Low temperature, proton exchange membrane fuel cells (PEMFC) are one of the promising and much investigated electrochemical energy conversion devices as a solution to the enormous world energy consumption demand. Hydrogen and methanol fuelled cells are of particular interest because of their high efficiency and low emission. However commercialization of these cells is hindered by their high cost, which mostly comes from the noble platinum catalyst and conventional Nafion membrane electrolyte. Research to reduce the amount of Pt by dispersing onto, high surface area support materials or to replace with non-precious catalysts have been studied widely to achieve minimal (~ µg_Pt/cm² loading) expenditure in this area. However, an alternative to expensive Nafion is still a challenge.

In our previous work [1], we have shown that the incorporation of monolayer graphene (grown on copper foil by chemical vapour deposited (CVD) method) on the membrane electrode assembly (MEA) reduces the problematic methanol crossover in a direct methanol fuel cell by 26 % without affecting the proton conductivity [2]. 45 % improvement in the fuel cell performance for the single layer graphene (SLG) fused cell was achieved in comparison to the cell without SLG [1].

Herein we report two approaches as an alternative to completely replace the solid Nafion membrane in PEMFC. In the first method, SLG incorporated direct membrane deposited [3] MEA is used in the cell. The thickness of the modified electrolyte layer was controlled and optimized by varying the quantity of used Nafion ionomer and scanning electron microscope (SEM) image analysis. Cheaper polybenzimidazole (PBI) membrane is used as the mechanical backing support for the SLG and used to assemble the MEA in conventional method for the second route. Polarization curve, linear sweep voltammetry, impedance spectroscopy and durability testing is implemented to test the practical fuel cell performance for the systems. Obtained results are analysed, compared and discussed with respect to thickness, fuel crossover and membrane resistance for the modified electrolyte cells over conventional solid membrane cell.

References

[1] Stuart M. Holmes, Orabhuraj Balakrishnan, Vasu. S. Kalangi, Xiang Zhang, Marcelo Lozada-Hidalgo, Pulickel M Ajayan, Rahul R. Nair., 2D Crystals Significantly Enhance the Performance of a Working Fuel Cell. Advanced Energy Materials 7 (2017) 1601216.

[2] S. Hu, M. Lozada-Hidalgo, F. C. Wang, A. Mishchenko, F. Schedin, R R. Nair, E. W. Hill, D. W. Boukhvalov, M. I. Katsnelson, R. A. W. Dryfe, I. V. Grigorieva, H. A. Wu, A. K. Geim, Proton transport through one-atom-thick crystals. Nature 516 (2014) 227-230.

[3] M. Klingele, M. Breitwieser, R. Zengerle, S. Thiele, Direct deposition of proton exchange membranes enabling high performance hydrogen fuel cells. Journal of Materials Chemistry A 3 (2015) 11239-11245.