Sulfur poisoning on the La0.75Sr0.25Cr0.5Mn0.5O3-δ-Gd0.1Ce0.9O2-δ fuel electrode for direct electrochemical CO2 reduction in solid oxide electrolysis cells

Abstract

As a promising energy conversion technology, solid oxide electrolysis cells (SOECs) can efficiently convert CO2 to CO by utilizing renewable energy sources and industrial waste heat. Sulfur poisoning of fuel electrode is a significant drawback to the electrochemical activity and long-term electrolysis performance of SOECs using sulfur-containing fuels. Traditional Ni-based cermet electrodes are susceptible to sulfur poisoning due to the low activation barrier and large enthalpy of the adsorbed sulfur species on the Ni surface. La0.75Sr0.25Cr0.5Mn0.5O3-δ-based materials which exhibit excellent redox stability have been considered as the promising candidates for substitution of Ni-based cermet electrodes. Herein, the sulfur poisoning behavior on the La0.75Sr0.25Cr0.5Mn0.5O3-δ-Gd0.1Ce0.9O2-δ (LSCM-GDC) fuel electrode under CO2–SO2 condition and the mechanism of sulfur poisoning are investigated. The results show that the LSCM-GDC fuel electrode possesses stable electrocatalytic activity as SO2 content up to 10 ppm. With increasing of SO2 content, metallic sulfide, amorphous sulfur and sulfate impurities can be detected on the electrode surface, which decrease the reactive sites and hinder the charge transfer and oxygen ions transport pathway, leading to degradation of the electrolysis performance. The plausible sulfur poisoning mechanism is divided into two categories, namely, thermodynamic and electrochemical processes. For thermodynamic process, SO2 molecules adsorb into oxygen vacancies and couple to coordinated oxygen lattices to form sulfates; for electrochemical process, the formation of amorphous sulfur and metallic sulfide impurities is caused by the binding of SO2 molecules to surface polarons at three phase boundaries under cathodic polarization. This work provides new insights into sulfur poisoning effect on the perovskite oxide electrodes.