Quantitatively unveiling the effect of mass transfer on CO2RR through operando EXAFS and HERFD-XAFS

Abstract

Electrocatalytic reduction reaction of carbon dioxide (CO₂RR) offers an economic and efficient solution towards carbon conversion. Herein, we assess the application of copper(II) phthalocyanine (CuPc) in CO₂RR as a model catalyst with definite local configurations, by employing operando X-ray spectroscopy under a three-electrode H-type cell (H-cell) and a gas-phase electrolyzer (flow-cell) to simulate the varying conditions of the mass transfer rate during CO₂RR. High-energy resolution fluorescence detected X-ray absorption fine structure (HERFD-XAFS) spectroscopy and routine XAFS were used to precisely identify changes of both electronic and atomic structures among the active sites during CO₂RR reactions, and the inverse relationship between the working current density and the reduced cluster size of the copper species was quantitatively depicted. Density functional theory (DFT) calculations indicated that the mass transfer rate was the major determinant of the local CO₂ concentration, which in turn affected the structural evolution of catalyst. In combination with in-situ synchrotron-radiation infrared adsorption spectroscopy (SR-IRAS), the size effect of Cu particles on the reaction kinetics of CO₂RR was revealed. This work not only offers a comprehensive view at the atomic scale towards the rational design of advanced devices with high mass transfer rates, but also emphasizes the advances of operando high-energy resolution spectroscopic characterizations to fully understand dynamic structural changes and reaction mechanisms of CO₂RR.