Rationally Designed Three-Dimensional N-Doped Graphene Architecture Mounted with Ru Nanoclusters as a High-Performance Air Cathode for Lithium-Oxygen Batteries

To enhance the electrochemical performance of lithium-air/oxygen batteries, it is extremely important to design and synthesize cathodes with porous structures and bifunctional catalytic activity. Graphene mounted with ruthenium nanoparticles is presently one of the best cathodes for the Li-O-2 battery, but its excellent characteristics are hampered by reduced graphene oxide (rGO) aggregation and irregular crispation, and the costliness of high Ru loading (20-40 wt %) makes its practical application infeasible. To overcome these problems, we prepared nitrogen-doped three-dimensional graphene (3D-NrGO) by the linkage of rGO nanosheets and mounted it with highly dispersed Ru nanoclusters to achieve a reduced Ru loading of 9.37 wt %. The 3D porous structure yields a material with a high specific surface area of 597 m(2).g(-1) and a high doped N content of 7.80 wt %. The resulting Li-O-2 battery with Ru/3D-NrGO as a cathode exhibits a high specific capacity of 23922 mA.h.g(-1) at 100 mA.g(-1), placing it among the best reported capacities thus far. It also achieves a cycling life of 200 cycles with a limited capacity of 1000 mA.h.g(-1) with a charge overpotential of 0.94 V. The battery also shows a high rate performance of 8830 mA.h.g(-1) at a large discharge current density of 1000 mA.g(-1). We find that the 3D linkages enhance the material's performance by over 20% compared with the material without 3D linkages (7061 mA.h.g(-1)). In light of the characterization results, we ascribe the ultrahigh performance of the material to its 3D linked-sheet structure, which yields a highly efficient surface area through effectively preventing aggregation and crimping in the graphene sheets. In addition, N doping and the mounting of Ru nanoclusters give the material high active site density and high ORR/OER activity.