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The hydrogen evolution reaction (HER), as a pivotal half-reaction, significantly hinders the advancement of energy conversion efficiency. Metal electrodeposition on catalysts has been demonstrated to effectively enhance the HER reactivity. Here, Ni3S2–Fe–Ni with a multilayer structure was obtained by the electrodeposition of Ni3S2 with dopants Fe/Ni, in which a number of active sites were achieved and the intrinsic conductivity of the catalyst was well improved. Elemental analyses revealed the multilayer structure consisting of Ni3S2, NiS, and Fe. The Ni3S2–Fe–Ni catalyst exhibited impressive electrochemical performance due to optimization of its structure with the overpotentials of the HER and OER of only 83 and 190 mV. Notably, at a higher current density of 100 mA cm−2, the overpotentials for the HER and OER are only 339 and 365 mV. As a bifunctional electrocatalyst, its total splitting voltage was only 1.55 V. The catalysis performance remained nearly unchanged even after 48 h of stability testing. Finally, density functional theory (DFT) calculations revealed that the potential barriers in each reaction step of the OER are evenly distributed, and optimizing the Ni3S2 structure with iron and nickel atoms reduced the reaction energy barriers during the electrochemical process, improving the OER/HER performance. [ABSTRACT FROM AUTHOR]

The progress of this research is the preparation of FeNi alloy thin films by magnetron sputtering. Each step of the experimental process is based on the electrocatalytic performance of the sample, and characterized by many characterizations means such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray energy spectrometry (EDS) and step gauge thickness test for morphology, structure and elemental composition, etc. The analysis of the characterization results is used as a support for the experimental process. Adjustment of various preparation process parameters for material growth and subsequent processing include doping of non-metallic elements and construction of nanostructures. Doping of C elements can make FeNi based alloy films further amorphous. Zn element is used as a pore-forming agent. The two processes of doping and high-temperature vacuum dealloying can make the film obtain a nanoporous structure, which greatly increases the specific surface area. These two strategies reduce the overpotential (η10) of oxygen evolution reaction (OER) of FeNi alloy thin films to 393 mV and 314 mV, which are reduced by 47 mV and 79 mV step by step. The electrochemical properties of the finally obtained alloy film are: overpotential of 314 mV, Tafel slope of 61.8 mV/dec and the stability of only 10% decay at a current density of 10 mA/cm2 for 12 h. In this study, low-cost transition metals were used as the main materials to design OER catalysts, and the catalytic efficiency was comparable to that of commercial noble metal catalysts. The physical preparation methods made each sample have good reproducibility. It provides the experimental basis and theoretical basis for the design and synthesis of new catalytic materials at a higher level. • The electrocatalytic thin films prepared by magnetron sputtering has the characteristics of high stability. • The addition of carbon can deepen the amorphization, thus improving the catalytic efficiency. • High-vacuum dealloying is characterized by high speed and good repeatability in preparing porous structures. [ABSTRACT FROM AUTHOR]

It's still a challenge to design reasonably efficient catalyst using non-noble metal for the oxygen evolution reaction (OER). In this paper, we use a simple one-step electrodeposition method to load Ce and S co-doped NiFe amorphous alloys onto Cu(OH) 2 nanorod arrays. The excellent oxygen electrocatalytic performance of the catalyst NiFeCeS/Cu(OH) 2 /CuF is attributed to the electronic environments of the active sites of Ni and Fe regulated by heteroatomic sulfur and cerium, which promote the transfer of the oxygen precipitation intermediates to the higher valence states. Meanwhile, the highly conductive substrate accelerates the electron transfer efficiency of the catalyst material, and the loose nanostructure increases the specific surface area, exposing more active sites. NiFeCeS/Cu(OH) 2 /CuF shows outsanding electrocatalytic activity for oxygen evolution with a low overpotential of 227 mV at a current density of 10 mA cm−2 in alkaline medium. Moreover, the nanocomposite catalyst also exhibits rapid reaction kinetics and long-term stability and durability. In this work, an efficient oxygen precipitation catalyst is reported, which indicates that non-precious metal-based electrocatalysts have great potential for application in water electrolysis and provides a basis for the rational design and synthesis of nanorod array catalysts with unique structures. Using a simple one-step electrodeposition method to load Ce and S co-doped NiFe amorphous alloys onto Cu(OH) 2 nanorod arrays. NiFeCeS/Cu(OH) 2 /CuF shows outsanding electrocatalytic activity for oxygen evolution with a low overpotential of 227 mV at a current density of 10 mA cm−2 in alkaline medium. [Display omitted] • Co-doping of Ce and S improved the intrinsic activity of NiFe catalysts. • Cu(OH) 2 nanorods increase the number of active sites in catalysts. • The one-step co-deposition technique is simple, efficient and repeatable. [ABSTRACT FROM AUTHOR]

