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Article

Iron-Doped Nickel Hydroxide Nanosheets as Efficient Electrocatalysts in Electrochemical Water Splitting

by
Palani Krishnamurthy
1,
Thandavarayan Maiyalagan
1,*,
Gasidit Panomsuwan
2,
Zhongqing Jiang
3 and
Mostafizur Rahaman
4
1
Electrochemical Energy Laboratory, Department of Chemistry, SRM Institute of Science and Technology, Kattankulathur 603203, Tamil Nadu, India
2
Department of Materials Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand
3
Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China
4
Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
*
Author to whom correspondence should be addressed.
Catalysts 2023, 13(7), 1095; https://doi.org/10.3390/catal13071095
Submission received: 2 June 2023 / Revised: 22 June 2023 / Accepted: 23 June 2023 / Published: 13 July 2023
(This article belongs to the Special Issue Advances in High Electrocatalytic Performance Electrode Materials)
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Abstract

:
The development of non-noble-metal-based electrocatalysts for water electrolysis is essential to produce sustainable green hydrogen. Highly active and stable non-noble-metal-based electrocatalysts are greatly needed for the replacement of the benchmark electrocatalysts of iridium, ruthenium, and platinum oxides. Herein, we synthesized non-noble-metal-based, Fe-doped, β-Ni(OH)2 interconnected hierarchical nanosheets on nickel foam via a conventional hydrothermal reaction. Iron doping significantly modified the electronic structure of β-Ni(OH)2 due to the electron transfer of iron to nickel hydroxide. Fe-doped β-Ni(OH)2 was investigated both as a cathode and anode electrode for hydrogen and oxygen evolution reactions (OERs and HERs). It facilitated significant improvements in electrochemical performance due to its huge intrinsic active sites and high electrical conductivity. As a result, the electrocatalytic activity of Fe-doped Ni(OH)2 exhibited a lesser overpotential of 189 and 112 mV at a current density of 10 mA cm−2 and a Tafel slope of 85 and 89 mV dec−1 for the OER and HER, respectively. The Fe-doped β-Ni(OH)2 displayed excellent durability for 48 h and a cell voltage of 1.61 V @ 10 mA cm−2. This work demonstrates that Fe-doped β-Ni(OH)2 is an efficient electrocatalyst with superior electrocatalytic performance towards overall water splitting that can be useful at the industrial scale.

Graphical Abstract

1. Introduction

Fossil fuel emissions are a severe form of pollution in the environment owing to the enormous amount of greenhouse gases produced and the continual climate changes on Earth. Thus, alternative renewable green energy resources such as water, wind, and solar energy are more appropriate for reducing fossil fuel emissions [1,2,3,4]. Electrochemical water electrolysis is the fastest and most effective way to produce a large amount of extremely pure hydrogen without generating any pollution [5,6]. Generally, water electrolysis involves two half-cell reactions: the cathodic electrode generates hydrogen gas through the hydrogen evolution reaction (HER), while the anodic electrode produces oxygen gas via the oxygen evolution reaction (OER) with a high energy barrier (237.2 kJ mol−1) [7,8,9]. This is largely due to the sluggish kinetics of the overall electrolysis. Recently, notable innovative noble-metal-based (Pt/C, IrO2, and RuO2) materials have been investigated as efficient electrocatalysts [10,11,12]. However, their scarcity, high material cost, and persistent lack of durability in alkaline conditions make them unsuitable for widespread commercial applications [13]. Recently, due to their high catalytic activity, non-precious-metal-based electrocatalysts such as various transition metal oxides, hydroxides, sulfides, phosphides, nitrides, and carbides have been considered as alternatives to precious-metal-based electrocatalysts (Rh/Ir/Pt) for water electrolysis [14]. One of them, transition metal hydroxide, has garnered momentous curiosity due to its high durability and excellent catalytic activity. In particular, nickel hydroxide has gained significant attention due to its multi-layer structure that acts as a matrix with unusual-valence cations [15]. Therefore, nickel hydroxide is appropriate for general water splitting reactions owing to its high capability to absorb protons on its nickel active sites [16]. However, the performance of bare nickel hydroxide is inferior to that of the standard electrocatalyst (Pt/C, IrO2) [17]. There are a few commonly adopted strategies to change the catalytic performance, which are heterostructure engineering (used to improve the charge transfer of a material), morphology control (used for active site creation), and dopant incorporation (used to achieve the modification of the electronic structure and intrinsic activity) [18]. Among them, doping is a more favorable method for changing the electronic environment of a catalyst and for the electrocatalytic activity of water splitting [19]. For example, Yan-Rathore et al. studied tungsten dopant which demonstrated significant improvements in the intrinsic activities of Ni(OH)2 for the OER and HER in alkaline electrolytes [20,21]. Liu and his group synthesized Mn-doped Ni(OH)2 nanosheets as efficient bifunctional UOR/HER catalysts [22]. Jain et al. studied Sn-doped Ni(OH)2 [23], and Zhao et al. synthesized V-doped Ni(OH)2 [24], which were also established to be favorable dopants to increase the intrinsic activities of monometallic transition metal hydroxides [25]. However, recent reports have established that the incorporation of Fe into Ni-hydroxide results in excellent oxygen evolution reaction (OER) performance boosting due to the partial substitution of Fe3+ for Ni2+ in the lattice of nickel hydroxide [18,26,27]. Consequently, Fe dopants modulate the electronic structure of nickel hydroxide and acts as an active site [28]. This results in decreasing the charge transfer resistance and boosting their kinetics, finally acting as a ground-breaking OER/HER electrocatalyst. However, the optimum catalytic activity and electronic structure of Fe-incorporated Ni(OH)2 remain unclear, and whether they involve Fe–O, Ni–O, Ni–O–Fe, or bulk electronic structures, which act as active sites, remains a challenging question [29,30,31,32].
In this study, a facile hydrothermal process was used to synthesize (Fe)-doped Ni(OH)2 nanosheets with abundant active sites. The effects of iron doping on Ni(OH)2 and its electrochemical performance were studied. With a water electrolysis cell voltage of 1.61 V at a current density of 10 mA/cm2, the Fe-doped Ni(OH)2/NF-2 electrode demonstrated excellent catalytic activity and durability for up to 48 h in an alkaline electrolyte. The iron dopant enhanced the abundant active sites, and the hierarchical nanosheets helped to increase the electrochemical active surface area and mass transfer of reactants.

