Insight into selenium vacancies enhanced CoSe₂/MoSe₂ heterojunction nanosheets for hydrazine-assisted electrocatalytic water splitting

The integration of interface engineering and vacancy engineering was a feasible way to develop highly efficient electrocatalysts toward water electrolysis. Herein, we designed CoSe₂/MoSe₂ heterojunction nanosheets with abundant Se vacancies (V_Se-CoSe₂/MoSe₂) for electrocatalytic water splitting. In the V_Se-CoSe₂/MoSe₂ electrocatalyst, the electrons more easily transferred from CoSe₂ to MoSe₂, and interface engineering not only modulated the electronic structure, but also supplied more heterointerfaces and catalytic sites. After chemical etching, partial Se atoms were eliminated, which further activated the inert plane of the V_Se-CoSe₂/MoSe₂ electrocatalyst and induced electron redistribution. The removal of surface Se atoms was also beneficial to expose inner reactive sites, which promoted adsorption toward reaction intermediates. Density functional theory calculations revealed that interface engineering and vacancy engineering collaboratively optimized the adsorption energy of the V_Se-CoSe₂/MoSe₂ electrocatalyst toward the intermediate H* during the hydrogen evolution reaction process, leading to better electrocatalytic activity. The density of state diagram manifested the refined electronic structure of the V_Se-CoSe₂/MoSe₂ electrocatalyst, and it exhibited a higher electronic state near the Fermi level, which indicated superior electronic conductivity, facilitating electron transport during the catalytic process. In alkaline media, the V_Se-CoSe₂/MoSe₂ electrocatalyst delivered low overpotentials of merely 74 and 242 mV to obtain 10 mA cm^-2 toward hydrogen evolution reaction and oxygen evolution reaction. This work illustrated the feasibility of combining two or more strategies to develop high-performance catalysts for water electrolysis.