Double-layer capacitors composed of interconnected silver particles and with a high-frequency response

Porous and multi-layer network of interconnected silver particles is deposited by galvanic displacement on a technologically relevant substrate, silicon with an aluminum/copper film. The mean particle diameter is approximately 200 nm and the particle density in a single layer is 10(9) particles per cm(2). Cyclic voltammetry and electrochemical impedance spectroscopy reveal that capacitance normalized to the electrode geometric area reaches a value of 1.7 +/- 0.2 mF/cm(2), which is about two orders of magnitude higher than that observed on a smooth silver/electrolyte interface. The specific surface area of silver particles, which are assumed to be spherical, is 2.7 m(2)/g. The electrolyte accessible surface area is slightly larger (3.5 m(2)/g) due to the surface roughness of silver particles. The frequency response of the porous network of silver particles is analyzed using the transmission line model. The "knee" frequency is determined to be around 200 Hz. The described capacitor could find applications for special electronic circuits where a high-frequency response is needed. (C) 2005 Elsevier Ltd. All rights reserved.