Journal
JOURNAL OF CO2 UTILIZATION
Volume 24, Issue -, Pages 81-88Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jcou.2017.12.008
Keywords
CO2 reduction; Nanostructured NtTiO(2)/NsCuO semiconductor; Methanol formation; p-n junction; Photoelectrocatalysis mechanism
Funding
- Brazilian Research Assistance Agency - FAPESP [2013/25343-8, 2008/10449-7]
- INCT [465571/2014-0]
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Aiming a selective reduction of CO2 to methanol, a p-n junction semiconductor was constructed based on CuO nanospheres (NsCuO) deposited at TiO2 nanotubes (NtTiO(2)). The NtTiO(2)/NsCuO material demonstrated smaller charge transfer resistance, smaller flat band potential and wider optical absorption when compared with NtTiO(2) and/or Ti/TiO2 nanoparticles coated by higher size particles of CuO (Ti/TiO2/CuO). The selective reduction of dissolved CO2 to methanol was promoted at lower potential of +0.2 V and UV-vis irradiation in 0.1 mol L-1 K2SO4 electrolyte pH 8 with 57% of faradaic efficiency. Even though the performance of the nanostructured material NtTiO(2)/NsCuO was similar to the non-completely nanostructured material Ti/TiO2/CuO (0.1 mmol methanol), the conversion to methanol has been significantly increased when hydroxyls (0.62 mmol L-1) and holes scavengers (0.71 mmol L-1), such as p-nitrosodimethylaniline (RNO) or glucose, respectively, were added in the supporting electrolyte. It indicates that photogenerated electron/hole pairs are spatially separated on p-n junction electrodes, which produces effective electrons and long-life holes, influencing the products formed in the reaction. A schematic representation of the heterojunction effect on the photoelectrocatalytic CO2 reduction is proposed under the semiconductor and each supporting electrolyte, which improves the knowledge about the subject.
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