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Developing high-performance and low-cost electrocatalysts for the hydrogen evolution reaction (HER) favorably promotes large-scale hydrogen production from water. Here, we design a nanocomposite of Co 9 S 8 -Ni 9 S 8 nanodiscs (CNS) in-situ grown from polypyrrole hollow nanospheres (PHS) on carbon paper (CP) via unipolar pulse electrodeposition (UPED) technique as HER catalyst in alkaline media. The lattice structure along with the interlacing nanodiscs-like morphology of the Co 9 S 8 -Ni 9 S 8 mischcrystal is controllable by UPED method. The optimal CNS/PHS/CP electrode obtained with pulse potential of − 0.80 V exhibits favorable catalytic activity with low overpotential (186 mV at 10 mA cm−2), superior stability performance (for 100 h with no current density decay), and high electrochemically active surface area up to 1925 cm2, which should be attributed to the interlacing Co 9 S 8 -Ni 9 S 8 mischcrystal with rich active sites, the ingenious combination with conductive polymer, and the integrated electron-proton conductive network. This work will provide a new sight to design low-cost bimetallic sulfide-based electrocatalysts for high-performance HER in water splitting. [Display omitted] • In-situ growth of Ni 9 S 8 -Co 9 S 8 is controllable by unipolar pulse electrodeposition. • Precise regulation of mischcrystal lattice works on the morphology optimization. • Escape from binder contributes to high conductivity and HER catalytic activity. • Integrated frame, large ECSA and rich active sites lift HER dynamics and stability. • The CNS-0.80 catalyst exhibits low overpotential and superior long-term stability. [ABSTRACT FROM AUTHOR]

A metal-free carbon catalyst is a kind of oxygen reduction catalyst with great prospects. It is an important material with potential to replace the traditional Pt catalyst. In this paper, a kind of irregular and ultra-thin carbon nanosheet (K180M-300-900) with high catalytic activity was synthesized by hydrothermal calcination using okra as a biomass and NH4Cl as an N source. The prepared nitrogen-doped metal-free catalyst with high pyridine-N and graphitic-N provides an extremely large number of active sites and has certain lattice defects. Ultra-thin carbon nanosheets promote sufficient contact between the catalyst and electrolyte, promote the diffusion of oxygen, and result in a faster transfer rate of electrons. The initial potential and half-slope potential of K180M-300-900 are 0.99 V and 0.82 V, respectively, which are comparable to those of 20% Pt/C. In addition, the stability and methanol tolerance of this catalyst (K180M-300-900) are better than 20% Pt/C, so it has great development potential and application value. This result provides a new method to prepare metal-free carbon materials that will take the place of traditional Pt catalysts. [ABSTRACT FROM AUTHOR]

FeCo2O4 is a potential OER catalyst, but its catalytic activity still needs to be further improved due to its poor electrical conductivity and low material utilization. In this paper, we construct oxygen-vacancy-rich two dimensional FeCo2O4 nanosheet materials using a liquid-phase reduction strategy. Benefiting from its large specific surface area, numerous surface catalytic sites, enhanced electrical conductivity, and modulated electronic structure, the catalyst exhibits an overpotential of only 270 mV at a current density of 10 mA cm−2, which is lower than that of the original FeCo2O4 nanosheets (420 mV). At the same time, the catalyst can run steadily for 20 hours without obvious decay. [ABSTRACT FROM AUTHOR]

