(524h) Electrocatalytic Methane Coupling on Exsolved Perovskite Anodes in Solid Oxide Cells: Spectroscopic and Microscopic Analysis

The oxidative coupling of methane (OCM) offers a direct route to produce C₂₊ hydrocarbons such as ethylene and propylene, which are key precursors in plastic manufacturing. However, traditional OCM pathways are limited by low selectivity and hydrocarbon yields. This is primarily due to the uncontrolled availability of oxygen in the reaction environment, which promotes the overoxidation of methane to CO and CO₂.

Using solid oxide cells (SOCs) with an oxygen-ion-conductive electrolyte to perform OCM can help address these challenges. In this configuration, oxygen ions are electrochemically transported through a dense oxide electrolyte. This setup can precisely control the oxygen supply via an applied external current without relying on molecular oxygen. This controlled oxygen delivery with SOCs allows better regulation of the reaction environment and helps suppress overoxidation.

In this work, we used high-temperature SOCs (800-850 °C) with an in-house developed B-site doped lanthanum ferrite perovskite oxide as the working electrode, which functions as the anode for the OCM reaction. We found that under a reducing methane environment, the perovskite gradually underwent exsolution. Over time, the B-site metal ions migrated from bulk to the surface and formed catalytically active bimetallic nanoparticles (NPs). As these NPs formed, we observed enhanced methane conversion and C₂₊ selectivity. This indicates a boost in the electrocatalytic performance of the working electrode.

We confirmed the structural transformation using XRD, XPS, XANES, and STEM, and evaluated the improvement in catalytic activity through DRIFTS and TPRxn tests. Electrochemical OCM measurements conducted across a range of current densities (OCV to 150 mA cm⁻²) showed steady methane conversion and favorable selectivity toward olefins.

Overall, this study reports that exsolving bimetallic NPs onto the host perovskite oxide, combined with electrochemical control of oxygen supply, is a promising strategy to overcome limitations in OCM.