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Article

Facile Synthesis of Copper Oxide-Cobalt Oxide/Nitrogen-Doped Carbon (Cu2O-Co3O4/CN) Composite for Efficient Water Splitting

by
Zaffar Ahmed Shaikh
1,*,
Nikita Moiseev
2,
Alexey Mikhaylov
3 and
Serhat Yüksel
4
1
Faculty of Computing Sciences & Information Technology, Benazir Bhutto Shaheed University, Lyari, Karachi 75660, Pakistan
2
Department of Mathematical Methods in Economics, Plekhanov Russia University of Economics, 117997 Moscow, Russia
3
Financial Research Institute of Ministry of Finance of the Russian Federation, 127006 Moscow, Russia
4
The School of Business, Istanbul Medipol University, 34810 Istanbul, Turkey
*
Author to whom correspondence should be addressed.
Appl. Sci. 2021, 11(21), 9974; https://doi.org/10.3390/app11219974
Submission received: 8 September 2021 / Revised: 20 October 2021 / Accepted: 22 October 2021 / Published: 25 October 2021
(This article belongs to the Special Issue Advances in Chemical and Thermochemical Water Splitting)
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Versions Notes

Abstract

:
Herein, we report a copper oxide-cobalt oxide/nitrogen-doped carbon hybrid (Cu2O-Co3O4/CN) composite for electrochemical water splitting. Cu2O-Co3O4/CN is synthesized by an easy two-step reaction of melamine with Cu2O-Co3O4/CN composite. The designed composite is aimed to solve energy challenges by producing hydrogen and oxygen via electrochemical catalysis. The proposed composite offers some unique advantages in water splitting. Carbon imparts superior conductivity, while the water oxidation abilities of Cu2O and Co3O4 are considered to constitute a catalyst. The synthesized composite (Cu2O-Co3O4/CN) is characterized by SEM, EDS, FTIR, TEM, and AFM in terms of the size, morphology, shape, and elemental composition of the catalyst. The designed catalyst’s electrochemical performance is evaluated via linear sweep voltammetry (LSV) and cyclic voltammetry (CV). The Cu2O-Co3O4/CN composite shows significant electrocatalytic activity, which is further improved by introducing nitrogen doped carbon (current density 10 mA cm−2, onset potential 91 mV, and overpotential 396 mV).

1. Introduction

The world is facing an energy crises nowadays. A rough estimation shows that, in 2050, the energy consumption will be doubled when compared to 2020 [1]. Now, the world is dependent on nonrenewable energy sources to meet energy requirements [2]. However, with the increase in energy prices, energy demand, and global warming, researchers are thinking about renewable energy resources [3,4]. The main reasons for the increase in energy demand are the world’s high growth rate and a great industrial revolution. Throughout the whole history of humankind, humans used energy from fossil fuels. In the past, only two types of fossils (wood and charcoal) were used, but, due to the industrial revolution, many more options, including oil, coal, and natural gas [5,6], have also been used to meet the energy requirements. According to a survey, fossil fuel reservoirs have been enough for decades, but, with time, these reservoirs are depleting [7,8].
Modern day research is focused on developing renewable energy sources, and water splitting is a promising source of energy [9,10]. There has been a noticeable increase in oxygen evolution reaction (OER) in recent years, and it is estimated that this increase will be doubled in future years [11,12]. The conventional method of hydrogen and oxygen output involves a steam reforming method [13]. Nowadays, O2 is also produced by using the photocatalytic method. In these methods, sunlight is used to create oxygen and hydrogen molecules. Solar water splitting methods of oxygen and hydrogen production include thermochemical and photobiological methods [14,15].
In the water-splitting process, sunlight is used as an energy source, and a water molecule is used as an electron donor to complete fuel cells [16]. Two half reactions are involved: the first one is the hydrogen evolution reaction, and the second one is the oxygen evolution reaction. Different types of charge separators are used to enhance the rate of reaction. Some of the charge separators are semiconductors, such as nanobelts, nanotubes, nanowires, and nanosheets [17,18]. Hetrojunction semiconductors are also being used for better charge separation. Cobalt is commonly used as a catalyst in hydrogen and oxygen evolution reactions [19]. Photolytic corrosion is the main problem in these reactions. This problem can be minimized by increasing electrodes’ stability and providing more active sites for the photocatalytic activity of hydrogen and oxygen [20]. Researchers are exploring other options, such as nitrides, phosphides, selenides, and carbides [21,22]. These types of non-nobel metal catalysts show high corrosion resistance and better electroconductivity [23,24,25,26,27,28]. Some highly efficient catalysts recently reported for HER are CoS2, FeS2, MoSe2, g-C3N4/Co-MOF (ZIF-67), g-C3N4/Nb2O5, CdS QD/MoO3–OV/g–C3N4, and NiS2 [1,2,3,4].
Nanotubes and nanosheets are used to increase active sites for electrocatalytic HER nanowires [28,29]. Metal carbides show similar behavior, in terms of catalytic properties and electronic band. Due to these reasons, carbides show high hydrogen adsorption and maximum electrical conductivity [30]. Due to the presence of a d-band structure, they show high electrical conductivity and low hydrogen adsorption capacity. Mo2C and WC are both categorized as non-Pt catalysts for hydrogen evolution reactions. These have been tested at different pH ranges and proved to be a stable support for HER [31].
Some catalysts can perform both oxygen and hydrogen evolution reactions [32,33]. Pt, Rh, and Ir-based catalysts can serve as bifunctional catalysts, but such types of catalysts are lower in number and have very high costs [34]. The great challenge in this field is to find a low cost, easily available bifunctional catalyst that can work both in acidic and basic environments [35,36]. The last few years’ foci have been shifted to a low cost and earth abundant transition metal, transition metal oxide, transition metal sulfides, transition metal nitrides, and transition metal carbides [37]. The most common metals used in these catalysts are iron, nickel, copper, and cobalt [38]. The catalysts prepared by these metals’ combinations have an exceptional ability for electrochemical water splitting and show improved reaction kinetics, fast charge transfer, and high conductivity. Cobalt based catalysts have been frequently used in water splitting and electrocatalysis [39,40,41]. The catalysts’ conductivity can be further enhanced by adding some dopants, such as nitrogen [42]. Melamine is a well known and common precursor for the preparation of nitrogen-doped carbon [43,44,45].
This study aims to synthesize an effective electrocatalyst for the oxygen evolution reaction (OER). Copper oxide-cobalt oxide/nitrogen-doped carbon hybrid (Cu2O-Co3O4/CN) composite is synthesized by a simple two-step method using low cost precursors. The material is characterized by different analytical techniques and applied for electrochemical water splitting.

