Efficient photoelectrochemical conversion of CO2 to ethylene and methanol using a Cu cathode and TiO2 nanoparticles synthesized in supercritical medium as photoanode.

The photoelectrochemical conversion of CO 2 into valuable products represents an attractive method to decrease the external electrical bias required in electrochemical approaches. In this work, TiO 2 nanoparticles with enhanced optical properties, large surface area, appropriate morphology, and superior crystallinity are synthesized in supercritical medium to manufacture light-responsive photoanodes. The photoelectrochemical CO 2 reduction tests are carried out in continuous mode using a photoanode-driven filter-press cell illuminated with UV LED lights (100 mW cm^-2), consisting on TiO 2 nanoparticles synthesized in supercritical medium (3 mg cm^-2) supported onto porous carbon paper as the photoanode, a Cu plate cathode, and 1 M KOH aqueous solution as the reaction medium. The main products obtained from CO 2 are ethylene in the gas phase, together with methanol in the liquid phase. The results show that reaction performance is improved under UV irradiation towards ethylene (r = 147.4 μmol m⁻² s⁻¹; FE = 46.6%) and methanol (r = 4.72 μmol m⁻² s⁻¹; FE = 15.3%) in comparison with the system performance in the dark (ethylene: r = 24.2 μmol m⁻² s⁻¹ and FE = 38.2%; methanol not detected), which can be mainly ascribed to the superior photocurrent densities reached that affect the selectivity of the reaction. Besides, the maximum solar-to-fuels values achieved for ethylene (5.4%) and methanol (1.9%) are markedly superior to those observed with illuminated TiO 2 -P25 photoanodes under the same reactor configuration and experimental conditions (3.7% and 1%, respectively). Therefore, these results demonstrate the benefits of using TiO 2 -based materials synthesized in supercritical medium for a more efficient continuous photoelectroreduction of CO 2 to value-added products. [Display omitted] [ABSTRACT FROM AUTHOR]