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

Abstract

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.

Octahedral spinel electrocatalysts for alkaline fuel cells

“…The high loadings of Co-Mn oxides are critical in practical membrane-electrode assembly measurements for a high peak power density of > 1 W/cm 2 (SI Appendix, Fig. S13), as we reported, in detail, in our recent work (25,26). In order to establish why MnCo 2 O 4 /C, CoMn 2 O 4 /C, and CoFe 2 O 4 stand out as the 3 most active electrocatalysts toward the ORR, thorough investigations of the morphology, crystal structure, and local chemical environment were carried out employing macroscopic-level XAS and microscopic-level STEM-EELS.…”

“…Cobalt oxides and manganese oxides have been reported to be effective electrocatalysts for the ORR (20,21). Furthermore, Co-based bimetallic oxides have been reported to exhibit enhanced activities for the ORR in alkaline media (22)(23)(24)(25)(26)(27)(28)(29)(30). Despite numerous studies of 3d metal oxide electrocatalysts, the electrocatalytic mechanism remains poorly understood (13,19).…”

A highly-active, stable and low-cost platinum-free anode catalyst based on RuNi for hydroxide exchange membrane fuel cells

“…Some Pt-free oxygen reduction reaction (ORR) catalysts (e.g. Fe–N–C, Ag, and Mn–Co oxides) have been developed in base 14 – 16 . They showed high activity and potential to replace the Pt-based cathode catalysts in HEMFCs.…”

Facile preparation of a Ag/graphene electrocatalyst with high activity for the oxygen reduction reaction

“…1,2 Many researches have been done to synthesize non-Pt electrocatalysts for alkaline anion exchange membranes fuel cells with different materials including Pd, Ag, Ni, and Mn-oxides. [3][4][5][6] Among them, Ag is one of the most suitable non-Pt electrocatalyst candidate for the oxygen reduction reaction (ORR) in alkaline media, as Ag is not only about 50 times cheaper than Pt, but also stable at high pH in terms of its thermodynamics and electrochemistry. [7][8][9][10][11][12][13] However, an issue with the conventional method to form Ag nanoparticles (Ag NPs) is that the particles are large in size (7-500 nm) and are not well dispersed.…”