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Developing energy production, storage, and conversion technologies based on sustainable or renewable energy is essential to address the energy and environmental crisis. Electrochemical water splitting is one of the most promising approaches to realize the production of green hydrogen. The design of catalytic materials with low cost, high activity, and long‐term stability and the exploration of specific reaction mechanisms are the key focus for the involved electrochemical hydrogen evolution reaction (HER). Recently, substantial efforts have been devoted to the rational design and synthesis of non‐noble metallic heterostructures with fascinating synergistic effects among different components. These heterostructured materials demonstrate comprehensive properties exceeding the estimations by the rule of mixtures and display high activity and long‐term stability in industrial conditions for HER. Herein, the reaction mechanism and key parameters for improving catalytic performance in the HER process are discussed in detail. The latest advances in heterostructures based on synthetic methods and electrocatalytic characteristics from experimental and computational perspectives are summarized according to the role of various components. Herein, insights are provided in this review into an in‐depth understanding of the heterostructures as HER electrocatalysts, and the opportunities and challenges to scale up future‐oriented developments are highlighted. [ABSTRACT FROM AUTHOR]

Abstract: The effect of surfactant on the formation, structure and properties of ZnO films synthesized by electrodeposition was studied in this work. It was carried out in an aqueous Zn(NO3)2 solution containing surfactant op-10 using cathodic galvanostatic method. The results showed that the additive surfactant effectively inhibited hydrogen evolution reaction on cathode surface, maintained stability of the solution pH and improved deposition rate of the films to two times. Grown ZnO films with uniform grain and smooth surface were observed by using atomic force microscopy. Optical characterizations indicated that average optical transmittance of such films was more than 80% in the visible wavelength range, and its optical band gap was near 3.21eV. [Copyright &y& Elsevier]

Ternary transition metal chalcogenide (TTMC) with multicomponent, different phases and unique electronic structures have been studied in electrocatalytic hydrogen evolution reaction (HER). However, the strong interaction between adsorbed H (H∗) and sulfur leads to the unfavorable hydrogen desorption properties of considerable TTMC. Herein, we constructed the hierarchical hollow NiCo 2 S 4 nanotube@NiCo 2 S 4 nanosheet arrays on Ni foam substrate (NT-NiCo 2 S 4 @NS-NiCo 2 S 4 /NF) by ion-exchange method. Homogeneous anion diffusion facilitates the formation of regular ultrathin nanosheets on hollow NiCo 2 S 4 nanotube arrays, which presents hierarchical architecture with more surface area and channels to active site exposure, electrolyte diffusion, and gas desorption for HER. As-synthesized optimal NT-NiCo 2 S 4 @NS-NiCo 2 S 4 /NF electrode demonstrates an excellent HER activity, especially an overpotential of 221 mV, a Tafel slope of 108 mV dec−1, and remarkable stability at current densities of 100 mA cm−2 in 1.0 M NaOH electrolyte. • Hierarchical hollow NT-NiCo 2 S 4 @NS-NiCo 2 S 4 arrays supported on nickel foam were synthesized by ion-exchange method. • Hierarchical structure assembled from TTMC can facilitate active sites accessibility and hydrogen desorption properties. • The optimized NT-NiCo 2 S 4 @NS-NiCo 2 S 4 /NF-1.0 exhibited an overpotential of 221 mV at 100 mA/cm2 and persistent stability. [ABSTRACT FROM AUTHOR]

Tailoring the architecture is of great significance for developing and designing highly active non-noble metal-based electrocatalysts for hydrogen evolution reaction (HER). Here, the architecture of the precursor was improved by alkali etching after the introduction of Prussian blue analogue (PBA). The coral-like precursor was transformed into bimetallic phosphide via phosphating. Detailed investigation disclares that the introduction of PBA could dramatically improves the electrochemical surface area of the material, and the abundant active site could be obtained via alkali etching. In addition, the removal of amorphous carbon may be the main reason for the enhanced conductivity. • In situ growth of PBA is helpful to improve the intrinsic activity of electrocatalyst. • The alkaline etching is helpful to increase the ECSA of electrocatalyst. • The excellent non-precious metal-based catalyst for HER were reported. • Coral-like structure formed by stacking nanoballs. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Development of highly-active and noble-metal-free electrocatalysts for hydrogen evolution reactions is a challenge, and optimizing the structure and the composition of the relative materials is critical to obtain the high-quality catalysts. Ni-based compounds are being explored as noble-metal-free electrocatalysts in hydrogen evolution reactions but the Ni-based needs to be modified effectively. In this work, we co-electrodeposited Ni nanoparticles, hydrophilic graphene and graphene oxide layers on Ni foam to synthesize Ni-HG-rGO/NF catalysts. It was presented a Datura-like shape allowing for high performance with current densities of −10 and −100 mA cm−2 for HER at overpotentials of −50 and −132 mV, a low Tafel slope of −48 mV dec−1 and excellent long-term stability in 1.0 M NaOH solution. These results demonstrate that the Ni-HG-rGO/NF electrode can be a competitive electrode materials for HER in alkaline conditions. [ABSTRACT FROM AUTHOR]

