Triple-interface heterojunctions as an advanced strategy for water electrolysis

Abstract

Interfacial engineering has emerged as a central strategy for enhancing electrocatalytic water electrolysis by regulating charge transfer, adsorption energetics, and reaction kinetics. However, despite extensive studies on single-phase catalysts and dual-phase heterojunctions, both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remain kinetically limited, largely due to the inability of conventional architectures to simultaneously optimize multiple elementary steps. While multicomponent systems are increasingly reported, a clear conceptual framework distinguishing electronically coupled triple-interface heterojunctions from simple multiphase composites lacking interfacial cooperativity has yet to be established. In this context, triple-interface heterojunctions, comprising three distinct solid phases that generate multiple interconnected interfacial coupling pathways, have recently emerged as a promising yet insufficiently understood design paradigm. Unlike conventional heterostructures, their functionality is generally associated with cooperative interfacial effects, enabling multidirectional charge redistribution, complementary adsorption environments, and coordinated reaction pathways. This review provides a critical and systematic analysis of triple-interface heterojunctions in water electrolysis. We establish an inclusive conceptual framework and distinguish them from conventional multiphase systems, followed by a classification based on interfacial connectivity and formation pathways. We further analyze their mechanistic roles in regulating charge transfer, intermediate adsorption, and reaction kinetics, with particular emphasis on insights obtained from in situ and operando characterization. Finally, we identify current limitations, unresolved questions, and future design strategies to guide the rational development of next-generation electrocatalysts.