Fabrication of highly effective self-humidifying membrane electrode assembly for proton exchange membrane fuel cells via electrostatic spray deposition

One major challenge associated with proton exchange membrane fuel cells is to preserve higher proton conductivity under low-humidity atmosphere. Elevation of water uptake in the perfluorinated polymeric membrane is crucial for the facilitated transportation of proton, which dominates the fuel cell performance. Development of an intrinsic mechanism that controls water balance through the membrane electrode assembly (MEA), eliminates the need for external water management system and thus makes the system suitable for portable applications, where size is an important criterion to be considered. Herein, we report a nano-sized dense-structure (NSDS) layer coated onto the conventional catalyst layer, forming a dual-layered electrode architecture that is favorable in promoting the self-humidification process. This self-humidifying layer is fabricated by the electrostatic spray deposition with sufficiently low deposition rate, which allows for a creation of more uniformly distributed porous structure with diameters smaller than 80 nm, enabling recirculation of the water generated for proper humidification. When experimentally investigated, the MEA employing the dual-layered electrode reveals a 3.15 times elevated current density at 0.6 V than conventional MEA under 0% relative humidity. Mechanism for the water retention in the proposed electrode is further evaluated by X-ray computed tomography, which reveals dramatically increased tortuosity of 4.43 for the NSDS layer in comparison to 1.9 for the conventional catalyst layer.