Sulfonated poly(ether ether ketone) membranes crosslinked with sulfonic acid containing benzoxazine monomer as proton exchange membranes

The incorporation of benzoxazine (Ba) or sulfonic acid containing benzoxazine (SBa) as a crosslinking agent in SPEEK proton exchange membrane (PEM) can substantially improve the SPEEK membrane performance. The SPEEK–SBa membranes give higher effective selectivity than corresponding SPEEK–Ba membranes under close crosslinker loading and thus are more suitable to be used in direct methanol fuel cells. The best achieved SPEEK–SBa composition (SBa40) gives reasonable proton conductivity (0.91 × 10−2 S cm−1) but significantly lower methanol permeability (6.5 × 10−8 S2 cm−1). The achieved effective selectivity (Φ = SPEEK–SBa40: 14.0 × 104 S s cm−3) is substantially higher than the plain SPEEK (Φ = 7.24 × 104 S s cm−3) which has great potential for practical applications in DMFCs.