Abstract

Identification of active sites is one of the main obstacles to rational design of catalysts for diverse applications. Fundamental insight into the identification of the structure of active sites and structural contributions for catalytic performance are still lacking. Recently, X-ray absorption spectroscopy (XAS) and density functional theory (DFT) provide important tools to disclose the electronic, geometric and catalytic natures of active sites. Herein, we demonstrate the structural identification of Zn-N2 active sites with both experimental/theoretical X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. Further DFT calculations reveal that the oxygen species activation on Zn-N2 active sites is significantly enhanced, which can accelerate the reduction of oxygen with high selectivity, according well with the experimental results. This work highlights the identification and investigation of Zn-N2 active sites, providing a regular principle to obtain deep insight into the nature of catalysts for various catalytic applications.

Highlights

  • Identification of active sites is one of the main obstacles to rational design of catalysts for diverse applications

  • The active sites of transition metal–nitrogen–carbon (TMNC) catalysts have not been well identified and are defined as TM-Nx based on information from X-ray photoelectron spectroscopy (XPS)[7,8,9,10,11]

  • Overall, combining extended X-ray absorption fine structure (EXAFS) with X-ray absorption near edge structure (XANES) spectra, the structure of the active sites for Zn-based TMNC material (ZnNC) can be confirmed without ambiguity to be the Zn-N2 structure

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Summary

Introduction

Identification of active sites is one of the main obstacles to rational design of catalysts for diverse applications. Combined EXAFS and XANES spectra analysis confirmed Zn-N2 as the structure of the active sites. The high degree of O-O bond stretching can accelerate the highly selective four-electron reduction of adsorbed oxygen on the surface of Zn-N2 active sites, which agrees well with the experimental results.

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