Photo-electrochemical CO2 reduction at CuInS2 thin-film cathodes modified with CuIn alloy particles derived from Cu2O particles

In order to reduce CO2 to ethanol, the CuIn alloy-particle modified CuInS2 (CuIn AP/CIS) composite thin-film electrodes have been suggested and their catalytic activity and selectivity have been examined. The CuIn AP/CIS composite thin films have been fabricated via by two-step electrodeposition route - electrodepositing the Cu2O particles on the CuInS2 thin films, followed by electrodeposition of metallic indium on the Cu2O/CuInS2 thin films. Compared to the Cu2O/CuInS2 composite thin-film electrode, the CuIn AP/CIS composite thin-film electrode exhibits high catalytic activity and selectivity for ethanol formation. At the CuIn AP/CIS composite thin-film electrode with electrodeposition of In for 30 s, ethanol concentration reaches 0.046 mM at 1.5 h. The results of the electrochemical impedance spectra show that the interface charge-transfer is the rate-determining step in the CO2 reduction process, and the CuIn AP/CIS composite thin-film electrode with electrodeposition of In for 30 s exhibits the smallest resistant of the interface charge-transfer. The study on the adsorbed intermediates shows that the surface modification of CuIn AP increases *CO coverage and decreases *H coverage significantly, thus promoting coupling of *CO. Therefore, the selectivity for ethanol formation is improved.