Porous Graphene Nanoarchitectures: An Efficient Catalyst for Low Charge-Overpotential, Long Life, and High Capacity Lithium–Oxygen Batteries

The electrochemical performance of lithium–oxygen (Li–O₂) batteries awaits dramatic improvement in the design of porous cathode electrodes with sufficient spaces to accommodate the discharge products and discovery of effective cathode catalysts to promote both oxygen reduction reactions and oxygen evolution reactions. Herein, we report the synthesis of porous graphene with different pore size architectures as cathode catalysts for Li–O₂ batteries. Porous graphene materials exhibited significantly higher discharge capacities than that of nonporous graphene. Furthermore, porous graphene with pore diameter around 250 nm showed the highest discharge capacity among the porous graphene with the small pores (about 60 nm) and large pores (about 400 nm). Moreover, we discovered that addition of ruthenium (Ru) nanocrystals to porous graphene promotes the oxygen evolution reaction. The Ru nanocrystal-decorated porous graphene exhibited an excellent catalytic activity as cathodes in Li–O₂ batteries with a high reversible capacity of 17 700 mA h g^–1, a low charge/discharge overpotential (about 0.355 V), and a long cycle life up to 200 cycles (under the curtaining capacity of 1000 mAh g^–1). The novel porous graphene architecture inspires the development of high-performance Li–O₂ batteries

Microwave-assisted Synthesis of Mesoporous Co₃O₄ Nanoflakes for Applications in Lithium Ion Batteries and Oxygen Evolution Reactions

Mesoporous Co₃O₄ nanoflakes with an interconnected architecture were successfully synthesized using a microwave-assisted hydrothermal and low-temperature conversion method, which exhibited excellent electrochemical performances as anode materials in lithium ion batteries and as catalysts in the oxygen evolution reaction (OER). Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) observations showed the unique interconnected and mesoporous structure. When employed as anode materials for lithium ion batteries, mesoporous Co₃O₄ nanoflakes delivered a high specific capacity of 883 mAh/g at 0.1C current rate and stable cycling performances even at higher current rates. Post-mortem analysis of <i>ex situ</i> FESEM images revealed that the mesoporous and interconnected structure had been well maintained after long-term cycling. The mesoporous Co₃O₄ nanoflakes also showed both OER active properties and good catalytic stability. This could be attributed to both the stability of unique mesoporous structure and highly reactive facets

Cross-Linking Hollow Carbon Sheet Encapsulated CuP₂ Nanocomposites for High Energy Density Sodium-Ion Batteries

Sodium-ion batteries (SIB) are regarded as the most promising competitors to lithium-ion batteries in spite of expected electrochemical disadvantages. Here a “cross-linking” strategy is proposed to mitigate the typical SIB problems. We present a SIB full battery that exhibits a working potential of 3.3 V and an energy density of 180 Wh kg^–1 with good cycle life. The anode is composed of cross-linking hollow carbon sheet encapsulated CuP₂ nanoparticles (CHCS-CuP₂) and a cathode of carbon coated Na₃V₂(PO₄)₂F₃ (C-NVPF). For the preparation of the CHCS-CuP₂ nanocomposites, we develop an <i>in situ</i> phosphorization approach, which is superior to mechanical mixing. Such CHCS-CuP₂ nanocomposites deliver a high reversible capacity of 451 mAh g^–1 at 80 mA g^–1, showing an excellent capacity retention ratio of 91% in 200 cycles together with good rate capability and stable cycling performance. <i>Post mortem</i> analysis reveals that the cross-linking hollow carbon sheet structure as well as the initially formed SEI layers are well preserved. Moreover, the inner electrochemical resistances do not significantly change. We believe that the presented battery system provides significant progress regarding practical application of SIB