Pre-coordination synthesis of active Fe single-atom catalyst enabling efficient and ultralong-life oxygen depolarized cathode applications

Chlor-alkali electrolysis with oxygen depolarized cathode (ODC), which can save up to 30 % in energy, primarily involves two electrochemical reactions: the chlorine evolution reaction (CER), and the oxygen reduction reaction (ORR). However, electrocatalysts used in this field is the platinum-group metals (PGMs), which significantly increase the preparation cost. Herein, we synthesize Fe single-atom anchored on carbon nanotubes (Fe-N@CNTs) via a pre-coordination strategy as an active and durable ORR catalyst. The resulting Fe-N@CNTs displays excellent ORR performance with a large half-wave potential (E 1/2 ) of 0.905 V and excellent durability over 30,000 CV test in 0.1 M KOH electrolyte. Projected density of states (PDOS) analysis demonstrates that geometric strain lowers the d-band center of Fe, weakening the adsorption strength of ORR intermediates at Fe N 4 active sites. Density functional theory (DFT) calculations show that geometric strain effects reduce the potential determining step (PDS) energy barrier and optimize the binding strength of *OH of ORR. Both Fe-N@CNTs-based aqueous Zn-air battery (A-ZAB) and quasi-solid-state Zn-air battery (QSS-ZAB) display excellent charge/discharge cycling stability with small charge/discharge voltage gaps over 1700 h and 100 h, respectively. Importantly, Fe-N@CNTs||RuO 2 chlor-alkali flow cell requires low cell potential of 1.58 V to reach 300 mA cm −2 at 80 °C, and delivers excellent stability over 230 and 110 h at 100 and 300 mA cm −2 , respectively. Fe-N@CNTs||RuO 2 maintains approximately 100 % caustic current efficiency at the current density of 300 mA cm −2 . This work contributes to the development of stable, uniformly dispersed atomic-scale metal ORR catalysts and expands their applications in chlor-alkali electrolyzer.