A Report for the Department for Environment, Food and Rural Affairs

OAKDENE HOLLINS

Environmentally Beneficial Nanotechnologies

Appendices

A report for the Department for Environment, Food and Rural Affairs

May 2007

This report has been prepared by: Ben Walsh

Checked as a final copy by:Jo Pearson

Reviewed by:Nick Morley

Date:May 2007

Contact:

File reference number:DEFR01 098 Appendix.doc

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Contents

APPENDIX 1Survey of environmentally beneficial nanotechnologies

A 1.1Energy generation and storage

A 1.2Water, air and land quality

A 1.3Energy saving

A 1.4Transport

A 1.5New materials

APPENDIX 2Justification of the ranking of EBNT

APPENDIX 3UK and EU Policies

A 3.1Innovation and Nanotechnology policy

A 3.2Current UK policy relevant to EBNT

A 3.3Research Funding

A 3.4Demonstration and Diffusion

A 3.5Procurement

A 3.6Communication and Awareness

APPENDIX 4National initiatives on nanotechnology

APPENDIX 5Further information on nanotechnology in photovoltaics

A 5.1Nanoparticle silicon systems:

A 5.2Mimicking photosynthesis.

A 5.3Nanoparticle encapsulation.

A 5.4Improved conversion efficiencies:

A 5.5Alternative materials

A 5.6Flexible film technology.

A 5.7Reduced manufacturing equipment costs

A 5.8General structural developments

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APPENDIX 1
Survey of environmentally beneficial nanotechnologies

This section details the EBNTs highlighted from the initial survey of nanotechnologies from which candidate technologies were investigatedfurther.

A 1.1Energy Generation and Storage

A 1.1.1Electricity storage

Overview

The continual diversification of portable consumer electronics is driving demand for lightweight, high powered, high power-density batteries. The main issues with current batteries are that they are expensive, difficult to dispose of, have low charge density, are toxic, spontaneously combust and have limited lifespans and power output. Nanotechnology is being utilised to build more efficient batteries.

The development of high power low cost batteries will widen the market for using these materials. One area of environmental interest is in the development of electric or hybrid cars. At present the cost of lightweight and high performance batteries is suppressing demand for this environmentally beneficial alternative.

Relevance to nanotechnology

There are several different research institutions incorporating nanostructured materials into the design of current and novel battery technology.

The incorporation of nanoporous catalysts into battery electrodes is helping increase catalyst performance and the power output of the batteries. Nanocrystalline metal oxides are being developed for high powered large scale Li-ion batteries. This should significantly reduce the cost to produce these batteries.

Supercapacitors are being developed using carbon nanotubes. Batteries generate electricity from a chemical reaction whereas capacitors store electricity on charged plates. Recharge times are significantly reduced and, in theory, the capacitors do not degrade. The major problem with supercapacitors is that the charge density is significantly less than a corresponding Li-ion battery. Most capacitors are made using porous carbon. To increase charge density, single walled carbon nanotubes (SWCNT) are being used.

Potential benefits

Lightweight batteries themselves are unlikely to deliver significant environmental savings. However, the wide scale use of batteries is likely to lead to environmental benefits:

A reduction in battery charge times improves recharge efficiency, which reduces energy wasted.
The development of novel materials can replace hazardous substances in the battery.
Incorporation of batteries into transport will improve town driving efficiency and increase town air quality. However, overall carbon reduction will be dependant on the efficiency of supply and method of electricity generation.
Hybrid vehicles will improve the fuel efficiency of city driving, while the development of cheap lightweight batteries will encourage more wide scale adoption of this technology.

Current risks

The development and use of novel materials in batteries could potentially increase problems of disposal.
Batteries are not seen as a realistic option for large scale storage of power (compared to hydrogen), although trials of a hybrid battery/fuel cell system, Regenesys, showed promise for large scale energy storage.
Without a clear way to generate clean electricity, batteries do not directly address the issue of the carbon impact of electricity generation.

