These mats of nanowires can be used as electrodes for batteries and capacitors.
Mats of free-standing manganese oxide (MnxOy ) nanowires have been fabricated as experimental electrode materials for rechargeable electro- chemical power cells and capacitors. Because they are free-standing, the wires in these mats are electrochemically accessible. The advantage of the mat- of-nanowires configuration, relative to other configurations of electrode materials, arises from the combination of narrowness and high areal number density of the wires. This combination offers both high surface areas for contact with electrolytes and short paths for diffusion of ions into and out of the electrodes, thereby making it possible to charge and discharge at rates higher than would otherwise be possible and, consequently, to achieve greater power densities.
The locations and sizes of the nanowires are defined by holes in templates in the form of commercially available porous alumina membranes. In experiments to demonstrate the present process, alumina membranes of various pore sizes and degrees of porosity were used. First, a film of Au was sputtered onto one side of each membrane. The membranes were then attached, variously, to carbon tape or a gold substrate by use of silver or carbon paste. Once thus attached, the membranes were immersed in a plating solution comprising 0.01 M MnSO4 +0.03 M (NH4)2SO4. The pH of the solution was kept constant at 8 by addition of H2SO4 or NH4OH as needed. MnxOy nanowires were potentiostatically electrodeposited in the pores in the alu- mina templates. Depending on the anodic deposition potentials, MnxOy was deposited in various oxidation states [divalent (Mn3O4), trivalent (Mn2O3),or tetravalent (MnO2)]. The MnxOy wires were made free-standing (see figure) by dissolving the alumina templates,variously, in KOH or NaOH at a concentration of 20 volume percent.
This work was done by Nosang Myung, William West, Jay Whitacre, and Ratnakumar Bugga of Caltech for NASA's Jet Propulsion Laboratory.
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Refer to NPO-30655,volume and number of this NASA Tech Briefs issue, and the page number.
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