Proton conductivity of graphene-based Nafion® catalyst layer for polymer electrolyte membrane fuel cell
Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are the most assuring alternative power sources for a clean energy/environmental future, however, performance needs to be improved for large-scale commercialization. One of major current technical challenges is limited proton conductivity in catalyst layers. Recent emerging material, i.e., graphene, has a great potential to improve key transport properties including proton conductivity throughout the unique two dimensional structure, large effective surface area, and anticipated enhanced surface transport phenomena. Graphene, carbon black (CB) and carbon nano tubes (CNT) are used as additives in the catalyst layer in order to improve and compare the proton conductivity. The additives were implemented to the Nafion® solution variable wt. %, which were sprayed over Nafion® membrane as test samples. For the proton conductivity measurement, the test samples were sandwiched between the two electrodes maintaining a uniform pressure to ensure the uniform mechanical/electrical contact between the electrodes and samples. This cell assembly was tested using a potentiometer, and the obtained impedance was analyzed through the Nyquist plot at specified conditions of current voltage range. The experimental results show that the proton conductivity enhancement increases with the increasing graphene content. The enhancement is also compared to those of CB- and CNT-based membrane, showing that graphene-based Nafion® membrane provides higher proton conductivity than the CB-based Nafion® membrane. This may be related to the unique graphene structures, and the further studies will be needed to articulate the role of the graphene on the proton conductivity. The results thus obtained, provide an insight into finding an optimal material for improving the proton transport of PEM aiming at the optimal catalyst layer material design.