A review on the hydrogen spillover effect for boosting the electrocatalytic hydrogen evolution reaction.

Abstract

Hydrogen spillover effect (HSE) has emerged as an important interfacial transport paradigm that connects hydrogen activation on metal sites with utilization on adjacent supports, enabling multi-site cooperative electrocatalysis for the hydrogen evolution reaction (HER). By spatially coupling hydrogen generation, interfacial migration, and recombination, HSE provides a promising route to overcome limitations imposed by hydrogen adsorption scaling relationships. However, it remains a qualitatively recognized yet quantitatively underdefined phenomenon, particularly regarding interfacial hydrogen migration mechanisms and its contribution to catalytic performance. This review critically summarizes recent progress in HSE-enabled HER catalysts, focusing on mechanistic understanding, advanced characterization techniques, and rational design strategies. We highlight experimental and operando methods, including spectroscopy, isotope-tracing, electrochemical analysis, and theoretical modeling, for probing hydrogen migration pathways. Representative catalyst systems spanning metal-oxide, hydroxide, carbide, sulfide, phosphide, and metallic interfaces are discussed, emphasizing interfacial electronic coupling and hydrogen transport behavior. Key design principles are distilled, including work function regulation, pathway shortening, interface engineering, and single-atom construction. Finally, we discuss remaining challenges in unambiguous identification, quantitative description, and realistic modeling of HSE. We propose that HSE should be recognized as a general multi-site hydrogen transport mechanism, and that integrating operando characterization with predictive theory is essential for rational catalyst design and next-generation HER optimization.