Operando visualization of the hydrogen evolution reaction with atomic-scale precision at different metal–graphene interfaces

The development of catalysts for the hydrogen evolution reaction is pivotal for the hydrogen economy. Thin iron films covered with monolayer graphene exhibit outstanding catalytic activity, surpassing even that of platinum, as demonstrated by a method based on evaluating the noise in the tunnelling current of electrochemical scanning tunnelling microscopy. Using this approach, we mapped with atomic-scale precision the electrochemical activity of the graphene–iron interface, and determined that single iron atoms trapped within carbon vacancies and curved graphene areas on step edges are exceptionally active. Density functional theory calculations confirmed the sequence of activity obtained experimentally. This work exemplifies the potential of electrochemical scanning tunnelling microscopy as the only technique able to determine both the atomic structure and relative catalytic performance of atomically well-defined sites in electrochemical operando conditions and provides a detailed rationale for the design of novel catalysts based on cheap and abundant metals such as iron.