Self-assembly of durable Nafion/TiO2 nanowire electrolyte membranes for elevated-temperature PEM fuel cells

TiO2 nanowire-reinforced Nafion composite membranes for elevated temperature fuel cells are developed by self-assembly of positively charged TiO2 nanowires and negatively charged Nafion molecules at low pH value condition. The TiO2 nanowires are synthesized using a hydrothermal process. The Nafion-TiO2 nanowire composite membrane, in which TiO2 nanowires were dispersed uniformly, is prepared by solution-casting assisted with self-assembly. At 50 RH% and 90 °C, the cell assembled with Nafion/TiO2 nanowires composite membranes (5 wt% TiO2) has a relatively stable performance, and achieves a voltage of 0.59 V at a current density of 600 mA cm−2, about 93% of that at 100 RH%. Self-assembly of the TiO2 nanowire also improves the mechanical properties of the composite membrane both at different temperatures and humidity conditions. At the temperature close to the glass transition temperature, the TiO2 nanowires remarkably reinforce the physical dimension of the membrane when the Nafion polymer structure is destroyed. In an in situ RH-cyclic accelerating experiment, the degradation of the open circuit voltage of the fuel cell assembled with Nafion-TiO2 nanowire composite membrane (5 wt%) reaches 6.1 mV/h, compared to 16.3 mV/h for a fuel cell assembled with a recasting of pure Nafion membrane.