High Temperature Polymer Electrolyte Membrane Fuel Cells with High Phosphoric Acid Retention

Phosphoric acid loss poses immense hurdles for the durability of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Here we report quaternary ammonium-biphosphate ion-pair HT-PEMFCs that do not lose phosphoric acids under normal and accelerated stress conditions. Our energetics study explains the acid loss behavior of the conventional phosphoric acid-polybenzimidazole (PA-PBI) system by two mechanisms. If PA loss occurs via acid evaporation, the acid loss is constant over time. On the other hand, when water activity in the PA-PBI system is high, exponential decay of PA loss occurs via the water replacement mechanism. Combined 31P NMR and computational studies show that the proposed ion-pair system has six times higher interaction energy, which allows for containing all PAs in the membrane electrode assemblies under a broad range of operating conditions. In addition, polar interactions between the phosphonic acid ionomer and phosphoric acid explain acid retention in the electrodes of the ion-pair HT-PEMFCs.

Automated summary

This article reports quaternary ammonium-biphosphate ion-pair high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) that do not lose phosphoric acids under normal and accelerated stress conditions. Energetics and computational studies show that the proposed ion-pair system has higher interaction energy and allows for containing all phosphoric acids in the membrane electrode assemblies. In addition, polar interactions between the phosphonic acid ionomer and phosphoric acid explain acid retention in the electrodes of the ion-pair HT-PEMFCs.