Establishing the potential dependent equilibrium oxide coverage on platinum in alkaline solution and its influence on the oxygen reduction

The oxidation process of polycrystalline platinum subjected to alkaline solution is re-examined using a combination of cyclic voltammetry and potential hold techniques in Ar, H2 and O2 purged 0.1 M KOH solution. The hydrogen oxidation reaction is used as a probe for forming a complete OH adlayer, whereas the comparison of cyclic voltammetry with potential hold techniques allows the investigation of the dynamics as well as a charge balance of the processes. Comparing the different findings in a parameterized form, we are able to discern the potential regions of OH and O adlayers as well as PtO formation at quasi steady state conditions: only low amount of OH exists up to 0.7 VRHE. Increasing the potential the OH coverage increases and a OH monolayer is formed at 0.93 VRHE, which gradually further oxidizes to Oad increasing the potential up to 1.08 V, above which PtO oxide is formed. Comparing the oxidation process to the oxygen reduction reaction it is shown that there is a clear correlation between the formation of a full OH adlayer and the inhibition of the oxygen reduction.

► A procedure for studying Pt under quasi steady state conditions is introduced.
► We determine different potential regions of oxide formation.
► A clear correlation between OH adlayer formation and inhibition of the ORR is shown.