Breaking the conductivity-selectivity trade-off in direct methanol fuel cells using oxygen plasma-treated monolayer graphene

Abstract

Direct methanol fuel cells (DMFCs) offer a simpler fuel system than hydrogen fuel cells and hold promise for portable and small-scale power generation. However, the methanol crossover issue of commercial Nafion membranes causes mixed potential in the cathode, lowering open circuit voltage (OCV) and overall performance. While incorporating monolayer graphene into Nafion membranes can mitigate methanol crossover and improve OCV, it often compromises proton conductivity. In this study, we demonstrate that oxygen plasma-treated monolayer graphene embedded in a Nafion membrane enhances both proton conductivity and selectivity. This dual improvement results in a 92.74 % increase in DMFC performance compared to commercial Nafion membranes, with power outputs of 134.56 mW cm⁻² at 60 °C and 254.84 mW cm⁻² at 90 °C. Molecular dynamics simulations indicate that oxygen-containing functional groups introduced through plasma treatment form nanopores that enhance interfacial affinity between graphene and Nafion, leading to better water distribution at the interface and improved proton conduction. This approach effectively breaks the conductivity-selectivity trade-off, offering a viable solution to improve DMFC performance.