Konstantina Mason, University of California, Davis

Abstract

As the urgency to find sustainable energy solutions increases, the conversion of carbon dioxide (CO2) into high value-added chemicals is gaining significant attention for its potential to mitigate greenhouse gas emissions and remove dependence on fossil fuels. This in turn motivates the design of materials capable of harnessing renewable energy for the conversion of captured atmospheric CO2 to alcohols, simultaneously reversing the greenhouse effect while creating alternative fuel sources. Multinary chalcogenides, such as Chevrel Phase (CP) materials and transition metal dichalcogenides (MX2), have shown promise for the electrocatalytic conversion of CO2 to alcohols given their ability to break scaling relations by stabilizing key intermediates in the CO2 reduction reaction (CO2RR). X-ray absorption spectroscopy (XAS) techniques provide valuable insights into the electron density localization as well as the local coordination structure of multinary chalcogenides and assist in the elucidation of possible reaction pathways during electrochemical reduction, via the ligand or ensemble effects. Depression of the S-K pre-edge in
X-ray absorption near edge spectroscopy (XANES) as a function of intercalant stoichiometry is indicative of electron density donation to the hybrid Mo-S orbitals of the CP, suggesting influence from the ligand effect. Furthermore, extended X-ray absorption fine structure spectroscopy (EXAFS) provides insights into the local coordination structure allowing us to observe changes in bond lengths of the CP framework upon intercalation or chalcogen substitution, possibly elucidating effects of the ensemble phenomenon. In this work, we investigate the effects of synthetic design principles on the behavior and selectivity of multinary chalcogenides for aqueous and non-aqueous CO2 reduction by utilizing key information provided by XAS techniques.