Hydrazine-assisted electrochemical water splitting is an important avenue toward low cost and sustainable hydrogen production, which can significantly reduce the voltage of electrochemical water splitting. Herein, we took a simple approach to fabricate NiFeP nanosheet arrays on nickel foam (NiFeP/NF), which exhibit superior electrocatalytic activity for the hydrogen evolution reaction (HER) and the hydrazine oxidation reaction (HzOR). Our investigations revealed that the excellent electrocatalytic activity of NiFeP/NF mainly arises from the bimetallic synergistic effect, abundant electrocatalytically active sites facilitated by the porous nanosheet morphology, high intrinsic conductivity of NiFeP/NF and strong NiFeP–NF adhesion. We assembled a hydrazine-boosted electrochemical water splitting cell using NiFeP/NF as a bifunctional catalyst for both electrodes, and the overall hydrazine splitting (OHzS) exhibits a considerably low overpotential (100 mV at 10 mA cm−2), and is stable for 40 h continuous electrolysis in a 1 M KOH + 0.5 M N2H4 electrolyte. When it is applied to hydrogen production by seawater electrolysis, its catalytic activity shows strong tolerance. This work provides a promising approach for low cost, high-efficiency and stable hydrogen production based on hydrazine-assisted electrolytic seawater splitting for future applications. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting has excellent application prospects in clean energy technology. However, due to the large overpotential required for the OER reaction during the water-splitting reaction, the modification of electrocatalysts is a vital strategy to address the slow kinetics of the OER reaction. In this paper, a simple and rapid two-step hydrothermal sulfidation method was used to prepare S-modified Ni(OH)2 nanosheets electrocatalysts at 120 °C. At the same time, the well-designed nanostructured catalyst on the nickel foam substrate exposes a large number of active sites, and the simultaneously generated oxygen vacancies are beneficial to the penetration of the electrolyte and release of O2, thus significantly improving the OER performance. In 1.0 M KOH electrolyte, Ni9S8/Ni(OH)2/NF exhibits excellent catalytic activity for OER. The catalyst requires only 430 mV overpotential at a current density of 100 mA cm-2. In addition, Ni9S8/Ni(OH)2/NF also has excellent long-term stability. This work reports the formation of Ni9S8/Ni(OH)2/NF heterojunctions by sulfiding Ni(OH)2 on porous nickel foam. Surprisingly, these Ni9S8/Ni(OH)2/NF heterojunctions exhibit excellent oxygen evolution reaction performance and long-term stability. This is superior to most reported electrocatalysts for oxygen evolution reactions. [ABSTRACT FROM AUTHOR]

Hybrid 1T/2H MoS 2 nanosheets with different 1T phase content are vertically grown on conductive carbon cloth and the simulation result shows that the catalytic activity presents a trend of first increasing and then decreasing with the 1T phase content increasing, which agrees well with the experimental results. [Display omitted] Implanting the octahedral phase (1 T) into the hexagonal phase (2H) of the molybdenum disulfide (MoS 2) matrix is considered one of the effective methods to enhance hydrogen evolution reaction (HER) performances of MoS 2. In this paper, hybrid 1 T/2H MoS 2 nanosheets array was successfully grown on conductive carbon cloth (1 T/2H MoS 2 /CC) via facile hydrothermal method and the 1 T phase content in 1 T/2H MoS 2 is regulated to gradually increase from 0 % to 80 %. 1 T/2H MoS 2 /CC with 75 % 1 T phase content exhibits optimal HER performances. The DFT calculation results show that S atoms in 1 T/2H MoS 2 interface exhibit the lowest hydrogen adsorption Gibbs free energies (ΔG H*) compared with other sites. The improvement of HER performances are primarily attributed to activating the in-plane interface regions of the hybrid 1 T/2H MoS 2 nanosheets. Furthermore, the relationship between 1 T MoS 2 content in 1 T/2H MoS 2 and catalytic activity was simulated by a mathematical model, which shows that the catalytic activity presents a trend of increasing and then decreasing with the increase of 1 T phase content. [ABSTRACT FROM AUTHOR]

Finding effective and affordable non-noble metal catalysts is one of the most important yet difficult tasks because of the sluggish kinetics of the oxygen evolution reaction (OER). Therefore, we synthesized vanadium-doped CoFe PBA nanosheets on nickel foam in a single step to change the electronic structure with metal doping. The sheet structure facilitates charge transfer, while vanadium doping modifies the electronic structure to enhance the catalytic activity. With just a 229 mV overpotential needed in the OER reaction to reach 10 mA cm−2, the as-synthesised electrocatalyst demonstrates high electrocatalytic activity. The produced electrocatalyst can operate at a current density of 10 mA cm−2 for 12 h, and it displays outstanding stability even at a high OER current density of 100 mA cm−2 for 12 h. This study will contribute to the development of efficient and affordable non-noble metal-based electrocatalysts. [ABSTRACT FROM AUTHOR]

