Contribution of CuxO distribution, shape and ratio on TiO2 nanotubes to improve methanol production from CO2 photoelectroreduction
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Many studies are focused on the development of materials for converting carbon dioxide into multicarbon oxygenates such as methanol and ethanol, because of their higher energy density and wider applicability. In this work, TiO2 nanotubes (NT/TiO2) were modified with CuxO nanoparticles in order to investigate the contribution of different ratio of Cu2O/CuO and its distribution over NT/TiO2 for CO2 photoelectro-conversion to methanol. The photoelectrodes were built by anodization process to obtain NT/TiO2 layer, and the decoration with CuxO hybrid system was carried out by electrodeposition process, using Na2SO4 or acid lactic as electrolyte, followed by annealing at different temperatures. X-ray photoelectron spectroscopy analysis revealed the predominance of Cu+1 and Cu+2 at 150 °C and 300 °C, respectively. X-ray diffraction and scanning electron microscopy indicated that under lactic acid solution, the oxide nanoparticles exhibited small size, cubic shape, and uniform distribution on the nanotube wall. While under Na2SO4 electrolyte, large nanoparticles with two different morphologies, octahedral and cubic shapes, were deposited on the top of the nanotubes. All modified electrodes converted CO2 in methanol in different quantities, identified by gas chromatograph. However, the NT/TiO2 modified with CuO/Cu2O (80:20) nanoparticles using lactic acid as electrolyte showed better performance in the CO2 reduction to methanol (0.11 mmol L−1) in relation to the other electrodes. In all cases, a blend among the structures and nanoparticle morphologies were achieved and essential to create new site of reactions what improved the use of light irradiation, minimization of charge recombination rate and promoted high selectivity of products.