A 1.1.2Hydrogen storage

If high levels of renewable energy generation are to be achieved, there is likely to be a need for an efficient energy storage medium. The generation of renewable energy, especially wind, wave and solar, is not constant and cannot be easily tuned to match demand. The National Grid has the ability to dampen the fluctuations in energy production but this effect probably cannot be maintained when high levels of renewable energy are generated. If renewable energy is to become a major part of the UK’s energy generation portfolio then there is a need to store surplus energy from renewable sources for use during peak times. Hydrogen is touted as a potential energy store, whereby excess electricity is used to split water into hydrogen and oxygen. This is then stored for reaction back to water and electricity using a fuel cell.

Although light, hydrogen is not easy to compress and liquefy, therefore current storage methods use high pressure cylinders and cryogenics which are energy intensive. This has the effect that comparatively large volume high pressure vessels are required to store hydrogen, which has implications for public safety. However, of greater concern is the storage of hydrogen for mobile applications, namely transport. One of the major obstacles facing the commercialisation of hydrogen-powered cars is the storage of enough fuel to allow the vehicle to have a practical range. This can be overcome to some extent in large commercial vehicles, for example in buses, where small scale trials are occurring throughout Europe with hydrogen stored in overhead compartments. However, innovative new storage media are required for hydrogen-powered cars.

Relevance to nanotechnology

The problems with storage of hydrogen need to be addressed on the extreme nano/molecular scale. Simple compression of the gas is not energy efficient or practical. In nanotechnology, several different strategies are being developed. They all centre on the premise of absorbing hydrogen onto the surface of a compound. This, in essence, condenses the gas with only minor changes in pressure allowing efficient storage. If a satisfactory solution is to be found, nanotechnology will probably be a major contributor to developing a viable hydrogen storage method.

Nanocrystalline magnesium powder and other nanocrystalline hydrides use the large surface area of the particles to absorb hydrogen and therefore represent a possible solution.
Zeolites (3 dimensional porous materials) are potentially well suited for hydrogen storage. Their sponge-like structure and huge surface area enables the zeolites to absorb large quantities of hydrogen.
In a similar process, the large surface area of carbon nanotubes and fullerene makes these novel carbon compounds ideal candidates for hydrogen storage.

Potential benefits

Hydrogen is a good medium for the long term storage and transportation of energy. Hydrogen storage is seen as one of the main barriers to wide use of hydrogen-powered fuel cells. Developing hydrogen storing devices will significantly reduce the energy cost of compression.

Potential risks

Hydrogen storage by itself will not have significant environmental benefits but is a key component in the development of the hydrogen economy. As there are no significant reservoirs of molecular hydrogen on earth, hydrogen is only as clean as its production method. Current commercial hydrogen production is via steam reforming of methane, a non-renewable fossil fuel, which generates CO2 at source. Whether the hydrogen economy of any size will ever materialise is uncertain. Therefore, large investment into hydrogen storage could ultimately be wasted. Alternative hydrogen sources, such as methanol, which is more practical to control, may prove more popular. Hydrogen is highly flammable and readily forms explosive mixtures with air, which has significant safety implications. Also specialist metal alloys are required to prevent hydrogen embrittling steel pipes.

A 1.1.3Photovoltaics

Overview

Photovoltaics is the science of turning light directly into electricity. The outcome of work to date has been to incorporate solar cells in applications as diverse as calculators to satellites. The majority of current commercial activities focus on producing solar cells using silicon wafers. Indeed, recent demand for solar cells has resulted in record silicon prices as demand outstrips supply for sufficiently pure silicon. However this is an issue to do with processing and not with availability of raw silicon. This commercial technology is over 40 years old and is well proven under real life conditions. The major drawback of this technology is the cost of the raw materials (especially silicon), but also the efficiency of commercial systems is limited to around 8% - 12%.

