Probing the Hydrogen Evolution Reaction and Charge Transfer on Platinum Electrodes on Femtosecond Timescales

Despite much study, the mechanism of the hydrogen evolution reaction (HER) on Pt is still controversial. Part of the challenge is that any comprehensive mechanism may have to describe processes on timescales from femtoseconds (interfacial electron transfer) to milliseconds (ion diffusion). Here we separate these timescales using a femtosecond perturbation approach: we collect cyclic voltammograms from several Pt electrodes with and without femtosecond laser irradiation. We find that laser irradiation at biases near hydrogen evolution lowers the barrier for H-2 generation, while in the H under potential deposition range it induces partial charge transfer along the Pt-H bond and interfacial dipole (re)arrangement. The trend in ultrafast partial charge transfer we measure, Pt(111)<Pt(100)<Pt(110)<< Pt microelectrode, is the same as for H-2 generation suggesting insight into both ultrafast electron transfer and slow double layer structural change is required to describe the HER mechanism.