Cation Effect on the Electrochemical Platinum Dissolution

Ensuring the stability of electrocatalysts is paramount to the success of electrochemical energy conversion devices. Degradation is a fundamental process involving the release of positively charged metal ions into the electric double layer (EDL) and their subsequent diffusion into the bulk electrolyte. However, despite its vital importance in achieving prolonged electrocatalysis, the underlying causality of catalyst dissolution with the EDL structure remains largely unknown. Here, we show that electrochemical Pt dissolution is strongly influenced by the identity of the alkali metal cation (AM⁺) in the electrolyte. By monitoring Pt dissolution in real-time, we found a trend of reduced Pt leaching in the sequence Li⁺ > Na⁺ > K⁺ > Cs⁺. Our computational predictions suggest that interfacial OH^- concentration plays a pivotal role in Pt dissolution, where OH^- facilitates the outward diffusion of dissolved Pt ions into the bulk electrolyte by neutralizing the Pt species, thereby screening the migration force for their redeposition. Combined with this theoretical result, we verify a strong correlation between the amount of dissolved Pt and the hydrolysis pK_a or acidity of AM⁺, indicating that the AM⁺ identity determines the local OH^- concentration and thereby modifies the amount of Pt dissolution. Our results underscore the need to tune the EDL structure to achieve durable electrocatalysis, a promising area for future research.