Triple-Interface Heterojunctions as an Advanced Strategy for Water Electrolysis

Abstract

Interfacial engineering has emerged as a central strategy for overcoming the intrinsic activity limitations of electrocatalysts for water electrolysis by regulating charge transfer, adsorption energetics, and reaction kinetics. While single-phase catalysts and conventional dual-phase heterojunctions have achieved significant improvements in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), they often struggle to simultaneously optimize the multiple elementary steps inherent to these kinetically complex processes. In this context, triple-interface heterojunctions, in which three distinct solid phases are spatially coupled through interconnected interfacial regions, are emerging as an advanced design strategy for water electrolysis electrocatalysts. Such architectures can enable multidirectional charge redistribution, offer complementary adsorption sites for reaction intermediates, and promote reaction kinetics while maintaining structural robustness under electrochemical operating conditions. This review critically examines the conceptual definition, construction pathways, and mechanistic roles of triple-interface heterojunctions in water electrolysis. Emphasis is placed on formation mechanisms, including ex situ assembly and in situ electrochemical reconstruction, as well as on mechanistic insights derived from operando and in situ characterization that reveal dynamic interfacial evolution during HER and OER. Finally, current challenges, unresolved questions, and future design strategies are discussed to guide the rational development of next-generation triple-interface electrocatalysts capable of efficient water electrolysis.