Current-Dependent Pathway Switching in Electrochemical Oxidative Dehydrogenation of Ethane Over an LSC Electrode in SOEC

Abstract

Electrochemical oxidative dehydrogenation (ODH) of ethane in solid oxide electrolysis cells (SOECs) offers a promising alternative to energy-intensive steam cracking. This work investigates the ODH mechanism using an LSC (La_0.6Sr_0.4CoO_3-δ) anode in a 5 cm*5 cm single cell, achieving high ethylene selectivity (∼44%) at 650°C. In contrast, operation at elevated temperatures (e.g., 700°C) leads to anode degradation and a shift in selectivity. Through a combination of electrochemical impedance spectroscopy with distribution of relaxation times (EIS-DRT) and detailed product analysis, we reveal a decisive shift in the dominant reaction pathway governed by the applied current density. At low current densities, the direct electrochemical oxidation of ethane by surface oxygen species prevails. As the current increases, the mechanism transitions to a tandem process where the oxygen evolution reaction occurs first, followed by the thermochemical ODH of ethane. This mechanistic crossover is rationalized by the competition between ethane diffusion to active sites and the rate of electrochemical oxygen supply. These findings provide fundamental insights into the interplay of electrochemical and thermochemical steps in high-temperature alkane electrolysis, highlighting current density as a key lever for controlling selectivity.