A proton exchange composite membrane (PECM) and a method of synthesizing the membrane are disclosed. The PECM may include a PBI membrane doped with an acid, an imidazolium-based dicationic ionic liquid, and a mesoporous material. This PECM can be used as an improved high-temperature polymer electrolyte membrane (HT-PEM) fuel cell. The disclosed fuel cell can provide improved proton conductivity, acid uptake, and thermal stability.