Probing Electrocatalytic Gas Evolution Reaction at Pt by Force Noise Measurements. Part 1. Hydrogen

Electrocatalytic processes occurring at a heterogeneous interface are complex, and their understanding at the molecular level remains challenging. Atomic force microscopy (AFM) can detect force interactions down to the atomic level, but so far it has been mainly used to obtain <i>in situ</i> images of electrocatalysts. Here, for the first time, we employ AFM to investigate gas evolution at a platinum ultramicroelectrode (Pt UME) under electrochemical conditions using force noise measurements. We detect excess force noise when individual H₂ gas bubble nucleation, growth, and detachment events occur at the Pt UME. Based on our <i>in situ</i> AFM, electrochemical, and optical microscopy analyses, we conclude that larger size H₂ gas bubbles remain pinned to the UME surface while smaller H₂ gas bubbles are released until an overpotential of -0.8 V vs RHE. This study demonstrates the viability of <i>in situ</i> AFM in studying gas evolution under electrocatalytic conditions and contributes to a mechanistic understanding of the H₂ gas bubble detachments during the hydrogen evolution reaction (HER).