2. Experimental

2.1. Chemical and Reagent

Cobalt chloride hexahydrate (CoCl2·6H2O), trisodium citrate (Na3C6H5O7) 99%, Nafion solution (C7HF13O5S) 5%, glycine (C₂H₅NO₂) 99.9%, potassium dihydrogen phosphate (KH2PO4) 99%, ethanolamine (C2H7NO) 98%, copper sulphate pentahydrate (CuSO4·5H2O) 99%, potassium hydroxide (KOH) 99%, dipotassium hydrogen phosphate (K2HPO4) 99%, and hydrogen peroxide 30% (H2O2) were purchased by Sigma Aldrich. Ethylene glycol (C2H6O2) 99.0% was obtained from Merck. Sulfuric acid (H2SO4) 98% was purchased from Riedel-de Haën.

2.2. Synthesis of Cu2O-Co3O4/CN Composite

In the first step, the Cu2O-Co3O4 composite was synthesized by using a reported method [46]. Briefly, a 0.5 mM solution of CuSO4·5H2O was prepared in 20 mL of water. A quantity of 13 mL of ethanol was added and stirred vigorously to form a clear solution. Then, 1 mM solution of CoCl2·6H2O, 10 g of trisodium citrate, 3 mL of 200 mL solution of KOH, and 0.3 mM solution of glycine were added to the reaction mixture. After vigorous stirring for a half hour, the reaction mixture was transferred to a Teflon lined stainless-steel autoclave. The autoclave was placed in a temperature programmed electric oven, and the mixture was kept for 12 h at 180 °C. After cooling to room temperature, the obtained product was filtered and washed several times with deionized water to remove the unreacted chemicals. The product was dried at 50 °C for 6 h in a vacuum oven. The dried product was calcined at 300 °C for 2 h to obtain Cu2O-Co3O4 composite.
For the synthesis of Cu2O-Co3O4/CN composite, 40 g of melamine, 1 g of glucosamine hydrochloride were mixed with Cu2O-Co3O4 composite, and 400 mL water was added. The mixture was heated at 80 °C till the water was dried. The solid product was ground and heat treated at 400 °C and 500 °C under a nitrogen atmosphere. The obtained product was cooled to room temperature and stored for further use.

2.3. Characterization of Composite

SEM analysis was carried out on a Hitachi SEM S-4700, Japan. For the TEM imaging, the Jeol JEM-F200 Multi-purpose Electron Microscope was used, equipped with an EDS detector. AFM images were recorded on a Bruker AFM (MultiMode 8-HR), Bruker, Germany. FTIR spectrum was recorded in transmission mode on Nicolet iS10 ThermoScientific, Germany.

2.4. Electrochemical Water Splitting

The electrochemical experiments were carried out on two modes of electrochemical workstations; cyclic voltammetry (CV) and linear swap voltammetry (LSV). CV measurements were performed on a three electrode system, standard electrode (Pt wire), reference electrode (Ag/AgCl), and the working electrode. Cu2O-Co3O4/CN composite was deposited on a glassy carbon electrode (working electrode) with a diameter of 3 mm. The synthesized catalyst’s electrochemical activity was studied in alkaline media (1 M KOH solution). Different electrochemical parameters, including potential window, scan rate, and pH, were also optimized to achieve maximum efficiency. The selected window range was from −1.0V to +1.0V, and the scan rate was 0.06 mV/s to 0.1 mV/s. The slurry for the glassy carbon electrode was prepared by mixing 4 mg of synthesized catalyst, 80 µL of Nafion, which acts as a binder, and 1 mL of water. This mixture was sonicated to form a dispersion for 30 min. This dispersion was then loaded onto the working electrode and dried at room temperature.

