HER-Driven Hydrogenation Promotes HER Electrocatalyst in Alkaline Media: A Case Demonstration of Heterocrystalline NiMo Alloy.

While operating alkaline water electrolysis, the hydrogen evolution reaction (HER) naturally produces abundant surface hydrogen species, creating an intrinsic chance for the catalyst to hydrogenate and activate itself. For Ni-based non-noble-metal catalysts, which are theoretically hydrogenatable, the ability to autonomously enhance their catalytic activity through the HER itself provides a new paradigm for catalyst design and operation. Herein, we demonstrate this self-hydrogenation concept using a heterocrystalline NiMo alloy electrodeposited on nickel foam (NiMo-NF) as a model HER catalyst. Benefiting from a dual-active-site architecture, the NiMo-NF catalyst undergoes in situ electrochemical hydrogenation under working conditions. Specifically, amorphous domains form metal-OH bonds that accelerate water dissociation and generate a locally hydrogen-rich environment, within which the crystalline-phase sites become hydrogenated. This structural evolution optimizes hydrogen adsorption energetics and shifts the reaction pathway from the Heyrovsky to the more efficient Tafel mechanism. As a result, the hydrogenated NiMo-NF electrode exhibits exceptional HER performance in alkaline media, requiring only 178 mV of overpotential to deliver 1000 mA cm-2. When implemented as the cathode in an alkaline electrolyzer, it achieves 1 A cm-2 at merely 1.73 V in 30 wt% KOH at 80°C and maintains excellent durability for over 2400 h under industrially relevant conditions.