Next Article in Journal
Fast Degradation of Azo Dyes by In Situ Mg-Zn-Ca-Sr Metallic Glass Matrix Composite
Previous Article in Journal
Radiation Response of Large-Area 4H-SiC Schottky Barrier Diodes
Previous Article in Special Issue
Influence of the Addition of Rare Earth Elements on the Energy Storage and Optical Properties of Bi0.5Na0.5TiO3–0.06BaTiO3 Polycrystalline Thin Films
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 16
Issue 6
10.3390/ma16062204
materials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Hierarchical CoNiO2 Microflowers Assembled by Mesoporous Nanosheets as Efficient Electrocatalysts for Hydrogen Evolution Reaction

by
Dingfu Zhang
1,
Jiaxin Yao
1,
Jinling Yin
1,
Guiling Wang
1,
Kai Zhu
1,*,
Jun Yan
1,
Dianxue Cao
1 and
Min Zhu
2,*
1
Key Laboratory of Superlight Materials and Surface Technology of Ministry of Education, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China
2
Technology Innovation Center of Industrial Hemp for State Market Regulation, College of Chemistry and Chemical Engineering, Qiqihar University, Qiqihar 161006, China
*
Authors to whom correspondence should be addressed.
Materials 2023, 16(6), 2204; https://doi.org/10.3390/ma16062204
Submission received: 15 February 2023 / Revised: 2 March 2023 / Accepted: 7 March 2023 / Published: 9 March 2023
(This article belongs to the Special Issue Preparation and Properties of Novel Energy Storage Materials)
Browse Figures
Versions Notes

Abstract

:
In order to alleviate the energy crisis and propel a low-carbon economy, hydrogen (H2) plays an important role as a renewable cleaning resource. To break the hydrogen evolution reaction (HER) bottleneck, we need high-efficiency electrocatalysts. Based on the synergistic effect between bimetallic oxides, hierarchical mesoporous CoNiO2 nanosheets can be fabricated. Combining physical representations with electrochemical measurements, the resultant CoNiO2 catalysts present the hierarchical microflowers morphology assembled by mesoporous nanosheets. The ultrathin two-dimensional nanosheets and porous surface characteristics provide the vast channels for electrolyte injection, thus endowing CoNiO2 the outstanding HER performance. The excellent performance with a fewer onset potential of 94 mV, a smaller overpotential at 10 mA cm−2, a lower Tafel slope of 109 mV dec−1 and better stability after 1000 cycles makes CoNiO2 better than that of metallic Co and metallic Ni.

1. Introduction

Fossil fuels are running out and the planet is getting worse, meaning it is really important to develop high-power and energy density alternative energy devices. There is no doubt that hydrogen (H2) is a renewable and clean energy that can be obtained from the environment [1,2,3,4]. It is well known that hydrogen is the most abundant element on earth; currently, 90% of H2 is acquired from fossil fuels, leading to the aggravation of the energy crisis [5]. Electrocatalytic water (H2O) splitting, using H2O as the hydrogen source and powered by renewable electricity, is regarded as a potential H2 synthesis strategy to minimize carbon emissions [6,7,8,9,10]. The hydrogen evolution reaction (HER) is, however, still limited by the large overpotential that is found in splitting H2O, which makes the reaction performance hover at a significantly lower level. It has been shown that certain noble metals with the low overpotential, such as platinum-based materials, are expected to serve as excellent catalysts for hydrogen production in practical application, though the scarcity of these materials and the high price make them difficult to use in practice [11,12,13,14]. To solve HER problems, we need efficient non-precious metal electrocatalysts [15,16,17,18,19,20].
To date, non-precious metals as the substitute materials have been extensively explored for HER to replace precious metals. By virtue of their structure design and synergistic effect, catalysts are capable of introducing hydrogen into a system at a higher performance level. There is a possibility of increasing the electrochemical HER performance by increasing the number of active sites in nanosheet structures. For example, Ni0.85Se nanosheet on graphene owns many active sites and well HER catalytic property [21]. It may also be advantageous to improve performance by taking advantage of the synergistic effects of bimetallic electrocatalysts. Singh et al. reported that the B-TiZr-2.5 catalyst has improved HER activity [22]. It is recognized that the single metal catalyst is not enough to make the HER catalyst active. Therefore, other metal oxide phases need to be added to obtain higher HER performance.
It is well known that most transition monometal oxides have a very good catalytic activity, but due to their low active site and specific surface area, their further applications are limited. Due to this, many efforts have been made in order to further enhance the catalytic properties of transition monometal oxides. Among them, the introduction of bimetallic oxides is a strategy. Wang et al. reported that NiCo2O4 @ Ni(OH)2/NiOOH catalyst has the improved HER activity [23]. In view of the synergistic effect, developing the efficient Co-Ni oxide catalysts by a simple and cost-effective method is attractive and necessary for HER [24]. Herein, hierarchical CoNiO2 microflowers assembled by mesoporous nanosheets are synthesized successfully by a simple hydrothermal method together with an annealing process. Benefitting from the large specific surface area and synergistic effect between Ni-Co metals, this resultant CoNiO2 shows stunning catalytic properties for HER, such as the low Tafel slope of 109 mV dec−1, small onset potential of 94 mV, low charge transfer resistance and a long-term stable behavior regarding catalysis.