3. Results and Discussion

3.1. Characterization of Cu2O-Co3O4/CN Composite

The synthesized Cu2O-Co3O4/CN composite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The morphology and particle size of the Cu2O-Co3O4 and Cu2O-Co3O4/CN composites were first characterized by TEM. TEM images of the Cu2O-Co3O4 and Cu2O-Co3O4/CN composites are shown in Figure 1a,b, respectively. From both the images, it is evident that each composites’ morphology is different from the other. This is due to an additional layer of nitrogen doped carbon on the Cu2O-Co3O4 composite. The calculated particle size is in the range of 80–100 nm. The morphology was also justified by SEM (Figure 1c,d) and AFM (Figure 1e,f). In the Cu2O-Co3O4 composites, particles are visible, and they are semispherical. However, after the addition of CN, there is a clear change in shape and morphology. This is formed by calcination at higher temperatures. AFM results show the surface of the products: the Cu2O-Co3O4 is rough as compared to the Cu2O-Co3O4/CN composite, which has a slightly smoother surface with fewer grooves. The elemental composition of the materials was determined by EDS analysis, which indicates the mass percentage of copper (41%), cobalt (33%), and oxygen (21%) in the Cu2O-Co3O4 composite. On the other hand, carbon (24%), nitrogen (11%), oxygen (17%), copper (27%), and cobalt (21%) are present in the Cu2O-Co3O4/CN composite.
FTIR analysis was carried out in transmittance mode to confirm the formation of composites (Figure 2). The transmittance peaks at 645 cm−1 and 540 cm−1 belongs to cobalt oxide and copper oxide, and it is present in both materials, while the peak at 1100 cm−1 is due to the presence of -O-C-O- vibrations [41]. The peak presence at 3300 cm−1 is due to hydroxyl groups, which are abundantly present on the surface of metal oxides. The FTIR results confirm the C=O bond of amide as the peaks appearing at 1668 cm−1 and 1570 cm−1, which indicates the stretching and bending of C=O. The peak at 1418 cm−1 indicates the presence of a hydroxyl group, and the symmetrical vibration peaks at 1635.74 cm−1 and 1733.65 cm−1 belong to C=O and C=N bands, respectively. The peak at 1703 cm−1 shows the interaction between the carbonyl group and the metal ions. The peaks for the metals’ coordination with COO appear at 1560 cm−1 and 1560 cm−1, respectively.