The exploration of efficient, stable, and economical electrocatalysts for oxygen evolution reaction (OER) is of great significance and challenge for the development of renewable energy. A series of Ni-based layered double hydroxides (LDHs) have been explored as promising electrocatalysts for OER on account of their earth abundance, low overpotential, and super stability. However, the low electrical conductivity of LDHs cannot satisfy the progressive requirements of water splitting. Herein, we introduce a template strategy to synthesize trimetallic nickel-chromium LDH–cobalt (NiCr-LDH–Co) nanosheets on nickel foam (NiCr-LDH–Co/NF) without any binders as efficient catalysts for OER. Compared with the reported NiCoCr-LDHs synthesized by one-step, our NiCr-LDH–Co/NF delivered a lower overpotential of 229.4 mV at 50 mA cm−2, which is even lower than that of all the reported bimetallic nickel-based LDHs (NiFe-LDH, NiCo-LDH, NiMn-LDH, NiTi-LDH, NiV-LDH, etc.) and the precious RuO2 catalyst. Furthermore, the NiCr-LDH–Co/NF was maintained for at least 24 h at a high current density of 50 mA cm−2 without much deviation in 1 M KOH solution. The effective integration of the layered structures of LDH and the high electronic conductivity of the Co element endow NiCr-LDH–Co/NF remarkable catalytic ability for the OER process. Furthermore, the strategy expands the possibility for improving the catalytic activity of trimetallic LDHs as OER catalysts. [ABSTRACT FROM AUTHOR]

Transition metal oxides and hydroxides have gradually become a new generation of oxygen evolution reaction(OER) catalysts due to their low cost and good activity. However, the high Tafel slope prevented them from replacing conventional Ir and Ru-based catalysts. In this paper, NiO nanosheets arrays were synthesized on the conductive ITO substrate by low-temperature self-deposition method, and then the NiO nanosheet arrays were modified based on the different activities of different cobalt salts in non-polar solvents (such as acetone), and mixed transition metal nanosheets arrays with different structures were successfully constructed. The introduction of chlorine salts would produce an etching effect on NiO nanosheets to generate porous CoNi-O nanosheets, while the introduction of nitrates would secondarily grow on the surface of NiO nanosheets to generate branched CoNi-O nanosheets. Furthermore, the introduction of Co salt not only endowed the material with a unique nanostructure, but also enhanced the oxygen evolution capability of the NiO nanosheet arrays. Compared with NiO nanosheets (56.9 mV/dec), the modified porous CoNi-O nanosheets (33.7 mV/dec) and branched CoNi-O nanosheets (29.1 mV/dec) have smaller Tafel slope in 0.1 mol/L KOH electrolyte. Therefore? the design strategy of constructing mixed oxide electrodes with different morphologies by surface modification can provide experience for the design of high performance and practical OKR catalytic activity. [ABSTRACT FROM AUTHOR]

Constructing a heterostructure is an efficient strategy to enhance the catalytic activity toward the oxygen evolution reaction (OER). Herein, Ce-modified Ni(OH)2 nanoparticles are anchored on Ni-MOF nanosheets by the electrodeposition strategy, forming a self-supporting electrode of Ce-m-Ni(OH)2@Ni-MOF. The Raman spectrum proves that both Ce(OH)3 and Ce doping exist in Ce-modified Ni(OH)2 nanoparticles. The heterostructure possesses an open nanosheet structure, with a good interaction between Ni-MOF and Ce-m-Ni(OH)2, which enables efficient mass/charge transfer and the synergetic effect between Ni and Ce, leading to a high-performance electrocatalyst. Specifically, Ce-m-Ni(OH)2@Ni-MOF achieves current densities of 50 and 100 mA cm−2 at low overpotentials of 219 and 272 mV, respectively, and retains high activity for at least 30 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metallic MoS 2 and amorphous CoNi(OH) 2 show a synergistic effect for HER in 0.1 M KOH. • MoS 2 -CoNi(OH) 2 composite has higher current response for HER than Pt/C at η greater than 0.19 V. • MoS 2 -CoNi(OH) 2 composite also shows highly efficient OER performance in 0.1 M KOH. We report the preparation of nanocomposite consisting of metallic MoS 2 and electrodeposited amorphous CoNi(OH) 2 nanosheets on carbon paper for efficient electrochemical water splitting in the alkaline solutions. The synergistic effect between metallic MoS 2 and amorphous CoNi(OH) 2 nanosheets enables the excellent catalytic activity of nanocompsite towards hydrogen evolution reaction (HER) in 0.1 M KOH with a low overpotential of 178 mV at a current density of 10 mA/cm2 and Tafel slope of 60.9 mV/decade. The current density of MoS 2 -CoNi(OH) 2 nanocomposite for HER at the overpotential of more than 0.190 V is even higher than that of the commercial Pt/C catalyst. Moreover, the MoS 2 -CoNi(OH) 2 nanocomposite is also active towards electrochemical oxygen evolution and can act as a bifunctional catalyst for water splitting in 0.1 M KOH. Our work povides a simple and effective way to engineer phases and prepare two-dimensional nanocomposites for effecient water splitting in alkaline aqueous solutions. [ABSTRACT FROM AUTHOR]

