Saturday, March 28, 2015

Electrostatic supercaps by ALD anodic alumina for energy harvesting [OPEN ACCESS]

Development of electrostatic supercapacitors by atomic layer deposition on nanoporous anodic aluminum oxides for energy harvesting applications [OPEN ACCESS]
Lucía Iglesias, Víctor Vega, Javier García, Blanca Hernando and Víctor M. Prida
Front. Phys., 25 March 2015 | doi: 10.3389/fphy.2015.00012 

Schematic view of the cross section of the supercapacitor engineered onto the NAAM indicating the CDC layered structure and defining the lattice parameters involved in the capacitance calculation. Conductive layers of AZO are in red and dielectric layer of alumina in brown. Outlined are the 3 different contributions to total capacitance of the-designed supercapacitor prototype.

Nanomaterials can provide innovative solutions for solving the usual energy harvesting and storage drawbacks that take place in conventional energy storage devices based on batteries or electrolytic capacitors, because they are not fully capable for attending the fast energy demands and high power densities required in many of present applications. Here, we report on the development and characterization of novel electrostatic supercapacitors made by conformal Atomic Layer Deposition on the high open surface of nanoporous anodic alumina membranes employed as templates. The structure of the designed electrostatic supercapacitor prototype consists of successive layers of Aluminum doped Zinc Oxide, as the bottom and top electrodes, together Al2O3 as the intermediate dielectric layer. The conformality of the deposited conductive and dielectric layers, together with their composition and crystalline structure have been checked by XRD and electron microscopy techniques. Impedance measurements performed for the optimized electrostatic supercapacitor device give a high capacitance value of 200 μF/cm2 at the frequency of 40 Hz, which confirms the theoretical estimations for such kind of prototypes, and the leakage current reaches values around of 1.8 mA/cm2 at 1 V. The high capacitance value achieved by the supercapacitor prototype together its small size turns these devices in outstanding candidates for using in energy harvesting and storage applications.
(A) TEM top view image of a planar section of the sample structure after being carefully prepared for displaying the nanopores after depositing the CDC structure. (B) TEM image showing the different CDC layers constituting the supercapacitor: BE and TE of AZO layers are represented in red color and the Al2O3 dielectric layer in green. (C) STEM image and (D) compositional analysis along the line-scan profile of the pore indicated in (C), where it is clearly evidenced the presence of three elements [zinc (blue), aluminum (red) and oxygen (green)], which spatially match with the CDC structure deposited on the NAAM.