2. Results and Discussion

2.1. XRD Analysis

The samples were subjected to X-ray diffraction (XRD) analysis to determine their phase compositions. As shown in Figure 1a, the three sharp peaks observed at 44.6°, 51.9°, and 76.4° were attributed to Ni foam corresponding to crystal planes of (111), (200), and (201), respectively [26], and the intense peaks observed at 19.210°, 33.130°, 38.690°, 59.210°, and 62.740° could be assigned to the (001), (100), (101), (102), (110), and (111) planes corresponding to Ni(OH)2. Conferring to the JCPDS number 14-0117 [18,27], the crystal structure of Ni(OH)2 is a hexagonal β-type, with (001), (100), and (101) planes. The doping of iron confirmed the shifts of the (101) plane toward the right direction, as shown in Figure 1b. The non-existence of any additional peaks suggests that Fe was completely incorporated into the Ni(OH)2. The peak diffraction exhibited lower intensity as the Fe content increased compared to pristine β-Ni(OH)2, due to the smaller size of Fe3+ (55 pm) occupying the lattice site of Ni2+ (69 pm) in the β-Ni(OH)2 phase [28]. Different concentrations of Fe-doped β-Ni(OH)2 samples were prepared under the same hydrothermal conditions with varying amounts of iron (III) nitrate nonahydrate (0, 7.5 mg, 15 mg, and 30 mg), which were denoted as bare β-Ni(OH)2/NF, Fe-doped β-Ni(OH)2/NF-1, Fe-doped β-Ni(OH)2/NF-2, and Fe-doped β-Ni(OH)2/NF-3, respectively.

2.2. FESEM and TEM Analysis

The surface morphologies of the prepared Fe-doped, Ni(OH)2/NF-2 interconnected nanosheets are shown in Figure 2a–c. The thickness of these nanosheets was calculated to be 42.2 nm, as indicated in Figure 2c. High-resolution TEM was employed to further characterize the surface morphologies of the Fe-doped Ni(OH)2/NF-2 nanosheets, which demonstrated distinct lattice fringes with an interplanar distance that was calculated to be 0.238 nm, which correlates to the (001) and (101) planes of β-Ni(OH)2, as shown in Figure 2d,e. The EDX analysis shown in Figure 2f confirms the existence of the main elements of Fe, Ni, and O.

2.3. XPS Analysis

The chemical and electronic states of the Fe-doped Ni(OH)2/NF-2 were analyzed via X-ray photoelectron spectroscopy (XPS) measurements, as shown in Figure 3. The survey spectra consistently identified the elements Fe, Ni, and O in the Fe-doped β-Ni(OH)2/NF-2 samples. The range of the survey spectra was from 0 to 1100 eV, as shown in Figure 3a. The binding energies of 856.0 and 873.1 eV corresponded to Ni 2p3/2 and Ni 2p1/2, respectively, and could also be assigned to Ni2+ [27,31]. Additionally, two satellite peaks (identified as “Sat.”) were observed at binding energies of 861.0 and 880 eV, as shown in Figure 3b [28]. The binding energies observed at 712 eV and 724.1 eV corresponded to Fe 2p3/2 and Fe 2p1/2 and could be assigned to Fe3+, as shown in Figure 3c [32,33,34]. The O 1s spectra exhibited two peaks at 530.7 eV and 531.7 eV, indicating the presence of metal–oxygen (M-O2−) and metal–hydroxyl (M-OH) bonds, respectively, as shown in Figure 3d [30].

2.4. Electrochemical Characterization

2.4.1. Electrocatalytic Performance of HER

To examine the electrocatalytic activity of the Fe-doped Ni(OH)2/NF-2, Fe-doped Ni(OH)2/NF-3, Fe-doped Ni(OH)2/NF-1, Ni(OH)2/NF, and NF samples, LSV was performed in a 1M KOH electrolyte using a typical three-electrode design at a rate of scan 2 mV s−1, as displayed in Figure 4a. Fe-doped Ni(OH)2/NF-2 provided better catalytic efficiency compared to pure nickel hydroxide, with an overpotential of 112 mV, 245 mV, and 291 mV at the current densities of 10 mA cm−2, 50 mA cm−2, and 100 mA cm−2, as shown in Figure 4b. This was considerably less than that of Fe-doped Ni(OH)2/NF-3 (153, 264, and 325 mV), Fe-doped Ni(OH)2/NF-1 (196, 316, and 402 mV), Ni(OH)2/NF (223, 347, and 455 mV), and NF (265, 391, and 501 mV).
The Tafel slope is the most essential parameter for measuring reaction kinetics. There are three typical reactions involved HER in an alkaline medium: the reaction of Volmer [H2O + e− → Hads + OH−], followed by either the reaction of Heyrovsky [Hads + H2O + e− → H2 + OH−] or the reaction of Tafel [2Hads → H2]. The Volmer reaction involves hydrogen absorption on the catalyst, while the Heyrovsky and Tafel reactions involve hydrogen molecule evolution on the catalyst. Usually, HER is a two-way reaction mechanism involving Volmer–Heyrovsky and Volmer–Tafel mechanisms [35]. The Fe-doped Ni(OH)2 catalyst follows the Volmer–Heyrovsky mechanism, and the Tafel slopes of 89 mV, 117 mV, 132 mV, and 153 mV correspond to the Fe-doped Ni(OH)2/NF-2, Fe-doped Ni(OH)2/NF-3, Fe-doped β-Ni(OH)2/NF-1, and Ni(OH)2/NF samples, as shown in Figure 4c. Insights into the charge transport kinetics of the electrocatalytic interface between the electrodes and electrolyte were obtained through EIS, as shown in Figure 4d. In the EIS Nyquist plots, the solution resistance (Rs) and charge transfer resistance (Rct) of the electrocatalyst could be determined. Lower charge transfer resistance indicates a faster electron transfer rate in electrocatalysis. When compared with electrocatalysts, including Fe-doped Ni(OH)2/NF-2 (4.3 Ω), Fe-doped Ni(OH)2/NF-3 (9.2 Ω), Fe-doped Ni(OH)2/NF-1 (18 Ω), and Ni(OH)2/NF (20 Ω), the interconnected Fe-doped Ni(OH)2/NF-2 nanosheets exhibited a low Rct value of 4.3 Ω. The lower charge transfer barrier of the catalysts showed excellent charge transport kinetics, as shown in Table 1.
Furthermore, HER stability is another crucial parameter to evaluate the performance of electrocatalysts. We investigated the sample durability of the electrode, which was further estimated using hydrogen production with the chronoamperometry long-term stability at 48 h in 1 M KOH, as shown in Figure 4e, and by comparing the LSV overpotential at a current density of 10 mA cm−2 before and after stability testing. The results showed that the Fe-doped Ni(OH)2/NF-2 electrode exhibited a mere 4 mV degradation in overpotential, from 112 mV before stability testing to 116 mV after stability testing, indicating its superior stability. Our synthesized electrocatalyst’s HER overpotential and reported non-precious Ni(OH)2-based catalysts in alkaline medium at 10 mA cm−2, as shown in Figure 4f [35,36,37,38,39,40,41,42,43,44,45]. The electrochemical properties of the synthesized sample are provided in Table 1.