The development of efficient and low-cost bifunctional catalysts for electrochemical water splitting is important for future sustainable hydrogen energy deployment. In this paper, a series of composition-controlled hybrid catalysts (Co 1.11 Te 2 /Te) were successfully constructed by introducing different proportions of Co source into the precursor solutions during the hydrothermal synthesis of Te nanosheets(Te NSs). The experimental results show that the content of Co3+active species in the hybrid materials can be adjusted by controlling the molar ratio of Co to Te, thereby significantly improving the electrocatalytic performance of the samples. Benefiting from the highest content of Co3+, the large specific surface area, and the great charge transfer ability, the Te-Co-3 electrode exhibited the best catalytic activity and durability among all samples. The hydrogen evolution reaction(HER) and oxygen evolution reaction(OER) overpotentials of the electrode were only 135 and 261 mV, respectively, to drive a current density of 10 mA cm−2 in an alkaline environment (1 M KOH). Furthermore, it required only a cell potential of 1.56 V to achieve overall water splitting at 10 mA cm−2. This work should be useful for the design and preparation of non-noble metal bifunctional catalysts. [ABSTRACT FROM AUTHOR]

Economical and efficient electrocatalysts are crucial to the hydrogen evolution reaction (HER) in water splitting to produce hydrogen. Heterostructured electrocatalysts generally exhibit enhanced HER catalytic activity due to the strong electron coupling effects and synergistic optimization of hydrogen adsorption–desorption. Herein, in-plane heterostructured MoN/Mo2N nanosheets are fabricated as high-efficiency HER electrocatalysts in the alkaline medium from bulk MoS2 by molten salt-assisted synthesis. Density-functional theory calculations and experiments show that the in-plane heterostructured MoN/Mo2N nanosheets facilitate interfacial electron redistribution from Mo2N to MoN, giving rise to more negative H2O adsorption energy and optimal hydrogen adsorption free energy (ΔGH* = −0.017 eV). Consequently, a low overpotential of 126 mV at 10 mA cm−2 and a small Tafel slope of 69.5 mV dec−1 are achieved in the 1M KOH electrolyte, demonstrating excellent HER characteristics. Moreover, the overpotential shows negligible change after operating at 50 mA cm−2 for 12 h, confirming the excellent stability. The results reveal a novel and effective strategy to design highly efficient 2D in-plane heterostructured HER electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]