3.2. Electrochemical Water Splitting by Cu2O-Co3O4/CN Composite

The electrochemical activity of the Cu2O-Co3O4/CN composite on a glassy carbon electrode was studied using linear sweep and cyclic voltammetry for water splitting. To obtain maximum efficiency, different parameters, such as scanning rate, potential window, and pH, were optimized for both Cu2O-Co3O4 and Cu2O-Co3O4/CN composites. Initially, the pH of the electrolyte solution was optimized. The blank solution’s electrochemical response and all the synthesized materials, including Cu2O-Co3O4, CN, Cu2O-Co3O4/CN at 400 °C, and 500 °C, were recorded at different pHs (7, 7.4, and 8). The figure shows that the composite shows maximum redox potential at pH 8. The electrochemical response of these catalysts is low, at 7 and 7.4. These results show that the current density of the synthesized composite at optimized conditions increases in the scan rate, from 0.06 mV/s to 0.1 mV/s.
The catalyst was prepared in a slurry and applied to GCE via micropipette. Then, the effect of catalyst volume was evaluated. Figure 3 explains the linear calibration curve and the volumetric activity of the synthesized catalyst. Different concentrations of Cu2O-Co3O4/CN give reversible cyclic voltammetric peaks, showing reduction as well as oxidation peaks. With the increasing volume of the catalyst, from 0.1 µL to 0.5 µL, the oxidation peak current (Ipa) increases from 2.99 µA to 5.879 µA. Cu2O-Co3O4/CN shows a peak potential (Epa) of 0.138 V, in comparison to 0.608 V for blank. Peak currents for different volumes of the catalyst, from 0.1 µL to 0.5 µL, are −4.104 µA, −4.505 µA, −5.764 µA, −7.514 µA, and -9.605 µA, respectively. For the Cu2O-Co3O4/CN composite, the cathodic peaks potential (EPC) is −0.018 V. Reduction and oxidation rates increase as the amount (volume of slurry) of synthesized catalyst increases. The reason is that, as the composite amount increases, the active sites for reduction and oxidation reaction also increase. The relationship between current and concentration is linear at pH 8, as shown in Figure 3b. R2 obtained for reduction and oxidation are 0.959 and 0.91, respectively.
The electrochemical activity of nitrogen doped carbon was monitored at different scan rates in 1 M KOH. Different ranges of current were obtained at different scan rates (Figure 4a). Initially, a 0.06 mV/s scan rate was set for electrochemical analysis and the redox phenomenon was observed in the voltammogram (0.618 V for oxidation and −1.101 V for reduction). The current obtained due to oxidation is 0.0458 mA, and for reduction is −0.0334 mA. The potential difference (∆E) is −1.710 V. This scan rate is very slow and consumes more time. The deposition and the results are not accurate, due to surface damage. The peak current for both oxidation and reduction increased at higher scan rates, as shown in Figure 5b. R2 for oxidation and reduction are 0.891 and 0.846, respectively. These results indicate that electrochemical activity is directly proportional to the scan rate.
The linear sweep voltammetry response in 1M KOH was also evaluated (Figure 4c), and a similar trend was obtained. The obtained current density is 0.890 mA/cm2, and the Tafel slope is 334 mV/decade (Figure 4d). Moreover, at η (overpotential) = 0.58876 V, current density is 1 mA/cm2. The reversible potential of OER is 1.19 and 0 V vs. reference electrodes, respectively. Therefore, as current density increases, the electrocatalytic activity of the material rises with the scan rate.
Similarly, the electrochemical response of Cu2O-Co3O4 composite was also measured in 1M KOH solution, using CV and LSV (Figure 6). A mild redox phenomenon is detected at a scan rate of 0.06 mV/s (Figure 5a). As the scan rate rises, the corresponding reduction and oxidation peaks are detected. The highest peak current is observed at 0.1 mV/s (Epa = −0.0884 V with Ipa = 3.21 mA and Epc = −0.9676 V at Ipc = −2.13 mA). The calibration curve for the scan rate vs. the corresponding current is presented in Figure 6b. The obtained curve for oxidation has a slope of 0.06355 with a standard error of 0.00562 and R2 = 0.96744. The correlation coefficient for reduction is 0.8742. LSV curves for the Cu2O-Co3O4 composite at different scan rates are shown in Figure 6c. At 0.1 mV/s, it shows the start potential of 1.64 V in OER’s direction, and has an anodic current that increases quickly when the extra potential is given. The experiment’s outcome indicates that the possible start of the Cu2O-Co3O4 composite is near the OER’s thermodynamic potential. Therefore, the Cu2O-Co3O4 composite provides a Tafel slope and a current density of 3.89 mA/cm2. Moreover, the η (overpotential) obtained from the Cu2O-Co3O4 composite is 0.370 V, with a current density of 1.07 mA/cm2 (Figure 5d).
The effect of the scan rate electrochemical activity of the Cu2O-Co3O4/CN composite synthesized at 400 °C and 500 °C was also studied in 1 M KOH. The voltammograms obtained for the Cu2O-Co3O4/CN composite synthesized at different temperatures are different from each other, which indicates that the temperature played a significant role in the formation of the final product. Figure 6a,c present the effect of the scan rate on the cyclic voltammograms of the Cu2O-Co3O4/CN composite synthesized at 400 °C and 500 °C. As discussed previously, at lower scan rates, a lower amount of current is produced, which increased with increasing scan rates and, finally, reached a maximum point at a scan rate of 0.1 mV/s. Calibration curves are plotted between scan rates, and currents are shown in Figure 6b,d for the Cu2O-Co3O4/CN composites synthesized at 400 °C and 500 °C, respectively. The obtained correlation coefficients are 0.7924 and 0.96502, respectively.
LSV experiments on the Cu2O-Co3O4/CN composite electrodes were studied in the 1M KOH solution. The effect of different scan rates on the LSV response of the Cu2O-Co3O4/CN composite synthesized at different temperatures is shown in Figure 7. Although the pattern is the same, the current density and Tafel slopes of the nitrogen doped carbon and the Cu2O-Co3O4/CN composite are different. A current of 0.1 mV/s shows a start potential of 1.682 V toward OER; the anodic current shows a rapid increase as the potential is applied. The catalyst synthesized at 400 °C shows better efficiency, as compared to the product synthesized at 500 °C. The main reason for the better efficiency of Cu2O-Co3O4/CN composite at 400 °C could be better electron transfer due to the higher conductivity of metal oxides and nitrogen doped carbon, and a higher surface area. The Tafel slope for the product synthesized at 400 °C is 281 mV/decade and the current density is 0.599 mA/cm2, as shown in Figure 7b. In addition, a current density of 10 mA/cm2 was recorded at η (overpotential) = 396 mV. These experiments explain the good electrocatalytic response of the Cu2O-Co3O4/CN composite toward OER. Similarly, at 500 °C, the overall catalytic performance is low. OER’s onset potential is 1.6194, Tafel slope 261 mV/decade and current density 0.771 mA/cm2, as shown in Figure 7c,d.
Using Ag/AgCl as the reference electrode for electrolytes is commonplace in potentiometry and voltammetry, and their importance in the chemical laboratory is unquestionable. Ag/AgCl electrodes are usually more effective for many purposes.
The electrochemical performance of Cu2O and Co3O4 particles and their different composites is well documented in literature [47,48,49,50,51,52,53]. Similarly, the electrical conductivity of nitrogen doped carbon is also reported [54,55,56,57,58]. Incorporating a nitrogen doped carbon into an already conductive Cu2O-Co3O4 composite resulted in the formation of a versatile catalyst. The Cu2O-Co3O4/CN composite shows low overpotential compared to several other reported materials. Two metal oxides and already conducting nitrogen doped carbon improved the catalytic water splitting performance in the 1 M KOH solution. The activity diagram of the Cu2O-Co3O4/CN composite is shown in Figure 8.

4. Conclusions

In combination with transition metals, such as copper and cobalt and their composites, carbon based materials are considered ideal candidates in electrocatalysis. In this research, a novel combination of nitrogen doped carbon with a cobalt oxide and copper oxide (Cu2O-Co3O4/CN) composite was synthesized. The Cu2O-Co3O4 composite is selected for its enhanced water splitting ability, while nitrogen doped carbon is chosen to enhance the catalyst’s electrical conductivity. The synthesis was completed in two steps, at two different temperatures, and the resulting composite was used as a catalyst for electrochemical water splitting. A 1 M KOH solution was used to study the oxygen evolution reaction (OER). Different electrochemical parameters were optimized for the best conditions for water splitting. The OER efficiency of the catalysts prepared at 400 °C and 500 °C also, compared material prepared at 400 °C, showed better electrochemical performance. These results demonstrate that this combination can be used commercially for renewable energy production from water with several optimizations. Synthesis is quite easy, and the materials used for synthesis are also low cost; thus, the proposed method would be cost effective and ideal for scale up.

