NiO/ZnO heterojunction nanorod catalyst for high-efficiency electrochemical conversion of methane

Electrochemical conversion is promising for selective partial oxidation of methane. We present a NiO/ZnO shell/ core nanorod catalyst used to enhance electrochemical conversion. The built-in potential at the NiO/ZnO interface and the 1D morphology of the nanorods allow for fast charge transfer, thereby enhancing electrochemical methane conversion. We achieved a high ethanol production rate of 1084.2 mu mol/gNiO/hr with a selectivity of 81 % for a 600-nm long NiO/ZnO nanorod catalyst. Mechanistic analyses with isotopic labeling reactions suggested ethanol production pathways involving generation of active oxygen by dissociative adsorption of the anionic CO32- oxidant, formation of methanol by methane activation, and coupling of deprotonated methanol and methane. Furthermore, we improved the ethanol yield by improving methane solubility in sulfolane cosolvent mixtures. We also demonstrated conversion with in situ generation of CO32- from a CH4/CO2 mixture.