Phosphate-Modified TiO 2 /ZrO 2 Nanofibrous Web Composite Membrane for Enhanced Performance and Durability of High-Temperature Proton Exchange Membrane Fuel Cells

An Aquivion/titanium zirconium oxide nanofibrous web composite membrane was prepared and tested as a proton exchange membrane in a hydrogen/air fuel cell. The incorporation of a small dose (9 wt % membrane) of a uniformly distributed electrospun titanium zirconium oxide (TiO 2 /ZrO 2; Ti/Zr = 1:1 atomic ratio) nanofibrous web significantly improved hydromechanical stability of the composite membranes, which exhibited approximately 2 times higher water retention and 30 times lower dimensional change than a pristine Aquivion membrane under in-water membrane hydration conditions. Phosphate functionalities were successfully added onto the nanofiber surface, as confirmed by X-ray photoelectron spectroscopy (XPS) analysis. The added phosphate functionality resulted in higher proton conductivity of the prepared composite membrane compared to the non-modified TiO 2 /ZrO 2 nanofibrous web composite membrane [e.g., 0.027 S cm –1 versus 0.021 S cm –1 at 120 °C and 40% relative humidity (RH)]. A single cell test also showed the effect of an added TiO 2 /ZrO 2 nanofibrous web. A single cell with an Aquivion/TiO 2 /ZrO 2 nanofibrous web composite membrane outperformed a single cell with a pristine Aquivion membrane in fully humidified conditions (100% RH at 75 and 90 °C). The Aquivion/phosphate-modified TiO 2 /ZrO 2 nanofibrous web composite membrane showed the best single cell performance at all four testing conditions, including the fully humidified medium-temperature conditions (e.g., P max = 1.18 W cm –2 at 75 °C and 100% RH, and P max = 0.97 W cm –2 at 90 °C and 100% RH) and partially humidified high-temperature conditions ( P max = 0.45 W cm –2 at 120 °C and 40% RH, and P max = 0.21 W cm –2 at 140 °C and 20% RH). The composite membrane also displayed excellent durability evidenced by the accelerated lifetime (ALT) test results. Overall, the phosphate-modified TiO 2 /ZrO 2 nanofibrous web composite membrane enhanced the electrical properties and durability of the fuel cell, especially at high temperatures (>120 °C).