High Performance FeNC and Mn-oxide/FeNC Layers for AEMFC Cathodes

Abstract

While the Anion Exchange Membrane Fuel Cell (AEMFC) is gaining interest due to high power performance recently achieved with platinum-group-metal (PGM) catalysts, its implementation will require high-performing PGM-free cathodes. FeNC catalysts have shown high activity and stability for the Oxygen Reduction Reaction (ORR) in alkaline electrolyte; however, the production of hydrogen peroxide during ORR can lead to premature degradation of FeNC and ionomer. In order to minimize the amount of peroxide formed on FeNC, α -MnO 2 , β -MnO 2 , δ -MnO 2 and α -Mn 2 O 3 were investigated as co-catalysts, with the aim of increasing the apparent activity of FeNC-based cathodes for the hydrogen peroxide reduction reaction (HPRR). The specific activity of α -Mn 2 O 3 for the HPRR was distinctly superior to the other Mn-oxides. The four Mn-oxides were mixed with a FeNC catalyst comprising atomically-dispersed FeN x sites, showing higher HPRR activity and higher four-electron ORR selectivity than FeNC alone. The stability of α -Mn 2 O 3 /FeNC was studied operando by on-line inductively-coupled plasma mass spectrometry, to evaluate the potential and time dependent leaching of Mn and Fe. Finally, FeNC and α -Mn 2 O 3 /FeNC were applied at the cathode of AEMFCs, both achieving similar or higher current density at 0.9 V than a Pt/C commercial cathode, and peak power densities of ca. 1 W·cm −2 .