2.4.2. Electrocatalytic Performance of OER

The polarization curve of the as-prepared samples demonstrated excellent OER properties under alkaline conditions (1 M KOH) in a three-electrode system. We further investigated the OER efficacy of Ni(OH)2/NF and 1, 2, and 3 Fe-doped β-Ni(OH)2 supported on a nickel foam substrate. The polarization curve of Fe-doped Ni(OH)2/NF-2 showed less overpotential compared to the nickel foam (354 mV) and, after the growth of Ni(OH)2 on the nickel foam substrate, the measured overpotential was 270 mV, which was further decreased by doping with different concentrations of Fe. The measured overpotentials were 266 mV, 189 mV, and 222 mV corresponding to 1, 2, and 3 of iron-doped nickel hydroxide at a measured current density of 10 mA cm−2, as revealed in Figure 5a. The OER overpotentials of the samples were given at current densities of 10, 50, and 100 mA cm−2, as shown in Figure 5b.
The OER kinetics behavior of these electrodes was investigated further using the Tafel plot in Figure 5c, which revealed that the Tafel slopes of Ni(OH)2 and 1%, 2%, and 3% Fe-doped Ni(OH)2 were 89.8, 82.5, 109, and 131 mV dec−1, respectively. Among all the samples, the 2% Fe-doped Ni(OH)2 displayed the lowest Tafel slope value (82.5 mV dec−1) and the most rapid mass and electron transport from the catalyst to the electrolyte during the water oxidation reaction. Therefore, it can be concluded that 2% Fe-doped Ni(OH)2 is an efficient catalyst for OER.
The electrocatalytic stability and durability of Fe-doped Ni(OH)2 were measured via chronoamperometry. The Fe-doped Ni(OH)2/NF-2 showed good stability, with no change in OER activity observed for 48 h at a 10 mA cm−2 current density (Figure 5d). However, the potential slightly increased from 189 to 194 mV to maintain the current density, possibly due to the dissolution of Ni2+ and Fe3+ ions into the electrolyte from the catalyst, which slightly reduced its OER performance. Nonetheless, the Fe-doped Ni(OH)2/NF-2 exhibited long-term durability even at a very high current density, as demonstrated by the polarization curves previous to the next OER stability test. Only a few highly active catalysts meet the commercial criteria for OER applications. Our synthesized catalyst’s OER overpotential was comparable to the reported non-precious Ni(OH)2-based catalysts in alkaline medium at 10 mA cm−2, as shown in Figure 5e [46,47,48,49,50,51,52,53,54,55]. Table 2 provides the electrochemical properties of the as-synthesized samples.
A basic CV test could measure the surface area of electrocatalysts (ECSA) from the capacitance double-layer (Cdl) in the non-Faraday boundary at numerous scan rates of 20, 40, 60, 80, and 100 mV s−1, as shown in Figure 6a–d. The accompanying Cdl-values of Fe-doped Ni(OH)2/NF-2, Fe-doped Ni(OH)2/NF-3, Fe-doped Ni(OH)2/NF-1, and Ni(OH)2 were calculated via linear fitting, and the calculated values were found to be 7.72, 6.44, 5.32, and 1.68 mF cm2, respectively, as shown in Figure 6e. The Fe-doped Ni(OH)2/NF-2 exhibited the highest Cdl values compared to other samples. If the cdl values increased, ECSA also increased [56,57,58,59]. The Fe-doped Ni(OH)2/NF-2 ECSA (193 cm2) was nearly five times higher than that of Ni(OH)2/NF (40 cm2). Detailed measurements and calculation methods are provided in Table 3.

2.5. Electrochemical Performance of Water Splitting

A two-electrode system was employed to evaluate the performance of Fe-doped Ni(OH)2/NF-2 as a bifunctional catalyst, the anode (+) Fe-doped Ni(OH)2/NF-2//Fe-doped Ni(OH)2 /NF-2 (−) cathode-generated oxygen and hydrogen, and the resulting polarization curve is shown in Figure 7a. The obtained results showed that the electrolyzer could achieve a current density of 10 mA cm−2 at an overall cell voltage of 1.61 V. Compared to other reported Ni-based electrocatalysts (Table 4), this catalyst demonstrated a lower potential value. Additionally, we conducted durability testing at a current density of 10 mA cm−2 and used chronoamperometry analysis to assess the long-term stability. Figure 7b shows that this electrode retained 97% of its catalytic activity for 48 h, demonstrating its high electrochemical stability.

3. Experimental Section

3.1. Materials and Methods

The materials and reagents used in the study were purchased from SRL, India, including iron (III) nitrate nonahydrate (Fe(NO3)3·9H2O), hydrochloric acid (HCl, 36%), potassium hydroxide (KOH, 82%), acetone, and ethanol. Commercially available Ni foam was used, and the oxide layer was removed via pre-treatment. Deionized water was obtained from a Millipore system.

3.2. Preparation of Fe Doped Ni(OH)2

Iron (III) nitrate nonahydrate was dissolved in 30 mL of deionized water with continuous stirring until it was fully dissolved. The nickel foam was sequentially sonicated in 3 M HCl, deionized water, and ethanol. A piece of nickel foam (1 cm × 2 cm) was placed with the iron nitrate solution in a Teflon-lined stainless steel autoclave, and a hydrothermal reaction was conducted at 150 °C for 6 h. After the reaction, the autoclave was cooled down to room temperature. The resulting Fe-doped β-Ni(OH)2 nanosheets were uniformly deposited on the Ni foam substrate. The Fe-doped β-Ni(OH)2 was washed with deionized water and ethanol and then dried in a vacuum oven at 80 °C for 12 h. Various concentrations of Fe-doped β-Ni(OH)2 samples were synthesized under the same hydrothermal conditions with different amounts of iron (III) nitrate nonahydrate (0, 7.5 mg, 15 mg, and 30 mg), which were signified as bare β-Ni(OH)2/NF, Fe-doped β-Ni(OH)2/NF-1, Fe-doped β-Ni(OH)2/NF-2, and Fe-doped β-Ni(OH)2/NF-3, respectively.

3.3. Physicochemical Characterization

X-ray diffraction analysis using Pan Analytical Bruker USA D8 Advance equipment, Davinci, Netherlands, determined the electrodes’ crystallinity and composition. Morphological and crystal structures were investigated through scanning electron microscope (SEM) images obtained from the FEI Quanta FEG 200 and transmission electron microscopy (TEM) images obtained from the JEOL Japan JEM-2100 Plus (200 kV with a LaB6 electron gun) instruments by using a Perkin-Elmer PHI 550 spectrometer. The samples were immersed in absolute ethanol under high-intensity ultrasonic conditions before being dropped onto copper grids. The X-ray photoelectron spectroscopy (XPS) analysis was conducted using HORIBA France PHI Versaprobe III scanning XPS equipment.

