Hydroxyl-mediated hydrogen spillover across spatially decoupled Co(OH)2@Mo2C tandem electrocatalyst

Alkaline hydrogen evolution reaction (HER) is constrained by the Sabatier principle, making it challenging to simultaneously optimize water dissociation and hydrogen desorption. Here, we report a spatially decoupled tandem catalyst, Co(OH) 2 @Mo 2 C, that circumvents this constraint via a hydroxyl-mediated hydrogen spillover pathway. Mo 2 C serves as the *H generation site via rapid water dissociation, while adjacent Co(OH) 2 functions as the *H acceptor and recombination center, with abundant surface hydroxyl groups on Co(OH) 2 accelerating hydrogen spillover from Mo 2 C to Co(OH) 2 and sustaining water dissociation kinetics. CH 3 I poisoning experiments, corroborated by in situ Raman spectroscopy and density functional theory calculations, reveal the critical mediating role of hydroxyl groups in hydrogen migration. The optimized catalyst achieves only 43 mV overpotential to reach 10 mA cm −2 in 1 M KOH, and durability over 150 h at 0.5 A cm −2 in an anion exchange membrane water electrolyzer. This work establishes a generalizable interfacial engineering strategy to circumvent the Sabatier limitation by accelerating hydrogen migration on spatially segregating elementary steps. A spatially decoupled Co(OH) 2 @Mo 2 C tandem electrocatalyst shows that Mo 2 C rapidly dissociates water while Co(OH) 2 efficiently shuttles *H to accelerate H 2 release, where Co(OH) 2 abundant surface hydroxyl groups accelerate hydrogen spillover from Mo 2 C to Co(OH) 2 and maintain water dissociation kinetics. Download: Download high-res image (179KB) Download: Download full-size image