(Invited) Advanced High Energy X-Rays Diffraction Techniques for Electrochemical Science
Authors: Drnec Jakub , Martens Isaac , Fuchs Timo , Wiegmann Tim , Vamvakeros Antonis , Chattot Raphaël , Magnussen Olaf M. 
Published: February 2020

Complete physico-chemical operando characterization of electrochemical devices in whole, or it’s constituent materials separately, is necessary to guide the development and to improve the performance. High brilliance synchrotron X-ray sources play a crucial role in this respect as they act as a probe with relatively high penetration power and low damage potential. These sources will undergo major upgrades in next decade and will provide even higher brilliance and, more importantly, coherence. These upgrades will be particularly advantageous for beamlines providing high energy X-rays as it will allow to use advanced scattering techniques with highly penetrating probe and therefore will bring the techniques typically used for ex-situ measurements to be used on materials in half-cells and operating electrochemical devices. In this contribution the new possibilities of using using high energy, high intensity X-rays to probe model systems and whole devices will be presented.
HESXRD (High Energy Surface X-ray Diffraction) [1] and TDS (Transmission Surface Diffraction) [2] provide ideal tools to study structural changes during reaction conditions on single crystal model electrodes. The main advantage of both techniques is the possibility to follow the structural changes precisely with atomic resolution. While HESXRD is ideally used to determine exact atomic position, the TSD is easier to use and allows studies with high spatial resolution. For example, HESXRD can be used to follow the atomic movement of Pt atoms during electrochemical oxidation and dissolution with very high precision, explaining the different catalyst degradation behaviors and suggesting possible routes to improve its durability. The TSD is used, for example, as an excellent tool to study advanced 2D catalysts, such as various dichalcogenides, during oxygen evolution or electrochemical deposition.
To study fuel cells or batteries as a whole, elastic scattering techniques such as wide angle and small angle scattering are typically employed as they can provide important complementary information to more standard X-ray imaging and tomography. The advantage is that the chemical contrast and sensitivity at atomic and nm scales is superior. Coupling these technique with the tomographic reconstruction (XRD-CT and SAXS-CT) is much less common as it requires bright synchrotron sources, fast 2D detectors and advanced instrumentation [3]. However, such combination allows 3D imaging of operational devices with unprecedented chemical sensitivity. This can be demonstrated, as an example, on imaging of standard 5 cm2 fuel cells during operation. The change in morphology and atomic arrangement of the catalysts, PEM hydration and water distribution can be followed in one experiment as a function of operating conditions. Furthermore, aging behavior can be assessed with high temporal and spatial resolution in the standard fuel cell, without compromises enforced by the liquid cells or specialized cell designs. These advanced scattering techniques open a door to holistic investigations of operational devices, which are needed to successfully incorporate new materials at the device level.
[1] J. Gustafson et al., Science 343, 758 (2014)
[2] F. Reikowski et al., J. Phys. Chem. Lett., 5, 1067-1071 (2017)
[3] A. Vamvakeros et al., Nat. Commun., 9, 4751 (2018)