Determining kinetics of electrochemical carbon dioxide reduction to carbon monoxide with scanning electrochemical microscopy

This study reports on determining kinetics of electrochemical reduction CO2 to CO on Au catalysts using the substrate generation/tip collection (SG/TC) mode of scanning electrochemical microscopy (SECM). We introduced a simple but effective method based on transient technique to obtain a series of apparent heterogeneous rate constants k based on Fick's second law by controlling the tip-substrate distance and the voltage of the substrate electrode within the SECM framework. By analysis the transient current recorded during the chronoamperometric characterization, we can successfully determine the apparent rate constant k for the simplified total conversion process of CO2 + 2H+ + 2e- -> CO + H2O onto Au catalyst electrode serving as an example, which increases from 5.02 x 10-2 cm & sdot;s- 1 to 7.16 x 10-2 cm & sdot;s- 1 in the low potential range of -2.2 to -2.6 V (vs. Pt/PPy) and decreases to 6.54 x 10-2 cm & sdot;s- 1 at -2.8 V (vs. Pt/PPy). The method proposed here can be applied to quantitatively analyze the kinetic of CO2 electrochemical reduction reaction, and thus provide a useful tool to guide the synthesis of catalyst as well as in -situ performance evaluation.