Soon Yee Liew

High total-electrode and mass-specific capacitance cellulose nanocrystal-polypyrrole nanocomposites for supercapacitors

For practical applications, new supercapacitor electrode materials need to exhibit a high mass-specific capacitance (CM/F g−1), a high total-electrode capacitance (CE/F cm−2), and high stability during charge–discharge cycling. Very often, newly developed materials display high CM values for thin films (nm or μm thickness) but these rapidly drop off in the thicker electrode structures needed for commercial devices. In this work, we describe the fabrication of thick nanocomposites of polypyrrole (PPY) and cellulose nanocrystals (CNXLs) with consistently high capacitance (CM = 240 F g−1) and performance. CE of the PPY-CNXL nanocomposite increased linearly with increasing film thickness up to a value of 1.24 F cm−2 and this increased to a maximum of 1.54 F cm−2 for even thicker films where non-linear CE increases were due to electrolyte diffusion limitations. Testing of a symmetric supercapacitor with these high CE electrodes showed that it retained half of its initial capacity after 50 000 charge–discharge cycles, demonstrating the excellent stability of PPY-CNXL supercapacitor electrode materials.

Separation of sulphuric acid from an acid suspension of cellulose nanocrystals by manual shaking

In this paper, the separation of sulphuric acid from a suspension of cellulose nanocrystal by manual shaking is described. Cellulose nanocrystals are prepared from acid hydrolysis of cotton using 64 wt% sulphuric acid at ca. 45 °C for 45 minutes. After the hydrolysis was complete, water was added to dilute the mixture to a resulting concentration of 30 wt% of the acid. This mixture was shaken rigorously in a closed container and after 48 hours, separation occurs such that cellulose nanocrystals float, with the bubbles introduced by the shaking, to give clear acid solution at the bottom. This shaking-floating process is repeatable for several cycles after the acid was removed from the bottom and more water was added. Using this simple process, the total acid recovery of > 90% has been achieved, and the concentration of all the acid recovered combined was 17.5 wt%. This work demonstrates a method that allows energy efficient and up-scalable separation of cellulose nanocrystals from the acidic suspension from which it was extracted.

Conducting Polymer Nanocomposite-Based Supercapacitors

The use of nanocomposites of electronically conducting polymers for supercapacitors has increased significantly over the past years, due to their high capacitances and abilities to withstand many charge-discharge cycles if properly structured. We have recently been investigating the use of nanocomposites of electronically conducting polymers containing conducting and nonconducting nanomaterials, such as carbon nanotubes and cellulose nanocrystals, for use in supercapacitors. In this contribution, we provide a summary of some of the key issues in this area of research. This discussion includes some history, fundamental concepts, the physical and chemical processes involved and the challenges that these nanocomposite materials must overcome in order to become technologically viable. Due to space limitations, this is not a complete review of all the work that has been done in this field and we have focussed on common themes that appear in the published work. Our aim is that this chapter will help readers to understand the advantages and challenges involved in the use of these materials in supercapacitors and to identify areas for further development.

Polysaccharides in Supercapacitors

In this part, the use of polysaccharides, either directly through composite approaches, or by carbonization will be described. In many cases, materials are obtained which are competitive in terms of capacitance and cycle lifetime. In this part, the use of polysaccharides, either directly through composite approaches, or by carbonization will be described. In many cases, materials are obtained which are competitive in terms of capacitance and cycle lifetime. The following part will focus mainly on cellulosic composites with conductive polymers since cellulose is most abundant and therefore has attracted much more research interest in this field whereas in the second part also other polysaccharides, such as chitin, xylans, alginates, pectins, dextrans and caragenaans have been used in carbonization experiments.

Phase Behaviour of Cellulose Nanocrystal Dispersion in Aqueous Sulphuric Acid and Development of an Energy Efficient Separation Technique for the Acid-Cellulose Nanocrystal System

In this paper, the phase behaviour of a cellulose nanocrystal (CNCs) dispersion in sulphuric acid solutions was investigated, aimed at the development of an energy efficient separation method for this mixture. The system in consideration was a mixture of 30 wt% aqueous sulphuric acid (ρl = 1219 kg/m3) containing 12.6 mg/ml of cellulose nanocrystals (CNCs) (ρs = 1590 kg/m3, volume fraction of CNCs less than 1%). This volume filling mixture was obtained directly from a CNC extraction process, as obtained after the hydrolysis of cotton using 64 wt% sulphuric acid at ca. 45 ̊C for 45 minutes (this condition was required for the extraction of CNCs from cotton) followed by quenching the hydrolysis with water. The CNCs form the desired product and need to be separated from the acid that can then be recycled. Conventionally this separation has been difficult and requires a large input of energy. This work addresses this problem by investigating into the phase behaviour and physicochemical and hydrodynamic character of this mixture. This understanding led to the development of a very energy efficient separation mechanism for this mixture, which is 5 orders of magnitude more energy efficient than the most widely used centrifugation systems.