2. Experimental

2.1. Synthesis of CoNiO2

The hierarchical CoNiO2 microflower was prepared [25,26]; concretely, an ethanol-water (2:1 v/v) mixture containing 0.73 g Ni(NO3)2·6H2O, 1.45 g Co(NO3)2·6H2O and 1.4 g hexamethylenetetramine (HMT). This was then transferred into a 50 mL autoclave lined with Teflon after it had been stirred for 30 min. Upon sealing the autoclave, it was placed into an electric oven which had been set at 95 °C for 8 h. We first cooled down the as-obtained Co-Ni precursors under a vacuum to room temperature, washed with water and ethanol several times to remove the unreacted residues, followed by drying at 60 °C for 8 h under vacuum to ensure the precursors were completely dry. Lastly, CoNiO2 was synthesized following annealing at 450 degrees Celsius in an Ar atmosphere for two hours at 1 °C per minute. For comparison, the individual Ni and Co catalysts were procured by the same method without adding Cobaltous nitrate hexahydrate and Nickel nitrate hexahydrate, respectively.

2.2. Characterizations

In terms of surface analysis, X-ray Photoelectron Spectroscopy (XPS, ESCALAB250) is a practical method that can be used for both qualitative and quantitative analyses of solid surfaces, as well as structural identification. X-ray diffraction (XRD, Rigaku TTR III) is a research method to obtain information such as the composition of materials, the structure or morphology of molecules in materials. Scanning electron microscope (FESEM, FEI Quanta 200 FEG) can not only observe the surface morphology, but also analyze the components and elements. Transmission Electron Microscopy (TEM) and High-Resolution TEM (HRTEM) are instruments for imaging and analyzing the microstructure of materials (FEI Tecnai G2 F20).

2.3. Electrochemical Measurements

It took 550 μL of 6/5 (v/v) water/ethanol solution, 5 mg of CoNiO2 powder and 20 μL of Nafion (5 wt %) to make the mixed solution and this was sonicated mildly for 30 min. Then, 5 μL of the prepared catalyst solution was evenly coated on carbon fiber cloth with an area of 1 cm2. Typical electrochemical measurements were carried out using a three-electrode setup involving the working electrode (the loaded carbon cloth), as well as the reference electrode (the Hg/HgO solution) and the counter electrode (the carbon rod). According to the equation below, the potentials reported in this study have been converted to the reversible hydrogen electrode (RHE) scale and are now expressed as follows: E(RHE) = E(Hg/HgO) + 0.098 + 0.0592 × pH. The electrocatalytic experiments were carried out on an Autolab PGSTAT 302 (Eco Chemie) workstation.

