  Laterally nanostructured surfaces give rise to a new dimension of
understanding and improving electrochemical reactions. In this study, we
present a peculiar mechanism appearing at a metal/insulator interface, which
can significantly enhance the Hydrogen Evolution Reaction (HER) from water
reduction by altering the local reaction conditions in two ways: facilitated
adsorption of hydrogen on the metal catalyst surface and improved transfer of
ions through the double layer. The mechanism is uncovered using electrodes
consisting of well-defined nanometer-sized metal arrays (Au, Cu, Pt) embedded
in an insulator layer (silicon nitride), varying various parameters of both the
electrode (size of the metal patches, catalyst material) and the electrolyte
(cationic species, cation concentration, pH). In addition, simulations of the
electrochemical double layer are carried out, which support the elaborated
mechanism. Knowledge of this mechanism will enable new design principles for
novel composite electrocatalytic systems.
