Polyaniline and nano-carbon composites as high performance supercapacitor materials
Creators: name: STOTT, ASHVEER
Publisher: name: University of Surrey
Year: 2021

description: Energy storage is an essential component in modern society for effciently
description: managing energy production, maintaining resilient power grids and powering
description: various portable electric device and electric vehicles. electrochemical capacitors (ECs) or 'Supercapacitors' are electrochemical energy storage devices (EESDs) characterised by high power densities and long cycle lives, as compared to batteries. Supercapacitors have many promising applications as high-power, transient energy storage devices in portable electronics, renewable energy systems, electric vehicles and grid energy management [1]. A current limitation of ECs is their low energy density compared to batteries, which hinders their application as an energy storage/delivery device. Pseudocapacitive materials, such as conducting polymers and metal oxides, that store charge by Faradaic and double layer capacitance, can be utilised to improve the energy density of ECs whilst maintaining high power capacitive performance.
description: This work explores the use of nanomaterial composites and novel fabrication methods to increase energy density and rate capability of polyaniline (PANI) pseudocapacitor electrodes. Composite materials were developed, comprising of PANI and nano-structured carbons, to utilise both electric double-layer (EDL) capacitance as well as pseudocapacitance in the same electrode. Additionally, nano-carbons were used to mitigate against the biggest drawback of PANI, the material stability. A variety of carbon materials were chosen, including graphene, carbon paper, carbon nanotube (CNT) coated carbon paper and CNT coated carbon cloth. Initially, a method to produce high-performance chemically polymerised PANI, and PANI-carbon composites, was developed and optimised by investigation of various synthesis parameters. Secondly, the electrochemical polymerisation of PANI was investigated as it offered the potential to produce binder-less, freestanding composite electrodes. Following this, a study of a novel three-layer structure of carbon encapsulated PANI was developed utilising a unique slow scan rate electrochemical deposition, which resulted in conformal deposition of PANI. Such electrodes exhibited specific capacitance of 571 F g-1 at 1 A g-1 with rate capability of 98.9% at 100 A g-1. With rate capability being the % loss of capacitance as the charging/discharging current density increases. Finally, it was deemed necessary to further study the interaction of the conformal PANI layer with the CNTs. This was done by investigating the effect of different deposition parameters on the composite, such as scan rate and cycles number used for PANI deposition. Additionally, a relatively new analysis technique, within the field of ECs, known as the distribution of relaxation times (DRT) was implemented to analyse impedance spectra and reveal the individual sub-processes occurring within the electrode and how changing deposition parameters affects these processes. This analysis revealed a trend toward lower scan rates producing higher performance electrodes. This was tested using a deposition scan rate of 2 mV s-1 for 25 cycles. The resultant champion electrode achieved specific capacitance, based on the mass of PANI alone, of 799 F g-1 with rate capability of 80%.