Abstract:
Rechargeable batteries and hydrogen production/fuel cells are pivotal technologies for achieving a sustainable society, where the fundamental properties of electrode and catalyst materials determine overall system efficiency. Understanding the underlying structure-property relationship is essential for developing advanced materials; however, the structural origins of electrochemical properties under operating conditions are often obscured by the complex hierarchical structure of active materials.
Recent advances in synchrotron radiation sources allow for a more comprehensive examination of crystalline and electronic structure changes and strain evolution in materials within electrochemical systems. Traditionally, changes in the crystalline structure and chemical states of transition metals (TMs) in oxide materials—key factors influencing lithium-ion battery (LIB) electrode properties—have been studied separately using scattering and spectroscopy techniques. However, resonant X-ray diffraction spectroscopy [1], which examines the energy spectrum of diffraction intensity (diffraction anomalous fine structure, DAFS), has shown that TM electrochemical activity is site-dependent, with migrated TMs becoming inactive and contributing to electrode degradation [2].
Furthermore, recent developments in Bragg coherent diffraction imaging (BCDI) have revealed dynamic behavior and strain evolution in alloy catalysts at elevated temperatures [3] and in fuel cells [4], challenging the conventional belief that catalysts remain unchanged before and after (electro)chemical reactions. These insights facilitate the rational design of more advanced materials, contributing to realizing a sustainable society powered by electrochemical devices. Future directions, enabled by the high coherent flux provided by APS-U, will also be discussed.

[1] T. Kawaguchi et al., J. Synchrotron Radiat., 21, 1247 (2014). 
[2] T. Kawaguchi et al., Phys. Chem. Chem. Phys., 17, 14064 (2015).
[3] T. Kawaguchi et al., Phys. Rev. Lett., 123, 246001 (2019).
[4] T. Kawaguchi et al., Nano Lett., 21, 5945 (2021).
 

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