Poly(ether imide) (PEI) membranes for polymer electrolyte membrane fuel cells (PEMFCs) are prepared by the electrospinning method. This approach produces a membrane with a high porosity and surface area that is suitable for accommodating proton-conducting materials. A composite membrane was prepared by impregnating the pores of the electrospun PEI membrane with Aquivion ionomer. Then, an inorganic proton conductor in the form of SiO2/heteropolyacid (HPA) nanoparticles was prepared by a microemulsion process and the particles added to the Aquivion ionomer. The membranes were characterized by field emission scanning electron microscopy (FE-SEM) and single-cell performance testing for PEMFC. The durability of the composite membrane was assessed via accelerated lifetime and on/off tests. The ionomer-impregnated electrospun PEI membrane showed good thermal stability, satisfactory mechanical properties, and high proton conductivity. The addition of the SiO2/HPA nanoparticles improved the proton conductivity of the composite membrane, thereby allowing the operating temperature in low humidity environments to be extended. The composite membrane exhibited promising properties for application in high-temperature PEMFCs.