Assembling bifunctional ceria-zirconia electrocatalyst for efficient electrochemical conversion of methane at room temperature

Abstract

The electrochemical conversion of methane to C2 compounds at room temperature is reported using CeO2-ZrO2 electrocatalysts. The mixed oxide electrocatalysts produced methanol, ethanol, and acetone, along with traces of acetaldehyde and isopropanol, under a polarization of 1.2 V with ∼ 50 % Faradaic efficiency. Detailed characterization of the CeO2-ZrO2 revealed the formation of nanoparticles (7–9 nm mean size) composed of ceria-zirconia solid solution or a mixture of ceria with both tetragonal and monoclinic zirconia polymorphs depending on the assembling configuration of the electrocatalyst. Samples with separated phases and limited solid solution formation showed the highest electrochemical activity, indicating that an optimal assembly of ceria and zirconia was crucial to achieving efficient conversion with high Faradaic efficiency and selectivity. Such high electrochemical activity observed for the phase separated CeO2-ZrO2 electrocatalyst suggests that a synergic effect between ceria and zirconia is required for the critical reaction steps, such as the activation and partial oxidation of methane. The experimental results point to credible routes to efficiently convert methane into valuable chemicals in mild conditions.