Kinetic study of electrochemically produced hydrogen bubbles on Pt electrodes with tailored geometries

Abstract

Understanding bubbles evolution kinetics on electrodes with varied geometries is of fundamental importance for advanced electrodes design in gas evolution reaction. In this work, the evolution kinetics of electro-generated hydrogen bubbles are recorded in situ on three (i.e. smooth, nanoporous, and nanoarray) Pt electrodes to identify the geometry dependence. The bubble radius shows a time-dependent growth kinetic, which is tightly-connected to the electrode geometry. Among the three electrodes, the smooth one shows a typical time coefficient of 0.5, in consistence with reported values; the nanoporous one shows a time coefficient of 0.47, less than the classic one (0.5); while the nanoarray one exhibits fastest bubble growth kinetics with a time coefficient higher than 0.5 (0.54). Moreover, the nanoarray electrode has the smallest bubble detachment size and the largest growth coefficient (23.3) of all three electrodes. Based on the experimental results, a growth model combined direct bottom- injection with micro-convection is proposed to illustrate the surface geometry dependent coefficients, i.e., the relationship between geometry and bubble evolution kinetics. The direct injection of generated gas molecules from the bottom of bubbles at the three phase boundaries are believed the key to tailor the bubble wetting states and thus determine the bubble evolution kinetics.