Combined Effect of Catholyte Gap and Cell Voltage on Syngas Ratio in Continuous CO2/H2O Co-electrolysis

Electrochemical devices are constructed for continuous syngas (CO + H2) production with controlled selectivity between CO2 and proton reduction reactions. The ratio of CO to H2, or the faradaic efficiency toward CO generation, was mechanically manipulated by adjusting the space volume between the cathode and the polymer gas separator in the device. In particular, the area added between the cathode and the ion-conducting polymer using 0.5 M KHCO3 catholyte regulated the solution acidity and proton reduction kinetics in the flow cell. The faradaic efficiency of CO production was controlled as a function of the distance between the polymer separator and cathode in addition to that manipulated by the electrode potential. Further, the electrochemical CO2 reduction device using Au NPs presented a stable operation for more than 23 h at different H2:CO production levels, demonstrating the functional stability of the flow cell utilizing the mechanical variable as an important operational factor.