Mo³⁺ hydride as the common origin of H₂ evolution and selective NADH regeneration in molybdenum sulfide electrocatalysts

Hydride transfers are key to a number of economically and environmentally important reactions, including H₂ evolution and NADH regeneration. The electrochemical generation of hydrides can therefore drive the electrification of chemical reactions to improve their sustainability for a green economy. Catalysts containing molybdenum have recently been recognized as among the most promising non-precious catalysts for H₂ evolution, but the mechanism by which molybdenum confers this activity remains debated. Here we show the presence of trapped Mo³⁺ hydride in amorphous molybdenum sulfide (a-MoS_x) during the hydrogen evolution reaction and extend its catalytic role to the selective hydrogenation of the biologically important energy carrier NAD to its active 1,4-NADH form. Furthermore, this reactivity applies to other HER-active molybdenum sulfides. Our results demonstrate a direct role for molybdenum in heterogeneous H₂ evolution. This mechanistic finding also reveals that molybdenum sulfides have potential as economic electrocatalysts for NADH regeneration in biocatalysis. [Figure not available: see fulltext.]