Novel covalent-ionically cross-linked membranes with extremely low water swelling and methanol crossover for direct methanol fuel cell applications

In this paper, a sulfonated poly(arylene ether ketone) bearing carboxylic acid groups (C-SPEEK) was first synthesized. Then a new series of covalent-ionically cross-linked membranes using a poly(ether ether ketone) bearing amino groups (Am-PEEK) as a cross-linker were prepared for direct methanol fuel cell applications. Lower water swelling and lower methanol permeability membranes with higher mechanical strength were obtained via this covalent-ionically cross-linking method. The cross-linked network structure greatly improved the thermal and oxidative stability as compared to C-SPEEK membrane. The proton conductivity of C-SPEEK/Am-PEEKs was lower than that of non-cross-linked membrane, but its selectivity was higher. The properties of the cross-linked membranes in particular C-SPEEK/Am-PEEK-10 were investigated to confirm their potential applicability in fuel cells.

Research highlights▶ C-SPEEK, as the hydrophilic part, and Am-PEEK, as a cross-linkable moiety were synthesized. ▶ Lower water swelling and lower methanol permeability membranes with higher mechanical strength were obtained via covalent-ionically cross-linking method. ▶ The cross-linked network structure greatly improved the thermal and oxidative stability as compared to C-SPEEK membrane. ▶ C-SPEEK/Am-PEEK-10 showed the best membrane performances among the cross-linked membranes.