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

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 degrees 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 degrees C. Among the measurements, the highest conductivity was obtained by PBI with 1 wt% TiP2O7, which was 3.85 mScm(-1) at 160 degrees 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, FBI with 2 wt% TiP2O7 achieved a maximum power density of 580 mWcm(-2) at 160 degrees C, outperformed PBI with 2 wt% TiO2(524 mWcm PBI with 1 wt% TiP2O7 (497 mWcm(-2)) and pristine FBI 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.