High-Loading Composition-Tolerant Co–Mn Spinel Oxides with Performance beyond 1 W/cm2 in Alkaline Polymer Electrolyte Fuel Cells

Hydrogen fuel cells operated in alkaline media enable the use of abundant nonprecious 3d metal oxides to replace Pt to catalyze the sluggish oxygen reduction reaction (ORR). Herein, we describe Co–Mn spinel oxide electrocatalysts with metal oxide loadings of up to 80 wt % on carbon supports. Despite little variation in ORR activity derived from rotating disk electrode (RDE) measurements, practical membrane electrode assembly (MEA) tests exhibited significant enhancement in performance when loadings increased from 40 to 80 wt %. This was ascribed to the enhanced mass transport through the thin catalyst layer at 80 wt % (<10 μm). This work highlights the importance of incorporating MEA tests, even in early-stage catalyst development. A benchmark peak power density (PPD) of 1.2 W/cm2 at 2.6 A/cm2 was achieved using MnCo2O4 (80 wt %). CoMn2O4/C also achieved a PPD of 1.1 W/cm2 under the same conditions, indicating that MEA performance of Co–Mn oxides is generally high and tolerant to compositional variations that may occur in larger-scale production.