A General Strategy to Boost Electrocatalytic NitrogenReduction on Perovskite Oxides via the Oxygen VacanciesDerived from A-Site Deficiency

摘要

The electrocatalytic N-2 reduction reaction (NRR) under ambient conditions is an attractive strategy for green synthesis of NH3. Due to the ultra-stable N(sic)N covalent triple bond, it is very challenging to develop highly selective and efficient electrocatalysts toward NRR. Here a general strategy to enhance the NRR activity through modulating A-site-deficiency-induced oxygen vacancies of perovskite oxides is reported. One successful example is LaxFeO3-delta (LxF, x = 1, 0.95, and 0.9) perovskite oxides with tunable oxygen vacancies that are directly proportional to the La-site deficiencies. As compared to the pristine LF, the L0.95F and L0.9F exhibit significantly improved NRR activities, which are positively correlated with the La-site deficiency and the amount of oxygen vacancies. Among them, the L0.9F delivers the best activity, with an NH3 yield rate of 22.1 mu g center dot h(-1)center dot mg(cat.)(-1) at -0.5 V and a Faradaic efficiency of 25.6% at -0.3 V, which are 2.2 and 1.6 times those of the pristine LF, respectively. Both experimental characterizations and theoretical calculations suggest that the enhanced NRR activity can be mainly attributed to the favorable merits produced by the oxygen vacancies: the promoted adsorption/activation of reaction species, and thus optimized reaction pathways. Previous studies on other perovskite oxides have generated similarly successful results.