Highly Active and Stable Fe-N-C Catalyst for Oxygen Depolarized Cathode Applications

Anion immunity toward the oxygen reduction reaction (ORR) has tremendous implications in electrocatalysis with applications for fuel cells, metal-air batteries, and oxygen depolarized cathodes (ODCs) in the anodic evolution of chlorine. The necessity of exploring ORR catalysts with immunity to anion adsorption is particularly significant considering that platinum group metal (PGM) catalysts are costly and highly vulnerable to impurities such as halides. Herein, we report a metal organic framework (MOF)-derived Fe-N-C catalyst that exhibits a dramatically improved half-wave potential of 240 mV compared to the state-of-the-art Rh_xS_y/C catalyst in a rotating disk electrode in the presence of Cl^-. The Fe-N₄ active sites in Fe-N-C are intrinsically immune to Cl^- poisoning, in contrast to Pt/C, which is severely susceptible to Cl^- poisoning. As a result, the activity of Fe-N-C decreases only marginally in the presence of Cl^-, far exceeding that of Pt/C. The viability of this catalyst as ODCs is further demonstrated in real-life hydrochloric acid electrolyzers using highly concentrated HCl solution saturated with Cl₂ gas as the electrolyte. The introduction of Fe-N-C materials as ODC catalysts here overcomes the limitations of (i) the low intrinsic ORR activity of Rh_xS_y/C as the state-of-the-art ODC catalyst; (ii) the vulnerability to Cl^- poisoning of Pt/C as the state-of-the-art ORR catalyst; and (iii) the high cost of precious metals in these two materials, resulting in a cost-effective ODC catalyst with the overall performance exceeding that of all previously reported materials.