The development of cost-effective and high-efficiency electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) still remains highly challenging. Exposing as many active sites as possible is the key method to improve activity of HER and OER performance. In this communication, we demonstrate a novel 3D hierarchical network NiCo 2 S 4 nanoflake grown on Ni foam (NiCo 2 S 4 -NF) as a highly efficient and stable electrochemical catalyst. The NiCo 2 S 4 -NF exhibits overpotentials as low as 289 and 409 mV at 100 mA cm −2 , superior long-term durability during a 20 h measurement, and a low Tafel slope of 89 and 91 mV dec −1 for HER and OER in 1.0 M NaOH solution. The outstanding performance is owe to the inherent activity of ultrathin NiCo 2 S 4 nanoflakes and the special structure of NiCo 2 S 4 -NF that can provide a huge number of exposed active sites, accelerate the transfer of electrons, and facilitate the diffusion of electrolyte simultaneously. [ABSTRACT FROM AUTHOR]

We report a novel and simple approach to synthesis highly efficient and stable electrochemical catalyst of Ni-(MoS 2 /GO) composite coatings by electrodeposition from aqueous solution with the nickel sulphamate precursor. Depositing under supergravity fields has been applied to scatter more MoS 2 /GO hybrids in the coatings and decrease the size of nickel particles as far as possible and increase large amount of exposed active sites. In 1.0 M NaOH solution, Ni-(MoS 2 /GO) only needs overpotentials as low as −33 mV and −132 mV at a current density of −10 mA cm −2 and −100 mA cm −2 , respectively. The behavior of Ni-(MoS 2 /GO) exceeds most of the same reported HER catalysts in previously literature. In addition, we also synthesized Ni-MoS 2 , Ni-GO and pure Ni catalysts use the same method. The results show that Ni-(MoS 2 /GO) exhibited better HER activity at a current density of −100 mA cm −2 than these catalysts. In the future research field of HER catalysis materials, the development of this material may be not limited to nickel based materials, also will be used in Fe, Co and other non noble metal based materials, outlining a general approach for the synthesis of nanostructured M-(MoS 2 /GO) as a class of new catalyst with efficient HER activity. [ABSTRACT FROM AUTHOR]

In this work, preparing three nickel-based carbon composite catalysts (Ni-OCNT, Ni-ONC and Ni-rGO) by supergravity field electrodeposition for hydrogen evolution reaction (HER) from nickel sulfamate bath containing suspended nano-sized carbon materials. The crystal structure, morphology and chemical compositions of the composite catalysts were characterized by XRD and SEM measurements. The electrochemical activity of composite coatings for HER was determined by polarization measurement and electrochemical impedance spectroscopy in 1.0 M NaOH solution. The prepared nickel-based carbon composite catalysts exhibit a significant enhancement in electrocatalytic activity for HER compared with pure Ni electrode. In addition, the Ni-rGO, Ni-ONC, Ni-OCNT catalysts prepared under supergravity field demand overpotentials of 245, 177, 91 mV and 286, 224, 154 mV and 330, 286, 222 mV to drive current densities of 80, 30, 10 mA cm −2 , respectively. Ni-rGO cathode presents excellent HER activity with lowest overpotentials. [ABSTRACT FROM AUTHOR]

