High-performance fuel cells using Nafion composite membranes with alignment of sulfonated graphene oxides induced by a strong magnetic field

Proton exchange membrane (PEM) is a key component of proton exchange membrane fuel cells (PEMFCs) and provides proton conduction between fuel and oxidant, and it is vitally important and practical to develop PEMs with high proton conductivity through membranes. However, it is still a major challenge to develop such membranes with high through-plane proton conductivity. In this study, Nafion composite membranes with sulfonated graphene oxides (SGOs) were prepared from self-assembly sol-gel either in or not in a strong magnetic field. Microstructures, water uptake, and proton conductivity of the SGO/Nafion composite membranes have been investigated extensively. For the SGO/Nafion composite membranes recast without a magnetic field, it is found that the water uptake and in-plane proton conductivity are greatly increased with the increasing SGO content. Interestingly, SGO/Nafion composite membranes with a low SGO content of ∼ 0.5 wt% exhibit lower crystallinity and higher in-plane proton conductivity. For the SGO/Nafion composite membranes recast in a strong through-plane magnetic field, it is very appealing to find their through-plane proton conductivity is significantly higher than that of the composite membranes recast without a magnetic field. This is attributed to that the protons transport in the membranes preferentially along the water channels primarily interconnected by the aligned SGOs through-plane induced by the strong magnetic field, as confirmed by SEM. Applied in a single PEMFC, the resultant SGO/Nafion composite membrane with 1 wt% SGOs, recast in a strong magnetic field of 1.5 T, demonstrates a high power-density of 1.056 W cm-2, which is far superior to those of pristine Nafion and SGO/Nafion composite membranes recast without a magnetic field. The study provides a novel strategy for preparing proton exchanging membranes with high performances for new-generation fuel cells.