Keep the Ligands: Potential Benefits for Fuel Cell Performance

Spinel oxides such as ternary cobalt manganese spinel oxides (CMOs) are promising electrocatalysts for oxygen reduction reaction (ORR) in anion exchange membrane fuel cells. Current efforts to enhance fuel cell cathode performance predominantly focus on tuning the ORR activity through the chemical and crystallographic engineering of the active material. However, the impact of ink formulation and film homogeneity on fuel cell performance remains poorly understood and under-investigated. Here we show that the deliberate retention of organic ligands can enhance the performance of a CMO/C composite by improving its film homogeneity. Surprisingly, retaining the organic ligands can optimize the catalyst-ionomer affinity and subsequent film homogeneity of this system, thus enhancing its fuel cell peak power density from 0.8 W/cm(2) to 1.2 W/cm(2). We demonstrate this effect by pre- and postsynthetic characterizations of single-batch and monodisperse CMO/C composites and films, in the presence (retained) and absence (removed) of organic ligands. Our results demonstrate that ink dispersion and film homogeneity are critical parameters in fuel cell electrocatalysis and how organic ligands can help enhance electrocatalytic film performance in systems that suffer from unfavorable electrocatalyst-ionomer interactions.