New insights into the photo-enhanced electrocatalytic reduction of carbon dioxide on MoS2-rods/TiO2 NTs with unmatched energy band

• Published in: Applied catalysis. B, Environmental Environmental, 2014-04, Vol.147, p.912-919
• Main Authors: Li, Peiqiang, Hu, Haitao, Xu, Jinfeng, Jing, Hua, Peng, Hui, Lu, Jing, Wu, Chenxiao, Ai, Shiyun
• Format: Article
• Language: English
• Subjects: Anodizing; Carbon dioxide; Electrocatalysis; Energy bands; Ethanol; Methyl alcohol; Molybdenum disulfide; MoS2-rods/TiO2 NTs; Nanostructure; PEEC reduction; Reduction; Titanium dioxide
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2013.10.010

The surface morphology of the prepared electrode are shown in Fig. a. It demonstrates that MoS2 grows to be hexagonal prism structure (length of 50–80μm), and grows randomly on the surface of TiO2 NTs. TiO2 NTs can be seen from the gap of MoS2. Fig. b shows that the prepared TiO2 NTs pile together with almost homogenous diameters (90–100nm). Fig. c and d are the further enlarged images of MoS2, it can be clearly seen that they are hexagonal prism structure and their diameters are about 5μm. Furthermore, surface morphologies on the MoS2 are rather flat without notable defects. It is reasonable to imagine that the regular structure would be beneficial to the electron transfer, which is further favorable to improve the catalytic ability. •MoS2-rods/TiO2 NTs was synthesized by a facile hydrothermal and potentiostatic anodic oxidation method.•The faradaic efficiency increased from 42.20% (EC) to 111.58% (PEEC).•The superior performance was explained from the overpotential, the electron transmission ability and the formation of p–n heterojunction. In this paper, the highly-ordered TiO2 nanotube arrays (TiO2 NTs) were obtained by improved anodic oxidation method and the MoS2-rods were assembled to the TiO2 NTs by a facile hydrothermal method, obtained the MoS2-rods/TiO2 NTs heterojunction. According to the UV–vis DRS and XPS analysis, the obtained MoS2-rods/TiO2 NTs exhibited excellent absorption in the visible area (400–600nm) and its energy band gap was 1.55eV, but its conduction band (−0.15eV) was more positive than the CO2 reduction potential, it indicated that MoS2-rods/TiO2 NTs had no ability for photocatalytic reduction of CO2. Electrocatalysis could reduce CO2, but the products yield was very low and the faraday efficiency gradually reduced with reaction going on. Interestingly, when illumination was introduced into the electrocatalytic process, the light greatly enhanced the CO2 electrocatalytic reduction ability of the MoS2-rods/TiO2 NTs. Furthermore, the faraday efficiency increased to 2.65 times from 42.20% (electrocatalysis) to 111.58% (photo-enhanced electrocatalysis), and the methanol yield increased to 2.29 times from 6.32mmolL−1 to 14.49mmolL−1. The new insights for how light enhanced electrocatalytic reduction of CO2 was elaborated systematically from three aspects, that is, reduction overpotential, enhanced electron transmission ability, and generated p–n heterojunction. Furthermore, the generation mechanism of methanol with photo-enhanced elec