Thin membranes with Cu-ion crosslinking for high temperature polymer electrolyte membrane fuel cells

High-temperature polymer electrolyte membrane fuel cells offer inherent impurity tolerance and simplified thermal/water management. However, conventional phosphoric acid-doped membranes must be relatively thick (typically >50 μm) to counteract H 3 PO 4 -induced mechanical degradation, leading to ohmic losses that limit fuel cell performance. Here we report a 20-μm-thin, mechanically robust phosphoric acid-doped membrane incorporating dynamic Cu-ion crosslinking for high-power-density high-temperature polymer electrolyte membrane fuel cells. The dynamic Cu-polymer coordination establishes dynamic crosslinking networks that provide exceptional toughness and extensibility, alongside spontaneous self-healing capability. Simultaneously, the Cu ions improve H 3 PO 4 retention and proton dissociation through electrostatic interactions and polarization of O–H bonds in H 3 PO 4 molecules. The resulting thin membranes exhibit minimal ohmic resistance (0.06 Ω cm 2 ) while maintaining low H 2 crossover current density (0.95 mA cm −2 ). Fuel cells incorporating this membrane achieved a peak power density of 3.08 W cm −2 at 200 °C (H 2 /O 2 ), with negligible degradation over 503 h at 1.0 A cm −2 and 160 °C.