3.4. Electrochemical Characterization

The electrochemical performance of HER and OER was studied using a Biologic SP-200 electrochemical workstation in a three-electrode cell setup. Nickel foam was used as the working electrode, while platinum wire and Hg/HgO served as the counter and reference electrodes, respectively. HER activity was measured using linear sweep voltammetry (LSV) at a scan rate of 2 mV s−1 with iR compensation relative to the solution resistance, in O2−-saturated 1 M KOH electrolyte solution over a potential range of 0 to 0.8 V vs. Hg/HgO. The reference electrode was calibrated to the reversible hydrogen electrode (RHE) for potential standardization: E(RHE) = E(Hg/HgO) + 0.098 + 0.059 pH. Tafel slopes were calculated using LSV, and electrochemical impedance spectra (EIS) were measured at different potentials in the frequency range of 100 kHz to 0.1 Hz at 10 mV AC amplitude voltage. The durability of electrodes was tested using chronoamperometry, and polarization curves were compared before and after the stability tests.

4. Conclusions

In this study, unique interconnected Fe-doped β-nickel hydroxide nanosheets were successfully synthesized via the hydrothermal method to investigate their performance towards the hydrogen and oxygen evolution reactions. This work delivers a simple and cost-effective approach to developing highly effective and durable catalysts under alkaline conditions. The presence of iron in the β-nickel hydroxide nanosheets enhanced the reaction kinetics of overall water splitting. During the HER, the Fe-doped Ni(OH)2/NF-2 nanosheets demonstrated an overpotential of 119 mV at 10 mA cm2, which is ideal for efficient electrochemical hydrogen evolution compared to the Ni(OH)2/NF nanosheets. In the OER, high intrinsic activity was observed with an overpotential of 189 mV at a 10 mA current density. Using the Fe-doped Ni(OH)2/NF-2 as the cathode and anode for total water splitting, the optimized electrocatalyst showed excellent bifunctional activities with a voltage of 1.61 V at a current density of 10 mA cm−2. We believe that this designed multi-site functionality catalyst can accelerate the development of further multi-metallic nanomaterial electrocatalysts with different structures and compositions, exhibiting distinct edges for numerous electrolytic applications such as CO2 reduction reactions and nitrogen reduction reactions.

Author Contributions

Experimental investigation, conceptualization, P.K. and T.M.; methodology, P.K.; software, P.K.; validation, T.M. and G.P.; formal analysis, P.K. and T.M.; investigation, P.K. and T.M.; resources, P.K. and T.M.; data curation, T.M. and G.P; writing—original draft preparation, P.K.; writing—review and editing, P.K., Z.J., M.R. and T.M.; visualization, P.K., Z.J., M.R. and T.M.; supervision, T.M.; project administration, T.M. and G.P.; funding acquisition, T.M. and G.P. All authors have read and agreed to the published version of the manuscript.

