Correlation between Gas Bubble Formation and Hydrogen Evolution Reaction Kinetics at Nanoelectrodes.

Abstract

We report the correlation between H2 gas bubble formation potential and hydrogen evolution reaction (HER) activity for Au and Pt nanodisk electrodes (NEs). Microkinetic models were formulated to obtain the HER kinetic information for individual Au and Pt NEs. We found that the rate-determining steps for the HER at Au and Pt NEs were the Volmer step and the Heyrovsky step, respectively. More interestingly, the standard rate constant ( k0) of the rate-determining step was found to vary over 2 orders of magnitude for the same type of NEs. The observed variations indicate the HER activity heterogeneity at the nanoscale. Furthermore, we discovered a linear relationship between bubble formation potential ( Ebubble) and log( k0) with a slope of 125 mV/decade for both Au and Pt NEs. As log ( k0) increases, Ebubble shifts linearly to more positive potentials, meaning NEs with higher HER activities form H2 bubbles at less negative potentials. Our theoretical model suggests that such linear relationship is caused by the similar critical bubble formation condition for Au and Pt NEs with varied sizes. Our results have potential implications for using gas bubble formation to evaluate the HER activity distribution of nanoparticles in an ensemble.