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

Abstract

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 electrocatalysis was also deduced. Especially, we deduced that the protons involving into the CO2 reduction came from two aspects, one was from the electrocatalytic oxidation water on the anode, and the other was from the in situ photocatalytic oxidation water on the cathode.