FeS/Fe heterojunctions for oxygen reduction reaction: Interfacial electron transfer modulates d-band center and enhances catalytic activity

Overcoming the sluggish kinetics of the oxygen reduction reaction (ORR) is crucial for advancing sustainable fuel cells and metal-air batteries. However, the development of high-performance non-precious metal ORR electrocatalysts remains challenging. Herein, a FeS/Fe heterojunction nanosheet embedded in a nitrogen-doped porous carbon matrix (denoted as S-50-FeS/Fe@CNS) is successfully synthesized. The constructed FeS/Fe heterojunction facilitates interfacial electron transfer from metallic Fe to FeS. Density functional theory (DFT) calculations indicate that this electron transfer downshifts the d-band center of Fe active sites, thereby optimizing the adsorption energy of ORR intermediates (*O, *OOH, *OH) to a "moderate" level and enhancing active site utilization and accelerating charge transfer kinetics. The optimized S-50-FeS/Fe@CNS electrocatalyst exhibits outstanding activity for the ORR, achieving a high half-wave potential of 0.856 V, good durability with 79% current retention after 40 h of continuous operation, and only a 2.7 mV decay in half-wave potential after 5000 cycles. This study provides important fundamental insights for designing efficient non-precious metal ORR electrocatalysts through heterojunction engineering.