Combined potential routines involving voltammetric sweeps and potential holdings covering the H-adatom potential range were applied to Pt electrodes in different aqueous acid solutions to produce an enhancement of the "third" H-atom electrodesorption current peak at ca. 0.22 V vs. RHE. This peak can be observed for Pt electrodes of different topographies. Seemingly, the corresponding cathodic current contribution appears in a potential range slightly more positive than the hydrogen evolution reaction threshold potential. The peak potential difference related to the conjugated redox reactions is consistent with an appreciable irreversibility of the process. The small charge involved in this pair of peaks is expected from a subsurface and an interstitial H-adatom state on Pt. This type of structure has been predicted from quantum chemistry calculations.
platinum electrodes; hydrogen evolution; H-adatoms; third H-adatom current peak
