Disentangling effects of pH, potential, and cation concentration in cathodic corrosion of platinum

Cathodic corrosion concerns the electrochemical etching of metals at negative polarization. While this process is detrimental for electrode stability and lifetime, the mechanism responsible for etching has not yet been fully elucidated. In this work, we determine the potential at which signs of cathodic corrosion on platinum electrodes are observed for different aqueous electrolytes, varying bulk pH and cation concentration. From cyclic voltammetry, we find that typical indicators of cathodic corrosion roughening the surface always appear at the same potential with respect to the standard hydrogen electrode, irrespective of the electrolyte. In contrast, we observe from microscopy that the degree of etch pit formation is strongly determined by the cation concentration. This therefore separates potential-induced effects of surface roughening from the rate of cation-mediated dissolution. The electrolyte-independent onset potential reveals aspects of the underlying corrosion mechanism, and our results are discussed in terms of the different roles of the electrolyte components at the interface.