Supercritical CO 2 (SCCO 2 ) is used to synthesize MnO 2 . This process is found to be promising for producing oxide nanorods ($5 nm in diameter) with little agglomeration. With suitable SCCO 2 pressure and temperature, nanocrystalline a-MnO 2 with an extremely high surface area of 245 m 2 g À1 (versus 80 m 2 g À1 for the oxide prepared in ambient air) was obtained. Introduction of graphene nanosheets and carbon nanotubes into MnO 2 with and without the aid of SCCO 2 is compared. SCCO 2 can help debundle the graphene nanosheets and uniformly disperse the MnO 2 nanorods in between, thus preventing graphene restacking. Since the oxide particles are sandwiched between the highly conductive sheets, a high electrochemical utilization is obtained. Accordingly, SCCO 2 -MnO 2 /graphene shows superior supercapacitor properties. The feasibility of using an ionic liquid (IL) as a conductive wrapping agent to improve the performance of the MnO 2 /graphene electrode is demonstrated.Because the intimate contact between the oxide and graphene can be ensured and the interfacial double-layer capacitance can be optimized, the electrode wrapped with an IL shows a higher capacitance, improved high-rate capability, and higher cyclic stability compared to those obtained without IL wrapping.
An eco-efficient synthetic route for the preparation of high-performance carbonate anodes for Li and Na batteries is developed. With supercritical CO (scCO ) as the precursor, which has gas-like diffusivity, extremely low viscosity, and near-zero surface tension, CoCO particles are uniformly formed and tightly connected on graphene nanosheets (GNSs). This synthesis can be conducted at 50 °C, which is considerably lower than the temperature required for conventional preparation methods, minimizing energy consumption. The obtained CoCO particles (ca. 20 nm in diameter), which have a unique interpenetrating porous structure, can increase the number of electroactive sites, promote electrolyte accessibility, shorten ion diffusion length, and readily accommodate the strain generated upon charging/discharging. With a reversible capacity of 1105 mAh g , the proposed CoCO /GNS anode shows an excellent rate capability, as it can deliver 745 mAh g in 7.5 min. More than 98 % of the initial capacity is retained after 200 cycles. These properties are clearly superior to those of previously reported CoCO -based electrodes for Li storage, indicating the merit of our scCO -based synthesis, which is facile, green, and can be easily scaled up for mass production.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.