Selective photoelectrocatalytic reduction of CO2 to ethanol with a CuO–MoO3/TiO2NTs composite photoelectrode†

Overusing fossil energy sources has led to global warming, seriously risking the habitability of the environments on which people depend. Photoelectrocatalytic (PEC) reduction of carbon dioxide (CO₂) is a promising strategy to reduce CO₂ into high-value-added chemicals and fuel products. However, photoelectrocatalysis faces problems related to low CO₂ conversion efficiency and uncontrollable product complexity. This study reports a CuO–MoO₃/TiO₂NTs composite photoelectrode prepared by pulsed electrodeposition for the photoelectrocatalytic (PEC) reduction of CO₂ to ethanol in a 1 M NaHCO₃ medium under visible light irradiation and at an applied potential of −0.3 V vs. SCE. Molybdenum trioxide plays a regulatory role in the structure and properties of the photoelectrode. Photoluminescence analysis suggests that this occurs by introducing new energy levels between those of CuO and TiO₂, which reduces the bandgap energy from 1.42 eV to 1.17 eV, promotes electron–hole pair separation, and significantly boosts photoelectrocatalytic activity. In addition, experimental results show that the doping of MoO₃ enhanced the adsorption strength of the intermediate products and promoted the C–C coupling process. The optimized composite photoelectrode achieves 89% Faraday efficiency for ethanol at −0.5 V versus SCE (saturated calomel electrode). No new phases were generated during the catalytic process, confirming the stability of the CuO–MoO₃/TiO₂NTs composite photoelectrode.