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Carbon Nanotube Foams And Nanoscale Manganese Oxide Make Improved Supercapacitor Electrodes Say Navy Scientists

Contributed by Alton Parrish (Editor)
Tue May 25 2010 05:34

The United States Navy (Washington, DC) garnered U.S. Patent 7,724,500 [ http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/PTO/srchnum.htm&r=1&f=G&l=50&s1=7,724,500.PN.&OS=PN/7,724,500&RS=PN/7,724,500 ] for a composite made of nanoscale manganese oxide (MnO2) on an ultraporous carbon nanoarchitecture which can be used to manufacture improved supercapacitor electrodes.

Inventors Jeffrey W. Long, Anne E. Fischer and Debra R. Rolison say the composite is a porous carbon structure with a surface and pores and a coating of MnO2 on the carbon surface, in which the coating does not completely fill or obstruct a majority of the pores. The coating is formed by self-limiting electroless deposition.

Electrochemical capacitors (also denoted as supercapacitors or ultracapacitors) are a class of energy-storage materials that offer significant promise in bridging the performance gap between the high energy density of batteries and the high power density derived from dielectric capacitors. Energy storage in an electrochemical capacitor is accomplished by two principal mechanisms: double-layer capacitance and pseudocapacitance.

Nanostructured MnO2-carbon nanoarchitecture hybrids can be designed as electrode structures for high-energy-density electrochemical capacitors that retain high power density. Homogeneous, ultrathin coatings of nanoscale MnO2 can be incorporated within porous, high-surface-area carbon substrates (such as carbon nanofoams) via electroless deposition from aqueous permanganate under controlled pH conditions.

The resulting hybrid structures exhibit enhanced gravimetric, volumetric, and area-normalized capacitance when electrochemically cycled in aqueous electrolytes. This design can be extended to other mesoporous and macroporous carbon forms possessing a continuous pore network.

The performance limitations of MnO2 for electrochemical capacitors can be addressed with a hybrid electrode design, by incorporating discrete nanoscale coatings or deposits of MnO2 onto porous, high-surface-area carbon structures (see FIG. 1).

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