Failure Point Analysis of Membrane Electrode Assemblies with Coating Irregularities

Cost has been one of the primary barriers to the commercialization of polymer electrolyte membrane fuel cells (PEMFCs), clean energy conversion devices used primarily for power generation applications. While system design improvements and the development of novel electrode materials with increased activity have helped lower costs, the primary driver of cost reduction will be manufacturing membrane electrode assemblies (MEAs) at high volume [1]. Recently developed in-line diagnostic tools to monitor quality have successfully detected a variety of electrode coating variations [2]. This work studies a subset of these electrode irregularities fabricated onto MEAs operating under accelerated stress tests (ASTs) to simulate stresses of real-world driving conditions while spatially monitoring the onset and development of failure points with a thermal camera. An understanding of the impact that electrode irregularities have on MEA lifetime will subsequently allow for (i) the potential classification of these irregularities as defects and (ii) the development of threshold detection limits for in-line quality control diagnostics. Catalyst-coated membranes (CCMs) and gas-diffusion electrodes (GDEs) were fabricated with an ExactaCoat Sono-Tek ultrasonic spray system. The active area and nominal loading of these Pt/C electrodes were 50 cm2 and 0.2/0.2 mgPt/cm2, respectively. Membrane material was NRE-212. These layers were laminated into edge-protected MEA structures using a hot-pressing process. The MEA structures were exposed to a combined chemical and mechanical AST by operating the fuel cell at 80°C and 0.5/0.5 SLM H2/Air under open circuit potential (OCV), and cycling between 0 and 80% relative humidity for a 30 second duty cycle. The hydrogen crossover limiting current and the OCV were indicators for a developing failure and the presence of a failure, respectively. A novel cell hardware shown in figure (a) was used to remove the cathode flow-field and conduct a spatial hydrogen crossover measurement. Any hydrogen crossing from the anode to the cathode exothermically reacts at the cathode catalyst with ambient air to produce a heat signature that is detected with the thermal camera [3]. Higher crossover rates at for example discrete failure points become apparent through a significant local temperature rise. Sample results of a pristine MEA tested as described above are shown in the figures. The graph (b) shows the hydrogen crossover limiting current density rapidly increasing after the OCV declined with an increasing rate. This indicated that the MEA developed a failure point. The images show the thermal response during the spatial hydrogen crossover measurements for the pristine MEA (c) prior to and (d) subsequent to aging. The heat signature indicated a failure point developed near the inlet of the cell. Results will include studies on MEA structures with intentionally and systematically introduced coating variations of various sizes and severities. References 1) S. Kamaruzzaman, and W.R. Daud. Renewable Energy 31.5 (2006). 2) M. Ulsh and B. Sopori and N.V. Aieta and G. Bender. ECS Transactions 50.2 (2013). 3) G. Bender and W. Felt, and M. Ulsh. Journal of Power Sources 253 (2014). Figure 1