Three-Dimensionally Ordered Polypyrrole Electrode: Electrochemical Study on Capacity and Degradation Process

Abstract

In this work we critically compare electrochemical stability and specific capacitance of the three-dimensional (3D) polypyrrole membrane and the dense polypyrrole film fabricated at the same conditions. Herein, we concern about study the influence of the electrode morphology on the kinetics of diffusion process by analyzing voltammetry, coulometry and impedance response. This allows us to calculate well-sustained values of the diffusion coefficient, specific capacitance and diffusion resistance, which summarize equilibrium parameters. The ultra-thin walls, uniform porosity and well-ordered structure called “inverse opal” ensure an efficient mass transport and fast charge exchange of the porous polypyrrole resulting in superior electrochemical performance. The calculated diffusion coefficient of anion doping process in 3D polypyrrole is more than two orders of magnitude higher comparing to the control sample. The improved electrochemical stability at high anodic potential is correlated with unique porous and dynamic structure of the polymer that is capable of handling volumetric changes upon electrode polarization. An effective diffusion length for the porous PPy remains unchanged during degradation process (overoxidation) and is significantly smaller in comparison to the dense polymer film, indicating that the degradation process for the porous system is somewhat hindered. This work provides an important insight for fast and scalable synthesis of 3D polymer electrode with improved electrochemical activity and stability for the future energy storage applications.