Local Spin‐State Tuning of Iron Single‐Atom Electrocatalyst by S‐Coordinated Doping for Kinetics‐Boosted Ammonia Synthesis

• Published in: Advanced materials (Weinheim) 2022-07, Vol.34 (28), p.e2202240-n/a
• Main Authors: Li, Yan, Ji, Yaxin, Zhao, Yingjie, Chen, Junxiang, Zheng, Sixing, Sang, Xiahan, Yang, Bin, Li, Zhongjian, Lei, Lecheng, Wen, Zhenhai, Feng, Xinliang, Hou, Yang
• Format: Article
• Language: English
• Subjects: Ammonia; Chemical reduction; Doping; Electrocatalysts; Haber Bosch process; Iron; iron single atoms; kinetics‐boosted catalysis; nitrogen reduction reaction; Polarization (spin alignment); Protonation; Selectivity; S‐coordinated doping; tunable spin states
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202202240

The electrochemical nitrogen reduction reaction (e‐NRR) is envisaged as alternative technique to the Haber–Bosch process for NH3 synthesis. However, how to develop highly active e‐NRR catalysts faces daunting challenges. Herein, a viable strategy to manipulate local spin state of isolated iron sites through S‐coordinated doping (FeSA‐NSC) is reported. Incorporation of S in the coordination of FeSA‐NSC can induce the transition of spin‐polarization configuration with the formation of a medium‐spin‐state of Fe (t2g6 eg1), which is beneficial for facilitating eg electrons to penetrate the antibonding π‐orbital of nitrogen. As a consequence, a record‐high current density up to 10 mA cm−2 can be achieved, together with a high NH3 selectivity of ≈10% in a flow cell reactor. Both experimental and theoretical analyses indicate that the monovalent Fe(I) atomic center in the FeSA‐NSC after the S doping accelerates the N2 activation and protonation in the rate‐determining step of *N2 to *NNH. An atomically dispersed monovalent iron(I) site with a medium‐spin state is developed to promote cleavage of the N≡N bonds and facilitate the rate‐determining step of N2 hydrogenation kinetics.