Revealing the Bonding Nature and Electronic Structure of Early-Transition-Metal Dihydrides
Curran Kalha (University College London)
Laura E. Ratcliff (University of Bristol)
Giorgio Colombi (TU Delft - ChemE/Materials for Energy Conversion and Storage)
Christoph Schlueter (Deutsches Elektronen-Synchrotron DESY)
Bernard Dam (TU Delft - ChemE/Materials for Energy Conversion and Storage)
Andrei Gloskovskii (Deutsches Elektronen-Synchrotron DESY)
Tien Lin Lee (Diamond Light Source)
Giancarlo Panaccione (Istituto officina dei materiali, Consiglio Nazionale Delle Ricerche)
Anna Regoutz (University College London)
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Abstract
Metal hydrides are potential candidates for applications in hydrogen-related technologies, such as energy storage, hydrogen compression, and hydrogen sensing, to name just a few. However, understanding the electronic structure and chemical environment of hydrogen within them remains a key challenge. This work presents a new analytical pathway to explore these aspects in technologically relevant systems using hard x-ray photoelectron spectroscopy (HAXPES) on thin films of two prototypical metal dihydrides: YH2-δ and TiH2-δ. By taking advantage of the tunability of synchrotron radiation, a nondestructive depth profile of the chemical states is obtained using core-level spectra. Combining experimental valence-band (VB) spectra collected at varying photon energies with theoretical insights from density functional theory (DFT) calculations, a description of the bonding nature and the role of d versus sp contributions to states near the Fermi energy are provided. Moreover, a reliable determination of the enthalpy of formation is proposed by using experimental values of the energy position of metal s-band features close to the Fermi energy in the HAXPES VB spectra.
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