powder of purity 99.8% was accurately weighed and stirred in 98% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e for 30 minutes. 3 g KMnO\u003csub\u003e4\u003c/sub\u003e crystal was added to the solution with continuous stirring. The beaker containing graphite powder dispersed in acidic solution was maintained below 20\u003csup\u003e0\u003c/sup\u003e C temperature by keeping it in an ice bath. The resulting mixture was stirred for 48 hours by keeping the temperature at 35\u003csup\u003e0\u003c/sup\u003e C. Then the reaction mixture was allowed to cool at room temperature and 45 ml deionized water was added to it with vigorous stirring. The obtained mixture was then treated with 5 ml of 30% H\u003csub\u003e2\u003c/sub\u003e0\u003csub\u003e2\u003c/sub\u003e and added 75 ml deionized water. Supernatant solution was filled in small vials and then centrifuged for 15 minutes at 5000 rpm using refrigerated micro centrifuge RC 4815 F. The filtered product is washed with 5% HCl and further with deionized water until the P\u003csup\u003eH\u003c/sup\u003e of the solution becomes 6\u0026ndash;7. The obtained residue was dried by keeping it in an oven at 60\u003csup\u003e0\u003c/sup\u003e C for 24 hours. The fine powder of graphene oxide synthesized was used as such for further studies.\u003c/p\u003e\n\u003c/span\u003e\u003cspan\u003e\n \u003cp\u003e\u003cstrong\u003e2.3 Fabrication of Cu-Co\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e3\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003eO4-rGO electrode\u003c/strong\u003e\u003c/p\u003e\n\u003c/span\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003ePrior to electrodeposition, copper foil was polished with different grades of emery paper (grade \u0026minus;\u0026thinsp;80, 120, 220) to make the surface homogeneous and moderately rough to enhance the nucleation during electrodeposition process. The sample was then cleaned with acetone and dilute HCl and finally with plenty of water and dried in room temperature. 1 cm\u003csup\u003e2\u003c/sup\u003e of the substrate surface was exposed for electrodeposition. The deposition was carried out by using platinum as positive electrode (anode) and copper foil as negative electrode (cathode). Current density was set at 0.5 mA and deposition was done for 30 minutes. The deposition bath was prepared by accurately weighing different amount of graphene oxide. 0.1 g to 0.3 g of graphene oxide was dispersed in 10 ml of deionized water under ultra-sonication and then magnetically stirred for 15 minutes at 500 rpm. To this solution, 0.2 g of CoSO\u003csub\u003e4\u003c/sub\u003e.7H\u003csub\u003e2\u003c/sub\u003eO, dissolved in 10 ml of deionized water is added and stirred continuously for 15 minutes. Graphene oxide was added to this solution of cobalt and was stirred using magnetic stirrer for 30 minutes at 500 rpm at a temperature of 40\u003csup\u003e0\u003c/sup\u003e C. The solution mixture was kept under agitating condition during electrodeposition. After electrodeposition, the coated electrode was washed with water and dried. Electrodeposition was performed using APLAB L 3205 regulated dual DC power supply rectifier. Effect of different concentration of rGO during deposition was also studied. Along with that Deposition was performed without addition of rGO.\u003c/p\u003e"},{"header":"3. RESULTS AND DISCUSSION","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1 FTIR-ATR analysis of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO electrode\u003c/h2\u003e \u003cp\u003eFTIR-ATR spectra of the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO electrode are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The spectra reveals that the major peak obtained at 517.2 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the low frequency can be assigned to metal oxygen bond stretching vibrations in Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Absorption band at 1354.06 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to C-OH stretching vibrations in graphene oxide and the appearance of a strong peak at 1087.6 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e belonging to the stretching vibration mode of C-O corresponding to carbonyl group present in graphene [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The broad peak appeared at 3324 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the high frequency area attributed to the O-H bending mode of water molecule. The presence of these types of groups reveals that functionalization was effective as evidenced from the stretching frequency in the FTIR spectrum.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2 SEM-EDAX analysis of the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO deposit\u003c/h2\u003e \u003cp\u003eThe result of EDAX analysis is consistent with the formation of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO composite electrode as revealed by the presence of distinct peaks for cobalt, carbon and oxygen as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. SEM image of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrode surface resembled cauliflower-like pattern, characteristic for Co deposits as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The morphology reveals that the flowers are made up of agglomerates and few porous islands which in turns build a porous surface feature. The flower like pattern observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb ascribed to the Co deposits within the graphene layer structure and its distribution on the graphene sheet tends to be uniform. Optimizing the deposition time could control the grain growth size and morphology of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles forming a uniform morphology. The more or less