Thermodynamic and Kinetic Effects at the Onset of Cathodic Corrosion on 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. Our results are discussed in terms of the different roles of the electrolyte components at the interface, and can be interpreted as a ‘stability-diagram’ for platinum electrodes at cathodic polarization.