Electrocatalytic water splitting is considered to be one of the most promising technologies for large-scale sustained production of H2. Developing non-noble metal-based electrocatalytic materials with low cost, high activity and long life is the key to electrolysis of water. Transition metal sulfides (TMSs) with good electrical conductivity and a tunable electronic structure are potential candidates that are expected to replace noble metal electrocatalysts. In addition, self-supported electrodes have fast electron transfer and mass transport, resulting in enhanced kinetics and stability. In this paper, TMS self-supported electrocatalysts are taken as examples and their recent progress as hydrogen evolution reaction (HER) electrocatalysts is reviewed. The HER mechanism is first introduced. Then, based on optimizing the active sites, electrical conductivity, electronic structure and adsorption/dissociation energies of water and intermediates of the electrocatalysts, the article focuses on summarizing five modulation strategies to improve the activity and stability of TMS self-supported electrode electrocatalysts in recent years. Finally, the challenges and opportunities for the future development of TMS self-supported electrodes in the field of electrocatalytic water splitting are presented. This paper summarizes five strategies for improving the activity and stability of transition metal sulfide self-supported electrodes. The key problems and challenges for the future development of electrocatalysts for the HER are also presented.

The construction of highly active non-precious-metal electrocatalysts is the key to achieving an efficient hydrogen evolution reaction (HER). In this paper, a N-doped carbon layer composite was successfully synthesized by a self-limiting domain carbon thermal reduction strategy, in which the carbon layer was embedded with Ni/VN heterogeneous nanoparticles and Ni metal nanoclusters as well as anchored with many highly active Ni single atoms (denoted as Ni/VN/Ni-NC). The optimized Ni/VN/Ni-NC provides an abundance of active sites and high conductivity to facilitate efficient charge and mass transfer. And the electronic structure of Ni/VN heterostructures is optimized by the complementary effects of 3d orbital electrons, which contribute to the HER kinetics. The Ni/VN/Ni-NC exhibits excellent HER performance (without iR compensation) at a current density of 10 mA cm(-2) with overpotentials of 84 mV (1 M KOH solution) and 166 mV (1 M PBS solution).

The synergistic effect of a highly active surface/interface and an optimized electronic structure of electrocatalysts is of great significance to improve the performance of the hydrogen evolution reaction. Herein, a superhydrophilic core@shell heterostructure nanorod-integrated electrode composed of an amorphous VOx nanoshell (3-7 nm) and a crystalline Ni3S2 core supported on Ni foam (CS-NS/NF) was prepared by an in situ conversion method. We prove that the amorphous VOx not only helps to kinetically decouple the adsorption/dissociation of hydroxyl/water, but also enriches the active sites, thereby significantly enhancing the electron transfer efficiency and electrocatalytic activity toward the hydrogen evolution reaction (HER). The optimized CS-NS/NF has excellent hydrogen production performance, with overpotentials of 335 and 394 mV at current densities of 500 and 1000 mA cm(-2), respectively, as well as superior durability for over 68 h in 1 M KOH.