PEDOT as a conducting layer in capacitors

One of the most widespread technical applications of PEDOT is its use as a counter-electrode in solid aluminum, tantaium and niobium electrolytic capacitors. As early as 1988 the application of PEDOT as a polymeric counter-electrode in a tantalum capacitor was described [32], 

The conducting polymer is roughly 1000 times more conductive than the traditionally used manganese dioxide cathode material and it penetrates more effectively into the porous metal-oxide anode structures, creating more robust capacitor structures. 

Additionally, self-healing properties have been attributed to PEDOTiPSS cathodes in capacitors. As a potential mechanism, it has been postulated that high temperatures caused by leakage currents locally render PEDOT PSS nonconductive [120], thus preventing further leakage and capacitor failure. 

The anode bodies of tantalum, aluminum and most recently niobium capacitors are made of highly porous metals. These bodies are obtained by sintering fine metal powders or by electrochemical etching of thin foils. A thin dielectric layer is then grown electrochemically on the metal surface. Due to the porous structure of the anode bodies, the cathode polymer must be able to penetrate into the pores and coat all internal surfaces in order to utilize the full potential capacitance of the anode. 

Because of the need to penetrate the porous anode stracture deeply, the PEDOT counter-electrode is preferentially formed by in situ polymerization of EDOT with a chemical oxidant. The preferred oxidizing agent is iron(III) p-toluenesulfonate. Monomer and oxidant are usually diluted in short-chain alcohols (ethanol or n-butanol) to obtain low-viscosity impregnation solutions. 

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