Author Contributions

Conceptualization, Z.A.S. and A.M.; methodology, Z.A.S. and N.M.; software, A.M. and S.Y.; writing—original draft preparation, Z.A.S. and N.M.; writing—review and editing, Z.A.S., N.M., A.M. and S.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Bekun, F.V.; Alola, A.A.; Sarkodie, S.A. Toward a sustainable environment: Nexus between CO2 emissions, resource rent, renewable and nonrenewable energy in 16-EU countries. Sci. Total Environ. 2019, 657, 1023–1029. [Google Scholar] [CrossRef]
  2. Zafar, M.W.; Shahbaz, M.; Hou, F.; Sinha, A. From nonrenewable to renewable energy and its impact on economic growth: The role of research & development expenditures in Asia-Pacific Economic Cooperation countries. J. Clean. Prod. 2019, 212, 1166–1178. [Google Scholar]
  3. Hansen, K.; Mathiesen, B.V.; Skov, I.R. Full energy system transition towards 100% renewable energy in Germany in 2050. Renew. Sustain. Energy Rev. 2019, 102, 1–13. [Google Scholar] [CrossRef]
  4. Gu, G.H.; Noh, J.; Kim, I.; Jung, Y. Machine learning for renewable energy materials. J. Mater. Chem. A 2019, 7, 17096–17117. [Google Scholar] [CrossRef]
  5. Ivakhnenko, A.; Bakytzhan, B. Characterization of Economic and Ecological Advantages and Challenges in Development of Conventional and Unconventional Hydrocarbon, Non-Hydrocarbon and Renewable Energy Sources for Resource-Based Economy in Kazakhstan. In Proceedings of the EGU General Assembly Conference, online, 4–8 May 2020. [Google Scholar]
  6. Winebrake, J.J.; Wang, M.Q.; He, D. Toxic emissions from mobile sources: A total fuel-cycle analysis for conventional and alternative fuel vehicles. J. Air Waste Manag. Assoc. 2001, 51, 1073–1086. [Google Scholar] [CrossRef] [Green Version]
  7. Zeng, K.; Zhang, D. Recent progress in alkaline water electrolysis for hydrogen production and applications. Prog. Energy Combust. Sci. 2010, 36, 307–326. [Google Scholar] [CrossRef]
  8. Tian, J.; Liu, Q.; Asiri, A.M.; Sun, X. Self-supported nanoporous cobalt phosphide nanowire arrays: An efficient 3D hydrogen-evolving cathode over the wide range of pH 0–14. J. Am. Chem. Soc. 2014, 136, 7587–7590. [Google Scholar] [CrossRef] [PubMed]
  9. Hosseini, S.E.; Wahid, M.A. Hydrogen production from renewable and sustainable energy resources: Promising green energy carrier for clean development. Renew. Sustain. Energy Rev. 2016, 57, 850–866. [Google Scholar] [CrossRef]
  10. Hosseini, S.E.; Wahid, M.A. Hydrogen from solar energy, a clean energy carrier from a sustainable source of energy. Int. J. Energy Res. 2020, 44, 4110–4131. [Google Scholar] [CrossRef]
  11. Acar, C.; Dincer, I. Comparative assessment of hydrogen production methods from renewable and nonrenewable sources. Int. J. Hydrogen Energy 2014, 39, 1–12. [Google Scholar] [CrossRef]
  12. Maggio, G.; Nicita, A.; Squadrito, G. How the hydrogen production from RES could change energy and fuel markets: A review of recent literature. Int. J. Hydrogen Energy 2019, 44, 11371–11384. [Google Scholar] [CrossRef]
  13. Hisatomi, T.; Domen, K. Reaction systems for solar hydrogen production via water splitting with particulate semiconductor photocatalysts. Nat. Catal. 2019, 2, 387–399. [Google Scholar] [CrossRef]
  14. Salomão, P.E.; Gomes, D.S.; Ferreira, E.J.C.; Moura, F.; Nascimento, L.L.; Patrocínio, A.O.T.; Pereira, M.C. Photoelectrochemical hydrogen production from water splitting using heterostructured nanowire arrays of Bi2O3/BiAl oxides as a photocathode. Sol. Energy Mater. Sol. Cells 2019, 194, 276–284. [Google Scholar] [CrossRef]
  15. Fajrina, N.; Tahir, M. A critical review in strategies to improve photocatalytic water splitting towards hydrogen production. Int. J. Hydrogen Energy 2019, 44, 540–577. [Google Scholar] [CrossRef]
  16. Kong, D.; Wang, H.; Cha, J.J.; Pasta, M.; Koski, K.J.; Yao, J.; Cui, Y. Synthesis of MoS2 and MoSe2 films with vertically aligned layers. Nano Lett. 2013, 13, 1341–1347. [Google Scholar] [CrossRef]
  17. Faraji, M.; Yousefi, M.; Yousefzadeh, S.; Zirak, M.; Naseri, N.; Jeon, T.H.; Choi, W.; Moshfegh, A.Z. Two-dimensional materials in semiconductor photoelectrocatalytic systems for water splitting. Energy Environ. Sci. 2019, 12, 59–95. [Google Scholar] [CrossRef]
  18. Wu, J.; Zhang, Y.; Zhou, J.; Wang, K.; Zheng, Y.-Z.; Tao, X. Uniformly assembling n-type metal oxide nanostructures (TiO2 nanoparticles and SnO2 nanowires) onto P doped g-C3N4 nanosheets for efficient photocatalytic water splitting. Appl. Catalys. B Environ. 2020, 278, 119301. [Google Scholar] [CrossRef]
