Unraveling the Electronic Structure and Dynamics of the Atomically Dispersed Iron Sites in Electrochemical CO2 Reduction

Yaqiong Zeng; Jian Zhao; Shifu Wang; Xinyi Ren; Yuanlong Tan; Ying-Rui Lu; Shibo Xi; Junhu Wang; Frédéric Jaouen; Xuning Li; Yanqiang Huang; Tao Zhang; Bin Liu

doi:10.1021/jacs.3c05457

Unraveling the Electronic Structure and Dynamics of the Atomically Dispersed Iron Sites in Electrochemical CO₂ Reduction

J Am Chem Soc. 2023 Jul 19;145(28):15600-15610. doi: 10.1021/jacs.3c05457. Epub 2023 Jul 7.

Authors

Yaqiong Zeng^{1

2}, Jian Zhao¹, Shifu Wang^{1

3}, Xinyi Ren^{1

2}, Yuanlong Tan¹, Ying-Rui Lu⁴, Shibo Xi⁵, Junhu Wang⁶, Frédéric Jaouen⁷, Xuning Li^{1

2}, Yanqiang Huang^{1

2}, Tao Zhang^{1

2}, Bin Liu⁸

Affiliations

¹ State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P.R. China.
² University of Chinese Academy of Sciences, Beijing 100049, P.R. China.
³ Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, P.R. China.
⁴ National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
⁵ Institute of Chemical and Engineering Sciences, A*STAR, Singapore 627833, Singapore.
⁶ Center for Advanced Mössbauer Spectroscopy, Mössbauer Effect Data Center, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P.R. China.
⁷ Institut Charles Gerhardt Montpellier, University of Montpellier, CNRS, ENSCM, Montpellier 34095, France.
⁸ Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR 999077, China.

PMID: 37418344
DOI: 10.1021/jacs.3c05457

Abstract

Single-atom catalysts with a well-defined metal center open unique opportunities for exploring the catalytically active site and reaction mechanism of chemical reactions. However, understanding of the electronic and structural dynamics of single-atom catalytic centers under reaction conditions is still limited due to the challenge of combining operando techniques that are sensitive to such sites and model single-atom systems. Herein, supported by state-of-the-art operando techniques, we provide an in-depth study of the dynamic structural and electronic evolution during the electrochemical CO₂ reduction reaction (CO₂RR) of a model catalyst comprising iron only as a high-spin (HS) Fe(III)N₄ center in its resting state. Operando ⁵⁷Fe Mössbauer and X-ray absorption spectroscopies clearly evidence the change from a HS Fe(III)N₄ to a HS Fe(II)N₄ center with decreasing potential, CO₂- or Ar-saturation of the electrolyte, leading to different adsorbates and stability of the HS Fe(II)N₄ center. With operando Raman spectroscopy and cyclic voltammetry, we identify that the phthalocyanine (Pc) ligand coordinating the iron cation center undergoes a redox process from Fe(II)Pc to Fe(II)Pc^-. Altogether, the HS Fe(II)Pc^- species is identified as the catalytic intermediate for CO₂RR. Furthermore, theoretical calculations reveal that the electroreduction of the Pc ligand modifies the d-band center of the in situ generated HS Fe(II)Pc^- species, resulting in an optimal binding strength to CO₂ and thus boosting the catalytic performance of CO₂RR. This work provides both experimental and theoretical evidence toward the electronic structural and dynamics of reactive sites in single-Fe-atom materials and shall guide the design of novel efficient catalysts for CO₂RR.