Unravelling the complex causality behind Fe-N-C degradation in fuel cells

Abstract

Beyond great advances in initial activity, Fe-N-C catalysts face the next challenge of stability issue in acidic medium that must be overcome to replace Pt in fuel cell cathode. However, the complex phenomena in fuel cells and consequential difficulty in understanding deactivation mechanisms of Fe-N-C cathodes impede solutions for prolonged stability. Here we show time-resolved changes in active site density and turnover frequency of Fe-N-C along with concurrent decrease in oxygen reduction reaction current in a temperature/gas controllable gas-diffusion electrode flow cell. Operando diagnosis of Fe leaching identifies a strong dependence of site density changes on operating parameters and draws a lifetime-dependent stability diagram that reveals a shift in the prime degradation mechanism during operation. A proof-of-concept strategy with site-isolated Pt ions as a non-catalytic stabilizer, supported by theoretical calculations, demonstrates enhanced fuel cell stability with reduced Fe dissolution, offering design principles for durable Fe-N-C catalysts. Inexpensive Fe-N-C single-atom catalysts are a promising solution to replace costly Pt-based cathode catalysts in fuel cells, but they typically suffer from low durability. Now, the degradation mechanisms of Fe-N-C catalysts are identified under operando conditions as a function of time, and potential solutions are proposed.