Funding

The authors acknowledge the financial support from the Scheme for Promotion of Academic and Research Collaboration (SPARC) of the Ministry of Human Resource Development (MHRD), Government of India, SPARC Grant No. SPARC/2018-2019/P1122/SL and Kasetsart University Research and Development Institute (KURDI), grant no. FF(KU) 25.64. The authors acknowledge the Researchers Supporting Project number (RSPD2023R674), King Saud University, Riyadh, Saudi Arabia for funding this research work.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Xue, B.W.; Zhang, C.H.; Wang, Y.Z.; Xie, W.W.; Li, N.-W.; Yu, L. Recent progress of Ni–Fe layered double hydroxide and beyond towards electrochemical water splitting. Nanoscale Adv. 2020, 2, 5555–5566. [Google Scholar] [CrossRef]
  2. Suen, N.-T.; Hung, S.-F.; Quan, Q.; Zhang, N.; Xu, Y.-J.; Chen, H.M. Electrocatalysis for the oxygen evolution reaction: Recent development and future perspectives. Chem. Soc. Rev. 2017, 46, 337–365. [Google Scholar] [CrossRef] [PubMed]
  3. Vij, V.; Sultan, S.; Harzandi, A.M.; Meena, A.; Tiwari, J.N.; Lee, W.-G.; Yoon, T.; Kim, K.S. Nickel-based electrocatalysts for energy-related applications: Oxygen reduction, oxygen evolution, and hydrogen evolution reactions. Acs Catal. 2017, 7, 7196–7225. [Google Scholar] [CrossRef]
  4. Maiyalagan, T.; Jarvis, K.A.; Therese, S.; Ferreira, P.J.; Manthiram, A. Spinel-type lithium cobalt oxide as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions. Nat. Commun. 2014, 5, 3949. [Google Scholar] [CrossRef] [Green Version]
  5. Kale, V.N.; Maiyalagan, T. Lollipop-shaped interconnected MnO2 nanotube/Co3O4 polyhedron composite derived from zeolitic-imidazolate framework-67 as an efficient electrocatalyst for oxygen evolution reaction. Mater. Today Chem. 2022, 26, 101063. [Google Scholar] [CrossRef]
  6. Guruprasad, K.; Maiyalagan, T.; Shanmugam, S. Phosphorus doped MoS2 nanosheet promoted with nitrogen, sulfur dual doped reduced graphene oxide as an effective electrocatalyst for hydrogen evolution reaction. ACS Appl. Energy Mater. 2019, 2, 6184–6194. [Google Scholar] [CrossRef]
  7. Zhang, J.; Zhang, Q.; Feng, X. Support and interface effects in water-splitting electrocatalysts. Adv. Mater. 2019, 31, 1808167. [Google Scholar] [CrossRef]
  8. Jiao, Y.; Zheng, Y.; Jaroniec, M.; Qiao, S.Z. Design of electrocatalysts for oxygen-and hydrogen-involving energy conversion reactions. Chem. Soc. Rev. 2015, 44, 2060–2086. [Google Scholar] [CrossRef]
  9. Xu, X.; Shao, Z.; Jiang, S.P. High-Entropy Materials for Water Electrolysis. Energy Technol. 2022, 10, 2200573. [Google Scholar] [CrossRef]
  10. Tang, J.; Xu, X.; Tang, T.; Zhong, Y.; Shao, Z. Perovskite-Based Electrocatalysts for Cost-Effective Ultrahigh-Current-Density Water Splitting in Anion Exchange Membrane Electrolyzer Cell. Small Methods 2022, 6, 2201099. [Google Scholar] [CrossRef]
  11. Jothi, V.R.; Karuppasamy, K.; Maiyalagan, T.; Rajan, H.; Jung, C.Y.; Yi, S.C. Corrosion and alloy engineering in rational design of high current density electrodes for efficient water splitting. Adv. Energy Mater. 2020, 10, 1904020. [Google Scholar] [CrossRef]
  12. Qin, C.; Tian, S.; Jiang, Z.-J.; Maiyalagan, T.; Jiang, Z. Low temperature plasma-assisted synthesis and modification of water splitting electrocatalysts. Electrochim. Acta 2023, 449, 142179. [Google Scholar] [CrossRef]
  13. Yi, H.; Liu, S.; Lai, C.; Zeng, G.; Li, M.; Liu, X.; Chen, L. Recent advance of transition-metal-based layered double hydroxide nanosheets: Synthesis, properties, modification, and electrocatalytic applications. Adv. Energy Mater. 2021, 11, 2002863. [Google Scholar] [CrossRef]
  14. Zhu, J.; Hu, L.; Zhao, P.; Lee, L.Y.S.; Wong, K.Y. Recent advances in electrocatalytic hydrogen evolution using nanoparticles. Chem. Rev. 2019, 120, 851–918. [Google Scholar] [CrossRef] [PubMed]
  15. Lee, S.-Y.; Oh, H.-J.; Kim, M.; Cho, H.-S.; Lee, Y.-K. Insights into enhanced activity and durability of hierarchical Fe-doped Ni(OH)2/Ni catalysts for alkaline oxygen evolution reaction: In situ XANES studies. Appl. Catal. B 2023, 324, 122269. [Google Scholar] [CrossRef]
  16. Saraj, C.S.; Singh, S.C.; Shukla, A.; Yu, W.; Fayyaz, M.U.; Guo, C. Single-step and sustainable fabrication of Ni(OH)2/Ni foam water splitting catalysts via electric field assisted pulsed laser ablation in liquid. Chem. Electro. Chem. 2021, 8, 209–217. [Google Scholar] [CrossRef]
  17. Han, L.; Dong, S.; Wang, E. Transition-metal (Co, Ni, and Fe)-based electrocatalysts for the water oxidation reaction. Adv. Mater. 2016, 28, 9266–9291. [Google Scholar] [CrossRef]
  18. Mahala, C.; Devi Sharma, M.; Basu, M. Fe-Doped Nickel Hydroxide/Nickel Oxyhydroxide Function as an Efficient Catalyst for the Oxygen Evolution Reaction. ChemElectroChem 2019, 6, 3488–3498. [Google Scholar] [CrossRef]
  19. Pang, L.; Liu, W.; Zhao, X.; Zhou, M.; Qin, J.; Yang, J. Engineering electronic structures of nickel cobalt phosphide via iron doping for efficient overall water splitting. Chem. Electro. Chem. 2020, 7, 4913–4921. [Google Scholar] [CrossRef]
  20. Rathore, D.; Banerjee, A.; Pande, S. Bifunctional tungsten-doped Ni(OH)2/NiOOH nanosheets for overall water splitting in an alkaline medium. ACS Appl. Nano Mater. 2022, 5, 2664–2677. [Google Scholar] [CrossRef]
  21. Yan, J.; Kong, L.; Ji, Y.; White, J.; Li, Y.; Zhang, J.; Ma, T. Single atom tungsten doped ultrathin α-Ni(OH)2 for enhanced electrocatalytic water oxidation. Nat. Commun. 2019, 10, 2149. [Google Scholar] [CrossRef] [Green Version]
  22. Liu, X.; Qin, H.; Ye, Z.; Yao, D.; Miao, W.; Mao, S. Interconnected Mn-doped Ni(OH)2 nanosheet layer for bifunctional urea oxidation and hydrogen evolution: The relation between current drop and urea concentration during the long-term operation. ACS EST Eng. 2022, 2, 853–862. [Google Scholar] [CrossRef]
