Sulphonated tetramethyl poly(ether ether ketone)/epoxy/sulphonated phenol novolac semi-IPN membranes for direct methanol fuel cells

The sulphonated phenol novolac (PNBS) which was used as a curing agent of epoxy was synthesised from phenol novolac (PN) and 1, 4-butane sultone and confirmed by FTIR and ¹H NMR. The degree of sulphonation (DS) in PNBS was calculated by ¹H NMR. The semi-IPN membranes composed of sulphonated tetramethyl poly(ether ether ketone) (STMPEEK) (the value of ion exchange capacity is 2.01 meq g^-1), epoxy (TMBP) and PNBS were successfully prepared. The semi-IPN membranes showed high thermal properties which were measured by differential scanning calorimeter (DSC) and thermogravimetric analyses (TGA). With the introduction of the cross-linked TMBP/PNBS, the mechanical properties, dimensional stability, methanol resistance and oxidative stability of the membranes were improved in comparison to the pristine STMPEEK membrane. Although the proton conductivities of the semi-IPN membranes were lower than those of the pristine STMPEEK membrane, the higher selectivity defined as the ratio of the proton conductivity to methanol permeability was obtained from the STMPEEK/TMBP/PNBS-14 semi-IPN membrane. The results indicated that the semi-IPN membranes could be promising candidates for usage as proton exchange membranes in direct methanol fuel cells (DMFCs).