3. Results and Discussion

The synthetic method can be demonstrated visually in Figure 1, in which a two-step method had been used to prepare the typical mesoporous CoNiO2. Hydrothermal processes are characterized by the hydrolysis of ethanol and hexamethylenetetramine, forming carbonate ion and hydroxide ion, which are then reacted with Ni2+ and Co2+ to form precursors of nickel and cobalt hydroxy-carbonates during the reaction. Secondly, under the Ar atmosphere, the as-prepared Ni-Co precursor was transformed into mesoporous CoNiO2 with a hierarchical structure. Furthermore, individual Co and Ni catalysts were prepared so that the synergistic effect of these components could be evaluated.
To investigate the crystal structure of the electrocatalyst, an XRD analysis has been carried out. The characteristic peaks of CoNiO2 in Figure 2 located at 36.8°, 42.8° and 61.8° correspond to the (111), (200) and (220) planes of the cubic CoNiO2 (JCPDS No. 10-0188) [25,26]. Meanwhile, the (111), (200) and (220) planes of metallic Ni can be matched to the diffraction peaks of Ni specimens at 44.5°, 51.8° and 76.4° (JCPDS No.04-0850) [27]. The characteristic peaks of the Co sample located at 41.7°, 44.7°, 47.6° and 75.9° are associated to the (100), (002), (101) and (110) of the metallic Cobalt’s planes (JCPDS No. 05-0727) [28]. It was observed that there were no significant peaks of impurities, which indicated that the products were phase pure. Particularly, compared with the single metallic Ni or Co specimen, CoNiO2 presents the weaker peak intensities. The relatively poor crystallinity means that CoNiO2 exhibits the thinner thickness and higher defects concentration, which is expected to show better activity in the hydrogen evolution reaction.
Electrocatalysts were characterized morphologically using scanning electron microscopy (SEM). As shown in the low-magnification SEM image (Figure 3a,b), the as-prepared CoNiO2 material presents the flower-like microsphere structure with an average diameter of about 9 μm. According to the high-resolution SEM images, it is also evident that the microflowers are a result of the two-dimensional thin nanosheets that are assembled into the microflowers (Figure 3c,d). For comparison, the morphologies of the metallic Ni and metallic Co were also provided, as shown in Figure 3e,f. It is worth noting that the individual Ni and Co samples are formed by spherical particles along with the severe agglomeration simultaneously. Having a regular and open hierarchical structure gives CoNiO2 a more specific surface area, makes electrolyte injection efficient and helps it be more catalytic. The conductivity of CoNiO2 material obtained after calcination is increased, which makes hydrogen evolution easier. The above results show that the prepared CoNiO2 material has a large specific surface area, exposed more active sites and good conductivity. Figure 3g–j shows the SEM picture and the elemental mapping pictures for CoNiO2 materials, indicating the good distribution of Ni, Co and O elements in the hierarchical flower-like nanosheets.
We investigated the morphology of the as-prepared CoNiO2 sample by transmission electron microscopy and high-resolution transmission electron microscopy in a further study. According to the TEM images of CoNiO2 shown in Figure 4a–d, the thin nanosheets are used to construct the microflowers, and therefore, TEM images are in agreement with SEM observations, where the nanosheets are assembled by thin walls. A distinctive characteristic of CoNiO2 microflowers is that they are formed by thin nanosheets of CoNiO2 over a thickness of approximately 100–300 nanometers. In Figure 4e, it is depicted that the lattice fringes with separations of 0.211 nanometers and 0.244 nanometers correspond to the crystallographic planes (200) and (111) for cubic CoNiO2, respectively. It is also worth mentioning that the SADE image exhibits a pattern along the zone axis of the [110] zone of cubic CoNiO2, which further confirms that CoNiO2 phase has been successfully generated (Figure 4f).
Further confirmations of surface elemental composition were done using X-ray photoelectron spectroscopy (Figure 5). Figure 5a shows the full scan spectrum of CoNiO2, in which Co, Ni and O elements coexist. According to the Co 2p spectra (Figure 5b), the binding energies at 795.0 eV and 779.8 eV correspond to the peaks of Co 2p1/2 and Co 2p3/2, respectively, while the satellite peaks of 803.3 eV and 785.9 eV are associated with its satellites [29]. A correlation was found between Ni 2p3/2 and Ni 2p1/2, as indicated by the characteristic peaks of Ni 2p in Figure 5c located at 854.0 eV and 872.8 eV, and the relevant satellite peaks were also observed at 861.1 eV and 879.5 eV [30]. There are also two characteristic peaks in the O 1s spectrum (Figure 5d); one at 529.6 eV represents oxygen species in the CoNiO2 phase and the other represents oxygen-containing residuals like H-O-H. Based on the above characterizations, the hierarchical CoNiO2 microspheres are synthesized successfully.
Using a typical three-electrode setup that contained a concentration of 1 M KOH, hierarchical CoNiO2, metallic Ni and metallic Co were investigated for their electrocatalytic activities. Figure 6a illustrates that HER polarization curves were measured at 1 mV s−1 with IR correction for CoNiO2, Ni, Co and bare carbon cloth. The CoNiO2 catalyst has a lower onset overpotential of 94 mV when compared to Ni and Co catalysts, and has a faster current response when the potential goes up, while pure carbon cloth has negligible electrocatalytic activity. Furthermore, CoNiO2 has only an overpotential of 170 mV at 10 mA cm−2, which is lower than that of Ni (188 mV) and Co (244 mV), showing that it has a superior catalytic activity compared to these two metals. The HER performance of CoNiO2 is also superior to other Co-Ni composite materials reported previously (Table 1), which benefits from the nanoflower structure providing more active sites and the synergistic effect.
We further explored the inherent properties of different catalysts by evaluating the reaction kinetics of HER using Tafel plots as a way. Figure 6b illustrates that the Tafel slope of CoNiO2 is 109 mV dec−1, a value lower than both Ni (149 mV dec−1) and Co catalysts (225 mV dec−1). As indicated by the Tafel slope of 109 mV dec−1, the hydrogen evolution process on CoNiO2 is governed by the Volmer-Heyrovsky mechanism, and the lower value is indicative of the more favorable characteristics of its kinetic behavior toward hydrogen evolution.
The stability and durability of the as-synthesized CoNiO2 are also evaluated in alkaline condition. Figure 6c shows that the chronopotentiometry curve shows no obvious degradation after 10 h at 10 mA cm−2. As can be seen from Figure 6c (inset), the polarization curve starts to overlap the initial curve almost completely, and this maintains the current density of 98.2% even after 1000 continuous sweeping cycles. All the above results prove that CoNiO2 has excellent HER activity, along with great stability.
Using electrochemical impedance spectroscopy (EIS), we conducted an analysis with an overpotential of −300 mV in order to better understand the HER kinetics of CoNiO2, metallic Ni and metallic Co. Figure 6d shows the corresponding Nyquist plots and Figure 6d inset shows the equivalent circuit model. It is clearly observed that CoNiO2 presents the lowest charge transport resistance (Rct), reflecting its better electronic conductivity. Specifically, CoNiO2, Ni and Co possess Rct values of 5.13, 5.27 and 5.35 Ω, respectively. Smaller Rct values indicate that CoNiO2 owns quicker charge transfer than other samples. During the HER process of CoNiO2, the electrons deliver directly and efficiently between the catalyst and the solution, contributing well to activity.
An electrochemical surface area with a higher value typically means there are more active sites in the electrochemical layer, which results in higher HER activity. In addition, the electrochemical surface area varies with the capacitance of the double layer, so that it is proportional to the surface area. There are several CV curves that can be seen in Figure 7a–c related to electrocatalysts that have been tested with a scan rate that ranges from 20 to 100 mV s−1, namely CoNiO2, metallic Ni and metallic Co in an alkaline electrolyte. At 0.77 V, we calculated the current density difference between the anode and cathode (∆j = Janode − Jcathode). It can be obtained twice the value of double-layer capacitance (Cdl) by fitting the scanning rate and ∆j together. As you can see in Figure 7d, CoNiO2 has a large Cdl value (8.05 * 10−4 mF cm−2) compared to metallic Ni (5.10 * 10−4 mF cm−2) and metallic Co (3.15 * 10−4 mF cm−2). There was a noticeable difference between CoNiO2 and all the other materials investigated in respect of their electrochemical surface area and HER activity in the alkaline electrolyte based on the results.
The composition of the CoNiO2 process was examined by XRD following the HER for 10 h. As shown in Figure 8a, the XRD curves before and after 10 h test of CoNiO2 in an alkaline electrolyte have been displayed. The results show that all the peaks after the 10 h test have remained approximately the same as they were before the test, which proves that the CoNiO2 in an alkaline electrolyte is a very stable compound. SEM images (Figure 8b) were taken of the same samples after 10 h of HER in an alkaline electrolyte, which indicate that the morphologies after the test are nanoparticles agglomerated compared to the ones before the test.
As shown in Figure 9a, the characteristic peak of the cobalt-nickel precursor located at 9.5° corresponds to the (001) planes of Co(OH)2 (JCPDS No. 51-1731), and is located at 19.3° (001) planes of Ni(OH)2 (JCPDS No. 14-0117). As shown in the SEM image (Figure 9a,b), the cobalt-nickel precursor presents the flower-like microsphere structure.
The surface elemental composition of the CoNiO2 process was examined by XPS following the post-HER. As shown in Figure 10, the XPS curves of CoNiO2 of the post-HER in an alkaline electrolyte have been displayed. The results show that the chemical surface composition of post-HER is the same as before and that there is no difference, which proves that the CoNiO2 in an alkaline electrolyte is a very stable compound.