Novel, efficient and stable Mo-Ni(OH) 2 /Fe x Ni y (OH) 3x+2y bifunctional electrocatalyst is synthesized. The Mo-Ni(OH) 2 /Fe x Ni y (OH) 3x+2y displays outstanding electrocatalytic performance, achieving 229 mV at 10 mA·cm−2 for OER and 57 mV at 10 mA·cm−2 for HER, respectively. The two-electrode cell integrated by Mo-Ni(OH) 2 /Fe x Ni y (OH) 3x+2y requires a low cell potential of 1.54 V at 10 mA cm−2 and retains stable for over 60 h at 10 mA cm−2. [Display omitted] The development of efficient bifunctional catalysts for overall water splitting is highly desirable and essential for the advancement of hydrogen technology. In this work, Mo-Ni(OH) 2 /Fe x Ni y (OH) 3x+2y with hierarchical nanotube structure is constructed on flexible carbon cloth (CC) through simple electrochemical deposition and hydrothermal method. The hollow tube-structure is in favor of both exposing active sites and enhancing mass transfer capability. Moreover, the doping of Mo can enhance the electronic conductivity of heterostructures. The interfacial interaction between amorphous and crystal can enhance effectively the charge transfer kinetics across the interface. Therefore, Mo-Ni(OH) 2 /Fe x Ni y (OH) 3x+2y can achieve a low overpotential of 57 mV for hydrogen evolution reaction (HER) and 229 mV for oxygen evolution reaction (OER) at 10 mA·cm−2. In addition, Mo-Ni(OH) 2 /Fe x Ni y (OH) 3x+2y needs a potential of only 1.54 V at 10 mA·cm−2 for overall water splitting, and retains for a long period of time (60 h) reliable. The work will provide a valuable approach to the construction of highly efficient electrocatalysts for overall water splitting. [ABSTRACT FROM AUTHOR]

An efficient and stable bifunctional electrocatalyst (Mo-NiS@NiFe LDH/NF) with a 3D multistage nanostructure was prepared on NiFe LDH substrate by in-situ growth method, through 3D hierarchy fabrication and Mo doping, which consists of ultrafine Mo-NiS nanosheets and in-situ grown NiFe LDH nanosheets. The unique 3D multistage nanostructure facilitates the provision of rich heterogeneous interfaces and active sites, optimized electronic structure, enhanced electron transport/mass diffusion and stable overall water separation in alkaline and neutral electrolyte solutions. [Display omitted] It is crucial to create a bifunctional catalyst with high efficiency and low cost for electrochemical water splitting under alkaline and neutral pH conditions. This study investigated the in-situ creation of ultrafine Mo-NiS and NiFe LDH nanosheets as an effective and stable electrocatalyst with a three-dimensional (3D) flower-cluster hierarchical structure (Mo-NiS@NiFe LDH). The strong interfacial connection between Mo-NiS and NiFe LDH enhances the formation of metal higher chemical states in the material, optimizes the electronic structure, increases OH– adsorption capacity improves electron transfer/mass diffusion, and promotes O 2 /H 2 gas release. As a result, at 10 mA cm−2, Mo-NiS@NiFe LDH/NF demonstrates the outstanding bifunctional electrocatalytic activity of just 107 mV (HER, hydrogen evolution reaction) and 184 mV (hydrogen evolution reaction) (OER, oxygen evolution reaction). The catalytic performance is remarkably stable after 72 h of continuous operation in 1 M KOH at high current densities (300 mA cm−2). More interestingly, in the overall water splitting system, the cell voltages for anode and cathode in both alkaline and neutral electrolytes for Mo-NiS@NiFe LDH/NF are only 1.54 V (alkaline) and 2.06 V (neutral) at 10 mA cm−2. These results demonstrated that the bifunctional electrocatalyst design concept is a viable solution for water splitting in both alkaline and neutral systems. [ABSTRACT FROM AUTHOR]