  19. Wang, J.; Cui, W.; Liu, Q.; Xing, Z.; Asiri, A.M.; Sun, X. Recent progress in cobalt-based heterogeneous catalysts for electrochemical water splitting. Adv. Mater. 2016, 28, 215–230. [Google Scholar] [CrossRef]
  20. Wang, H.; Gao, C.; Li, R.; Peng, Z.; Yang, J.; Gao, J.; Yang, Y.; Li, S.; Li, B.; Liu, Z. Ruthenium-cobalt nanoalloy embedded within hollow carbon spheres as a bifunctionally robust catalyst for hydrogen generation from water splitting and ammonia borane hydrolysis. ACS Sustain. Chem. Eng. 2019, 7, 18744–18752. [Google Scholar] [CrossRef]
  21. Sun, H.; Yan, Z.; Liu, F.; Xu, W.; Cheng, F.; Chen, J. Self-supported transition-metal-based electro-catalysts for hydrogen and oxygen evolution. Adv. Mater. 2020, 32, 1806326. [Google Scholar] [CrossRef]
  22. Joe, J.; Yang, H.; Bae, C.; Shin, H. Metal chalcogenides on silicon photocathodes for efficient water splitting: A mini overview. Catalysts 2019, 9, 149. [Google Scholar] [CrossRef] [Green Version]
  23. Kötz, R.; Stucki, S. Oxygen Evolution and Corrosion on Ruthenium-Iridium Alloys. J. Electrochem. Soc. 1985, 132, 103–107. [Google Scholar] [CrossRef]
  24. Devarayapalli, K.C.; Lee, K.; Nam, N.D.; Vattikuti, S.V.P.; Shim, J. Microwave synthesized nano-photosensitizer of CdS QD/MoO3–OV/g–C3N4 heterojunction catalyst for hydrogen evolution under full-spectrum light. Ceram. Int. 2020, 46, 28467–28480. [Google Scholar] [CrossRef]
  25. Devarayapalli, K.C.; Vattikuti, S.V.P.; Sreekanth, T.V.M.; Nagajyothi, P.C.; Shim, J. Pyrolysis-Synthesized g-C3N4/Nb2O5 Nanocomposite for Enhanced Photocatalytic Activity under White LED Light Irradiation. ChemistrySelect 2019, 4, 13250–13258. [Google Scholar] [CrossRef]
  26. Devarayapalli, K.; Vattikuti, S.V.P.; Sreekanth, T.V.M.; Yoo, K.S.; Nagajyothi, P.C.; Shim, J. Hydrogen production and photocatalytic activity of g-C3N4/Co-MOF (ZIF-67) nanocomposite under visible light irradiation. Appl. Organomet. Chem. 2020, 34, e5376. [Google Scholar] [CrossRef]
  27. Vattikuti, S.P.; Devarayapalli, K.C.; Nagajyothi, P.C.; Shim, J. Microwave synthesized dry leaf-like mesoporous MoSe2 nanostructure as an efficient catalyst for enhanced hydrogen evolution and supercapacitor applications. Microchem. J. 2020, 153, 104446. [Google Scholar] [CrossRef]
  28. Matsumoto, Y.; Manabe, H.; Sato, E. Oxygen Evolution on La1-xSrx Fe1-y Co y O3 Series Oxides. J. Electrochem. Soc. 1980, 127, 2360–2364. [Google Scholar] [CrossRef]
  29. Qu, Y.; Yang, M.; Chai, J.; Tang, Z.; Shao, M.; Kwok, C.T.; Yang, M.; Wang, Z.; Chua, D.; Wang, S.; et al. Facile synthesis of vanadium-doped Ni3S2 nanowire arrays as active electro-catalyst for hydrogen evolution reaction. ACS Appl. Mater. Interfaces 2017, 9, 5959–5967. [Google Scholar] [CrossRef]
  30. Yu, Y.; Zhou, J.; Sun, Z. Novel 2D Transition-Metal Carbides: Ultrahigh Performance Electrocatalysts for Overall Water Splitting and Oxygen Reduction. Adv. Funct. Mater. 2020, 30, 2000570. [Google Scholar] [CrossRef]
  31. Liu, Z.Q.; Cheng, H.; Li, N.; Ma, T.Y.; Su, Y.-Z. ZnCo2O4 quantum dots anchored on nitrogen-doped carbon nanotubes as reversible oxygen reduction/evolution electro-catalysts. Adv. Mater. 2016, 28, 3777–3784. [Google Scholar] [CrossRef] [PubMed]
  32. Ding, J.; Ji, S.; Wang, H.; Gai, H.; Liu, F.; Linkov, V.; Wang, R. Mesoporous nickel-sulfide/nickel/N-doped carbon as HER and OER bifunctional electro-catalyst for water electrolysis. Int. J. Hydrogen Energy 2019, 44, 2832–2840. [Google Scholar] [CrossRef]
  33. Wu, A.; Xie, Y.; Ma, H.; Tian, C.; Gu, Y.; Yan, H.; Zhang, X.; Yang, G.; Fu, H. Integrating the active OER and HER components as the heterostructures for the efficient overall water splitting. Nano Energy 2018, 44, 353–363. [Google Scholar] [CrossRef]
  34. Zhang, H.; Maijenburg, A.W.; Li, X.; Schweizer, S.L.; Wehrspohn, R.B. Bifunctional heterostructured transition metal phosphides for efficient electrochemical water splitting. Adv. Funct. Mater. 2020, 30, 2003261. [Google Scholar] [CrossRef]
  35. Li, Y.; Zhang, H.; Jiang, M.; Zhang, Q.; He, P.; Sun, X. 3D self-supported Fe-doped Ni2P nanosheet arrays as bifunctional catalysts for overall water splitting. Adv. Funct. Mater. 2017, 27, 1702513. [Google Scholar] [CrossRef]
  36. Wang, Z.; Xu, L.; Huang, F.; Qu, L.; Li, J.; Owusu, K.A.; Liu, Z.; Lin, Z.; Xiang, B.; Liu, X.; et al. Copper-Nickel Nitride Nanosheets as Efficient Bifunctional Catalysts for Hydrazine-Assisted Electrolytic Hydrogen Production. Adv. Energy Mater. 2019, 9, 1900390. [Google Scholar] [CrossRef]
