Preparation and characterization of polypyrrole films for three-dimensional micro supercapacitor

As electro-active electrodes for supercapacitors, micro polypyrrole (PPy) films doping with ClO4− (PPyClO4PPyClO4) and Cl− (PPyCl) are prepared on Ni layers modified three-dimensional (3D) structures in Si substrates. The key process to fabricate the 3D structures is high-aspect-ratio deep reactive ion etching, which result in significant increase of available surface area. Homogeneous conformal Ni layers and PPy films are deposited on the 3D structures by electroless plating and electropolymerization, respectively. The supercapacitor properties of PPy films are investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge with three-electrode system in NaCl solution. It is shown that doping with ClO4− results in ideal supercapacitor behaviors with rectangle-like CV shapes at scan rates from 5 to 200 mV s−1, linear galvanostatic charge/discharge curves at current loads from 0.5 to 2 mA and stable cyclic property. However, doping with Cl− gives rise to non-ideal properties of supercapacitor. SEM of the PPyClO4PPyClO4 shows that the surface of the PPyClO4PPyClO4 electrode is smooth and the thickness of the PPyClO4PPyClO4 film is about 2.5 μm. The geometric capacitance of PPyClO4PPyClO4 is calculated as 0.030 F cm−2 from CV at scan rate of 100 mV s−1, 0.023 F cm−2 from EIS and 0.027 F cm−2 from galvanostatic discharge at 1 mA cm−2 current density.