A CoMoO₄-Co₂Mo₃O₈ heterostructure with valence-rich molybdenum for a high-performance hydrogen evolution reaction in alkaline solution

The hydrogen evolution reaction (HER) is a promising clean and renewable energy source. Thus, efficient and inexpensive electrocatalysts for the HER have attracted considerable attention. Here, we report a two-step method for the synthesis of a unique CoMoO₄-Co₂Mo₃O₈ heterostructure. The CoMoO₄-Co₂Mo₃O₈ heterostructure exhibited superior HER activity that included a low overpotential of 57 mV, a Tafel slope of 55 mV dec^-1 in a 1 M KOH solution, and excellent long-term stability given its high intrinsic activity and superior conductivity. Density functional theory calculations indicated that CoMoO₄ and Co₂Mo₃O₈ synergistically optimized electron distribution to reduce hydrogen adsorption energy and significantly enhance electrocatalytic activity. Our work may provide novel ideas for improving the HER performance of valence-rich transition element oxides.