Sulfonated holey graphene oxide paper with SPEEK membranes on its both sides: a sandwiched membrane with high performance for semi-passive direct methanol fuel cells

The sandwiched membrane which consists of the sulfonated holey graphene oxide paper with the deposition of the sulfonated poly(ether ether ketone) (SPEEK/SHGO/SPEEK) membrane on its both sides has been prepared. This membrane is reported to have higher proton conductivity (155.6 +/- 1.6 mS cm(-1)), but lower methanol permeability (7.05 +/- 0.21 x 10(-6) cm(2) s(-1)) than Nafion (R) 112 at 80 degrees C, whose respective values are 138.6 +/- 1.4 mS cm(-1) and 15.40 +/- 0.46 x 10(- 6) cm(2) s(-1), respectively. The specific structure of the SHGO comprising the sulfonated and holey graphitic plane plays an important role in the high performance of the SPEEK/SHGO/SPEEK membrane. First, the sulfonated structure could increase the overall density of the sulfonic acid groups in the membranes, which increases the number of proton exchange groups participating in the proton transport. Second, the holey structure of the SHGO provides an additional path for the proton transport, which well avoids the blockage of the proton transport by the high aspect ratio graphitic planes. Third, the sulfonated and holey structure could also increase the interlayer spacing of the graphitic planes in the SHGO paper, which would promote the proton transport as well. Finally, the presence of the SHGO paper with the layer-by-layer stacked graphitic plane would effectively retard the diffusion of methanol through the membrane. When evaluated in the semi-passive direct methanol fuel cell (DMFC), the cell with the SPEEK/SHGO/SPEEK membrane shows higher stability and exhibits a maximum power density 61.1% higher than with Nafion (R) 112, which strongly suggests that the SPEEK/SHGO/SPEEK membrane could be used as the proton exchange membrane for DMFCs. (C) 2017 Elsevier Ltd. All rights reserved.