Cationic vanadium vacancy-enriched V2−xO5 on V2C MXene as superior bifunctional electrocatalysts for Li-O2 batteries

The development of cationic vacancies has been extensively examined as an effective strategy to improve the activity of electrocatalysts. However, it is a challenge to effectively introduce cationic vacancies on the material surface. Their specific effects on the electrochemical performance of lithium-oxygen (Li-O 2 ) batteries are rarely reported. In this work, vanadium pentoxide with abundant vanadium vacancies (V 2− x O 5 ) is in situ prepared on the V 2 C MXene (V 2− x O 5 @V 2 C MXene) surface, and their bifunctional catalytic activity toward the oxygen electrode reaction in Li-O 2 batteries is systematically examined. The results show that the V 2− x O 5 @V 2 C MXene-based Li-O 2 battery exhibits excellent performance. It delivers a high energy efficiency of 83.4% at 100 mA g −1 and excellent cycling performance of more than 500 cycles. Furthermore, density functional theory calculations confirm that the presence of cationic vanadium vacancies can provide abundant active sites to reduce the reaction barrier and optimize the adsorption of reactants, increasing the oxygen electrode reactions in the Li-O 2 battery. This work provides a meaningful view that modulating the electronic structure by creating cationic metal vacancies can improve the electrocatalytic activity of transition metal oxides.