Carbon Nanofiber-Based Thin Gas Diffusion Layers for Polymer Electrolyte Fuel Cells

In polymer electrolyte fuel cells (PEFCs), mass transport is directly related to energy conversion efficiency, limits chemical reaction rates, and determines the output voltage and power density. Recently, there has been increasing demand for a thinner gas diffusion layer (GDL) to further improve FC performance, the power density per unit volume of the cell stack. Herein, we prepared carbon nanofiber (CNF) nonwoven sheets with a mean diameter of 510 nm, 90% porosity, and a mean pore size of 2.5 μm for the GDL substrate and investigated the effect of the thin CNF substrate on the electrochemical properties and initial PEFC performance, including liquid water accumulation. The 50 μm-thick CNF-based cathode GDL within the fuel cell outperformed the commercial 150 μm-thick carbon paper-based cathode GDL, particularly at high current densities. The improved performance of the CNF-based GDL was mainly attributed to a reduced diffusion overpotential, indicating enhanced mass transport within the GDL. The CNF-based GDL also improved the oxygen transport property and facilitated the diffusion of water vapor from the catalyst layer into the channels due to the thin substrate with high porosity. X-ray imaging clearly showed a significant reduction in liquid water accumulation within the CNF-based GDL. These results demonstrate that a thinner bilayer GDL composed of a CNF substrate and a microporous layer is a promising option as a practical GDL in PEFCs.