Novel, efficient and stable γ-FeOOH/Ni 3 S 2 bifunctional electrocatalyst is fabricated. The γ-FeOOH/Ni 3 S 2 heterostructure displays outstanding electrocatalytic performance, achieving 279 mV at 50 mA⋅cm−2 for OER and 92 mV at 10 mA⋅cm−2 for HER, respectively. The two-electrode cell integrated by γ-FeOOH/Ni 3 S 2 heterostructure requires a low potential of 1.66 V at 10 mA⋅cm−2 and retains stable for 120 hours at 10 mA⋅cm−2. [Display omitted] Obtaining efficient, stable, and low-cost electrocatalysts is the key to realizing large-scale water splitting. In this work, three-dimensional (3D) hierarchical γ-iron oxyhydroxide (γ-FeOOH)/Ni 3 S 2 electrocatalyst on Ni foam is constructed for electrochemical overall water splitting. The 3D γ-FeOOH/Ni 3 S 2 heterostructure can effectively enhance active sites and charge transfer capability, also the heterostructure can benefit electronic effect at the interfaces and synergistic effect of multiple components. Therefore, the γ-FeOOH/Ni 3 S 2 exhibits excellent electrocatalytic activity with low overpotentials of 279 mV at 50 mA⋅cm−2 for oxygen evolution reaction and 92 mV at 10 mA⋅cm−2 for hydrogen evolution reaction, respectively. In addition, only a potential of 1.66 V is needed to attain 10 mA⋅cm−2 for the overall water splitting. In particular, the γ-FeOOH/Ni 3 S 2 exhibits long-term stability for 120 h at 10 mA⋅cm−2 without significant degradation. This work provides a valuable idea for obtaining low-cost and high performance bifunctional electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]

Efficient electrocatalyst for alkaline oxygen evolution reaction is the critical core to the wide application of metal-air energy storage and water electrolysis hydrogen energy. Therefore, appropriate design of highly active and stable non-noble metal oxygen evolution electrocatalyst with good electronic structure and multilevel structure is both a goal and a challenge. Here, we report a Fe–Ni 2 P electrocatalyst (NiFeP-MOF) with multilevel structure, which was obtained by anion exchange on the basis of Fe–Ni(OH) 2 (NiFe-MOF) grown on nickel foam in situ by solvothermal method. As expected, Fe substitution regulates the Ni oxidation state in the NiFeP-MOF and realizes electronic structure coupling, showing a highly active and stable oxygen evolution reaction (OER) in alkaline electrolyte solution. Specifically, the NiFeP-MOF demonstrates an ultralow overpotentials (232 mV, 10 mA cm−2; 267 mV 100 mA cm−2), respectively, an extremely small Tafel slope (34 mV dec−1). Separately, the electrocatalyst shows an excellent cycle stability at 10 mA cm−2 for 12 h (43,200 s). More importantly, this work come up with an available policy for the preparation of excellent alkaline hydrolysis electrolysis catalysts and air cathodes with excellent performance. • Fe–Ni 2 P (NiFeP-MOF) electrocatalyst with multilevel structure is obtained. • The synthesized catalysts have excellent OER performance and catalytic stability. • The catalyst with Ni:Fe ratio of 2:1 has high activity and good stability. • Fe substitution regulates the Ni oxidation state realizes electronic structure coupling. [ABSTRACT FROM AUTHOR]

