Solution Processable Polyaniline with High Electrochemical Charge Capacity

Abstract

Polyaniline (PANI) is a charged polymer well-known for its high charge storage capacity and moderate electrical conductivity. PANI is often prepared by chemical or electro-polymerization, however, these polymerization methods limit options for substrate material, electrode/device geometry, and polymer morphology. To address these limitations, it is attractive to form PANI films by solution-casting. In this study, we examine the electrochemical properties of solution-cast PANI films formed from a commercially available PANI suspension containing excess dinonylnaphthalenesulfonic acid (DNNSA). Films prepared by solution casting of PANI-DNNSA have been previously characterized in terms of conductivity, morphology, and optical properties, however the electrochemical behavior of these films has been largely unexplored. Here, we present an electrochemical analysis of these solution-cast PANI films using quartz crystal microbalance, electrochemical impedance spectroscopy, and cyclic voltammetry. As cast, we find that the polymer exhibits limited electrochemical activity, but that postprocessing the material with electrolyte and crosslinking solutions increases the charge capacity up to 95 mAh/g – 86% of the charge capacity typically reported for electrodeposited PANI films. Ion-exchange processes, electrochemical capacitance, and energy storage capabilities of the chemically treated solution-cast films are assessed and compared to those of electro-deposited and chemically oxidized PANI. We demonstrate redox-active PANI films on both (a) conductive and insulating, and (b) planar and porous substrates. Finally, symmetric faradaic supercapacitor devices were constructed using spin-coated PANI electrodes in aqueous electrolyte, and the stability of these devices was examined by repeat galvanostatic charging/discharging at low current, achieving up to 88% capacity retention after 500 charge-discharge cycles.