▎ 摘　　要

The oxygen reduction reaction (ORR) is one of the most important reactions in renewable energy conversion and storage devices. The full deployment of these devices depends on the development of highly active, stable, and low-cost catalysts. Herein, a new hybrid material consisting of Na2Ta8O21-x/Ta2O5/Ta3N5 nanocrystals grown on N-doped reduced graphene oxide is reported. This catalyst shows a significantly enhanced ORR activity by approximate to 4 orders of magnitude in acidic media and by approximate to 2 orders of magnitude in alkaline media compared to individual Na2Ta8O21-x on graphene. Moreover, it has excellent stability in both acid and alkaline media. It also has much better methanol tolerance than the commercial Pt/C, which is relevant to methanol fuel cells. The high ORR activity arises not only from the synergistic effect among the three Ta phases, but also from the concomitant nitrogen doping of the reduced graphene oxide nanosheets. A correlation between ORR activity and nitrogen content is demonstrated. Deep insights into the mechanism of the synergistic effect among these three Ta-based phases, which boosts the ORR's kinetics, are acquired by combining specific experiments and density functional theory calculations.