Quantification on Degradation Mechanisms of Polymer Electrolyte Membrane Fuel Cell Catalyst Layers during an Accelerated Stress Test

Abstract

The long-term durability of the catalyst layers of a low-working temperature fuel cell such as a polymer electrolyte membrane fuel cell (PEMFC) is of significant scientific interest because of their operation criteria and high initial cost. Identification of degradation mechanisms quantitatively during an accelerated stress test (AST) is essential for assessing and improving the durability of such catalyst layers. In this study, we present a quantitative analysis of the degradation mechanisms such as (i) electronic connectivity loss due to carbon support corrosion, (ii) proton connectivity loss due to ionomer/catalyst interface loss, (iii) catalyst loss due to dissolution or detachment, and (iv) physical surface area loss due to particle growth that is responsible for the electrochemical surface area (ECSA) loss in Pt-based catalyst layers for PEMFCs during an AST performed through potential cycling (linear sweep cyclic voltammetry) between 0.4 and 1.6 V for 7000 cycles in Ar-saturated 1 M H2SO4. Using a half-membrane electrode assembly (half-MEA), where a gas diffusion electrode with genuine three-phase boundaries is used as a working electrode through a solid electrolyte, we have observed the ECSA loss due to ionomer/catalyst interface loss and identified a catalyst heterogeneous degradation pattern during an AST. Results suggest a significant ECSA loss due to catalyst isolation (∼64% of ECSA loss) from loss of electron and proton connectivities by catalyst support corrosion (∼45%) and ionomer/catalyst interface loss (∼19%), followed by particle growth (∼30%) and dissolution/detachment (6%). Such knowledge and methodology can effectively contribute to catalyst material screening and electrode structure development to advance the PEMFC technology.