(17f) Utilizing Grazing Incidence XAS to Investigate Operando CO2 Reduction on Au Electrodes

Authors: 
Feaster, J., Stanford University
Fleischman, S. D., SLAC National Accelerator Laboratory
Davis, R., SLAC National Accelerator Laboratory
Mehta, A., SLAC National Accelerator Laboratory
Jaramillo, T. F., Stanford University

While the electrochemical reduction of carbon dioxide (CO2) to viable fuels and chemicals remains an appealing approach to partner with renewable, carbon-neutral energy sources, there remains a lack of fundamental understanding of how the surface of the catalyst changes during electrochemical experiments. Accurately probing the surface of the catalyst in operando conditions would allow one to not only observe structural and electronic effects of the catalyst that could otherwise not be detected, but potentially observe intermediates for the reaction bind to the catalyst surface. This would offer critical insight into the CO2 reduction reaction, as well as pave the path forward to developing novel understanding of current catalysts for this reaction.

Our work reports using grazing incidence x-ray absorption spectroscopy (GIXAS) to analyze the surface electronic structure of Au catalysts. We designed an operando electrochemical cell that allowed beam access to the Au catalyst for GIXAS experiments while continuously supplying CO2 to the electrode surface. Products of CO2 reduction on Au were confirmed on the electrode surface, and a difference in the XANES region of the spectra was observed between open circuit voltage (no applied bias) and operando conditions. Analysis of the EXAFS region showed no difference, making it likely that the difference in the spectra was caused by CO2 reduction. The changes in the spectra were also studied as a function of potential; the white line of Au disappears once a negative potential vs RHE is applied, but reappears when the potential becomes cathodic enough to drive CO2 reduction. Furthermore, a peak appears only in the spectra for CO2 reduction, which could represent the binding of intermediates to the electrode surface.