XAFS Helps Researchers Decipher Near-free Single-atom Dynamics

  • [2020-03-09]

    Recently, a team led by Prof. YAO Tao from National Synchrotron Radiation Laboratory, University of Science and Technology of China (USTC), discovered near-free platinum (Pt) single-atom dynamics during electrochemical reduction processes via operando synchrotron X-ray absorption fine structure (XAFS) technique. The dynamics greatly enhanced the hydrogen evolution reaction (HER) of Pt single-atom catalysts in pH solutions. The work was published on Nature Communication on 25 Feb. The first author is FANG Shi, a master student from USTC.

    Operando XAFS characterization of Pt single atom catalysts and evolution of their near-free state

    In the field of energy and catalysis, it is of great significance for fundamental research on designing catalysts to capture the dynamic changes of the atomic-scale structure of the catalysts in reactions. In recent decades, the advances on nanoscale materials, especially theories and control techniques in nano scale, have greatly promoted the basic and applied research in catalytic science. Particularly, single-atom catalysts have been a research hit on account of its maximum atom efficiency, outstanding reactivity and excellent selectivity. 

    The activity and selectivity of single-atom catalysts highly depend on the localized atom and electron structure of the central metal atoms with the supports. However, under the reaction state, the single-atom catalysts carry on structural evolution in response to temperature, electric field, light and so on. It is important to character those special response behaviors in situ and in real time. Meanwhile, XAFS is one of the most powerful tools for charactering the localized space and electronic structure of the catalytic center, which can detect gas, liquid and solid samples in the actual catalytic environment. Herein, high-resolution XAFS provided an opportunity to study the looming problem.

    The research team selected the Pt single-atom catalyst with highly uniform active sites as the model catalyst, and real-time monitored the evolution of single Pt atom in the electroreduction via operando synchrotron X-ray absorption spectroscopy. They observed when applying negative potential during the reaction, the hybridization between Pt and nearby C/N atoms from support decreased, which meant the valence of Pt almost decreased to that of single Pt atom. According to their theoretical simulations, the d-band of Pt was improved in the process which promoted single-atom Pt active sites absorbed H2O and benefited to the absorption-desorption of the catalyst-H intermediate. All of these made the catalyst show high performance in wide-pH electrolytes. 

    In short, the study precisely plotted 3D atomic and electronic structure of Pt1/N-C and discovered a common evolution of near-free atom dynamics in the electrocatalytic stage. 

    This research was funded by National Natural Science Foundation of China, Fundamental Research Funds for the Central Universities, and Youth Innovation Promotion Association CAS.

    Reference

    1. https://www.nature.com/articles/s41467-020-14848-2 (Open Access)


    (Written by ZHAO Xiaona, edited by YE Zhenzhen, USTC News Center)


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