Operando X-ray absorption and resonant photoemission spectroscopy of transition metal oxides

This thesis aims to critically explore the electronic properties of heterogeneous catalysts under operando conditions and superconductive nickelate thin films, combining experiments and theory in X-ray spectroscopy. Employing X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS), photoemission spectroscopy (PES), and resonant photoemission spectroscopy (RPES) probed the dynamics of spin, charge, and (co)valence in transition metal oxides (TMOs). Chapter 1 gives an overview of the main properties of transition metal ions and their hybridization with oxygen in TMOs, as well as the fundamentals of electrocatalysis and thermocatalysis. Chapter 2 reviews core-level X-ray spectroscopy, giving insight into experimental and theoretical approaches, with a focus on the distinction between Density Functional Theory one-particle approximation and charge transfer multiplet theory. Chapter 3 investigates the covalence of LaFeO3/LaNiO3 thin films in solid-liquid system by in situ hard X-ray XAS. Chapter 4 explores the spin and oxidation state of LaMn1-xCoxO3 in solid-gas system by operando soft X-ray XAS. Chapter 5 examines the local and non-local state in TM K-edge of La2CoMnO6 nanoparticles and thin films by 1s2p RIXS. Chapter 6 highlights the dynamics of valence near-surface of La2CoMnO6 for oxygen evolution reaction using operando high energy resolution fluorescence detected XAS. Chapter 7 studies the ground state properties of recently discovered superconductive nickelate thin films by RPES guided by impurity calculations.