The electrocatalytic reduction of CO 2 on gold cathodes was found to differ significantly between a standard batch electrochemical cell and a flow cell incorporating a porous gold cathode. While the well-known influence of KHCO 3 concentration on product selectivity was observed in the batch cell, the selectivity of the CO 2 reduction reaction was shown to be independent of KHCO 3 concentration in the flow cell. The Faradaic efficiency for CO production was found to be 80–90% regardless of the KHCO 3 concentration whereas in the batch cell it decreased from 75% to 35% as the KHCO 3 concentration is increased from 0.05 to 0.5 mol L −1 . The current density was found to be independent of the KHCO 3 concentration and similar in both cells (−4 to −10 mA cm −2 at −1.3 V vs Ag|AgCl). As the KHCO 3 concentration effect is normally attributed to changes in the local pH at the cathode–electrolyte interface brought about by the buffering action of the electrolyte, the results found in this work suggest that pH buffering can be suppressed or manipulated in some cell/electrode configurations. In the flow cell used in this work, it is suggested that poor transport of the KHCO 3 through the porous cathode support to the active surface results in higher local pH than that found at the surface of a cathode immersed in a traditional batch cell.
Ahangari, H. T., Portail, T., & Marshall, A. T. (2019). Comparing the electrocatalytic reduction of CO 2 to CO on gold cathodes in batch and continuous flow electrochemical cells. Electrochemistry Communications, 101, 78–81. https://doi.org/10.1016/j.elecom.2019.03.005