FUEL CELL MEMBRANE-ELECTRODE-ASSEMBLIES WITH PGM-FREE CATALYST NANOFIBER CATHODES

Abstract

The hydrogen/air proton-exchange membrane fuel cell (PEMFC) is a clean and energy-efficient alternative to internal combustion engines in motor vehicles. A significant obstacle to the large-scale commercialization of such fuel cells is the need for costly platinum-based catalysts, which are presently the electrode material of choice for both the hydrogen gas oxidation reaction and the cathodic oxygen reduction reaction. Over the past ten years, a family of low-cost platinum group-metal-free catalysts (PGM-free catalysts) have been developed with moderately high activity for oxygen reduction in a PEMFC. Unfortunately, these catalytic powders degrade quickly when used as the cathode catalyst during fuel cell operation due to chemical attack by electro-generated peroxide. The experimental work for this dissertation was focused on solving this problem by incorporating PGM-free catalyst powders into nanofiber mat fuel cell cathodes with a hydrophobic polymer binder, where the electrode hydrophobicity would quickly drive water and dissolved peroxide out of the cathode. Fiber mat electrodes were fabricated, characterized, and evaluated in fuel cell membrane-electrode-assemblies. Some electrospun nanofibers were prepared with catalyst powder, provided by Pajarito Powder, LLC, and a mixture of Nafion perfluorosulfonic acid ionomer and hydrophobic polyvinylidene (PVDF), where the Nafion/PVDF weight ratio was varied from 1/5 to 1/1. Other fiber mats contained only Nafion as the catalyst binder. The best cathode, in terms of maximizing both fuel cell power output and durability, was a hybrid mixture of electrospun catalyst/Nafion nanofibers and catalyst powder, with a hydrophobic polymer dispersed outside the fibers.