Electrochemical reduction of CO2 to CO on Zn electrodes prepared by electrodeposition method

Abstract

In this work, the effect of substrates including Cu and Ti on the catalytic activity of Zn electrocatalysts prepared by electrodeposition method was investigated in the electrochemical reduction of CO2 (CO2ER). As analyzed by SEM-EDX and XRD results, it indicated that the different substrates did not have any influence on the morphologies of catalysts and the conductivity of substrate was the main factor on the CO2ER performance. The effect of Zn precursor concentration in the range of 0.025 M to 0.4 M was further studied on the characteristics and the activity of Zn/Cu catalysts in the CO2ER. . At low concentrations of Zn precursor (0.025M and 0.05M), the catalysts exhibited the same dendrite structure. Increasing Zn concentration to 0.1 M, the morphology changed into mossy structure with the highest amount of Zn deposited. On the contrary, at higher concentration of Zn precursor than 0.1M, lower amount of Zn was deposited because of the faster H2 evolution rate. In addition, larger amount of oxide layer was covered on Zn surface, which impeded the performances of the CO2ER. Among the prepared catalysts, the best catalyst was 0.05 Zn/Cu, which provided the highest faradaic efficiency (FE) of CO due probably to the highest amount of catalytic active Zn (101) facet. Finally, comparing the use of 0.05Zn/Cu electrocatalysts in aqueous electrolyte and ionic liquid, the results showed that ionic liquid decreased the applied potential in the CO2ER but the Zn catalyst was not stable and then, fell off the catalyst surface. In contrast, the Zn catalyst in aqueous solution could re-deposit on the substrate after CO2ER. The highest %FE of CO was achieved in 0.1 M KHCO3. Moreover, 0.05Zn/Cu provided the nearly 1.5 times higher %FE of CO than Zn foil, indicating that the dendrite structure enhanced the CO2ER activity.