  23. Jian, J.; Kou, X.; Wang, H.; Chang, L.; Zhang, L.; Gao, S.; Xu, Y.; Yuan, H. Fascinating Tin Effects on the Enhanced and Large-Current-Density Water Splitting Performance of Sn–Ni(OH)2. ACS Appl. Mater. Interfaces 2021, 13, 42861–42869. [Google Scholar] [CrossRef] [PubMed]
  24. Zhao, P.; Ma, L.; Guo, J. Vanadium doped nickel hydroxide nanosheets for efficient overall alkaline water splitting. J. Phys. Chem. Solids 2022, 164, 110634. [Google Scholar] [CrossRef]
  25. Babar, P.; Lokhande, A.C.; Karade, V.; Pawar, B.; Gil Gang, M.; Pawar, S.; Kim, J.H. Bifunctional 2D electrocatalysts of transition metal hydroxide nanosheet arrays for water splitting and urea electrolysis. ACS Sustain. Chem. Eng. 2019, 7, 10035–10043. [Google Scholar] [CrossRef]
  26. Krehula, S.; Ristić, M.; Wu, C.; Li, X.; Jiang, L.; Wang, J.; Musić, S. Influence of Fe(III) doping on the crystal structure and properties of hydrothermally prepared β-Ni(OH)2 nanostructures. J. Alloys Compd. 2018, 750, 687–695. [Google Scholar] [CrossRef]
  27. Kou, T.; Wang, S.; Hauser, J.L.; Chen, M.; Oliver, S.R.J.; Ye, Y.; Guo, J.; Li, Y. Ni foam-supported Fe-doped β-Ni(OH)2 nanosheets show ultralow overpotential for oxygen evolution reaction. ACS Energy Lett. 2019, 4, 622–628. [Google Scholar] [CrossRef]
  28. Zhu, K.; Liu, H.; Li, M.; Li, X.; Wang, J.; Zhu, X.; Yang, W. Atomic-scale topochemical preparation of crystalline Fe3+-doped β-Ni(OH)2 for an ultrahigh-rate oxygen evolution reaction. J. Mater. Chem. A 2017, 5, 7753–7758. [Google Scholar] [CrossRef]
  29. Stevens, M.B.; Trang, C.D.M.; Enman, L.J.; Deng, J.; Boettcher, S.W. Reactive Fe-sites in Ni/Fe (oxy) hydroxide are responsible for exceptional oxygen electrocatalysis activity. J. Am. Chem. Soc. 2017, 139, 11361–11364. [Google Scholar] [CrossRef]
  30. Long, X.; Li, J.; Xiao, S.; Yan, K.; Wang, Z.; Chen, H.; Yang, S. A strongly coupled graphene and FeNi double hydroxide hybrid as an excellent electrocatalyst for the oxygen evolution reaction. Angew. Chem. Int. Ed. 2014, 53, 7584–7588. [Google Scholar] [CrossRef]
  31. Qiao, X.; Kang, H.; Li, Y.; Cui, K.; Jia, X.; Liu, H.; Wu, G. Porous Fe-Doped β-Ni(OH)2 Nanopyramid Array Electrodes for Water Splitting. ACS Appl. Mater. Interfaces 2020, 12, 36208–36219. [Google Scholar] [CrossRef] [PubMed]
  32. Suryanto, B.H.R.; Wang, Y.; Hocking, R.K.; Adamson, W.; Zhao, C. Overall electrochemical splitting of water at the heterogeneous interface of nickel and iron oxide. Nat. Commun. 2019, 10, 5599. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  33. Guo, C.X.; Li, C.M. Room temperature-formed iron-doped nickel hydroxide on nickel foam as a 3D electrode for low polarized and high-current-density oxygen evolution. Chem. Commun. 2018, 54, 3262–3265. [Google Scholar] [CrossRef] [PubMed]
  34. Wu, Y.; Ji, S.; Wang, H.; Pollet, B.G.; Wang, X.; Wang, R. A highly efficient water electrolyser cell assembled by asymmetric array electrodes based on Co, Fe-doped Ni(OH)2 nanosheets. Appl. Surf. Sci. 2020, 528, 146972. [Google Scholar] [CrossRef]
  35. Wang, Y.; Wang, J.; Xie, T.; Zhu, Q.; Zeng, D.; Li, R.; Zhang, X.; Liu, S. Ru doping in Ni(OH)2 to accelerate water reduction kinetics for efficient hydrogen evolution reaction. Appl. Surf. Sci. 2019, 485, 506–512. [Google Scholar] [CrossRef]
  36. Chen, X.; Yang, L.; Huang, Y.; Ge, S.; Zhang, H.; Cui, Y.; Xiao, Z. Fabrication of a Hierarchical Ni(OH)2@Ni3S2/Ni Foam Electrode from a Prussian Blue Analogue-Based Composite with Enhanced Electrochemical Capacitive and Electrocatalytic Properties. Chem.–A Eur. J. 2020, 26, 1111–1116. [Google Scholar] [CrossRef]
  37. Patil, B.; Satılmış, B.; Khalily, M.A.; Uyar, T. Atomic layer deposition of NiOOH/Ni(OH)2 on PIM-1-based N-doped carbon nanofibers for electrochemical water splitting in alkaline medium. Chem. Sus. Chem. 2019, 12, 1469–1477. [Google Scholar] [CrossRef] [Green Version]
  38. Zhao, G.; Lin, Y.; Rui, K.; Zhou, Q.; Chen, Y.; Dou, S.X.; Sun, W. Epitaxial growth of Ni(OH)2 nanoclusters on MoS2 nanosheets for enhanced alkaline hydrogen evolution reaction. Nanoscale 2018, 10, 19074–19081. [Google Scholar] [CrossRef] [Green Version]
  39. Briones-Martínez, R.; Garcia-Gomez, N.A.; Sepúlveda-Guzmán, S.; de la Parra-Arciniega, S.M.; Sánchez, E.M. Self-supported Ni3Se2/Ni(OH)2 and Ni3Se2 on Ni-foam: Nanostructured arrays for the hydrogen evolution reaction. J. Nanoparticle Res. 2020, 22, 1–10. [Google Scholar] [CrossRef]
  40. Subbaraman, R.; Tripkovic, D.; Strmcnik, D.; Chang, K.C.; Uchimura, M.; Paulikas, A.P.; Markovic, N.M. Enhancing hydrogen evolution activity in water splitting by tailoring Li+-Ni(OH)2-Pt interfaces. Science 2011, 334, 1256–1260. [Google Scholar] [CrossRef]
  41. Patil, K.; Babar, P.; Bae, H.; Jo, E.; Jang, J.S.; Bhoite, P.; Kolekar, S.; Kim, J.H. Enhanced electrocatalytic activity of a layered triple hydroxide (LTH) by modulating the electronic structure and active sites for efficient and stable urea electrolysis. Sustain. Energy Fuels 2022, 6, 474–483. [Google Scholar] [CrossRef]
  42. Cheng, W.; Xue, L.; Wang, J.; Chen, X.; Sun, H.; Huang, C.; Yao, W. Surface-engineered Ni(OH)2/PtNi nanocubes as cocatalysts for photocatalytic hydrogen production. ACS Appl. Nano Mater. 2021, 4, 8390–8398. [Google Scholar] [CrossRef]
  43. Deng, Y.; Lai, W.; He, X.; Xu, L.; Xu, B. Facile electrochemical synthesis of Ni(OH)2/MoSx catalyst on oxidized carbon fiber for efficient alkaline hydrogen evolution reaction. Chem. Eng. Process. Process Intensif. 2020, 155, 108090. [Google Scholar] [CrossRef]
  44. Jia, X.; Wang, Y.; Tang, J.; Song, K.; Zhang, H.; Lin, B.; Zheng, H. FeNi-LDH@Ni film modified stainless-steel as self-supported electrodes for efficient and stable overall water splitting in alkaline environments. Surf. Coat. 2023, 464, 129502. [Google Scholar] [CrossRef]
  45. Li, G.; Wu, X.; Guo, H.; Guo, Y.; Chen, H.; Wu, Y.; Zheng, J.; Li, X. Plasma transforming Ni(OH)2 nanosheets into porous nickel nitride sheets for alkaline hydrogen evolution. ACS Appl. Mater. Interfaces 2020, 12, 5951–5957. [Google Scholar] [CrossRef]
