Development of In Situ Formed Metal Pyrophosphates (MP₂O₇, Where M = Sn, Ti, and Zr)/PA/PBI Based Composite Membranes for Fuel Cells

Abstract Development of high temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) at elevated temperatures is important for the enhancement of tolerance toward CO impurities and for the development of non‐precious metal catalysts. The key challenge in such HT‐PEMFCs is the high temperature polymer electrolyte membranes. Herein, the development of in situ formed metal pyrophosphates (MP₂O₇, where M = Sn, Ti, and Zr) in phosphoric acid doped polybenzimidazole (PA/PBI) composite membranes for HT‐PEMFCs is reported. The formation mechanism of MP₂O₇, and characteristics of MP₂O₇/PA/PBI composite membranes are studied in detail. In contrast to the rapid decay in performance of pristine PA/PBI membrane cells, the in situ formed MP₂O₇/PA/PBI composite membranes show significantly higher proton conductivity, improved performance, and stability at elevated temperatures of 200–250 °C. The best results are obtained on the in situ formed SnP₂O₇/PA/PBI composite membrane cells, exhibiting a high peak power density of 476 mW cm⁻² and proton conductivity of 51.3 mS cm⁻¹ at 250 °C. The excellent durability of SnP₂O₇/PA/PBI composite membrane is due to the uniform distribution of in situ formed SnP₂O₇ nanoparticles in PBI membranes and the formation of a gel‐like region, thin and irregular amorphous layer on the SnP₂O₇ with the high acid retention ability. This effectively alleviates the PA leaching at elevated temperatures of the new HT‐PEMFCs.