Mapping the Nucleation of H Bubbles on Polycrystalline Pt via Scanning Electrochemical Cell Microscopy.

Electrochemically generated bubbles are gaining increasing attention for their detrimental effects on the efficiency of electrocatalysis involving gaseous products, including hydrogen evolution reaction (HER). As a model system, bubble nucleation is also of fundamental interest. Herein, we report a single-entity approach to map the nucleation of H bubbles on polycrystalline Pt via scanning electrochemical cell microscopy (SECCM). Individual H bubbles (∼500 nm radius) are generated via HER in the attoliter electrochemical cell of an SECCM instrument. Nucleation and growth of a H bubble results in a characteristic voltammetric peak current, which is related to the concentration and activation energy required for nucleation. By mapping the local voltammograms at various locations on the polycrystalline Pt, we found a heterogeneous distribution of energetics of nucleation for H bubbles on the Pt surface. However, such heterogeneity is not correlated with crystal grains or grain boundaries.