4. Conclusions

In summary, it can be concluded that the hierarchical mesoporous CoNiO2 has been successfully prepared, and that this CoNiO2 can be used as a catalyst in water to catalyze the HER reaction. In HER, CoNiO2 only has an onset potential of 94 mV and an overpotential of 170 mV at 10 mA cm−2 due to the synergistic effect, compared with metallic Co and metallic Ni. Meanwhile, CoNiO2 presents the improved kinetic characteristics with a Tafel slope (109 mV dec−1). The enhanced reaction kinetics of CoNiO2 can be attributed to the high surface area, and are beneficial for contacting with electrolytes and enhancing the transport of charges. Additionally, CoNiO2 shows very good long-term stability and can withstand for over 10 h. The excellent electrocatalytic activity with high stability makes CoNiO2 promising for application in HER.

Author Contributions

Methodology, D.Z.; formal analysis and investigation, J.Y. (Jiaxin Yao) and J.Y. (Jinling Yin); writing—original draft preparation, G.W. and K.Z.; writing—review and editing, J.Y. (Jun Yan) and M.Z.; and validation, D.C. All authors have read and agreed to the published version of the manuscript.

Funding

The work was supported by a grant from the Fundamental Research Funds for Central Universities (No. 3072021CFT1001) and a grant from the Natural Science Foundation of Heilongjiang Province (No. LH2021B007).

Informed Consent Statement

Not applicable for studies not involving humans.

Data Availability Statement

Due to privacy, data is not provided at this time.

Acknowledgments

We gratefully acknowledge financial support of the Fundamental Research Funds for Central Universities and the Natural Science Foundation of Heilongjiang Province.

Conflicts of Interest

Neither the authors nor any of their collaborators declare any competing financial interests.

