Fabrication of Foamed Polyethersulfone–Zeolite Mixed Matrix Membranes for Polymer Electrolyte Membrane Fuel Cell Humidification

Polymer electrolyte membrane (PEM) fuel cell efficiency must be improved in order to become cost competitive with fossil fuel-based technologies. Approaches to increasing cost efficiency include raising fuel cell operating temperature, reducing component cost, and properly controlling fuel cell humidification. We sought to fulfill all three requirements by developing a new low-cost, high-temperature humidification membrane material. Currently, Nafion dominates the membrane humidifier market due to its excellent water transport characteristics, but its high price (∼$1000/m²) and low maximum operating temperature (<90 °C) drive up fuel cell cost. We developed a competing polyethersulfone (PES)–zeolite mixed matrix membrane (MMM) with a porous microstructure. Solvent casting was used to form the initial PES–zeolite films, followed by solid-state foaming to alter the film morphology and create a porous structure. The effects of both zeolite weight loading and foaming duration on membrane permeability were investigated. Membrane measurement results show that both foaming and increased zeolite weight loading enhance membrane water permeability close to levels seen in Nafion. Meanwhile, the membranes satisfy the Department of Energy (DOE) crossover gas requirement for humidification membrane materials.