Modelling and simulation of the degradation of perfluorinated ion-exchange membranes in PEM fuel cells

Abstract

A polymer-electrolyte membrane fuel cell model that incorporates chemical degradation in perlfluorinated sulfonic acid membranes is developed. The model is based on conservation principles and includes a detailed description of the transport phenomena. A degradation sub-model describes the formation of hydrogen peroxide \/\it via\/ distinct mechanisms in the cathode and anode, together with the subsequent formation of radicals \/\it via\/ Fenton reactions involving metal-ion impurities. The radicals participate in the decomposition of reactive end groups to form carboxylic acid, hydrogen fluoride and CO_2. Degradation proceeds through unzipping of the polymer backbone and cleavage of the side chains. Simulations are presented and the numerical code is shown to be extremely time efficient. Known trends with respect to operating conditions are qualitatively captured and the exhibited behaviour is shown to be robust to changes in the rate constants. The feasibility of a chemical degradation mechanism based on peroxide and radical formation is discussed