It remains an important project for the development of water splitting electrolyze to design and synthesis of more efficient non-noble metal catalyst. In this work, a structured Ni–MoS 2 composite coating has been synthesized under supergravity fields with nickel sulphamate bath containing suspended MoS 2 submicro-flakes. X-ray diffraction patterns indicate that the MoS 2 submicro-flakes have been successfully incorporated into the Ni matrix. Additionally, SEM shows that the prepared Ni–MoS 2 composite coatings display finer grain size than the pure Ni coatings, which can increase the electrochemistry surface area and the active site of hydrogen evolution reaction. Therefore, due to the synergistic effect of molybdenum disulfide and nickel, the Ni–MoS 2 composite coatings are directly used as binder-free electrode, which exhibits outstanding electrocatalytic activity for HER in 1.0 M NaOH solution at room temperature. The Ni–MoS 2 composite coatings demonstrated an outstanding performance toward the electrocatalytic hydrogen production with low overpotential (100 mA cm −2 at η = 207 mV), a Tafel slope as small as 65 mV dec −1 , and stable cycling performance (1200 cycles). The preeminent HER performance of this catalyst suggests that it may hold great promise for practical applications. [ABSTRACT FROM AUTHOR]

Metal Ni is a plentiful resource that can actively split water toward hydrogen evolution reaction (HER) in alkaline solution, but exploiting high-efficiency Ni-based composite catalysts is still a significant assignment. Therefore, we design a catalytic material with one-step approach to co-electrodeposit Ni nanoparticles and reduced graphene oxide (rGO) sheets on a three-dimensional Ni foam. When the carbon content existed in Ni-rGO composite catalyst is 3.335 at%, the catalyst exhibits excellent activity on HER with a low Tafel slope (b = 77 mV dec −1 ), a high exchange current density (j 0 = 3.408 mA cm −2 ), small overpotentials of only 36, 129, and 183 mV to drive 10, 60, and 100 mA cm −2 respectively, and high stability under the different current densities. Such remarkable hydrogen evolution performance is attributed to good electrical conductivity, large specific surface area and harmonious synergistic effect between Ni particles and rGO sheets. In addition, density functional theory (DFT) calculations explain that Ni-rGO composite material presents superior interfacial activity in adsorption/desorption of H* compared with pure Ni and rGO sheet. [ABSTRACT FROM AUTHOR]

Ni–S/CeO 2 composite materials for hydrogen evolution reaction (HER) have been prepared by an electrodeposition method under supergravity field from nickel sulfamate. With the different mass concentrations of CeO 2 , the morphology and X-ray diffraction patterns of Ni–S/CeO 2 are diverse. Apparently, the CeO 2 contents of Ni–S/CeO 2 composite electrodes under supergravity fields are higher than that under normal gravity field. In addition, the HER catalytic activity of Ni–S/CeO 2 composite electrodes can be measured in 1.0 M NaOH at 298 K. The results show that overpotential of Ni–S/CeO 2 electrode of 7 g/L CeO 2 under 3000 rpm is the least, suggesting perhaps too much content of CeO 2 hinder the desorption of H ads , or too little CeO 2 can not play palpable roles in improving the catalytic activity and increasing oxygen vacancies. And the exchange current density j 0 value of Ni–S/CeO 2 composite electrode prepared under the speed of 3000 rpm, which is 1.16 times larger than the Ni–S/CeO 2 of 0 g/L CeO 2 , is 1.9 times higher than that under normal gravity field. EIS results suggest that there exists a synergetic effect on HER between CeO 2 and Ni–S alloy matrix. [ABSTRACT FROM AUTHOR]

In this work, supergravity fields are performed to prepare Ni-CNTs composite cathodes with wool-ball-like morphology from the Watts bath containing well-distributed functionalized CNTs. The prepared Ni-CNTs composite cathodes are used as noble metal-free electrocatalyst with favorable electrocatalytic activity for hydrogen evolution reaction (HER) in alkaline solutions. The crystal structure and morphology of the composite cathodes are characterized by XRD and SEM measurements. The electrochemical activities of the cathodes are characterized through Tafel polarization measurement, electrochemical impedance spectroscopy and cyclic voltammetric study in 1.0 M NaOH solution. The results indicate that catalytic activities of the Ni-CNTs cathodes prepared under supergravity fields are enhanced significantly, and the sample prepared at rotating speed 3000 rpm from the bath containing 1 g dm −3 CNTs exhibits the highest HER activity with smallest Tafel slope and largest exchange current density of 823.9 μA cm −2 . Furthermore, the effects of both the CNTs concentrations and the intensities of supergravity fields on the properties of the Ni-CNTs cathodes are investigated. [ABSTRACT FROM AUTHOR]