Enriching the active sites of catalysts and artificially regulating the directional migration of photogenerated carriers are effective means to improve the catalytic activity of photocatalysts. In this work, CeO2 nanosheets are prepared by calcination at high temperatures, and the S‐scheme heterojunction photocatalyst CeO2@Co9S8 is prepared by coupling the Co9S8 nanoparticles prepared by hydrothermal method on CeO2 nanosheets. The large specific surface area of CeO2 nanosheets provides sufficient loading sites for Co9S8 and Co9S8 nanoparticles can effectively disperse with the help of CeO2 nanosheet structure, which effectively inhibits the agglomeration of nanoparticles. The high photosensitivity of Co9S8 increases the utilization of CeO2@Co9S8 S‐scheme heterojunction to visible light. The construction of S‐scheme heterojunction improves the separation efficiency of photogenerated carriers, prolongs the service life of photogenerated charges, retains the photogenerated electrons and holes with strong reduction and oxidation ability in the catalyst system, and improves the performance of photocatalytic hydrogen production. The hydrogen yield of 15 wt% Co9S8 supported CeO2@Co9S8 can reach 15.7 times CeO2 and 2.5 times Co9S8, and the composite catalyst has good stability. This work provides a new way for adjusting the surface structure and carrier behavior of photocatalysts. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction is a key process in hydrogen production from water splitting. The development of non-noble metal electrode materials with high efficiency and low cost has become the key factor for large-scale hydrogen production. Binary NiCo-layered double hydroxide (LDH) has been used as a non-noble metal electrocatalyst for OER, but its overpotential is still large. The microstructure of the catalyst is tuned by doping Mo ions into the NiCo-LDH/NF nanowires to form ternary NiCoMo-LDH/NF nanosheet catalysts for the purpose of enhancing the active sites and reducing the initial overpotential. Only 1.5 V (vs. reversible hydrogen electrode (RHE), ≈270 mV overpotential) is required to achieve a catalytic current density of 10 mA cm−2 and a small Tafel slope of 81.46 mV dec−1 in 1 M KOH solution, which manifests the best performance of NiCo-based catalysts reported up to now. Electrochemical analysis and micro-morphology show that the high catalytic activity of NiCoMo-LDH/NF is attributable to the change of the microstructure. The interconnected nanosheet arrays have the obvious advantages of electrolyte diffusion and ion migration. Thus, the active sites of catalysts are significantly increased, which facilitates the adsorption and desorption of intermediates. We conclude that NiCoMo-LDH/NF is a promising electrode material for its low cost and excellent electrocatalytic properties. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting has attracted great attention for hydrogen production, yet is still limited by capable electrocatalysts. Herein, the ultrathin porous nickel–cobalt phosphide nanosheets (NiCoP NS) are successfully synthesized by microwave‐assisted technique and used as a robust bifunctional catalyst for overall water splitting. The NiCoP NSs can show excellent catalytic activity with a low overpotential (η10) of 105 mV at 10 mA cm−2 for hydrogen evolution reaction and a small overpotential (η10) of 240 mV at 10 mA cm−2 for oxygen evolution reaction. The water splitting device of NiCoP NSs can give lower cell voltage of 1.45 and 1.67 V at a current density of 10 and 100 mA cm−2. The better electrochemical performance should be attributed to the synergetic effect of nickel and cobalt, porous morphology, and large surface area. These key factors boost the reactant's adsorption energy, number of exposed active sites, and produce different channels for charge transfer and reactant/electrolyte diffusion. [ABSTRACT FROM AUTHOR]

Layered double hydroxide (LDH) has emerged as a promising electrocatalyst; however, the synthetic method usually requires high temperature and high pressure, and sulfate-intercalated LDH is rarely reported. Herein, the sulfate-intercalated CoFe LDH nanosheets were successfully fabricated at ambient temperature via a facile strategy, using two-dimensional ZIF-9(III) as a template and FeSO4 as both etchant and iron source. When the as-prepared sulfate-intercalated CoFe LDH acts as an electrocatalyst, it presents superior electrocatalytic performance for the oxygen evolution reaction (OER), requiring low overpotential (η@10 mA cm−2 = 218 mV) with a small Tafel slope of 59.9 mV dec−1 in 1.0 M KOH, which compares favorably with commercial RuO2 and most reported transition-metal electrocatalysts. The high catalytic activity of CoFe LDH might be ascribed to the large interlayer space distance originating from special SO42− ions and the strong synergistic effects between Fe and Co. This work provides a novel and feasible approach to designing highly efficient electrocatalysts based on advanced LDH materials for OER. [ABSTRACT FROM AUTHOR]

Nanostructured Bismuth-based materials are promising electrodes for highly efficient electrochemical reduction processes such as hydrogen evolution reaction (HER). In this work, a novel sort of nanocomposite made up of partially reduced Bi2O3 into metallic Bi anchored on a 3D network of Ni-foam as a high-performance catalyst for electrochemical hydrogen reduction. The application of the hybrid material for HER is shown. The high catalytic activity of the fabricated electrocatalyst arises from the co-operative effect of Bi/Bi2O3 and Ni-foam which provides a highly effective surface area combined with the highly porous structure of Ni-foam for efficient charge and mass transport. The advantages of the electrode for the electrochemical reduction processes such as high current density, low overpotential, and high stability of the electrode are revealed. An overall comparison of our as-prepared electrocatalyst with recently reported works on related work is done. [ABSTRACT FROM AUTHOR]