Angstrom‐Scale Electrochemistry at Electrodes with Dimensions Commensurable and Smaller than Individual Reacting Species

In nature and technologies, many chemical reactions occur at interfaces with dimensions approaching that of a single reacting species in nano‐ and angstrom‐scale. Mechanisms governing reactions at this ultimately small spatial regime remain poorly explored because of challenges to controllably fabricate required devices and assess their performance in experiment. Here we report how efficiency of electrochemical reactions evolves for electrodes that range from just one atom in thickness to sizes comparable with and exceeding hydration diameters of reactant species. The electrodes are made by encapsulating graphene and its multilayers within insulating crystals so that only graphene edges remain exposed and partake in reactions. We find that limiting current densities characterizing electrochemical reactions exhibit a pronounced size effect if reactant's hydration diameter becomes commensurable with electrodes’ thickness. An unexpected blockade effect is further revealed from electrodes smaller than reactants, where incoming reactants are blocked by those adsorbed temporarily at the atomically narrow interfaces. The demonstrated angstrom‐scale electrochemistry offers a venue for studies of interfacial behaviors at the true molecular scale.