Investigation of the Structure of Atomically Dispersed NiNx Sites in Ni and N-Doped Carbon Electrocatalysts by 61Ni Mössbauer Spectroscopy and Simulations

David M Koshy; Md Delowar Hossain; Ryo Masuda; Yoshitaka Yoda; Leland B Gee; Kabir Abiose; Huaxin Gong; Ryan Davis; Makoto Seto; Alessandro Gallo; Christopher Hahn; Michal Bajdich; Zhenan Bao; Thomas F Jaramillo

doi:10.1021/jacs.2c09825

Investigation of the Structure of Atomically Dispersed NiN_x Sites in Ni and N-Doped Carbon Electrocatalysts by ⁶¹Ni Mössbauer Spectroscopy and Simulations

J Am Chem Soc. 2022 Nov 30;144(47):21741-21750. doi: 10.1021/jacs.2c09825. Epub 2022 Nov 17.

Authors

David M Koshy^{1

2}, Md Delowar Hossain^{2

3}, Ryo Masuda⁴, Yoshitaka Yoda⁵, Leland B Gee⁶, Kabir Abiose^{1

7}, Huaxin Gong^{1

2}, Ryan Davis⁸, Makoto Seto^{4

9}, Alessandro Gallo³, Christopher Hahn¹⁰, Michal Bajdich³, Zhenan Bao^{1

2}, Thomas F Jaramillo^{1

2

3}

Affiliations

¹ Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA.
² SUNCAT Center for Interface Science and Catalysis, Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA.
³ SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
⁴ Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka 590-0494, Japan.
⁵ Japan Synchrotron Radiation Research Institute, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan.
⁶ Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
⁷ Department of Mechanical Engineering, Stanford University, Stanford, California 94305, USA.
⁸ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
⁹ National Institutes for Quantum Science and Technology (QST), Sayo, Hyogo 679-5148, Japan.
¹⁰ Materials Sciences Division, Lawrence Livermore National Laboratory, Livermore, California 94550, USA.

PMID: 36394993
DOI: 10.1021/jacs.2c09825

Abstract

Ni and nitrogen-doped carbons are selective catalysts for CO₂ reduction to CO (CO₂R), but the hypothesized NiN_x active sites are challenging to probe with traditional characterization methods. Here, we synthesize ⁶¹Ni-enriched model catalysts, termed ⁶¹NiPACN, in order to apply ⁶¹Ni Mössbauer spectroscopy using synchrotron radiation (⁶¹Ni-SR-MS) to characterize the structure of these atomically dispersed NiN_x sites. First, we demonstrate that the CO₂R results and standard characterization techniques (SEM, PXRD, XPS, XANES, EXAFS) point to the existence of dispersed Ni active sites. Then, ⁶¹Ni-SR-MS reveal significant internal magnetic fields of ∼5.4 T, which is characteristic of paramagnetic, high-spin Ni²⁺, in the ⁶¹NiPACN samples. Finally, theoretical calculations for a variety of Ni-N_x moieties confirm that high-spin Ni²⁺ is stable in non-planar, tetrahedrally distorted geometries, which results in calculated isotropic hyperfine coupling that is consistent with ⁶¹Ni-SR-MS measurements.