Modelling of Radical Reactions at Platinum Deposits in Polymer Electrolyte Membranes

Abstract

Hydroxyl radicals are the leading cause of chemical degradation observed in polymer electrolyte membranes (PEM). Recent experimental studies have shown that Pt nano-deposits in the PEM (PITM), which originate from Pt dissolution in the catalyst layer, could play a dual role in radical-initiated membrane degradation [1]. Surface reactions at Pt particles could facilitate the formation as well as the scavenging of radicals. The net effect of Pt surface processes on the radical balance depends on the local equilibrium conditions around the Pt nano-deposits, specifically, their equivalent local electrode potential [2]. In this presentation, we will first discuss the potential distribution at PITM as a function of externally controlled thermodynamic conditions. Thereafter, we will present a Density Functional Theory investigation of the surface reactions at the Pt(111)|water interface that involve O2, H2O, H2O2 and OH radical species. We calculate the effective rates of radical production at PITM by incorporating the local conditions obtained in the above steps. The results are compared to experimental measurements of fluoride emission under varying pressure settings in Pt impregnated PEMs.