Incorporation of titanium pyrophosphate in polybenzimidazole membrane for medium temperature dry PEFC application

Abstract In the interest of adopting acid-modified metal oxide additives in polymer electrolyte membrane fuel cell membrane, titanium pyrophosphate (TiP2O7) was synthesized via direct modification of TiO2-P25 with 85% orthophosphoric acid (stochiometric ratio of P/Ti = 2.0) using a modified synthesis path and calcined at 600 °C for 5 h. Low amounts of TiP2O7 (1 and 2 wt%) were successfully introduced into polybenzimidazole (PBI), upon confirmation by FT-IR and SEM-EDS. The obtained membranes were doped with 8 mol phosphoric acid doping level (PADL) prior to proton conductivity measurement under dry condition from 160 to 50 °C. Among the measurements, the highest conductivity was obtained by PBI with 1 wt% TiP2O7, which was 3.85 mScm−1 at 160 °C, followed by PBI with 2 wt% TiP2O7 (2.69 mScm−1). Both samples exhibited higher conductivity compared to PBI with 2 wt% TiO2 (2.03 mScm−1) and pristine PBI (1.53 mScm−1). For the fuel cell performance under the same condition, PBI with 2 wt% TiP2O7 achieved a maximum power density of 580 mWcm−2 at 160 °C, outperformed PBI with 2 wt% TiO2 (524 mWcm−2), PBI with 1 wt% TiP2O7 (497 mWcm−2) and pristine PBI 454 mWcm−2. Acid leaching test and long term stability evaluation with 0.2 Acm−2 constant current density test revealed that TiP2O7 inherited the acid retention ability of TiO2 while the pyrophosphate group significantly improved the proton conductivities of composite membrane.