References

  1. Schlapbach, L.; Zuttel, A. Hydrogen-storage materials for mobile applications. Nature 2001, 414, 353–358. [Google Scholar] [CrossRef] [PubMed]
  2. Schlapbach, L. Technology: Hydrogen-fuelled vehicles. Nature 2009, 460, 809–811. [Google Scholar] [CrossRef] [PubMed]
  3. Yan, Q.; Liu, Z.; Bai, X.; Zhang, X.; Gao, R.; Yuan, W.; Chen, Z.; Li, Z.; Li, Y. In situ formed edge-rich Ni3S2-NiOOH heterojunctions for oxygen evolution reaction. J. Electrochem. Soc. 2022, 169, 054532. [Google Scholar] [CrossRef]
  4. Battiato, S.; Bruno, L.; Pellegrino, A.L.; Terrasi, A.; Mirabella, S. ×Optimized electroless deposition of NiCoP electrocalysts for enhanced water splitting. Catal. Today 2022, in press. [Google Scholar] [CrossRef]
  5. Ledendecker, M.; Mondschein, J.S.; Kasian, O.; Geiger, S.; Gohl, D.; Schalenbach, M.; Zeradjanin, A.; Cherevko, S.; Schaak, R.E.; Mayrhofer, K. Stability and activity of non-noble-metal-based catalysts toward the hydrogen evolution reaction. Angew Chem. Int. Ed. Engl. 2017, 56, 9767–9771. [Google Scholar] [CrossRef]
  6. Walter, M.G.; Warren, E.L.; McKone, J.R.; Boettcher, S.W.; Mi, Q.; Santori, E.A.; Lewis, N.S. Solar water splitting cells. Chem. Rev. 2010, 110, 6446–6473. [Google Scholar] [CrossRef]
  7. Deng, J.; Zhang, H.; Zhang, Y.; Luo, P.; Liu, L.; Wang, Y. Striking hierarchical urchin-like peapoded NiCo2O4@C as advanced bifunctional electrocatalyst for overall water splitting. J. Power Source 2017, 372, 46–53. [Google Scholar] [CrossRef]
  8. Fang, L.; Jiang, Z.; Xu, H.; Liu, L.; Guan, Y.; Gu, X.; Wang, Y. Crystal-plane engineering of NiCo2O4 electrocatalysts towards efficient overall water splitting. J. Catal. 2018, 357, 238–246. [Google Scholar] [CrossRef]
  9. Wang, L.Y.; Gu, C.D.; Ge, X.; Zhang, J.L.; Zhu, H.Y.; Tu, J.P. A NiCo2O4 shell on a hollow Ni nanorod array core for water splitting with enhanced electrocatalytic performance. Chemnanomat 2018, 4, 124–131. [Google Scholar] [CrossRef]
  10. Chhetri, K.; Muthurasu, A.; Dahal, B.; Kim, T.; Mukhiya, T.; Chae, S.H.; Ko, T.H.; Choi, Y.C.; Kim, H.Y. Engineering the abundant heterointerfaces of integrated bimetallic sulfide-coupled 2D MOF-derived mesoporous CoS2 nanoarray hybrids for electrocatalytic water splitting. Mater. Today Nano 2022, 17, 100146. [Google Scholar] [CrossRef]
  11. Liu, Q.; Wang, E.; Sun, G. Layered transition-metal hydroxides for alkaline hydrogen evolution reaction. Chin. J. Catal. 2020, 41, 574–591. [Google Scholar] [CrossRef]
  12. Hu, C.; Lv, C.; Liu, S.; Shi, Y.; Song, J.; Zhang, Z.; Cai, J.; Watanabe, A. Nickel phosphide electrocatalysts for hydrogen evolution reaction. Catalysts 2020, 10, 88. [Google Scholar] [CrossRef] [Green Version]
  13. Wei, Y.; Soomro, R.A.; Xie, X.; Xu, B. Design of efficient electrocatalysts for hydrogen evolution reaction based on 2D MXenes. J. Energy Chem. 2021, 55, 244–255. [Google Scholar] [CrossRef]
  14. Shahroudi, A.; Esfandiari, M.; Habibzadeh, S. Nickel sulfide and phosphide electrocatalysts for hydrogen evolution reaction: Challenges and future perspectives. RSC Adv. 2022, 12, 29440–29468. [Google Scholar] [CrossRef] [PubMed]
  15. Anantharaj, S.; Kundu, S.; Noda, S. Progess in nickel chalcogenide electrocatalyzed hydrogen evolution reaction. J. Mater. Chem. A 2020, 8, 4174–4192. [Google Scholar] [CrossRef]
  16. Ge, Z.; Fu, B.; Zhao, J.; Li, X.; Ma, B.; Chen, Y. A review of the electrocatalysts on hydrogen evolution reaction with an emphasis on Fe, Co and Ni-based phosphides. J Mater. Sci. 2020, 55, 14081–14104. [Google Scholar] [CrossRef]
  17. Bai, S.; Yang, M.; Jiang, J.; He, X.; Zou, J.; Xiong, Z.; Liao, G.; Liu, S. Recent advances of MXenes as electrocatalysts for hydrogen evolution reaction. NPJ 2D Mater. Appl. 2021, 5, 78. [Google Scholar] [CrossRef]
