Attapulgite solvent-free nanofluids modified SPEEK proton exchange membranes for direct methanol fuel cells

Abstract

Sulfonated poly(ether ether ketone) (SPEEK) is currently considered to be one of the most potential candidates of commercial perfluorinated sulfonic acid proton exchange membranes. Although SPEEK with high sulfonation degree exhibits high proton conductivity, over high content of polar sulfonic groups will lead to over-swelling of membranes, which in turn result in degraded mechanical properties and alcohol resistance. Herein, to balance the overall performance of SPEEK, attapulgite solvent-free nanofluids (ATP-IL) with special flow behavior were prepared for the first time, and then a series of SPEEK/ATP-IL composite membranes were successfully fabricated and evaluated. The grafted organic long-chain ions on the surface of ATP can not only promote the dispersion of ATP in SPEEK matrix, but also endow ATP with proton conduction ability and thus form channel-like proton transport pathway in the composite with the aid of one-dimension shape of ATP. As a result, the composite membranes demonstrated simultaneously improved strength and toughness. Moreover, the maximum conductivity was 50.7 mS cm−1 for the composite membrane with 5 wt% of ATP-IL at 25 °C and 100% R.H., which was 40% higher than that of SPEEK membrane (only 36.4 mS cm−1).