porous morphology observed enacts larger surface area for the deposit. Small nanoparticles and large specific surface area can shorten the transmission path of charge, which is believed to be beneficial to increase specific capacitance and multiplier capacity. This could result in increased specific surface area there by number of active sites is increased, and the Faraday redox reaction is more active, which may influence the electrochemical performance of the deposit [39]. The Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec and d shows the surface topography of the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrode after OER. The morphology shows not much difference from the earlier fresh sample revealing that the electrode surface is stable and more adherent to the substrate. The plate like morphology seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec exposes the graphene layered surface laced within the composite matrix during OER.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElemental percentage analysis of the deposit of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrode.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElement\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWeight %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e21.81\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eO K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e27.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCo K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50.53\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.3 XPS analysis of the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGOelectrode\u003c/h2\u003e \u003cp\u003eElemental composition and oxidation state of C, Co and O in the electrode were determined using XPS technique. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, XPS survey spectrum revealed the presence of core level signals for Co 2p, O 1s, C 1s. This is clear from intense peak observed for specific oxidation state of the elements and also reveals the absence of other impurities. Gaussian fitting method was adopted for high magnification XPS studies of\u003c/p\u003e \u003cp\u003eC 1s, Co 2p, O 1S spectrum. XPS spectrum of Co-reduced graphene composites exhibited peaks for Co, O, and C elements, that reveals cobalt nanoparticles get co-deposited on the graphene sheets during electrodeposition. In Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, four component peaks ascribed to\u003c/p\u003e \u003cp\u003eC 1s attributed to C-C bond at 283 eV and energy peak at 284 eV is associated with C\u0026thinsp;=\u0026thinsp;C. The other two component peaks at 287 eV and 288 eV were assigned to C-O and O-C\u0026thinsp;=\u0026thinsp;O groups respectively [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The peaks reveals that the process of functionalization was effective for graphene. High-resolution Co 2p spectrum can be deconvoluted in to two distinct peaks centered with the binding energies (BEs) of 780.0 eV and 795.0 eV, which attributed to the spin orbit peaks of Co 2p\u003csub\u003e3/2\u003c/sub\u003eand Co 2p\u003csub\u003e1/2\u003c/sub\u003e because of the spin orbit coupling as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The BEs of 2p\u003csub\u003e3/2\u003c/sub\u003e and 2p\u003csub\u003e1/2\u003c/sub\u003e spin orbitals of Co\u003csup\u003e3+\u003c/sup\u003eand Co\u003csup\u003e2+\u003c/sup\u003e was observed at 779.6 eV / 795 eV and 781 eV / 796.7 eV respectively. 2 Satellite peaks are related to the formation of CoO in the deposit [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed clearly reveals the three distinct peaks at 529.8 eV, 531 eV, and 532.5 eV for O 1s associated to Co-O bond in Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGo, C-O, and chemisorbed and physiosorbed water molecule on the electrode surface. XPS analysis of the sample after OER was performed and it shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The spectrum showed no major shift in binding energies of the components reported earlier when compared with the fresh sample. It is observed that even after OER studies the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrode was stable as revealed from XPS analysis. C 1s and O 1s peak do not have any significant changes in BE when compared with fresh sample, that strongly supports that graphene oxide which act as catalyst support is having a stable microstructure even after OER activity. This was supplemented by SEM analysis where the surface was intact after OER activity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Electrocatalytic Studies towards Oxygen Evolution Reactions (OER)\u003c/h2\u003e \u003cp\u003eTafel plot reflects the electrochemical kinetics of OER activity of the electrode that reveals the key parameters usually used to characterize the catalytic activity of an electrocatalyst [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. In this work, linear sweep voltammogram (LSV), tafel and cyclic voltammetry method were carried out to assess the electro-catalytic activity of the electrode with a typical three-electrode system. In accordance with the Nernst equation (\u003cem\u003eE\u003c/em\u003e \u003csub\u003eRHE\u003c/sub\u003e = \u003cem\u003eE\u003c/em\u003e (vs. SCE)\u0026thinsp;+\u0026thinsp;\u003cem\u003eE\u003c/em\u003e\u003csub\u003eSCE\u003c/sub\u003e (0.241)\u0026thinsp;+\u0026thinsp;0.0591 \u0026times; pH), the measured values of potential Vs SCE (Saturated Calomel Electrode) were converted into a reversible hydrogen electrode (RHE). It is important that the supporting electrolyte 1 M KOH solution should be saturated with N\u003csub\u003e2\u003c/sub\u003e so as to fix the O\u003csub\u003e2\u003c/sub\u003e / H\u003csub\u003e2\u003c/sub\u003eO equilibrium potential at 1.23 V vs. RHE. Electrochemical activity of as-synthesized Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 exhibits the lowest onset potential of 1.48 V vs. RHE among all the other electrodes. The working potential at a current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e is an essential parameter to evaluate OER activity. Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGo2 shows relatively low working potential of 1.48 V (over potential of 259 mV) at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, compared to Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO1(1.52 V, 301 mV), Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGo3 (1.506 V, 276 mV), and Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (1.65 V, 422 mV) electrodes. From this it is assumed that there should be some optimum concentration of rGO in the metal composite in order to achieve better OER activity as revealed from the LSV analysis. In practical application, the electrochemical kinetics of OER can be judged based on the magnitude of Tafel slope. Tafel plots derived from the LSV curves are shown in\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. These plots are based on the Tafel formula of \u003cem\u003eη\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003ea\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eb\u003c/em\u003e log(\u003cem\u003ej\u003c/em\u003e), in which \u003cem\u003eη\u003c/em\u003e refers to the overpotential \u0026lsquo;\u003cem\u003ea\u003c/em\u003e\u0026rsquo; represents the intercept on the Y axis, \u0026lsquo;\u003cem\u003eb\u003c/em\u003e\u0026rsquo; indicates the Tafel slope, and \u003cem\u003ej\u003c/em\u003e refers to the current density. The Tafel graphs were plotted through the corresponding polarization curves. The value of Tafel slope can be considered as a prime factor for evaluating OER activity. Specifically, higher OER activity is clearly evident from the smaller value of tafel slope which in turn increase the rate of reaction [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The results show that the Tafel slope for Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 (116 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is lower than that of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO1 (122 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGo3 (119 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) denoted as b,c and d in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The Tafel slope for Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrodes was low when compared with Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and it shows a Tafel value of 167 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The excellent electrochemical performance can be ascribed to the fact that incorporation of rGO, reduces the resistance of the catalyst there by improving its catalytic nature.\u003c/p\u003e \u003cp\u003eThe excellent electrochemical performance can be ascribed to the fact that the catalytic activity is greatly enhanced due to addition of conductive rGO. The results strongly reveal the synergistic effect of catalysis between Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and rGO which is responsible for the highest performance attained by the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrode. The homogeneous distribution of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e along the defective plane of rGO improve the catalytic activity that could influence electrochemical performance of the electrode. Further enhanced OER activity and long-term stability of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 suggests that incorporation of rGO provides conducting platform along with large number of active sites for water oxidation reaction. Both bare rGO and pure Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e exhibited lower catalytic activity as revealed by higher Tafel slope and the over potential observed for the OER confirmed the effective interaction between Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and electron rich rGO in the developed electrode and these findings are in good agreement with literature reports.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurther a detailed study was conducted on the effect of concentration of rGO in the electrode towards OER. As the concentration of rGO in the deposit continued to increase from 0.01 gml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 0.03 gml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, it is observed that the values of over potential and tafel slope shows a negative gradation despite an increase in rGO concentration beyond 0.02 gml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. As per reaction mechanism of OER, the metal cations are the reaction centres for redox reaction. In addition, the metal cations in octahedral site place an efficient role in OER. Therefore, superior electrochemical activity can be achieved through fine tuning the concentration of various components in the electrode matrix. By increasing the concentration of rGO to 0.03 gml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO3) the number of metal active centres present within the graphene layer decreased due to agglomeration of rGO that has an adverse effect on the over potential and Tafel slope as revealed from the analysis. Thus, higher electrocatalytic activity of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 sample compared to other samples confirmed that there should be some optimum concentration of rGO and cobalt in the electrode to show greater OER activity. Comparison of LSV data for water oxidation in 1 M KOH at different concentration of rGO are listed