Electrospun Nanofiber Electrodes for High and Low Humidity PEMFC Operation

MEAs with nanofiber mat electrodes containing Pt/C catalyst and Nafion binder were fabricated and evaluated. The electrodes were prepared by electrospinning a solution of catalyst powder, salt-form Nafion (with Na⁺, Li⁺, or Cs⁺ as the sulfonic acid counterion), and a carrier polymer of either polyethylene oxide or poly(acrylic acid). The carrier polymer was extracted prior to MEA testing by a hot water soaking step. The resulting fibers were 15%-17% porous, with a core-shell-like morphology (a coating of primarily Nafion on the fiber surface). MEAs with anode/cathode catalyst loadings of 0.1 mg_Pt cm⁻² each and a Nafion 211 membrane produced high power at both high and low relative humidity (RH) conditions in H₂/air fuel cell tests, e.g., a maximum power density of 919 mW cm⁻² at 100% RH and 832 mW cm⁻² at 40% RH for a test at 80 °C and 200 kPa_abs. The presence of nm-size pores within the fibers trapped water via capillary condensation during low RH feed gas testing, thus maintaining a high proton conductivity of the Nafion binder in the anode and cathode while minimizing/eliminating ionic isolation of catalyst particles in low water content, poorly conductive binder.