Electrocatalytic water splitting is a promising route for the generation of clean hydrogen. However, the anodic oxygen evolution reaction (OER) suffers greatly from low reaction kinetics and thereby hampers the energy efficiency of alkaline water electrolysers. In recent years, tremendous efforts have been dedicated to the pursuit of highly efficient, low cost and stable electrocatalysts for oxygen evolution reaction. Herein, an amorphous FeOOH roughened capillary-liked CoAl layered double hydroxide (LDH) catalyst grown on nickel foam (denoted as FeOOH–CoAl LDH/NF) was reported for OER electrolysis. The developed FeOOH–CoAl LDH/NF electrode shows excellent OER activity with overpotentials of 228 mV and 250 mV to deliver a current density of 50 mA cm−2 and 100 mA cm−2 in 1.0 M KOH solution, respectively, ranking it one of the most promising OER catalysts based on transition-metal-based LDH. This is owed to the formed capillary-liked hierarchy structure with high-porosity as well as the strong electronic interaction between FeOOH and CoAl LDH. The developed morphological engineering approach to build hierarchal porous structures together with facile amorphous FeOOH modification may be extended to other layered double hydroxide catalyst for enhanced OER activities. [Display omitted] • Amorphous FeOOH decorated capillary-liked CoAl LDH structure was synthesized. • The amorphous structure induces sufficient active sites for water oxidation. • The interfacial interaction facilitates the mass transport and charge transfer. [ABSTRACT FROM AUTHOR]

• MoS x -decorated CoAl LDHs were fabricated in situ by a chemical reduction process. • The MoS x nanosheets were homogenously distributed on CoAl LDHs and amorphous in nature. • The thickness and density of MoS x was controllable by adjusting the reduction time. • A greater number of active sites and accelerated electron transfer were responsible for OER activity. The high demand for renewable energy storage and conversion has led to the exploration of highly efficient, low cost electrocatalysts for the oxygen evolution reaction (OER). Herein, CoAl layered double hydroxides (LDHs) hybridized with amorphous MoS x nanosheets (CoAl-MoS x -X, where X is the reduction reaction time) were synthesized in situ through a two-step procedure. Among these electrocatalysts, CoAl-MoS x -12 exhibited the highest OER performance with an overpotential of 330 mV at 10 mA cm−2 and a Tafel slope of 59 mV dec−1 in alkaline solution. The underlying mechanism revealed that the density and the thickness of the MoS x nanosheets on CoAl LDHs both play key roles in the enhanced OER activity by offering more exposed active sites and accelerated electron transfer. In addition, the in situ growth provides an intimate contact between MoS x and the CoAl LDHs which is responsible for the relatively long-lasting stability of the electrocatalyst. This strategy adds to the methods available for the synthesis of LDH-supported materials as electrocatalysts with enhanced activity for renewable energy storage and conversion. [ABSTRACT FROM AUTHOR]

In this study, unique Co 3 S 4 /Fe 3 S 4 heterostructures (denoted as CoFe-HM-T) were synthesized from CoFe layered double hydroxides (LDHs) by a two-step hydrothermal process (hydrazine monohydrate and thiourea treatment). The effect of Co 3 S 4 /Fe 3 S 4 heterostructures on the electrocatalytic water splitting was investigated in alkaline solution. The CoFe-HM-T electrode exhibited excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalytic activity with overpotentials of 320 mV and 200 mV at the current density of 100 mA cm−2, respectively. CoFe-HM-T also possessed the smallest Tafel slope among the prepared samples, which was estimated to be 38.1 mV dec−1 and 144.9 mV dec−1 for OER and HER, respectively. Serving as bifunctional catalysts, the CoFe-HM-T electrode reached the state-of-art current density of 10 mA cm−2 at a cell voltage of 1.70 V with excellent stability. The enhanced electrocatalytic activity was ascribed to the interconnected structure facilitating the mass transport, the heterojunction accelerating the charge transfer, and the synergistic effect between them. This study offered a new strategy for in situ synthesizing the heterojunction electrocatalysts with unique interface by readily tuning the metal components in transition-metal LDHs. [Display omitted] • The Co 3 S 4 /Fe 3 S 4 heterostructures was fabricated by two-step hydrothermal process. • The interconnected structure of Co 3 S 4 /Fe 3 S 4 junction facilitates the mass transport. • The Co 3 S 4 /Fe 3 S 4 heterojunction accelerates the charge transfer. • The synergistic effect is responsible for the outstanding electrocatalytic activity. [ABSTRACT FROM AUTHOR]