Photoelectrocatalytic performance of nanostructured p-n junction NtTiO2/NsCuO electrode in the selective conversion of CO2 to methanol at low bias potentials

• Published in: Journal of CO2 utilization 2018-03, Vol.24, p.81-88
• Main Authors: Brito, Juliana Ferreira de, Hudari, Felipe Fantinato, Zanoni, Maria Valnice Boldrin
• Format: Article
• Language: English
• Subjects: CO2 reduction; Methanol formation; Nanostructured NtTiO2/NsCuO semiconductor; p-n junction; Photoelectrocatalysis mechanism
• ISSN: 2212-9820; 2212-9839
• DOI: 10.1016/j.jcou.2017.12.008

[Display omitted] •Photoelectrochemical CO2 reduction at an n-p NtTiO2/NsCuO semiconductor.•Selective formation of methanol by CO2 reduction.•Oxidation of formed products by hydroxyl radicals generated by water oxidation.•Influence of holes and hydroxyl scavenger in CO2 reduction.•Mechanism of photoelectrocatalytic reduction of CO2 under different electrolytes. Aiming a selective reduction of CO2 to methanol, a p-n junction semiconductor was constructed based on CuO nanospheres (NsCuO) deposited at TiO2 nanotubes (NtTiO2). The NtTiO2/NsCuO material demonstrated smaller charge transfer resistance, smaller flat band potential and wider optical absorption when compared with NtTiO2 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 NtTiO2/NsCuO was similar to the non-completely nanostructured material Ti/TiO2/CuO (0.1 mmol L−1 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.