  18. Kandel, M.R.; Pan, U.N.; Paudel, D.R.; Dhakal, P.P.; Kim, N.H.; Lee, J.H. Hybridized bimetallic phosphides of Ni–Mo, Co–Mo, and Co–Ni in a single ultrathin-3D-nanosheets for efficient HER and OER in alkaline media. Compos. Part B Eng. 2022, 239, 109992. [Google Scholar] [CrossRef]
  19. Battiato, S.; Pellegrino, A.L.; Pollicino, A.; Terrasi, A.; Mirabella, S. Composition-controlled chemical bath deposition of Fe-doped NiO microflowers for boosting oxygen evolution reaction. Int. J. Hydrogen Energy 2023, in press. [Google Scholar] [CrossRef]
  20. Kim, J.; Jang, Y.J.; Jang, Y.H. Electrodeposition of Stable Noble-Metal-Free Co-P Electrocatalysts for Hydrogen Evolution Reaction. Materials 2023, 16, 593. [Google Scholar] [CrossRef]
  21. Zhu, M.; Yan, Y.D.; Yan, Q.; Yin, J.L.; Cheng, K.; Ye, K.; Zhu, K.; Yan, J.; Cao, D.X.; Wang, G.L. In situ growth of Ni0.85Se on graphene as a robust electrocatalyst for hydrogen evolution reaction. Int. J. Hydrogen Energy 2020, 45, 10486–10493. [Google Scholar] [CrossRef]
  22. Singh, K.P.; Shin, C.H.; Lee, H.Y.; Razmjooei, F.; Sinhamahapatra, A.; Kang, J.; Yu, J.S. TiO2/ZrO2 nanoparticle composites for electrochemical hydrogen evolution. ACS Appl. Nano Mater. 2020, 3, 3634–3645. [Google Scholar] [CrossRef]
  23. Wang, S.; Yang, P.; Sun, X.; Feng, L.; Jin, C.; Ren, M.; Xing, H.; Shi, J. Fabrication of the flower-like NiCo2O4 @ Ni(OH)2/NiOOH composites supported on nickel foam by the green solvent dimethyl sulfoxide with high performance in supercapacitor and hydrogen evolution reaction. J. Phys. Chem. Solids 2021, 159, 110257. [Google Scholar] [CrossRef]
  24. Zhang, L.; Zheng, Y.; Wang, J.; Geng, Y.; Zhang, B.; He, J.; Xue, J.; Frauenheim, T.; Li, M. Ni/Mo Bimetallic-Oxide-Derived Heterointerface-Rich Sulfide Nanosheets with Co-Doping for Efficient Alkaline Hydrogen Evolution by Boosting Volmer Reaction. Small 2021, 17, e2006730. [Google Scholar] [CrossRef]
  25. Liu, Y.; Zhao, Y.; Yu, Y.; Ahmad, M.; Sun, H. Facile synthesis of single-crystal mesoporous CoNiO2 nanosheets assembled flowers as anode materials for lithium-ion batteries. Electrochim. Acta 2014, 132, 404–409. [Google Scholar] [CrossRef]
  26. Liu, Y.; Zhao, Y.; Yu, Y.; Li, J.; Ahmad, M.; Sun, H. Hierarchical CoNiO2 structures assembled from mesoporous nanosheets with tunable porosity and their application as lithium-ion battery electrodes. New J. Chem. 2014, 38, 3084–3091. [Google Scholar] [CrossRef]
  27. Yeom, H.C.; Moon, D.J.; Lee, K.Y.; Kim, S.W. Formation and characterization of Ni nanofiber catalysts on nickel metallic foam by electrospinning process. J. Nanosci. Nanotechnol. 2015, 15, 5167–5170. [Google Scholar] [CrossRef]
  28. Wang, D.; Guo, J.; Hu, D.; Xu, Q.; Zhang, L.G.; Wang, J.D. Co@Co3O4 Prepared in situ from metallic Co as an efficient semiconductor catalyst for photocatalytic water oxidation. ACS Sustain. Chem. Eng. 2018, 6, 8300–8307. [Google Scholar] [CrossRef]
  29. Yan, X.; Li, K.; Lyu, L.; Song, F.; He, J.; Niu, D.; Liu, L.; Hu, X.; Chen, X. From water oxidation to reduction: Transformation from Ni(x)Co(3-x)O4 nanowires to NiCo/NiCoO(x) heterostructures. ACS Appl. Mater. Interfaces 2016, 8, 3208–3214. [Google Scholar] [CrossRef]
  30. Xiao, Y.; Zhang, P.; Zhang, X.; Dai, X.; Ma, Y.; Wang, Y.; Jiang, Y.; Liu, M.; Wang, Y. Bimetallic thin film NiCo-NiCoO2@NC as a superior bifunctional electrocatalyst for overall water splitting in alkaline media. J. Mater. Chem. A 2017, 5, 15901–15912. [Google Scholar] [CrossRef]
  31. Wang, Z.; Zeng, S.; Liu, W.; Wang, X.; Li, Q.; Zhao, Z.; Geng, F. Coupling molecularly ultrathin sheets of NiFe-layered double hydroxide on NiCo2O4 nanowire arrays for highly efficient overall water-splitting activity. ACS Appl. Mater. Interfaces 2017, 9, 1488–1495. [Google Scholar] [CrossRef] [PubMed]