  46. Li, D.; Hao, G.; Guo, W.; Liu, G.; Li, J.; Zhao, Q. Highly efficient Ni nanotube arrays and Ni nanotube arrays coupled with NiFe layered-double-hydroxide electrocatalysts for overall water splitting. J. Power Sources 2020, 448, 227434. [Google Scholar] [CrossRef]
  47. Xiao, C.; Zhang, B.; Li, D. Partial-sacrificial-template synthesis of Fe/Ni phosphides on Ni foam: A strongly stabilized and efficient catalyst for electrochemical water splitting. Electrochim. Acta 2017, 242, 260–267. [Google Scholar] [CrossRef]
  48. Wang, X.; He, P.; Yang, Y.; Zhang, F.; Tang, J.; Que, R. In situ synthesis of Fe-doped NiC2O4 nanorods for efficient oxygen evolution activity and overall water splitting. Electrochim. Acta 2020, 345, 136228. [Google Scholar] [CrossRef]
  49. Wu, Z.; Zou, Z.; Huang, J.; Gao, F. Fe-doped NiO mesoporous nanosheets array for highly efficient overall water splitting. J. Catal. 2018, 358, 243–252. [Google Scholar] [CrossRef]
  50. Youn, D.H.; Park, Y.B.; Kim, J.Y.; Magesh, G.; Jang, Y.J.; Lee, J.S. One-pot synthesis of NiFe layered double hydroxide/reduced graphene oxide composite as an efficient electrocatalyst for electrochemical and photoelectrochemical water oxidation. J. Power Sources 2015, 294, 437–443. [Google Scholar] [CrossRef]
  51. Jadhav, H.S.; Roy, A.; Desalegan, B.Z.; Seo, J.G. An advanced and highly efficient Ce assisted NiFe-LDH electrocatalyst for overall water splitting. Sustain. Energy Fuels 2020, 4, 312–323. [Google Scholar] [CrossRef]
  52. Zhang, B.; Jiang, K.; Wang, H.; Hu, S. Fluoride-Induced Dynamic Surface Self-Reconstruction Produces Unexpectedly Efficient Oxygen-Evolution Catalyst. Nano Lett. 2019, 19, 530–537. [Google Scholar] [CrossRef] [PubMed]
  53. Lu, X.; Zhao, C. Electrodeposition of hierarchically structured three-dimensional nickel–iron electrodes for efficient oxygen evolution at high current densities. Nat. Commun. 2015, 6, 6616. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  54. Bandal, H.A.; Jadhav, A.R.; Kim, H. Facile synthesis of bicontinuous Ni3Fe alloy for efficient electrocatalytic oxygen evolution reaction. J. Alloy. Compd. 2017, 726, 875–884. [Google Scholar] [CrossRef]
  55. Dai, L.; Chen, Z.; Li, L.; Yin, P.; Liu, Z.; Zhang, H. Ultrathin Ni (0)-Embedded Ni(OH)2 Heterostructured Nanosheets with Enhanced Electrochemical Overall Water Splitting. Adv. Mater. 2020, 32, 1906915. [Google Scholar] [CrossRef]
  56. Dinh, K.N.; Zheng, P.; Dai, Z.; Zhang, Y.; Dangol, R.; Zheng, Y.; Li, B.; Zong, Y.; Yan, Q. Ultrathin porous NiFeV ternary layer hydroxide nanosheets as a highly efficient bifunctional electrocatalyst for overall water splitting. Small 2018, 14, 1703257. [Google Scholar] [CrossRef]
  57. Wang, P.; Lin, Y.; Wan, L.; Wang, B. Autologous growth of Fe-doped Ni(OH)2 nanosheets with low overpotential for oxygen evolution reaction. Int. J. Hydrogen Energy 2020, 45, 6416–6424. [Google Scholar] [CrossRef]
  58. McCrory, C.C.L.; Jung, S.; Ferrer, I.M.; Chatman, S.M.; Peters, J.C.; Jaramillo, T.F. Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices. J. Am. Chem. Soc. 2015, 137, 4347–4357. [Google Scholar] [CrossRef] [Green Version]
  59. Wang, S.; Lu, A.; Zhong, C.-J. Hydrogen production from water electrolysis: Role of catalysts. Nano Converg. 2021, 8, 1–23. [Google Scholar] [CrossRef]
  60. Xue, J.Y.; Li, F.L.; Zhao, Z.Y.; Li, C.; Ni, C.Y.; Gu, H.W.; Lang, J.P. A hierarchically-assembled Fe–MoS2/Ni3S2/nickel foam electrocatalyst for efficient water splitting. Dalton Trans. 2019, 48, 12186–12192. [Google Scholar] [CrossRef]
  61. Zheng, M.; Du, J.; Hou, B.; Xu, C.L. Few-Layered Mo1−xWxS2 Hollow Nanospheres on Ni3S2 Nanorod Heterostructure as Robust Electrocatalysts for Overall Water Splitting. ACS Appl. Mater. Interfaces 2017, 9, 26066–26076. [Google Scholar] [CrossRef] [PubMed]
  62. Li, Q.; Wang, D.; Han, C.; Ma, X.; Lu, Q.; Xing, Z.; Yang, X. Construction of amorphous interface in an interwoven NiS/NiS2 structure for enhanced overall water splitting. J. Mater. Chem. A 2018, 6, 8233–8237. [Google Scholar] [CrossRef]
  63. Luo, J.; Im, J.-H.; Mayer, M.T.; Schreier, M.; Nazeeruddin, M.K.; Park, N.-G.; Tilley, S.D.; Fan, H.J.; Grätzel, M. Water photolysis at 12.3% efficiency via perovskite photovoltaics and Earth-abundant catalysts. Science 2014, 345, 1593–1596. [Google Scholar] [CrossRef]
  64. Zhong, X.; Tang, J.; Wang, J.; Shao, M.; Chai, J.; Wang, S.; Pan, H. 3D heterostructured pure and N-Doped Ni3S2/VS2 nanosheets for high efficient overall water splitting. Electrochim. Acta 2018, 269, 55–61. [Google Scholar] [CrossRef]
  65. Wu, C.; Liu, B.; Wang, J.; Su, Y.; Yan, H.; Ng, C.; Wei, J. 3D structured Mo-doped Ni3S2 nanosheets as efficient dual-electrocatalyst for overall water splitting. Appl. Surf. Sci. 2018, 441, 1024–1033. [Google Scholar] [CrossRef]
  66. Ren, J.-T.; Yuan, G.-G.; Weng, C.-C.; Chen, L.; Yuan, Z.-Y. Uniquely integrated Fe-doped Ni(OH)2 nanosheets for highly efficient oxygen and hydrogen evolution reactions. Nanoscale 2018, 10, 10620–10628. [Google Scholar] [CrossRef] [PubMed]
Catalysts 13 01095 g001 550
Figure 1. (a). XRD patterns of as-synthesized samples and (b) extended X ray spectra of β-Ni(OH)2 and Fe-doped β-Ni(OH)2.
Figure 1. (a). XRD patterns of as-synthesized samples and (b) extended X ray spectra of β-Ni(OH)2 and Fe-doped β-Ni(OH)2.
Catalysts 13 01095 g001
Catalysts 13 01095 g002 550
Figure 2. (a–c) SEM images, (d) TEM image, (e) SAED patterns, and (f) EDX spectra of Fe-doped Ni(OH)2/NF-2 nanosheets.
Figure 2. (a–c) SEM images, (d) TEM image, (e) SAED patterns, and (f) EDX spectra of Fe-doped Ni(OH)2/NF-2 nanosheets.
Catalysts 13 01095 g002
Catalysts 13 01095 g003 550
Figure 3. XPS spectra of Fe-doped Ni(OH)2/NF-2, (a) survey spectra, and (b) Ni 2p spectra (c). Fe 2p spectra and (d) O 1s spectra.
Figure 3. XPS spectra of Fe-doped Ni(OH)2/NF-2, (a) survey spectra, and (b) Ni 2p spectra (c). Fe 2p spectra and (d) O 1s spectra.
Catalysts 13 01095 g003
Catalysts 13 01095 g004 550
