Dual Metal Fe-Mn-N-C Sites with Improved Stability for the Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell.

Low-cost and durable hydrogen fuel cells are crucial for the success of the hydrogen economy. While Fe-N-C catalysts are amongst the most promising low-cost alternative to platinum (Pt) for the oxygen reduction reaction, their unsatisfactory durability is the grand challenge faced by the field due to iron demetallation, carbon corrosion and electrode collapse. Herein, a dual-metal single-atom Fe-Mn-N-C catalyst with superior stability (49% loss in peak power density) than Fe-N-C catalysts (66% loss) over 96 h of continuous operations in H-O fuel cells is reported. Advanced operando electrochemical and post-mortem physical measurements shed light on the underlying mechanism. The iron-manganese bond anchors the iron strongly in the Fe-Mn-N-C centre, which lowers the hydrogen peroxide yield as a result. Operando electrochemical measurements reveal a more stable triple-phase boundary environment for the Fe-Mn-N-C catalyst than for Fe-N-C. Specifically, a combination of cyclic voltammetry and impedance spectroscopy with the distribution of relaxation times reveals that the iron demetallation and carbon corrosion are respectively 20% and 30% slower for the Fe-Mn-N-C catalyst than the Fe-N-C catalyst in hydrogen fuel cells. Altogether, this dual-metal site strategy paves the way for improving the stability of Pt-free catalysts for hydrogen fuel cells.