  32. Faid, A.Y.; Barnett, A.O.; Seland, F.; Sunde, S. Ni/NiO nanosheets for alkaline hydrogen evolution reaction: In situ electrochemical-Raman study. Electrochim. Acta 2020, 361, 137040. [Google Scholar] [CrossRef]
  33. Wei, B.B.; Wu, J.; Mei, G.; Qi, Z.B.; Hu, W.S.; Wang, Z.C. NiCo2O4 nanowire arrays rich in oxygen deficiencies for hydrogen evolution reaction. Int. J. Hydrogen Energy 2019, 44, 6612–6617. [Google Scholar] [CrossRef]
  34. Kong, Q.; Feng, W.; Ma, S.; Sun, F.; Xie, X.; Sun, C. Hydrothermal synthesis of nanoporous NiO rods self-supported on Ni foam as efficient electrocatalysts for hydrogen evolution reaction. JOM 2018, 71, 621–625. [Google Scholar] [CrossRef]
  35. Hao, S.; Cao, Q.; Yang, L.; Che, R. Morphology-optimized interconnected Ni3S2 nanosheets coupled with Ni(OH)2 nanoparticles for enhanced hydrogen evolution reaction. J. Alloys Compd. 2020, 827, 154163. [Google Scholar] [CrossRef]
  36. Sung, M.C.; Lee, G.H.; Kim, D.W. CeO2/Co(OH)2 hybrid electrocatalysts for efficient hydrogen and oxygen evolution reaction. J. Alloys Compd. 2019, 800, 450–455. [Google Scholar] [CrossRef]
  37. Ullah, N.; Xie, M.; Chen, L.; Yaseen, W.; Zhao, W.; Yang, S.; Xu, Y.; Xie, J. Novel 3D graphene ornamented with CoO nanoparticles as an efficient bifunctional electrocatalyst for oxygen and hydrogen evolution reactions. Mater. Chem. Phys. 2021, 261, 124237. [Google Scholar] [CrossRef]
  38. Mohan Kumar, G.; Ilanchezhiyan, P.; Siva, C.; Madhankumar, A.; Kang, T.W.; Kim, D.Y. Co-Ni based hybrid transition metal oxide nanostructures for cost-effective bi-functional electrocatalytic oxygen and hydrogen evolution reactions. Int. J. Hydrogen Energy 2020, 45, 391–400. [Google Scholar] [CrossRef]
  39. Ibupoto, Z.H.; Tahira, A.; Tang, P.; Liu, X.; Morante, J.R.; Fahlman, M.; Arbiol, J.; Vagin, M.; Vomiero, A. MoSx@NiO composite nanostructures: An advanced nonprecious catalyst for hydrogen evolution reaction in alkaline media. Adv. Funct. Mater. 2019, 29, 1807562. [Google Scholar] [CrossRef] [Green Version]
Materials 16 02204 g001 550
Figure 1. The fabrication procedure is illustrated in this schematic diagram for hierarchical CoNiO2 microflowers assembled by mesoporous nanosheets.
Figure 1. The fabrication procedure is illustrated in this schematic diagram for hierarchical CoNiO2 microflowers assembled by mesoporous nanosheets.
Materials 16 02204 g001
Materials 16 02204 g002 550
Figure 2. An XRD pattern showing the crystalline structure of CoNiO2, Ni and Co.
Figure 2. An XRD pattern showing the crystalline structure of CoNiO2, Ni and Co.
Materials 16 02204 g002
Materials 16 02204 g003 550
Figure 3. SEM images of (a–d) the hierarchical CoNiO2, (e) the metallic Ni and (f) the metallic Co. SEM picture of (g) CoNiO2 and (h–j) the homologous elemental mapping pictures of Co, Ni and O for CoNiO2 materials.
Figure 3. SEM images of (a–d) the hierarchical CoNiO2, (e) the metallic Ni and (f) the metallic Co. SEM picture of (g) CoNiO2 and (h–j) the homologous elemental mapping pictures of Co, Ni and O for CoNiO2 materials.
Materials 16 02204 g003
Materials 16 02204 g004 550
Figure 4. (a–d) TEM figures, (e) HRTEM figure and (f) SAED pattern of CoNiO2.
Figure 4. (a–d) TEM figures, (e) HRTEM figure and (f) SAED pattern of CoNiO2.
Materials 16 02204 g004
Materials 16 02204 g005 550
Figure 5. (a) Survey spectrum, (b) Co 2p, (c) Ni 2p and (d) O 1s for CoNiO2 of XPS spectra.
Figure 5. (a) Survey spectrum, (b) Co 2p, (c) Ni 2p and (d) O 1s for CoNiO2 of XPS spectra.
Materials 16 02204 g005
Materials 16 02204 g006 550