Figure 4. (a) HER LSV curves for prepared electrocatalysts, (b) comparison of overpotential for the prepared catalyst, (c) Tafel plot corresponding to the polarization curve, (d) EIS spectra of the prepared catalysts, (e) stability test of chronoamperometry and LSV previous to the next stability test of Fe-doped Ni(OH)2/NF-2, and (f) comparison of electrochemical performance of Ni(OH)2-based reported electrocatalysts.
Figure 4. (a) HER LSV curves for prepared electrocatalysts, (b) comparison of overpotential for the prepared catalyst, (c) Tafel plot corresponding to the polarization curve, (d) EIS spectra of the prepared catalysts, (e) stability test of chronoamperometry and LSV previous to the next stability test of Fe-doped Ni(OH)2/NF-2, and (f) comparison of electrochemical performance of Ni(OH)2-based reported electrocatalysts.
Catalysts 13 01095 g004
Catalysts 13 01095 g005 550
Figure 5. (a) OER polarization curves for the corresponding catalysts, (b) overpotential for the prepared catalyst, (c) Tafel plot derived after the polarization curve, (d) chronoamperometry for Fe-doped Ni(OH)2/NF-2 and the LSV curve measured before and after stability testing, and (e) electrochemical performance comparison of Fe-doped Ni(OH)2/NF-2 with reported Ni(OH)2-based electrocatalysts.
Figure 5. (a) OER polarization curves for the corresponding catalysts, (b) overpotential for the prepared catalyst, (c) Tafel plot derived after the polarization curve, (d) chronoamperometry for Fe-doped Ni(OH)2/NF-2 and the LSV curve measured before and after stability testing, and (e) electrochemical performance comparison of Fe-doped Ni(OH)2/NF-2 with reported Ni(OH)2-based electrocatalysts.
Catalysts 13 01095 g005
Catalysts 13 01095 g006 550
Figure 6. Cyclic voltammetry of (a) β-Ni(OH)2/NF, (b) Fe-doped β-Ni(OH)2/NF-1, (c) Fe-doped β-Ni(OH)2/NF-3, (d) Fe-doped β-Ni(OH)2/NF-2, and (e) the capacitive current density (anodic–cathodic) of the double-layer capacitance.
Figure 6. Cyclic voltammetry of (a) β-Ni(OH)2/NF, (b) Fe-doped β-Ni(OH)2/NF-1, (c) Fe-doped β-Ni(OH)2/NF-3, (d) Fe-doped β-Ni(OH)2/NF-2, and (e) the capacitive current density (anodic–cathodic) of the double-layer capacitance.
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Catalysts 13 01095 g007 550
Figure 7. (a) LSV curves of Fe-doped Ni(OH)2/NF-2 // Fe-doped Ni(OH)2/NF-2 with a two-electrode system in 1 M KOH and (b) Chronoamperometry at 1.61 V over 48 h.
Figure 7. (a) LSV curves of Fe-doped Ni(OH)2/NF-2 // Fe-doped Ni(OH)2/NF-2 with a two-electrode system in 1 M KOH and (b) Chronoamperometry at 1.61 V over 48 h.
Catalysts 13 01095 g007
Table
Table 1. The electrochemical HER performance of the as-prepared electrocatalysts in 1M KOH electrolyte.
Table 1. The electrochemical HER performance of the as-prepared electrocatalysts in 1M KOH electrolyte.
Catalystηonset (mV)η (mV)
at 10 mA cm−2		j (mA cm−2)Rct (Ω)Tafel Slope mV dec−1
Fe-doped β-Ni(OH)2/NF-2561122454.389
Fe-doped β-Ni(OH)2/NF-3971533569.2117
Fe-doped β-Ni(OH)2/NF-113719645318132
β-Ni(OH)2/NF16522334020153
NF18526537658203
Eonset = onset potential. η = overpotential. ηonset = onset overpotential. j = current density. EOER = OER potential. Rct = charge transfer resistance.
Table
Table 2. The electrochemical OER performance of the as-prepared electrocatalysts in 1M KOH electrolyte.
Table 2. The electrochemical OER performance of the as-prepared electrocatalysts in 1M KOH electrolyte.
CatalystEonset (V)ηonset (mV)EOER (V) at 10 mA cm−2η (mV)
at 10 mA cm−2		j (mA cm−2)Tafel Slope mV dec−1
Fe-doped Ni(OH)2/NF-21.323931.41918931385
Fe-doped Ni(OH)2/NF-31.3491191.45422431094
Fe-doped Ni(OH)2/NF-11.4221921.496266520123
β-Ni(OH)2/NF
NF		1.496
1.527		266
297		1.542
1.584		312
354		530
340		137
163
Table
Table 3. The electrochemical OER performance of the Fe-doped β-Ni(OH)2/NF-2, Fe-doped β-Ni(OH)2/NF-3, Fe-doped β-Ni(OH)2/NF-1, and Ni(OH)2/NF electrocatalyst in 1M KOH electrolyte.
Table 3. The electrochemical OER performance of the Fe-doped β-Ni(OH)2/NF-2, Fe-doped β-Ni(OH)2/NF-3, Fe-doped β-Ni(OH)2/NF-1, and Ni(OH)2/NF electrocatalyst in 1M KOH electrolyte.
CatalystCdl
(mF cm−2)		ECSA
(cm2)
Fe-doped β-Ni(OH)2/NF-27.72193
Fe-doped β-Ni(OH)2/NF-36.44161
Fe-doped β-Ni(OH)2/NF-15.32133
β-Ni(OH)2/NF1.6841
Table
Table 4. The overall water splitting performance of Fe-doped β-Ni(OH)2/NF-2 compared to other well-performing reported electrocatalysts.
Table 4. The overall water splitting performance of Fe-doped β-Ni(OH)2/NF-2 compared to other well-performing reported electrocatalysts.
CatalystEOER(V)@10 mA cm−2Reference
2% Fe-doped Ni(OH)2/NF1.61Present Work
FeMoS2/Ni3S2/NF1.61[60]
Mo(1−x)Wx−S2@Ni3S21.62[61]
NiS/NiS21.62[62]
FeNi-LDH1.63[63]
N-Ni3S2/VS21.64[64]
Mo-doped Ni3S2 nanosheets1.67[65]
Fe-doped Ni(OH)2/NF1.67[66]
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Krishnamurthy, P.; Maiyalagan, T.; Panomsuwan, G.; Jiang, Z.; Rahaman, M. Iron-Doped Nickel Hydroxide Nanosheets as Efficient Electrocatalysts in Electrochemical Water Splitting. Catalysts 2023, 13, 1095. https://doi.org/10.3390/catal13071095

AMA Style

Krishnamurthy P, Maiyalagan T, Panomsuwan G, Jiang Z, Rahaman M. Iron-Doped Nickel Hydroxide Nanosheets as Efficient Electrocatalysts in Electrochemical Water Splitting. Catalysts. 2023; 13(7):1095. https://doi.org/10.3390/catal13071095

Chicago/Turabian Style

Krishnamurthy, Palani, Thandavarayan Maiyalagan, Gasidit Panomsuwan, Zhongqing Jiang, and Mostafizur Rahaman. 2023. "Iron-Doped Nickel Hydroxide Nanosheets as Efficient Electrocatalysts in Electrochemical Water Splitting" Catalysts 13, no. 7: 1095. https://doi.org/10.3390/catal13071095

APA Style

Krishnamurthy, P., Maiyalagan, T., Panomsuwan, G., Jiang, Z., & Rahaman, M. (2023). Iron-Doped Nickel Hydroxide Nanosheets as Efficient Electrocatalysts in Electrochemical Water Splitting. Catalysts, 13(7), 1095. https://doi.org/10.3390/catal13071095

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