Maryam Farmand1 Alan Landers2 Christopher Hahn3 Walter Drisdell1

1, Lawrence Berkeley National Laboratory, Berkeley, California, United States
2, Stanford University, Palo Alto, California, United States
3, SLAC National Accelerator Laboratory, Menlo Park, California, United States

The primary challenge in electrochemical CO2 reduction lies in tuning the catalytic selectivity for desired solar fuels products. Molecular-scale knowledge of the catalytic mechanism for CO2 reduction is required, ideally for systems with controlled morphology that can be directly compared to first principles calculations. Achieving this control is difficult, as CO2 reduction competes with hydrogen evolution and only proceeds with appreciable efficiency at high current densities, and suffers from mass transport limitations due to low solubility of CO2. I present a new electrochemical flow cell system designed collaboratively in the Joint Center for Artificial Photosynthesis (JCAP) at Lawrence Berkeley National Laboratory and SLAC National Accelerator Laboratory, which uses a fast liquid flow design to enable grazing incidence X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) of a smooth planar catalyst surface (top 2-4 nm) during operation. These measurements characterize the chemical state, local electronic structure, and long-range atomic structure of the catalyst surface as a function of electrochemical conditions, including full catalytic chemistry at high current density. I demonstrate the surface sensitivity and electrochemical control of the technique, and present early data on model CO2 reduction catalysts.