Internal stress-free phosphoric acid doped polybenzimidazole membranes for high temperature proton exchange membrane fuel cells

The serious polarization and stability induced by the doped phosphoric acid hinder their practical applications of phosphoric acid-based high-temperature proton exchange membrane fuel cells. Herein, we report that the internal stress inside the phosphoric acid-doped polymer electrolyte membrane generated during membrane formation process is the major driving force for acid leaching that in turn affects the performance, consistency, and stability of the accordingly assembled fuel cells. Based on this finding, we develop an in-situ solution phosphoric acid-doping strategy to fabricate internal stress-free phosphoric acid-doped polybenzimidazole membranes. The specific proton conductivity of optimized membrane reaches 123.1 Scm -2 and remains stable for 1200 h at 160 °C. The thus-assembled fuel cell exhibits extremely low ohmic and concentration polarization, reaching peak power densities of 1.35 and 2.63 Wcm -2 at 160 °C with back pressure of 200 kPa under H 2 /air and H 2 /O 2 conditions, respectively, markedly outperforming the performance of current fuel cells.