in the Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparisons of LSV data for water oxidation in 1 M KOH with different concentration of rGO\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSl.NO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eElectrocatalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eConcentration of cobalt ions\u003c/p\u003e \u003cp\u003e(gml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eConcentration of rGO\u003c/p\u003e \u003cp\u003e(gml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWorking potential\u003c/p\u003e \u003cp\u003e(V)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eOverpotential\u003c/p\u003e \u003cp\u003e(mV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTafel slope\u003c/p\u003e \u003cp\u003e(mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1)\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e422\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e167\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCu-Co3O4-rGO1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e301\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e122\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCu-Co3O4-rGO2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e259\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e116\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCu-Co3O4-rGO3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e276\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e119\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the nature of LSV curve for the electro catalyst during the first and\u003c/p\u003e \u003cp\u003e1000th cycle in 1 M KOH solution. It is clear from the figure that, after 1000th CV cycle, the working potential of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 shows a slight shift in potential as revealed from analysis. It is indicated that presence of rGO enhances easy electron transfer through high specific surface area and superior chemical stability towards water oxidation. The stability testing methods mentioned above demonstrate that this catalyst has a reasonably good durability and is a good candidate to use as OER catalysts [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Presence of more active sites on the catalyst surface can rapidly enhance OER activity. On the other hand, higher the conductivity of the catalyst, the more favourable the electron transfer that leads to higher catalytic activity for corresponding OER performance. All these observations suggests that electrocatalytic activity of as-synthesized Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 modified electrodes towards OER performance was superior to those with higher stability performance\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe CV measurements were conducted within the potential range of -1 V to +\u0026thinsp;1 V (vs. Ag/AgCl). The analysis revealed the super capacitor behaviour of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO electrodes as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The CV curves of the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 measured at typical scan rates from 30 mVs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 200 mVs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. In addition, these were found that the obtained CV curves are highly symmetrical. The peak current remarkably increases along with the increase in scan rates, peak position also changes accompanied by the increase of scan rates. The peaks obtained in the anodic sweep shifted to a higher potential value, while the peaks which originated from the cathodic sweep moved towards a lower potential value and no significant distortion was observed with respect to CV curves obtained at 30 mVs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 200 mVs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. It has also been confirmed that with increase in scan rate the current density increase and the potential shifts towards more positive confirms that the OER on Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrocatalytic systems is diffusion-controlled process towards water oxidation. All these factors suggest that the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 electrode developed shows quasi reversibility and the pseudo capacitive behaviour [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the Electrochemical impedance spectroscopic studies of bare Cu, Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-, Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO1, Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 and Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO3. The impedance results were simulated using Z-view software and the fitted equivalent circuit model is shown as an inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. Circuit consisting of solution resistance (\u003cem\u003eR1\u003c/em\u003e) in series with one constant phase element-resistance (\u003cem\u003eQ2\u003c/em\u003e) and in parallel with charge transfer resistance (\u003cem\u003eR2\u003c/em\u003e) and Warburg resistance (\u003cem\u003eWd2\u003c/em\u003e) fits the experimental data well at all the electrodes tested. Significant difference in the EIS spectra of modified electrodes with respect to bare copper clearly indicate the surface modification of developed electrodes. The diameter of semicircle is equivalent to charge transfer resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003et\u003c/sub\u003e) and it corresponds to electron transfer process. