Approaches towards the development of heteropolyacid-based high temperature membranes for PEM fuel cells

Operating proton exchange membrane fuel cells (PEMFCs) at higher temperatures (above the boiling point of water) offer several advantages. It enhances the electrodes' kinetics, allows the recovery of useful heat, and offers better water management due to the for-mation of water in the vapor phase. There is a crucial need to either, modify the existing perfluorosulfonic acid membranes (i.e. Nafion) or develop a new class of membranes that can withstand higher temperature operation. Heteropolyacids (HPAs) represent a class of inorganic materials that have been investigated as additives in PEMFCs membranes for the purpose of: 1) enhancing the proton conductivity and, 2) reducing the fuel crossover. This review focuses on discussing the recent developments attained upon the introduction of HPAs in proton exchange membranes. The review summarized the various efforts made on either modifying the existing Nafion membranes with HPAs, or by immobilizing them in other polymers such as PBI and SPEEK. Remarkable enhancements in proton conductiv-ities, as well as a significant reduction in fuel crossover, were reported. However, the leaching of HPAs is still a major obstacle. The current review concludes that the successful implementation of HPAs in PEMFCs membranes can be achieved upon developing proper immobilization techniques within the polymers' matrix. & COPY; 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

Operating PEMFCs at higher temperatures offers benefits such as enhanced kinetics, heat recovery, and better water management. However, existing membranes need modification or new membranes need to be developed to withstand high temperature operation. Heteropolyacids (HPAs) have been investigated as additives in PEMFCs membranes to improve proton conductivity and reduce fuel crossover. Successful implementation of HPAs requires proper immobilization techniques in the polymer matrix.