Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

With the increasing demands in energy consumption and increasing environmental concerns, it is of vital significance for developing renewable and clean energy sources to substitute traditional fossil fuels. As an outstanding candidate, hydrogen is recognized as a green energy carrier due to its high gravimetric energy density, zero carbon footprints, and earth-abundance. Currently, water splitting in alkaline electrolytes represents one of the most promising methods for sustainable hydrogen production, and the key challenge lies in the development of high-performance electrocatalysts for the hydrogen evolution reaction (HER). Given the rapid advances in the design and development of efficient catalysts towards the alkaline HER, especially capable transition metal (TM)-based materials, this review aims to summarise recent progress in the theoretical understanding of the alkaline HER and TM-based electrocatalysts. TM-based catalysts classified by their different anionic compositions (metals, alloys, oxides, hydroxides, sulfides, selenides, tellurides, nitrides, phosphides, carbides, and borides) are comprehensively showcased. Special attention is given to mainstream strategies that can improve the catalytic properties of each category, as well as the underlying structure–activity regimes. Additionally, the challenges for the future development of novel catalysts are also analyzed.

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Recent advances in transition metal-based electrocatalysts for alkaline hydrogen evolution

Electrochemical water splitting has been highly valued as a clean and sustainable method to produce hydrogen with high purity and large quantity. Platinum (Pt) possesses excellent performance for hydrogen evolution reaction (HER), however, the expensiveness and rareness still restricts its broad application. Here, an environmentally-friendly and template-free method is developed to synthesize N-doped molybdenum carbide in three different forms: nanobelts, nanorods and nanoparticles. During the synthesis, no additional acid or alkali aqueous solution is used and the morphology is controlled by adjusting water content and treatment time. The corresponding physicohemical and electrochemical results display that the nanobelts with porous nanostructure exhibit excellent activity and good stability for HER both in acidic and alkaline electrolytes. In the latter case (1.0 M KOH aqueous solution), nanobelts show a small onset potential value (–52 mV), yield a current density of 10 mA cm−2 at a relatively low overpotential (110 mV) and exhibit a low Tafel slope (49.7 mV dec−1). From the obtained results is deduced that this is a facile way to prepare cost-effective molybdenum carbide with high efficiency for hydrogen evolution.

N-Doped Porous Molybdenum Carbide Nanobelts as Efficient Catalysts for Hydrogen Evolution Reaction

The sluggish water dissociation kinetics of low-cost Ni3S2 electrocatalysts severely hinders the hydrogen evolution reaction (HER), resulting in unsatisfied overall water splitting in alkaline media. Herein, we demonstrate the self-assembly of a new nanoforest electrocatalyst by ultrathin Ni(OH)2/Ni3S2 heterogeneous nanosheets (∼1.8 nm) using a high-temperature and large-potential electrodeposition technique. The surface atomic configuration of Ni3S2 is well-modulated by hetero-interface engineering with the Ni(OH)2 cocatalyst, effectively accelerating the Volmer step and OH− adsorption during the HER without sacrificing the oxygen evolution reaction (OER). The resultant electrocatalysts exhibit superior and stable electrocatalytic activity toward the HER and OER in 1 M KOH with small overpotentials of 50 mV and 210 mV at 10 mA cm-2, respectively. Using the Ni(OH)2/Ni3S2 nanoforest as dual-functional electrocatalysts, an alkaline electrolyzer can render 100 mA cm-2 at a very low cell voltage of 1.64 V while keep stable for 120 h at 1.55 V, which outperforms the best report for Ni-based electrocatalysts. This finding gives a new insight into the modulating surface atomic configuration for achieving highly active electrocatalysts for water splitting.

Heterogeneous interface engineered atomic configuration on ultrathin Ni(OH)2/Ni3S2 nanoforests for efficient water splitting

Recent progress on earth abundant electrocatalysts for hydrogen evolution reaction (HER) in alkaline medium to achieve efficient water splitting – A review

Electrochemical water splitting has been highly recognized as a clean and sustainable method to produce hydrogen with high purity. An one-pot method to synthesize boron-doped RhFe alloy with excellent catalytic performance for hydrogen evolution is reported in the present work. Rhodium-Iron (RhFe) alloy nanoparticles, with diameter ranging from 1 to 5 nm, are distributed uniformly on the carbon support. The corresponding physicochemical and electrochemical results display that the sample of Rh:Fe = 2:1 post-treated at 200 °C (BRF21) shows the best performance for hydrogen evolution in 0.5 M H2SO4 aqueous solution; it exhibits good catalytic activity at a near zero onset potential. The required overpotential is found to be of about 25 mV at a current density of 10 mA cm–2, which is 4 mV less than that of commercial Pt/C (29 mV); the Tafel slope is also comparable (32 mV dec–1) with Pt/C (30 mV dec–1). This work may provide a facile and environmentally-friendly method to prepare B-doped catalysts with high electrochemical hydrogen evolution efficiency.

One-pot synthesized boron-doped RhFe alloy with enhanced catalytic performance for hydrogen evolution reaction

Remarkably efficient PtRh alloyed with nanoscale WC for hydrogen evolution in alkaline solution

The invention discloses a preparation method of a nitrogen-doped nano catalyst adopting a double-shell-layer structure The method comprises the following operation steps: (1) a carrier and a metal precursor are added to a solvent and stirred, a reducing agent is added for reduction, filtration, cleaning and drying are performed, and a primary product is obtained; (2) the primary product is placed in a high-temperature reaction furnace, gas is introduced for calcination, and a nitrogen-doped nano alloy catalyst is obtained; (3) dealloying treatment is performed and the nitrogen-doped nano catalyst adopting the double-shell-layer structure is obtained The oxygen reduction quality activity of the catalyst at 09 V is 5-19 times that of a commercial 20wt% Pt/C catalyst, the catalyst prepared with the method has higher oxygen reduction catalytic performance, and a technological foundation is laid for mass application of proton exchange membrane fuel cells

Preparation method of nitrogen-doped nano catalyst adopting double-shell-layer structure

Hydrogen energy is considered one of the cleanest and most promising alternatives to fossil fuel because the only combustion product is water. The development of water splitting electrocatalysts with Earth abundance, cost-efficiency, and high performance for large current density industrial applications is vital for H2 production. However, most of the reported catalysts are usually tested within relatively small current densities (< 100 mA cm−2), which is far from satisfactory for industrial applications. In this minireview, we summarize the latest progress of effective non-noble electrocatalysts for large current density hydrogen evolution reaction (HER), whose performance is comparable to that of noble metal-based catalysts. Then the design strategy of intrinsic activities and architecture design are discussed, including self-supporting electrodes to avoid the detachment of active materials, the superaerophobicity and superhydrophilicity to release H2 bubble in time, and the mechanical properties to resist destructive stress. Finally, some views on the further development of high current density HER electrocatalysts are proposed, such as scale up of the synthesis process, in situ characterization to reveal the micro mechanism, and the implementation of catalysts into practical electrolyzers for the commercial application of as-developed catalysts. This review aimed to guide HER catalyst design and make large-scale hydrogen production one step further.

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Lishang Zhang

Papers

N-Doped Porous Molybdenum Carbide Nanobelts as Efficient Catalysts for Hydrogen Evolution Reaction

One-pot synthesized boron-doped RhFe alloy with enhanced catalytic performance for hydrogen evolution reaction

Remarkably efficient PtRh alloyed with nanoscale WC for hydrogen evolution in alkaline solution

Preparation method of nitrogen-doped nano catalyst adopting double-shell-layer structure

Design Strategies for Large Current Density Hydrogen Evolution Reaction