Boosting the oxygen reduction reaction behaviour of atomic Fe–N4 active sites in porous honeycomb-like carbon via P heteroatom doping

Abstract

Fe–N–C single atom electrocatalysts (SAECs) with porphyrin-like Fe–N₄ species are one of the most promising alternatives to the platinum-group-metal-based electrocatalysts used for oxygen reduction reaction (ORR). However, limited attention is paid on delicately optimizing the free energy barrier of Fe–N₄ active sites through heteroatom doping in the carbon skeleton. Herein, Fe single atoms (SAs) on heteroatoms N- and P-codoped porous honeycomb-like carbon (Fe–N₄/NP-PHC) have been rationally designed. The as-developed Fe–N₄/NP-PHC catalyst with abundant accessible active sites showed an impressive onset potential (E_onset = 1.0 V) and half-wave potential (E_1/2 = 0.89 V) under low electrocatalyst loading capacity, which is more positive than those of Pt/C and most SAECs. Encouragingly, the experimental results and DFT calculations systematically demonstrated that the optimized adsorption energy of the Fe–N₄ sites in the P-doped carbon matrix facilitated the release of OH* and thus boosted the ORR performance. The metal–air battery containing Fe–N₄/NP-PHC exhibited high peak power density and long-term working feasibility with a low voltage gap at large current densities. This study demonstrates that P doping in carbon matrix is an effective strategy to promote catalytic properties and presents a novel avenue for developing high-performance electrocatalysts for various electrochemical reactions.