X-ray Spectroscopy properties of photocatalysts in Aqueous Environment
This research project is part of a joint theory-experiment collaboration for the development of new “operando spectroscopy” methodologies based on synchrotron spectroscopy in combination with theoretical simulations. The latter are based on classical and ab-initio Molecular Dynamics (MD) or Monte Carlo (MC) calculations and spectroscopy simulations based on Density Functional Theory (DFT). Our goal is to investigate and design the next generation of efficient energy materials targeting electrochemical water-solid interfaces, molecules and catalysts in water environment in order to improve the mechanisms of water oxidation and CO2 reduction for the production of solar fuels. This will be achieved by the computation of soft X-ray spectra like X-ray Absorption Spectroscopy (XAS), Photo-Electron Spectroscopy (PES), and Scanning Tunneling Microscopy (STM). Recently operando X-ray spectroscopy experiments have been performed under realistic conditions of higher pressures and temperatures [1,2]. The experiments involve the investigation of solid-liquid interfaces and solvated molecular systems employing liquid microjets [3, 4]. In a recent paper  the use of soft X-ray spectroscopies + DFT calculations to resolve the mechanism of CO2 reduction reaction catalyzed by Ru-complexes in vacuum was analyzed. The computed PES and XAS spectra showed fingerprints of the electrochemical properties indicating that X-ray based experimental techniques are a proper approach to resolve the reaction mechanisms. Here, we will include the solvation effects in the protonated and deprotonated Ru complexes, as [RuII(bpy)2(py)(OH)2]2+ [RuIII(bpy)2(py)(OH)]2+, [RuIV(bpy)2(py)(O)]2+, [RuIII(bpy)2(py)(OH)2]3+, [RuII(bpy)2(py)(OH)]+, as a precondition to investigate the yet unknown reaction pathways. Snapshots of MD and MC will be selected including a particular shell of water molecules for the first-principles calculations based on the analysis of time correlation and radial distribution functions (Performed by Prof Kaline R. Coutinho, Sao Paulo University, Brazil). We will account for several factors that affect the spectra of molecules in the liquid phase: distortions of the molecule driven by the interaction with the water; distortions of the water molecules; changes in the water positions and number around the molecule. These calculations are costly, since to obtain a meaningful representation of the liquid environment we have performed preliminary calculations with approximately 100 snapshots, with promising results. The project will continue with other potentials hybrid systems which have given experimentally very encouraging results in terms of their catalytic properties, as Fe based clusters and organic macrocycle molecules anchored to several types of substrates as carbon nanotubes and polymer blends. 1. Schnadt J. et al. Journal of Synchrotron Radiation 2012,19, 701. 2.Risch M, et al. Energy & Environmental Science 2015, 8, 661. 3.Winter B. Nuclear Instruments & Methods in Physics Research Section a. 2009, 601, 139. 4.Ogletree DFet al. Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment 2009, 601, 151. 5. Rocío Sánchez-de-Armas, et al. Phys. Chem. C 2015, 119, 22899.