Activity and stability in proton exchange membrane fuel cells of iron-based cathode catalysts synthesized with addition of carbon fibers

In this work, we report attempts to improve mass performance and durability of a catalyst prepared by ball milling a precursor consisting of a zinc-based zeolitic imidazolate framework (ZIF-8) mixed with 1,10-phenanthroline and ferrous acetate. The latter was then heat-treated at 1050 °C in argon to produce an oxygen reduction catalyst, identified as NC-Ar, for polymer electrolyte membrane fuel cells. Mass performance at 0.6 V of NC-Ar tested in either H2/O2 or H2/Air remained unchanged after adding 26 wt% highly graphitized carbon fibers into its precursor, but its equivalent mass performance improved by 35% under these conditions. The catalyst produced after a heat-treatment at 1050 °C in argon of the carbon fiber-containing precursor is identified as NC-Ar (F90). The durability performance of NC-Ar (F90) over 100 h in H2/Air is the same as that for NC-Ar. However, the durability performance of NC-Ar (F90) may be improved by performing a post-heat-treatment of NC-Ar (F90) with optimized temperature and duration. The best performing and most durable catalyst in this work is identified as NC-Ar (F90) + R985-1080 30 min. After 100 h in H2/Air fuel cell operating at 80 °C and 2 bar absolute pressure, the latter produces about 0.5 A/cm2 at 0.4 V (about 0.20 W/cm2), values that are higher than those (about 0.35 A/cm2 at 0.4 V; or about 0.14 W/cm2) reported under similar experimental conditions (except for a higher absolute pressure of 2.8 bar) by Zelenay and collaborators (2011 [28]) for their most durable catalyst.