Redefining the determinant of apparent electrocatalytic hydrogen evolution in alkaline media

The complex multicomponent interactions in realistic electrochemical hydrogen evolution reaction significantly challenge the conventional theoretical frameworks established relying on simplified binary adsorption models, resulting in the discrepancy between the theoretical intrinsic activity and apparent activity due to the absence of the local mass transport factors. The underlying governing principles of the apparent catalytic activity is still unclear. Herein, by experimentally quantifying interfacial mass transfer kinetics of platinum group metals in alkaline media, we have established a robust positive correlation between local proton conduction and apparent activity, thereby redefining the key factor in practical hydrogen electrocatalysis. The essence underlying the hierarchal interplay is attributed to the catalyst intrinsic property-induced regulation of the interfacial hydrogen-bond microenvironment. Its unique volcanic domination to proton transport demonstrates the trade-off between connectivity and flexibility of proton-hopping pathways. The definition and mechanistic comprehension of local proton mass transport as the bridge linking surface-interface characteristics to macroscopic electrochemistry offer a transformative approach to resolving the long-standing challenge of identifying performance determinant for apparent electrocatalytic systems.