  37. Dalle, K.E.; Warnan, J.; Leung, J.J.; Reuillard, B.; Karmel, I.S.; Reisner, E. Electro- and Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes. Chem. Rev. 2019, 119, 2752–2875. [Google Scholar] [CrossRef] [PubMed]
  38. Roger, I.; Shipman, M.A.; Symes, M.D. Earth-abundant catalysts for electrochemical and photoelectrochemical water splitting. Nat. Rev. Chem. 2017, 1, 0003. [Google Scholar] [CrossRef]
  39. Wang, J.; Choi, S.; Kim, J.; Cha, S.W.; Lim, J. Recent Advances of First d-Block Metal-Based Perovskite Oxide Electrocatalysts for Alkaline Water Splitting. Catalysts 2020, 10, 770. [Google Scholar] [CrossRef]
  40. Wang, J.; Gao, Y.; Kong, H.; Kim, J.; Choi, S.; Ciucci, F.; Lim, J. Non-precious-metal catalysts for alkaline water electrolysis: Operando characterizations, theoretical calculations, and recent advances. Chem. Soc. Rev. 2020, 49, 9154–9196. [Google Scholar] [CrossRef]
  41. Wang, J.; Zhao, H.; Gao, Y.; Chen, D.; Chen, C.; Saccoccio, M.; Ciucci, F. Ba0. 5Sr0. 5Co0. 8Fe0. 2O3− δ on N-doped mesoporous carbon derived from organic waste as a bi-functional oxygen catalyst. Int. J. Hydrogen Energy 2016, 41, 10744–10754. [Google Scholar] [CrossRef]
  42. Janani, G.; Yuvaraj, S.; Surendran, S.; Chae, Y.; Sim, Y.; Song, S.-J.; Park, W.; Kim, M.-J.; Sim, U. Enhanced bifunctional electrocatalytic activity of Ni-Co bimetallic chalcogenides for efficient water-splitting application. J. Alloy. Compd. 2020, 846, 156389. [Google Scholar] [CrossRef]
  43. Wang, J.; Ciucci, F. Boosting Bifunctional Oxygen Electrolysis for N-Doped Carbon via Bimetal Addition. Small 2017, 13, 1604103. [Google Scholar] [CrossRef] [PubMed]
  44. Wang, J.; Kim, J.; Choi, S.; Wang, H.; Lim, J. A Review of Carbon-Supported Nonprecious Metals as Energy-Related Electrocatalysts. Small Methods 2020, 4, 2000621. [Google Scholar] [CrossRef]
  45. Wang, J.; Kong, H.; Zhang, J.; Hao, Y.; Shao, Z.; Ciucci, F. Carbon-based electrocatalysts for sustainable energy applications. Progr. Mater. Sci. 2021, 116, 100717. [Google Scholar] [CrossRef]
  46. Surendran, S.; Sivanantham, A.; Shanmugam, S.; Sim, U.; Kalai Selvan, R. Ni2P2O7 microsheets as efficient Bi-functional electrocatalysts for water splitting application. Sustain. Energy Fuels 2019, 3, 2435–2446. [Google Scholar] [CrossRef]
  47. An, T.-Y.; Surendran, S.; Kim, H.; Choe, W.-S.; Kim, J.K.; Sim, U. A polydopamine-mediated biomimetic facile synthesis of molybdenum carbide phosphide nanodots encapsulated in carbon shell for electrochemical hydrogen evolution reaction with long-term durability. Compos. Part B Eng. 2019, 175, 107071. [Google Scholar] [CrossRef]
  48. Sim, Y.; Kim, S.J.; Janani, G.; Chae, Y.; Surendran, S.; Kim, H.; Yoo, S.; Seok, D.C.; Jung, Y.H.; Jeon, C.; et al. The synergistic effect of nitrogen and fluorine co-doping in graphene quantum dot catalysts for full water splitting and supercapacitor. Appl. Surf. Sci. 2020, 507, 145157. [Google Scholar] [CrossRef]
  49. Dayong, N.; Mikhaylov, A.; Bratanovsky, S.; Shaikh, Z.A.; Stepanova, D. Mathematical modeling of the technological processes of catering products production. J. Food Process Eng. 2020, 43, e13340. [Google Scholar] [CrossRef]
  50. Zhang, X.; Cui, X.; Sun, Y.; Qi, K.; Jin, Z.; Wei, S.; Li, W.; Zhang, L.; Zheng, W. Nanoporous Sulfur-Doped Copper Oxide (Cu2OxS1−x) for Overall Water Splitting. ACS Appl. Mater. Interfaces 2018, 10, 745–752. [Google Scholar] [CrossRef]
  51. Wang, S.; He, T.; Yun, J.-H.; Hu, Y.; Ziao, M.; Du, A.; Wang, L. New Iron-Cobalt Oxide Catalysts Promoting BiVO4 Films for Photoelectrochemical Water Splitting. Adv. Funct. Mater. 2018, 28, 1802685. [Google Scholar] [CrossRef]
  52. Surendran, S.; Shanmugapriya, S.; Ramasamy, H.; Janani, G.; Kalpana, D.; Lee, Y.S.; Sim, U.; Selvan, R.K. Hydrothermal deposition of CoS nanostructures and its multifunctional applications in supercapattery and water electrolyzer. Appl. Surf. Sci. 2019, 494, 916–928. [Google Scholar] [CrossRef]
  53. Yumashev, A.; Ślusarczyk, B.; Kondrashev, S.; Mikhaylov, A. Global Indicators of Sustainable Development: Evaluation of the Influence of the Human Development Index on Consumption and Quality of Energy. Energies 2020, 13, 2768. [Google Scholar] [CrossRef]
  54. Nie, D.; Panfilova, E.; Samusenkov, V.; Mikhaylov, A. E-Learning Financing Models in Russia for Sustainable Development. Sustainability 2020, 12, 4412. [Google Scholar] [CrossRef]
