Reducing d-p band coupling to enhance CO2 electrocatalytic activity by Mg-doping in Sr2FeMoO6-δ double perovskite for high performance solid oxide electrolysis cells

Abstract Solid oxide electrolysis cells (SOECs) could convert CO2 greenhouse gas into valuable fuels and chemicals with high energy efficiency. Unfortunately, the lack of efficient cathode materials obstructs their practical applications. Herein, a promising cathode material with high activity and stability is developed, with the partial replacement of the transition metal Mo by the alkaline-earth metal Mg in the double perovskite structure of Sr2FeMoO6-σ. The replacement of Mo by Mg could not only improve its redox stability, but also enhance the CO2 electrolysis performance. In the same test environment, the electrolytic current of the LSGM electrolyte-supported single cell with Sr2FeMo2/3Mg1/3O6−δ as the cathode is almost two times higher than that of the Sr2FeMoO6-σ cathode. Density functional theory with Hubbard correlation reveals that the improved electrocatalytic performance results from the reduced d-p band coupling introduced by the dopant of Mg, which is short of d electrons, favoring the formation of oxygen vacancies for the MgB-VO-FeB′ and FeB-VO-FeB′ bonds. These newly formed oxygen vacancies have highly catalytic activity toward CO2 activation and the subsequent dissociation process. Our strategy demonstrates a general method for the development of promising new catalysts for efficient CO2 reutilization by modulating the electronic structures using d-electron-free elements.