Figure 6. (a) Polarization curves and the corresponding (b) slopes of Tafel of CoNiO2, metallic Ni and metallic Co, respectively. (c) Chronopotentiometry curve of CoNiO2 at 10 milliampere square centimeter for 24 h. This inset shows the polarization curves of the material before and after a 1000 cycles period. (d) Nyquist plots of the CoNiO2, metallic Ni and metallic Co at −300 mV overpotential.
Figure 6. (a) Polarization curves and the corresponding (b) slopes of Tafel of CoNiO2, metallic Ni and metallic Co, respectively. (c) Chronopotentiometry curve of CoNiO2 at 10 milliampere square centimeter for 24 h. This inset shows the polarization curves of the material before and after a 1000 cycles period. (d) Nyquist plots of the CoNiO2, metallic Ni and metallic Co at −300 mV overpotential.
Materials 16 02204 g006
Materials 16 02204 g007 550
Figure 7. The CV curves of (a) CoNiO2, (b) metallic Ni and (c) metallic Co. (d) The double−layer capacitance values CoNiO2, metallic Ni and metallic Co in 1 M KOH.
Figure 7. The CV curves of (a) CoNiO2, (b) metallic Ni and (c) metallic Co. (d) The double−layer capacitance values CoNiO2, metallic Ni and metallic Co in 1 M KOH.
Materials 16 02204 g007
Materials 16 02204 g008 550
Figure 8. (a) XRD patterns of before and after a 10 h test of CoNiO2 in an alkaline electrolyte. (b) SEM images of after a 10 h test of CoNiO2 in an alkaline electrolyte.
Figure 8. (a) XRD patterns of before and after a 10 h test of CoNiO2 in an alkaline electrolyte. (b) SEM images of after a 10 h test of CoNiO2 in an alkaline electrolyte.
Materials 16 02204 g008
Materials 16 02204 g009 550
Figure 9. (a) XRD patterns of the cobalt-nickel precursor. (b,c) SEM images of the cobalt-nickel precursor.
Figure 9. (a) XRD patterns of the cobalt-nickel precursor. (b,c) SEM images of the cobalt-nickel precursor.
Materials 16 02204 g009
Materials 16 02204 g010 550
Figure 10. (a) Survey spectrum, (b) Co 2p, (c) Ni 2p and (d) O 1s for CoNiO2 post-HER of XPS spectra.
Figure 10. (a) Survey spectrum, (b) Co 2p, (c) Ni 2p and (d) O 1s for CoNiO2 post-HER of XPS spectra.
Materials 16 02204 g010
Table
Table 1. In 1 M KOH, CoNiO2 electrocatalyst performance in HER was compared with that of cobalt- and nickel-based electrocatalysts.
Table 1. In 1 M KOH, CoNiO2 electrocatalyst performance in HER was compared with that of cobalt- and nickel-based electrocatalysts.
CatalystCurrent Density
(mA·cm−2)		Potential
(mV)		Reference
NiFe-LDH/NiCo2O410192[31]
NiCo2O4 nanowies10294[31]
Ni/NiO10226[32]
Air- NiCo2O410226[33]
Ni@NiO10192[34]
Ni3S2@Ni(OH)210237[35]
CeO2/Co(OH)210317[36]
CoO-3D graphen10360[37]
Co-Ni hybrid oxides10378[38]
MoSx@NiO10406[39]
CoNiO210170This work
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Zhang, D.; Yao, J.; Yin, J.; Wang, G.; Zhu, K.; Yan, J.; Cao, D.; Zhu, M. Hierarchical CoNiO2 Microflowers Assembled by Mesoporous Nanosheets as Efficient Electrocatalysts for Hydrogen Evolution Reaction. Materials 2023, 16, 2204. https://doi.org/10.3390/ma16062204

AMA Style

Zhang D, Yao J, Yin J, Wang G, Zhu K, Yan J, Cao D, Zhu M. Hierarchical CoNiO2 Microflowers Assembled by Mesoporous Nanosheets as Efficient Electrocatalysts for Hydrogen Evolution Reaction. Materials. 2023; 16(6):2204. https://doi.org/10.3390/ma16062204

Chicago/Turabian Style

Zhang, Dingfu, Jiaxin Yao, Jinling Yin, Guiling Wang, Kai Zhu, Jun Yan, Dianxue Cao, and Min Zhu. 2023. "Hierarchical CoNiO2 Microflowers Assembled by Mesoporous Nanosheets as Efficient Electrocatalysts for Hydrogen Evolution Reaction" Materials 16, no. 6: 2204. https://doi.org/10.3390/ma16062204

APA Style

Zhang, D., Yao, J., Yin, J., Wang, G., Zhu, K., Yan, J., Cao, D., & Zhu, M. (2023). Hierarchical CoNiO2 Microflowers Assembled by Mesoporous Nanosheets as Efficient Electrocatalysts for Hydrogen Evolution Reaction. Materials, 16(6), 2204. https://doi.org/10.3390/ma16062204

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop