Nanomaterials for smart energy systems: from led to Supercapacitors and solar cells.

Abstract

It has been forecast that there will be a severe impact on world economics and ecology in future by energy consumption/production that rely on the combustion of fossil fuels. Therefore more sustainable and more environmentally friendly alternative energy/power generation sources are currently under serious consideration. One such alternative is electrochemical energy production. Systems for electrochemical energy storage and conversion include batteries, fuel cells and electric double layer capacitors (EDLCs). Although the energy storage and the conversion mechanisms are different, there are “electrochemical similarities” of these three systems. Electric double layer capacitors, also known as supercapacitors or ultracapacitors, have tremendous potential as high energy high power sources for use in low weight hybrid systems. Commercial applications for such devices include uninterruptible power applications, telecommunication and transportation. The total energy stored in a conventional capacitor is proportional to both the number of charges stored and the potential between the plates. Essentially the former is a function of the size of the electrode while the later is determined by the breakdown of dielectric between the plates. Different voltages, hence energy stored, can be generated when different dielectric materials are used to separate the plates. Materials can be optimized to produce high energy densities for a given size of a capacitor. In contract to conventional capacitors, supercapacitors do not have a conventional dielectric. Instead, two layers of the same substrate and their electrical properties are used in order to effectively separate the charges despite vanishingly thin (on the order of nanometer) physical separation of the layers. Higher energy storage density can be achieved in supercapacitors when nanomaterials or materials with nanoporous structure are used because such materials offer enormous surface to volume ratio. Activated carbon is a material with unique properties especially in relation to its nanoporosity and can therefore be used in supercapacitors. Sri Lanka is one of the worlds’ best coconut shell based activated carbon producer. Besides, carbon nanotube (CNT, either MWCNT or SWCNT) can also be used in supercapacitors as electrode material where charge storage capacity can be increased to a much higher value. Ceylon vein graphite is a good source for the production of CNT. Further, the use of nano-TiO2 in conjunction with light absorbing material in cost effective solar cells is a well established process. The charge carrier generation process in solar cells mimics natural photosynthesis (green energy). At present such solar cells have efficiency nearly 11 %. Again Sri Lanka inherits a vast naturally occurring TiO2 deposit, the range of benefits of which is yet to be explored and harvested to produce nano-TiO2. Therefore nanomaterials in Sri Lanka has a wide spectrum of application and in this presentation, the opportunities to develop smart energy systems using Sri Lankan nanomaterials will be presented.