Breaking the kinetic pH effect in hydrogen evolution via strain-induced interfacial water reorganization

Abstract

The long-unresolved non-Nernstian kinetic pH effect in the hydrogen evolution reaction, manifested as the order-of-magnitude kinetic gap between acidic and alkaline media, underlies the substantial activity gap between these electrolytes. While theoretical paradigms propose interfacial water reorganization as essential for mitigating pH-dependent kinetics, the development of practical systems to precisely manipulate this microenvironment while breaking the inherent trade-off between activity and stability remains a formidable challenge, hindering a comprehensive understanding of the mediating role of the interfacial microenvironment. Herein, the engineering of grain-boundary-rich electrocatalysts provides a well-defined system to precisely decouple and modulate the interfacial microenvironment. A combination of in situ spectroscopy and theoretical simulations reveals that grain-boundary-induced strain regulates surface oxophilicity, thereby strategically modulating the connectivity of interfacial hydrogen-bond networks rather than merely altering intrinsic reaction energetics. This enhanced connectivity fosters a local microenvironment that facilitates water and proton transfer, enabling nearly pH-independent kinetics with unprecedented gap factors approaching unity. At the device level, an anion exchange membrane water electrolyzer utilizing the optimized GB-PtIr@CNT cathode delivers a current density of 2 A cm-2 at only 1.84 V, while maintaining robust stability for 1,000 h at 1 A cm-2. These findings underscore grain boundary engineering as a robust strategy for the precise tailoring of electrochemical interfaces, offering a pathway to accelerate pH-dependent reaction kinetics.