Promoting nitrate electroreduction to ammonia over A-site deficient cobalt-based perovskite oxides

Abstract

Cobalt-based perovskite oxides have shown great potential in electrocatalysis, but their employment in boosting nitrate electroreduction (NO₃ER) to ammonia is unexplored. Here we report an effective strategy to promote the NO₃ER activity by tuning the A-site deficiencies of cobalt-based perovskite oxides. Using a (Ba_0.5Sr_0.5)_1−xCo_0.8Fe_0.2O_3−δ (x = 0, 0.05, 0.10, 0.15, and 0.20) series as proof-of-concept catalysts, we demonstrate that their NO₃ER activity shows a volcano-type dependence on the x values, with the maximum point at x = 0.15. Among them, at −0.45 V (vs. RHE), (BS)_0.85CF shows the highest activity (143.3 mg h⁻¹ mg_cat⁻¹ or 0.86 mmol h⁻¹ cm⁻²) and selectivity (97.9%) for ammonia, together with excellent stability (200 h), better than those of most reported NO₃ER catalysts. These optimized NO₃ER properties could be ascribed to the physicochemical properties being modulated by the A-site deficiencies, such as creating a moderate amount of oxygen vacancies and introducing a moderate distance between the band center and Fermi level. This work opens up a new avenue for rational design of advanced cobalt-based perovskite oxides for catalyzing NO₃ER.