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Building one involves transferring aligned carbon nanotube arrays from a silicon wafer over to a PDMS (polydimethylsiloxane) layer in which they are partly embedded. Polyaniline is then polymerised onto the surface of the nanotubes.
In capacitors made from the structure, the polyaniline exhibits supercapacitive characteristics due to pseudocapacitance (redox) behaviour – the carbon nanotubes and PDMS add slightly to this through ‘double-layer’ supercapacitive characteristics. At the same time, the nanotubes provide support for the polyaniline which accommodates its expansion and shrinkage as charge cycles in and out.
The composite electrode offers “outstanding energy storage properties with exceptional mechanical integrity”, said Surrey. “The team’s supercapacitor retains most of its capacitance after numerous cycles at different bending conditions.”
The maximum capacitance achieved was 408mF/cm2 or 265F/g at 1mA/cm2, and energy storage was up to 20μWh/cm2 at a power density of 100μW/cm2 (0 – 2V), or 25.5Wh/kg at a power density of 126.6W/kg.
Retention was 76% after 5,000 cycles and capacitance did not drop by much more than 20% when the devices were flexed considerably.
The numbers above are taken from a paper which describes the research: ‘An easy to assemble PDMS/CNTs/PANI flexible supercapacitor with high energy-to-power density‘, published in Nanoscale – payment required to read the whole paper.
The University of Surrey’s Advanced Technology Institute (pictured) worked with the Federal University of Pelotas in Brazil (UFPel). The materials were grown and characterised in Surrey, while electrochemical measurements were carried out at UFPel.