  55. An, J.; Mikhaylov, A.; Jung, S.-U. The Strategy of South Korea in the Global Oil Market. Energies 2020, 13, 2491. [Google Scholar] [CrossRef]
  56. An, J.; Mikhaylov, A.; Kim, K. Machine Learning Approach in Heterogeneous Group of Algorithms for Transport Safety-Critical System. Appl. Sci. 2020, 10, 2670. [Google Scholar] [CrossRef]
  57. Yumashev, A.; Mikhaylov, A. Development of Polymer Film Coatings with High Adhesion to Steel Alloys and High Wear Resistance. Polym. Compos. 2020, 41, 2875–2880. [Google Scholar] [CrossRef]
  58. Sawant, S.Y.; Cho, M.H.; Kang, M.; Han, T.H. Carbothermal process-derived porous N-doped carbon for flexible energy storage: Influence of carbon surface area and conductivity. Chem. Eng. J. 2019, 378, 122158. [Google Scholar] [CrossRef]
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Figure 1. TEM, SEM, and AFM images of Cu2O-Co3O4 (a,c,e) and Cu2O-Co3O4/CN composites (b,d,f).
Figure 1. TEM, SEM, and AFM images of Cu2O-Co3O4 (a,c,e) and Cu2O-Co3O4/CN composites (b,d,f).
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Figure 2. FTIR of Cu2O-Co3O4 and Cu2O-Co3O4/CN composites.
Figure 2. FTIR of Cu2O-Co3O4 and Cu2O-Co3O4/CN composites.
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Figure 3. (a) CV curves of Cu2O-Co3O4/CN composite at slurry volume range from 0.1 to 0.5 µL in 1 M KOH; (b) linear calibration curve for oxidation and reduction at different concentrations.
Figure 3. (a) CV curves of Cu2O-Co3O4/CN composite at slurry volume range from 0.1 to 0.5 µL in 1 M KOH; (b) linear calibration curve for oxidation and reduction at different concentrations.
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Figure 4. (a) Cyclic voltammogram and (b) calibration curve; (c) LSV curves and (d) the corresponding Tafel plots of nitrogen doped carbon at different scan rates in 1 M KOH.
Figure 4. (a) Cyclic voltammogram and (b) calibration curve; (c) LSV curves and (d) the corresponding Tafel plots of nitrogen doped carbon at different scan rates in 1 M KOH.
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Figure 5. (a) LSV curves for Cu2O-Co3O4 composite and the (b) calibration curve, (c) LSV curves, and (d) the corresponding Tafel plots for Cu2O-Co3O4 composite, in 1 M KOH, at different scan rates.
Figure 5. (a) LSV curves for Cu2O-Co3O4 composite and the (b) calibration curve, (c) LSV curves, and (d) the corresponding Tafel plots for Cu2O-Co3O4 composite, in 1 M KOH, at different scan rates.
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Figure 6. Effect of scan rate on electrochemical performance of Cu2O-Co3O4/CN composite synthesized (a) at 400 °C, (b) its calibration curve; (c) at 500 °C, and (d) its calibration curve obtained at scan rates in 1 M KOH.
Figure 6. Effect of scan rate on electrochemical performance of Cu2O-Co3O4/CN composite synthesized (a) at 400 °C, (b) its calibration curve; (c) at 500 °C, and (d) its calibration curve obtained at scan rates in 1 M KOH.
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Figure 7. LSV curves of Cu2O-Co3O4/CN composite synthesized at (a) 400 °C and (c) 500 °C and corresponding Tafel slops (b,d) at different scan rates, in 1 M KOH.
Figure 7. LSV curves of Cu2O-Co3O4/CN composite synthesized at (a) 400 °C and (c) 500 °C and corresponding Tafel slops (b,d) at different scan rates, in 1 M KOH.
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Figure 8. Activity diagram of Cu2O-Co3O4/CN composite.
Figure 8. Activity diagram of Cu2O-Co3O4/CN composite.
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Shaikh, Z.A.; Moiseev, N.; Mikhaylov, A.; Yüksel, S. Facile Synthesis of Copper Oxide-Cobalt Oxide/Nitrogen-Doped Carbon (Cu2O-Co3O4/CN) Composite for Efficient Water Splitting. Appl. Sci. 2021, 11, 9974. https://doi.org/10.3390/app11219974

AMA Style

Shaikh ZA, Moiseev N, Mikhaylov A, Yüksel S. Facile Synthesis of Copper Oxide-Cobalt Oxide/Nitrogen-Doped Carbon (Cu2O-Co3O4/CN) Composite for Efficient Water Splitting. Applied Sciences. 2021; 11(21):9974. https://doi.org/10.3390/app11219974

Chicago/Turabian Style

Shaikh, Zaffar Ahmed, Nikita Moiseev, Alexey Mikhaylov, and Serhat Yüksel. 2021. "Facile Synthesis of Copper Oxide-Cobalt Oxide/Nitrogen-Doped Carbon (Cu2O-Co3O4/CN) Composite for Efficient Water Splitting" Applied Sciences 11, no. 21: 9974. https://doi.org/10.3390/app11219974

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