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ect\u003c/em\u003e\u003c/sub\u003e values calculated from EIS spectrum of each material as for bare Cu was about 922 Ω, for Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e was about 262.1 Ω, for Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO1, Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 and Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO3 were about 33.96 Ω,62.42 Ω and 76.21 Ω respectively. The substantially reduced charge transfer resistance achieved for Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 in comparison to others is clearly evident from its smallest semicircle diameter. All these suggests optimum value of rGO enhances rapid charge transfer kinetics between the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 and electrolyte during the OER process among all samples.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe present work investigates on the fabrication of Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO composite electrodes which has been synthesized by simple electro deposition method. The physico chemical analysis of the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO composite electrode revealed characteristic surface topography and superior coting strength. The EDAX and FTIR analysis showed characteristic peaks and percentage abundance of different elements in the electrode. XPS study confirms the oxidation state of composite elements and the mechanism take place during OER activity. The results of electrochemical analysis such as Cyclic voltammetry, LSV curves, Tafel plots and EIS studies strongly suggests that Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO composite electrode can be used as an electrocatalyst for OER. The results demonstrates that synergistic interaction between Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and rGO is responsible for the high performance attained by the Cu-Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-rGO2 catalyst toward OER. From the results it was confirmed that there should be some optimum concentration of rGO and Cobalt oxide inorder to show OER activity. The fabrication of these type of electrocatalytic electrode can be applied as low-cost substitutes for noble metal OER catalysts. Development of these types of electrocatalytic electrodes is noteworthy considering the simplicity of the process and the materials used.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eThe two authors listed for the manuscript have equal contribution and the complete report is prepared with mutual discussion taking full confidence\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eAuthor Ms. Aiswarya. P acknowledges CSIR-UGC for the award of junior research fellowship to carry out the present work. Authors are thankful to the financial assistance received from DST-FIST, New Delhi, for the instruments purchased with the assistance. Authors also thankful to technical officers at CMET, University of Kerala, and University of Calicut for extending help in doing analysis.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWu L-K, Wu W-Y, Xia J, Cao H-Z, Hou G-Y, Tang Y-P, Zheng G-Q (2017) A nanostructured nickel\u0026ndash;cobalt alloy with an oxide layer for an efficient oxygen evolution reaction. J Mater Chem A 5(21):10669\u0026ndash;10677. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1039/C7TA02754K\u003c/span\u003e\u003cspan address=\"10.1039/C7TA02754K\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDarband GB, Aliofkhazraei M, Rouhaghdam AS, Kiani MA (2019) Three-dimensional Ni-Co alloy hierarchical nanostructure as efficient non-noble-metal electrocatalyst for hydrogen evolution reaction. 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Appl Sci (Switzerland) 10:1\u0026ndash;12. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/app10041208\u003c/span\u003e\u003cspan address=\"10.3390/app10041208\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Electrodeposition, Nano Composite, electrode, rGO, OER","lastPublishedDoi":"10.21203/rs.3.rs-4589766/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4589766/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn the present work a facile method was adopted for the fabrication of highly active and dimensionally stable cobalt-reduced graphene oxide (rGO) based composite electrode for OER process. The metal loading and the amount of graphene was optimized for better performance of the electrode. The development of these type of electrodes is noteworthy taking the advantage of the method and the materials used. The morphology and the composition were analyzed through scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and X-ray photo electron spectroscopy (XPS). Spectroscopic characterization was done using Fourier transform infrared (FTIR) analysis. Electrochemical characterization revealed excellent electro-catalytic activity of the prepared electrode and strongly suggest synergistic reaction between Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and rGO. The developed electrode can realize excellent Oxygen Evolution Reaction (OER) activity in alkaline media with low over potential and low tafel slope with long-term stability as evidenced from various analysis.\u003c/p\u003e","manuscriptTitle":"Development of highly active and robust Cu-Co–rGO electro-catalytic electrode for OER","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-15 17:51:50","doi":"10.21203/rs.3.rs-4589766/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0b389f3f-b241-42db-a6ea-803bb931b909","owner":[],"postedDate":"July 15th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-07-15T17:51:53+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-15 17:51:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4589766","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4589766","identity":"rs-4589766","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}