Voltammetric and Scanning Electrochemical Microscopy Investigations of the Hydrogen Evolution Reaction in Acid at Nanostructured Ensembles of Ultramicroelectrode Dimensions: Theory and Experiment

Abstract

Mechanistic studies of the hydrogen evolution reaction (HER) on nanoelectrode ensembles of ultramicroelectrode dimensions (UME-NEEs) are demonstrated using addressable nanoelectrode membrane arrays (ANEMAs). A kinetic model considering simultaneous occurrence of all elementary steps and the effects of mass transport to/from the UME-NEE surface was developed and used to interpret HER steady-state voltammograms (SSVs). The analysis accounts for the effect of fraction of covered area, f, and roughness factor, fR, of the nanoelectrodes on HER SSVs and illustrates the roles of these parameters in mechanistic studies of electrocatalyzed multistep reactions on UME-NEEs. The behavior of bare Au UME-NEEs was studied in acid solution, and characterization of the HER on these electrodes was performed by SSV and scanning electrochemical microscopy (SECM) in the substrate generation-tip collection mode (SG-TC). The activity of Au NEEs for the HER was found to be similar to that of macrosized polycrystalline Au. Selective electrodeposition of Pt NPs was performed on Au UME-NEEs, and SSV was used to study the kinetic mechanism of the HER in acid on the Pt-modified UME-NEEs with different f values. UME-NEEs with excess Pt showed HER activity equivalent to polycrystalline Pt, while those with small, almost undetectable, amounts of Pt showed HER behavior that could not be explained as the addition of pure Au and pure Pt contributions. SECM activity screening on Pt-modified ANEMAs detected changes in the apparent electrocatalytic activity for the HER, in agreement with corresponding SSVs.