A simple and fast diagnostic tool has been developed for analyzing polymer-electrolyte fuel-cell degradation. The tool is based on analyzing changes in polarization curves of a cell over its lifetime. The shape of the polarization-change curve and its sensitivity to oxygen concentration are found to be unique for each degradation pathway based on analysis from a detailed 2-D numerical model of the cell. Using the polarization-change curve methodology, the primary mechanism for degradation (kinetic, ohmic, and/or transport related) can be identified. The technique is applied to two sets of data to explain performance changes after two different cells undergo voltage-cycling accelerated stress test, where it is found that changes are kinetic and then ohmic or transport in nature depending on the cell type. The diagnostic tool provides a simple method for rapid determination of primary degradation mechanisms. Areas for more detailed future investigations are also summarized. Polymer-electrolyte fuel cells (PEFCs) have gained increasing interest as an efficient energy-conversion technology.1 However, further improvements in PEFC performance and durability are desired.
2While inventing new materials and cell architectures are crucial in enhancing PEFC performance and durability, developing new diagnostics techniques is equally important to understand the phenomena controlling the cell performance at the beginning of life (BOL) and after degradation, or at end of life (EOL). To study the durability of difference PEFC materials, several accelerated-stress-test (AST) protocols have been developed. 3 The ASTs are helpful in simulating and enhancing the underlying stressors that the cell may experience over its lifetime.Performance degradation during PEFC lifetime can happen due to changes of different cell components via multiple decay mechanisms. These mechanisms result in increases in overpotential due to: a) kinetics, b) ohmic, c) transport, or d) crossover. Some common examples of each of these performance-loss categories include: a) kinetic losses from reduction in catalyst area, which can happen due to sintering, dissolution, contamination, and oxidation; 2,4-6 b) ohmic losses from irreversible ionomer degradation or loss in connectivity, thermal effects, and ion contamination; 7,8 c) transport losses from changes in hydrophobicity, porosity loss from carbon corrosion, layer delamination, etc.; 7,9,10 and d) reactant losses and mixed potentials from increased crossover, which is primarily due to membrane thinning and pinhole formation. 11,12 There are a plethora of diagnostic methods to analyze PEFC degradation mechanisms, 2,7,12-15 e.g., cyclic volammetry, impedance spectroscopy, oxygen-gain analysis, and X-ray tomography to name a few. While these methods can provide detailed analysis on the reasons for performance degradation during PEFC operation, they can be time and capital expensive. Furthermore, most of the diagnostic methods are suitable to investigate only a single phenomenon in detail. Since the degradat...