Surface Structure and Grain Boundary Effects on the Oxygen Evolution Reaction at Gold Electrodes.

The surface structure of an electrocatalyst plays a crucial role in determining the activity. As a model system, gold has been widely investigated as an electro-oxidation catalyst, although there has been much less research on the oxygen evolution reaction (OER) in the potential region of gold oxidation. Here, we combine voltammetric scanning electrochemical cell microscopy (SECCM) and electron backscatter diffraction (EBSD), at different spatial and angular resolutions, respectively, to correlate the local crystallographic structure of polycrystalline goldfocusing on grains close to (113), (011), (114), and (111) orientationswith the electrocatalytic behavior for the OER. By recording potential-dependent electrochemical movies, grain-dependent gold oxidation and gold oxide reduction are clearly visualized. In contrast, the OER demonstrates less grain dependence. High-resolution SECCM also provides a powerful way to map the electrochemical activity for OER at grain boundaries, where distinct boundaries exhibit either enhanced or suppressed activity, revealing a strong correlation with the electrochemical active surface area, together with effects from surface roughness and dislocation densities. This latter aspect of the work further emphasizes the important role of grain boundaries in electrocatalysis and the ability of SECCM to directly target and map the activity of these underexplored regions.