NANOTECHNOLOGY IN ENERGY Draft RoadMaps on Solar Cells Thermoelectricity Battaries and Supercapacitors Heat Insulation/Conductance Ottilia Saxl THE INSTITUTE OF NANOTECHNOLOGY, UK Jitka Kubatova TECHNOLOGY CENTRE AS CR, CR ___________________________________________________ The 3rd Czech Days for European Research, Prague, 26 October 2005

The NanoRoadMap (NRM) project, co-funded by the European Commission (EC), is aimed at roadmapping nanotechnology related applications in three different areas: Materials Health & Medical Systems Energy This presentation is related to the Energy sector. It is based on 4 draft roadmaps elaborated by Ottilia Saxl, CEO of The Institute of Nanotechnology (IoN), UK, and her team. It also utilizes the Sectoral report on Energy elaborated earlier within the NRM project by Esko Kauppinen from VTT Technical Research Centre of Finland.

List of energy-related applications of nanotechnology Solar cellsENERGY CONVERSION Fuel cells Thermoelectricity Rechargeable batteriesENERGY STORAGE Hydrogen storage Supercapacitors InsulationENERGY SAVING Glazing technology for insulation More efficient lighting Combustion For details see the Sectoral report ENERGY on

Solar cells Use: Electricity production for homes and villages in remote areas without a connection to the electricity grid Powering electronic equipment in wireless applications Function: Direct transformation of light in electric energy Principle: Creation of electron-hole pairs by absorption of light and their separation on barriers Functional materials: Predominantly silicon (single-crystalline, poly-crystalline, amorphous, thin films) Thin film copper indium diselenide (CIS),cadmium telluride (CdTe)

Gallium arsenide (GaAs) Dye sensitised cells (DSC) Main production problems: High efficiency materials are costly. Cheap materials show low efficiency. Impact of nanotechnology: Nanoparticles, thin films, nanostructures and nanoporous materials have a large ratio of the surface to the bulk. This property has made them attractive for research leading to an improvement of the solar cells efficiency. Research topics: Thin film solar cells Dye sensitised silicon solar cells New dyes for DSCs Light absorbing nanomaterials in electrically conductive polymers Nanostructures (quantum wells and quantum dots) embedded in different inorganic and organic solar cells Silicon or germanium nanocrystals as luminescence convertors

Experts opinion: At present nanotechnology impact on solar cells is in the basic research phase. Thin films are seen as the most promising area for solar cells. By 2009 first applications and by 2014 current applications are expected. Solar cells incorporating nanocrystalline materials is the further technology which can reach commercial applications by Technologies including dye-based cells, quantum dots, fullerenes and carbon nanotubes are not expected to have applications by 2014.

Thermoelectricity Use: Thermoelectric modules (featured with no moving parts, small size and light in weight) have been widely used for cooling, heating or electric power generation within medical, industrial, consumer, laboratory, electro-optic, telecommunications, military etc. areas. Refrigerators or power generator to reuse waste heat are examples as well as tiny generators reacting on the body heat. Function: Transformation of thermal energy into electricity Transformation of electric energy into thermal energy (heat, cold) Principle: A junction of two materials having different thermal conductivities exposed to a thermal gradient is a source of electric current. Passing electric current through such a junction results in cooling or heating.

Functional materials: TE materials should have low thermal conductivity, high electrical conductivity and high Seebeck coefficient (in mV/K). Impact of nanotechnology: Nanomaterials and nanostructures decrease thermal conductivity, increase electrical conductivity and improve thermo power possibility ZT. Research topics: Super lattice structures BiTe /SbTe Bi nanowires Bi-Te compounds New materials (skutterudites, clathrates) Experts opinion: Nanotechnology will play an important role in thermoelectricity applications by 2014

New materials with high ZT will be identified and developed by 2009 with first applications (energy generation from waste heat in vehicles) by The types of new materials are expected to be thin films, nanocrystalline materials, nanoparticles, nanowires and superlattices, with the thin films and nanocrystalline materials expected to be first into application.

Rechargeable Batteries and Supercapacitors Use: Source of electrical energy in remote areas and for portable electronics, computers and cameras Function: Storage of electrical energy Principle: Batteries store electrical energy in a chemical form. Supercapacitors store electrical energy as the charge of electrons in an electrochemical double layer on the surface. Functional materials of the commercial products: Batteries - lithium-ion, nickel-cadmium (NiCd), nickel-metal- hydride (NiMH) and Li-polymer Supercapacitors – carbon, metal (nickel, manganese, ruthenium, iridium) oxides, electron conducting polymers

Main production or functional problems: Batteries can store lots of energy but the charge and discharge times are long. Lifetime is short. Wastes contain hazardous materials. Conventional capacitors can be charged and discharged very quickly but store little energy. Supercapacitors offer combination of good properties of batteries and capacitors, i.e. can store moderately high energy and can be discharged moderately quickly. Impact of nanotechnology: Nanocrystalline materials and nanotubes greatly improve power density, lifetime and charge/discharge rates in batteries. Nanotubes are used to replace the normal graphite of lithium- graphite-electrodes. A new class of materials known as aerogels made of 10 nm particles creates a highly porous structure suitable for electrodes and battery structures.

In supercapacitors instead of metal plates, porous carbon electrodes are used. The extremely small pores give the material very large active internal surface. For the same reason multi-walled carbon nanotubes as well as nanoporous metal (iron, nickel, molybdenum) oxides are used. Experts opinion: Nanotechnology is expected to play an important role in rechargeable batteries and supercapacitors as early as The main R&D focus is expected to be on electrode development with some on electrolytes.

Heat Insulation/Conductance Use: Insulating materials keep the temperature constant in an enclosed space Function: Thermal insulation provides a resistance to the heat flow (heat conduction, convection, radiation) through the insulation material. Principle: Low thermal conductivity materials (fibre glass, rock wool, porous materials, air) prevent heat to flow through the insulating barrier. Reflective surfaces and coatings reflect heat coming from outside or inside back.

Impact of nanotechnology: Particles and pores of aerogels are smaller than the wavelength of light. Though very expensive they are suitable for insulation due to their low conductivity, low density, high porosity, high surface area and high dielectric constant. Glazing technology is based on large area, low cost, multilayer thin film coatings. Smart Glazing terms a glass that reacts to its environment by altering its transparency and opacity. Smart Glazing can be classified as thermochromic, photochromic, electrochromic or gasochromic according to the environmental impact. Nanocoatings are made of indium-tin-oxide, ZnO, WO3, V2O5, LiNiO2 etc. Experts opinion: Nanoparticles and thin films are expected to play the main role in electrochromic (switchable) coatings for glazing products.