The Hydrogen Evolution Reaction at a Silver Nanoparticle Array and a Silver Macroelectrode Compared: Changed Electrode Kinetics between the Macro- and Nanoscales

Abstract

The hydrogen evolution reaction (HER) is based on the electroreduction of protons (H+) at a metal electrode surface. We compare this reaction at the macro- and nanoscales. For the latter, silver nanoparticles were synthesized via citric reduction of AgNO3 and arrays constructed by modification of a basal plane pyrolytic (BPPG) electrode with the colloidal suspension. We report the reduction of protons at these silver nanoparticle arrays, for three sizes of AgNPs, over a range of surface coverages, under conditions where the electrolysis occurs exclusively at the nanoparticles and not at the underlying BPPG electrode. A clear relationship exists between peak potential for the reduction and the corresponding increase in the extent of surface coverage on the substrate electrode. The cyclic voltammetry (CV) of H+ reduction was numerically simulated for regular and random distributions of nanoparticles allowing for contrasting diffusional effects between the macroelectrode and the nanoparticle arrays. Such simulation facilitates quantification of kinetic parameters, viz., the electrochemical rate constant of the electron transfer and the transfer coefficient. Fitting of the experimental data demonstrated a distinction between the transfer coefficient and standard electrochemical rate constants at a silver macrodisc electrode (αmacrodisk ≈ 0.36, ko = 6 × 10−12 cm s−1) and that at a NP-array (αarray ≈ 0.16, ko = 1 × 10−6 cm s−1), indicating a specific nanoeffect at the array in the sense of overall significantly changed electrode kinetics operating at the nanoscale as compared to the macroscale.