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 CO 2 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 Sr 2 FeMoO 6-σ . The replacement of Mo by Mg could not only improve its redox stability, but also enhance the CO 2 electrolysis performance. In the same test environment, the electrolytic current of the LSGM electrolyte-supported single cell with Sr 2 FeMo 2/3 Mg 1/3 O 6−δ as the cathode is almost two times higher than that of the Sr 2 FeMoO 6-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 Mg B -V O -Fe B′ and Fe B -V O -Fe B′ bonds. These newly formed oxygen vacancies have highly catalytic activity toward CO 2 activation and the subsequent dissociation process. Our strategy demonstrates a general method for the development of promising new catalysts for efficient CO 2 reutilization by modulating the electronic structures using d -electron-free elements. • A highly active and stable cathode material for SOECs is successfully obtained. • The formation energy of oxygen vacancy in SFM is obviously reduced by Mg doping. • Mg doping reduces the coupling between the d bands of metals and p bands of oxygen. • The CO 2 activation and the subsequent dissociation process are optimized by Mg doping. • It is a promising method for efficient CO 2 reutilization by using d -electron-free elements.