Co-filling of ZIFs-derived porous carbon and silica in improvement of sulfonated poly(ether ether ketone) as proton exchange membranes for direct methanol fuel cells

This work reports on the co-filling of sulfonated zeolitic imidazolate framework-derived porous carbon (ZIF-CSO3H) and sulfonated silica (SSiO2) to improve the performance of the sulfonated poly(ether ether ketone) (SPEEK) membrane. Dependent on the individual properties of the ZIF-C-SO3H and the SSiO2, the obtained SSiO2 and ZIF-C-SO3H filled SPEEK (SSiO2/ZIF-C-SO3H@SPEEK) membrane with the optimum weight percentages of the ZIF-C-SO3H and the SSiO2 shows higher proton conductivity and lower methanol permeability than Nafion 115. The high performance of the SSiO2/ZIF-C-SO3H@SPEEK membrane mainly originates from its co-filled structure. Specifically, the ZIF-C-SO3H filling improves the proton conductivity and lowers methanol permeability, and the SSiO2 filling further lowers methanol permeability of the SSiO2/ZIF-C-SO3H@SPEEK membrane. Additionally, the specific interactions of the ZIF-C-SO3H and the SSiO2 with the SPEEK matrix also endue the SSiO2/ZIF-C-SO3H@SPEEK membrane with improved mechanical and oxidation stabilities and good durability towards the acid etching. When used in direct methanol fuel cells (DMFCs), the SSiO2/ZIF-C-SO3H@SPEEK membrane can exhibit a maximum power density of 128.6 +/- 4.6 mW cm(-2), which is similar to twice that of Nafion 115. The result strongly suggests the great potential of using the SSiO2/ZIF-C-SO3H@SPEEK membrane as a proton exchange membrane for the DMFC.