Physicochemical Properties of Short-Side-Chain Perfluorosulfonic Acid Membranes at Elevated Temperatures

Abstract

Water and CO2 electrolysis at elevated temperature in cells equipped with short-side-chain perfluorosulfonic acid membranes could potentially allow for new approaches to tune catalyst kinetics and selectivity, but the membrane characteristics under such conditions remain to be described. In this work, a short-side-chain perfluorosulfonic acid membrane (Aquivion) is characterized at temperatures up to 150 °C at high humidification levels with respect to tensile behavior, ionic conductivity, permeability of hydrogen and methanol, and stability. The membrane is found to retain mechanical robustness at temperatures up to at least 130 °C while dehydration at temperatures above 100 °C under ambient pressure results in a significant conductivity decay. The densification of the membrane matrix at temperatures above the boiling points of water under varied pressures leads to the reduced hydrogen and methanol permeability. Pressurization up to 5 bar effectively mitigates the conductivity decay due to the presence of liquid water but also results in increased permeability. The membrane stability test, as characterized by hydrogen crossover measurements, shows the humidification is a harsher stressor than temperature in the studied range.

Keywords: Short-side-chain perfluorosulfonic acid, elevated temperature and pressure, conductivity, permeability, tensile strength