Rate‐Adaptive Site Transformation Catalyst for Parallel Water Dissociation and Hydrogen Adsorption in Alkaline Hydrogen Evolution

ABSTRACT Anion exchange membrane water electrolyzers (AEMWE) offer great potential for large‐scale hydrogen production. However, typical alkaline HER catalysts are inefficient as they employ active sites for both water dissociation and hydrogen adsorption, where competition creates a severe bottleneck. This work presents a rate‐adaptive site transformation design strategy that enables the catalysts to make more active sites available under high demand. The electrocatalyst is synthesized by intercalating a silver‐ethylenediamine complex into layered Co 9 S 8 (AE‐i‐Co 9 S 8 ). Experimental and computational results both reveal that water dissociation preferentially occurs at Co sites adjacent to the intercalant, while H* adsorption occurs on neighboring Co sites without internal competition. In‐situ Raman spectroscopy further uncovers that spare H‐adsorption sites can be activated into secondary H 2 O‐adsorption sites, enabling adaptive rate capability. Remarkably, AE‐i‐Co 9 S 8 achieves an exceptionally low overpotential of 52.2 mV at 50 mA cm −2 , setting a record among Co 9 S 8 ‐based catalysts. This enables a high current density of 4.2 A cm −2 at 2.0 V in an AEMWE system, outperforming Pt/C by 62%, with outstanding stability exceeding 300 h at 1 A cm −2 . This rate‐adaptive strategy distributes the catalytic workload to dedicated sites, adding a new dimension to sustaining high rates in HER catalysts.