Ultrasonic Bonding of Membrane Electrode Assemblies for Low Temperature Proton Exchange Membrane Fuel Cells

Abstract

Low temperature proton exchange membrane (PEM) fuel cells currently dominate the fuel cell market, yet there are materials-, cost-, reliability-, and manufacturing-related challenges that hinder widespread commercial success of this promising technology. With regards to manufacturing, one of the main process bottlenecks is thermal bonding of electrode and membrane components into a unitized membrane electrode assembly (MEA). Recent work has shown that ultrasonic bonding can serve as a direct replacement for thermal bonding for high-temperature PEM fuel cells with dramatic reductions in cycle time and energy consumption but no significant degradation in performance. This paper investigates the possible use of ultrasonic bonding for low-temperature PEM MEAs operated at 65 °C. Polarization curves and 1000 Hz impedance were measured for MEAs with a five-layer architecture comprised of Nafion 115 membrane and carbon paper-based gas diffusion electrodes (GDE) that were thermally bonded and ultrasonically bonded using commercial equipment. The effect of membrane condition (conditioned and dry), electrode type (commercially available, custom-made with lower platinum loadings), and process conditions are investigated. Experimental results demonstrate clear trends. Both custom-made GDEs with lower platinum loading performed best suggesting that electrode architecture and composition can be optimized for ultrasonic bonding. There was little difference in performance between dry and conditioned membrane, which helps explain current industrial practice. Statistical analysis of an experimental design where ultrasonic bonding energy and pressure were varied suggests that neither parameter significantly affects MEA performance and that the process is robust. Similar analysis of thermal bonding with temperature and pressure varied suggests that temperature has a significant effect on MEA performance. However, the most important results of all experimentation are that process cycle time and energy consumption are reduced by nearly two orders-of-magnitude using ultrasonic bonding.