Dynamically Unveiling Metal-Nitrogen Coordination during Thermal Activation to Design High-Efficient Atomically Dispersed CoN4 Active Sites

Yanghua He; Qiurong Shi; Weitao Shan; Xing Li; A Jeremy Kropf; Evan C Wegener; Joshua Wright; Stavros Karakalos; Dong Su; David A Cullen; Guofeng Wang; Deborah J Myers; Gang Wu

doi:10.1002/anie.202017288

Dynamically Unveiling Metal-Nitrogen Coordination during Thermal Activation to Design High-Efficient Atomically Dispersed CoN₄ Active Sites

Angew Chem Int Ed Engl. 2021 Apr 19;60(17):9516-9526. doi: 10.1002/anie.202017288. Epub 2021 Mar 10.

Authors

Yanghua He¹, Qiurong Shi¹, Weitao Shan², Xing Li³, A Jeremy Kropf⁴, Evan C Wegener⁴, Joshua Wright⁵, Stavros Karakalos⁶, Dong Su³, David A Cullen⁷, Guofeng Wang², Deborah J Myers⁴, Gang Wu¹

Affiliations

¹ Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY, 14260, USA.
² Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA.
³ Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA.
⁴ Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, 60439, USA.
⁵ Illinois Institute of Technology, Chicago, IL, 60616, USA.
⁶ Department of Chemical Engineering, University of South Carolina, Columbia, SC, 29201, USA.
⁷ Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.

PMID: 33492674
DOI: 10.1002/anie.202017288

Abstract

We elucidate the structural evolution of CoN₄ sites during thermal activation by developing a zeolitic imidazolate framework (ZIF)-8-derived carbon host as an ideal model for Co²⁺ ion adsorption. Subsequent in situ X-ray absorption spectroscopy analysis can dynamically track the conversion from inactive Co-OH and Co-O species into active CoN₄ sites. The critical transition occurs at 700 °C and becomes optimal at 900 °C, generating the highest intrinsic activity and four-electron selectivity for the oxygen reduction reaction (ORR). DFT calculations elucidate that the ORR is kinetically favored by the thermal-induced compressive strain of Co-N bonds in CoN₄ active sites formed at 900 °C. Further, we developed a two-step (i.e., Co ion doping and adsorption) Co-N-C catalyst with increased CoN₄ site density and optimized porosity for mass transport, and demonstrated its outstanding fuel cell performance and durability.

Keywords: Co-N-C; fuel cells; in situ XAS; oxygen reduction reaction; single metal site.

Abstract

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