Photoelectrocatalytic oxidation of methane into methanol and formic acid over ZnO/graphene/polyaniline catalyst**Project supported by the National Natural Science Foundation of China (Grant Nos. 51602021 and 51474017) and the Fundamental Research Funds for the Central Universities (Grant No. FRF-TP-15-107A1).

Abstract

ZnO/graphene/polyaniline (PANI) composite is synthesized and used for photoelectrocatalytic oxidation of methane under simulated sun light illumination with ambient conditions. The photoelectrochemical (PEC) performance of pure ZnO, ZnO/graphene, ZnO/PANI, and ZnO/graphene/PANI photoanodes is investigated by cyclic voltammetry (CV), chronoamerometry (J–t) and electrochemical impedance spectroscopy (EIS). The yields of methane oxidation products, mainly methanol (CH3OH) and formic acid (HCOOH), catalysed by the synthesized ZnO/graphene/PANI composite are 2.76 and 3.20 times those of pure ZnO, respectively. The mechanism of the photoelectrocatalytic process converting methane into methanol and formic acid is proposed on the basis of the experimental results. The enhanced photoelectrocatalytic activity of the ZnO/graphene/PANI composite can be attributed to the fact that graphene can efficiently transfer photo-generated electrons from the inner region to the surface reaction to form free radicals due to its superior electrical conductivity as an inter-media layer. Meanwhile, the introduction of PANI promotes solar energy harvesting by extending the visible light absorption and enhances charge separation efficiency due to its conducting polymer characteristics. In addition, the PANI can create a favorable π-conjunction structure together with graphene layers, which can achieve a more effective charge separation. This research demonstrates that the fabricated ZnO/graphene/PANI composite promises to implement the visible-light photoelectrocatalytic methane oxidation.