A Facile Ammonium Peroxo-polymolybdate-tailoring Assistant Method To Fabricate Freestanding Graphene Nanosheets For Electrochemical Energy Storage

Li air batteries have been considered as the most promising electric energy storage systems with high energy density and power density. Considerable efforts have been devoted to explore effective strategies to design advanced electrode materials or electrocatalysts with high activity, low costs, and excellent stability for Li ion batteries or Li air batteries. Various groups work on reasonable structures, such as freestanding thin layers, and hybrid architectures using various approaches including electrochemical and hydrothermal approaches. However, alternative strategies for the synthesis of low cost and highly efficient electrode materials for Li ion batteries and Li air batteries are still very desirable.Vertically aligned graphitic carbon nanosheets(VAGN) on substrates are promising materials in various areas, but the synthesis of VAGN is challenging. Herein, we present a facial approach for the fabrication of VAGN on Ni foams using a ammonium peroxo-polymolybdate-tailoring assistant self-assembly. The resulting VAGN films possess controllable sizes of nanosheets and pores by adjusting rate of charge in hydrothermal, and the films behave good electronic conductivity and strong adhesion. In electrochemical energy storage, such unique features are favorable for providing efficient mass transport as well as abundant and accessible active sites. The VAGN films were tested as electrodes in supercapacitors and Li-O2 batteries, and exhibit enhanced specific capacities in both of the two systems.The VAGN can act as efficient catalyst for oxygen reduction reaction(ORR) and OER in the Li air batteries. The VAGN behaves a discharge capacity of 6500 m Ah·g–1 at a current density of 0.1 A·g–1 in the potential range of 2-4.2 V. The battery can maintain more than 100 cycles before the discharge/charge voltages over 1.5 or 4.5 V using 0.5 A·g–1 current density within 500 mh A·g–1 capacity limitation.When employed as supercapacitor electrodes, At a current density of 20 A·g–1, VAGN presents a specific capacitance of 634 F·g–1, which is higher than the theoretical EDL capacitance of 550 F·g–1 for pure graphene. Even at the high current density of 200 A·g–1, the capacitance still remains 240 F·g–1.Herein, we use a highly oxidizing ion, peroxo-polymolybdate, to synthesize graphitic foam by means of hydrothermal. The peroxo-polymolybdate ions serve as tailoring agent in foam forming, which can adjust the sizes of graphitic nanosheets and the pores in foam. Moreover, the produced oxide, Mo O2, endows the foam a favorable electric conductivity owing to its high conductivity of around 104 S.cm–1. The merits of our graphitic foam lead outstanding performances as self-supported electrodes in Li ion batteries and Li-air batteries.When employed as cathode for Li air batteries. The graphitic foam behaves a discharge capacity of 6500 m Ah·g–1 at a current density of 0.1 A·g–1 in the potential range of 2-4.3 V. The battery can maintain more than 60 cycles using 0.5 A·g–1 current density within 500 m Ah·g–1 capacity limitation, before the discharge/charge voltages over 2.0 or 4.5 V.When act as a Li ion battery anode material. The battery can release 1300 m Ah·g–1 at 0.1 A·g–1 and 100 m Ah·g–1 at 100 A·g–1. The battery can cycle more than 250 rounds at a 50 A·g–1 rate current, and maintains a near 100% coulombic efficiency all through the test.