Second-Shell Sulfur Coordination Engineering of Iron Single-Atom Catalysts for Enhanced Oxygen Reduction Reaction
Dan Wang, Jinxiang Chou, Yifan Yan, Sujuan Zha, Yankun Wei, Penghui Ren, Yukai Chen, Xiaojiao Du, Wenchang Wang, Zhidong Chen
Abstract
High Resolution Image Download MS PowerPoint Slide Precisely modulating the local coordination microenvironment of metal centers to synthesize high-efficiency Fe–N–C single-atom catalysts remains critical yet challenging for optimizing the oxygen reduction reaction (ORR) performance. Especially, the influence and mechanism of second-shell coordination engineering on Fe centers remain ambiguous and often overlooked. Herein, a facile strategy is proposed to synthesize Fe–N 4 single atoms with precisely controlled second-shell sulfur coordination on hierarchical porous carbon (Fe–N, S-HPC). Density functional calculations first reveal that second-shell sulfur coordination can redistribute charge density, upshift the d-band center, and strengthen the adsorption of oxygen-containing intermediates, thereby significantly reducing energy barriers and accelerating ORR kinetics. As expected, the Fe–N, S-HPC catalyst demonstrates a half-wave potential of 0.908 V and an enhanced turnover frequency of 1.68 s –1 for ORR. Furthermore, the assembled Zn-air battery delivers a high specific capacity of 702.7 mAh g –1 and a large energy density of 886.1 Wh kg Zn –1 along with long-term charge/discharge stability. This work reveals the correlation between second-shell sulfur coordination and enhanced ORR activity and offers a valuable design principle for advanced single-atom catalysts.