Overcoming the Conductance versus Crossover Trade-off in State-of-the-Art Proton Exchange Fuel-Cell Membranes by Incorporating Atomically Thin Chemical Vapor Deposition Graphene
Nicole K. Moehring, Abdul Bashith Mansoor Basha, Pavan Chaturvedi, Thomas F. Knight, Xiaozong Fan, Peter N. Pintauro, Michael S. H. Boutilier, Kunal Karan, Piran R. Kidambi
Abstract
High Resolution Image Download MS PowerPoint Slide Permeance–selectivity trade-offs are inherent to polymeric membranes. In fuel cells, thinner proton exchange membranes (PEMs) could enable higher proton conductance and increased power density with lower area-specific resistance (ASR), smaller ohmic losses, and lower ionomer cost. However, reducing thickness is accompanied by an increase in undesired species crossover harming performance and long-term efficiency. Here, we show that incorporating atomically thin monolayer graphene synthesized via scalable chemical vapor deposition (CVD) and tunable defect density into PEMs (Nafion, ∼5–25 μm thick) can allow for reduced H 2 crossover (∼34–78% of Nafion of a similar thickness) while maintaining adequate areal proton conductance for applications (>4 S cm –2 ). In contrast to most prior work using >50 μm symmetric Nafion sandwich structures, we elucidate the interplay of graphene defect density and Nafion proton transport resistance on the performance of Nafion|graphene composite membranes and find high-quality low-defect density CVD graphene (G) supported on Nafion 211 (∼25 μm); i.e., N211|G has a high areal proton conductance (∼6.1 S cm –2 ) and the lowest H 2 crossover (∼0.7 mA cm –2 ). Fully functional centimeter-scale N211|G fuel-cell membranes demonstrate performance comparable to that of state-of-the-art Nafion N211 at room temperature as well as standard operating conditions (∼80 °C, ∼150–250 kPa-abs) with H 2 /air (power density ∼0.57–0.63 W cm –2 ) and H 2 /O 2 feed (power density ∼1.4–1.62 W cm –2 ) and markedly reduced H 2 crossover (∼53–57%).