Multistep Kinetic Models for Oxygen Reduction Reaction and Platinum Dissolution in Polymer Electrolyte Membrane Fuel Cell

Abstract

Oxygen electrochemistry on platinum comprises of three well-known phenomena - oxygen reduction reaction (ORR), platinum oxide growth and reduction during cyclic voltammetry (CV) and logarithmic growth of oxides potentiostatically at high potentials. Many of the elementary reaction steps are common to the three reaction systems but usually separate kinetic models for the three phenomena are reported in the literature. In this thesis, we present a single reaction framework comprising multistep mechanism, that captures the key characteristics of ORR, CV and potentiostatic oxide growth. Comparison between experimental data and proposed model as well as other models is presented in this work. Furthermore, a mechanism for platinum dissolution was developed within the reaction framework. The proposed dissolution model captured transient platinum dissolution trends reported experimentally. Finally, an impedance model for the cathode catalyst layer was developed assuming the agglomerate structure. Analytical solution to oxygen transport within the catalyst agglomerate were derived.