Ultrasonic bonding of low temperature PEM membrane electrode assemblies has shown to cut the cycle time and energy input of manufacturing by over an order of magnitude each as compared to the industry standard of thermal pressing. Ultrasonic bonding uses high-frequency mechanical oscillations to convert electrical energy into heat energy which bonds the membrane electrode assembly components. This reduction in manufacturing resource requirement and time helps make fuel cell energy more economical as an alternative electrical power source. This paper will discuss ultrasonic and thermal bonding for low temperature Nafion fuel cells with 10 cm2 active area including process optimization and the effects of electrode type and membrane conditioning on ultrasonically bonded MEA performance.
A design set of experiments was created for both ultrasonic bonding and thermal pressing process optimization using commercially available electrodes and conditioned Nafion 115 membrane. Analysis of Variance suggests that neither energy nor pressure have a statistically significant effect on the performance on ultrasonically bonded MEAs. For thermally pressed MEAs, temperature was found to have a significant effect on performance while pressure was not. Neither manufacturing technique found interaction effects to be statistically significant.
Three different electrode compositions were tested on both ultrasonic and thermal MEA bonding methods. Electrodes investigated include two that were custom made in-house with catalyst loadings of 0.16 and 0.33 mg Pt/cm2, and one commercial electrode with 0.5 mg Pt/cm2. The lower loaded custom electrode had greater performance than the commercial electrode, which had higher platinum loading, indicating electrode architecture is an important factor in the performance of ultrasonically bonded MEAs.
Membrane electrode assemblies made using Nafion membranes that were pretreated with a conditioning process showed decreased performance compared to MEAs ultrasonically bonded from dry, unconditioned membrane in short-term testing. MEAs thermally pressed with the custom made electrodes performed better with conditioned membranes while the commercial electrodes showed decreased performance with conditioning.
Current electrodes have been optimized for thermal pressing as demonstrated by the two commercial electrodes having the largest performance decreases between thermally and ultrasonically manufactured MEAs. Future work includes intelligently designing an electrode for optimizing the ultrasonic bonding process for low temperature fuel cells to increase the performance of this manufacturing technique.