Relevance to nanotechnology

Cutting edge research into photovoltaics is trying to move away from using traditional p-n junction semiconductors. Several avenues of approach which are relevant to nanotechnology are:

Organic solar cell (Graetzel cell). These devices use organic molecules to produce electricity and nanocrystalline titanium dioxide as an electron conductor. These cells are extremely cheap and easy to make but there are issues with lifetime of the cell and overall efficiencies.
Nanocrystalline solar cells. These incorporate cadmium selenide and cadmium telluride nanoparticles onto a conducting glass layer. Although in the early stages of research, this technology has advantages that the quantities of material used are very low, processing costs are minimised and, because the materials are ceramic, light and heat degradation of the materials should be minimised.

Related to nanocrystalline solar cells is the use of fullerenes and SW/MW carbon nanotubes (CNT) as photon absorbers. However, these materials may suffer from degradation under real world conditions.

Advanced deposition techniques are being used to reduce material costs of silicon by reducing the layer thickness of the semiconductor to produce ultra-thin films of silicon. However, these cells have low efficiencies compared to traditional silicon solar cells. There is research into using nanoparticles to enhance their efficiencies through a ‘plasmon’ effect.

Potential benefits

Solar energy has the potential to completely decouple energy from carbon dioxide emissions. Even at the current 8-12% efficiency, only a small proportion of the earth surface would need to be covered to supply the world’s energy needs.

Current risks

Cloudy Western Europe is not the ideal location for the implementation of this technology, although some European countries, notably Germany, are making very large investments in PV capacity. High intensity sunlight in equatorial regions is ideal for deployment of large scale solar installations. However this brings several technical and political barriers:

Energy storage and transport from these equatorial regions are significant technical challenges.
Our sensitivity to reliance on other nations for our energy supply is an important issue.
Cost of delivering large scale solar installations is prohibitive.

The alternative, and probably more favourable approach for the UK, will be micro generation incorporating PV into suitable roofing tiles and industrial facilities. As already expressed in the energy review, solar is likely to be one of a portfolio of renewable energies to reduce our carbon impact of electricity generation and distributed generation appears to be a suitable solution.

Technical issues include:

Storage of excess energy for cloudy-day or night time use
Longevity of new solar cells
Efficiencies of new solar cells.

A 1.1.4Thermovoltaics

Overview

A potential is generated when a thermal gradient is applied to a circuit containing dissimilar metals. This effect is most well known in reverse: the Peltier Effect in which passing a current through dissimilar metals cools one metal while heating the other. Peltier coolers are used in specialist cooling applications where traditional refrigerants are not viable. By applying a heat gradient between the two metals a simple electricity generator can be made. The technology is nearly 200 years old but the relative inefficiency and high expense of the components has prevented wide scale adoption. However, the technology could be used for microgeneration of electricity using waste heat from combustion.

Relevance to nanotechnology

Advances in nanotechnology have reinvigorated research in this area. These advances have produced material which is more than twice as efficient as current thermovoltaic materials. Techniques involving thin films, nanowires and nanorods, although in early stage development, are yielding promising results.

Potential benefits

This technology could greatly increase energy efficiency of combustion engines by generating power from wasted heat. A 10% conversion of the heat generated from an internal combustion engine will result in a 25% emissions reduction in transport use. Other applications could involve the replacement of batteries in personal devices. By removing the requirement to replace batteries, there could be significant material and energy savings, eliminating issues with disposal. There are reports of prototype watches which are powered using thermovoltaics, but this could easily be expanded to other devices and ‘wearable electronics’.

Potential risks

The technology is still in relatively early stage development. Costs of production are currently prohibitively high (this technology is only used to any extent in space exploration and military applications). The efficiencies are very low. On its own, it is unlikely that this product will contribute significantly to electricity generation.

A 1.1.5Fuel cells

Overview

Fuel cells are electrochemical engines that directly convert chemical energy into electrical energy. A controlled reaction between two chemicals separated by an ionic barrier is used to generate electricity. In practice, this is a considerably more efficient method of electricity generation than conventional electricity generation, which uses chemical reactions (combustion) to generate heat then mechanical energy and finally electricity.

These devices are seen as a potential replacement for batteries and small to medium electricity generation and storage. Applications range from use in mobile phones and laptops, powering electric cars to combined heat and power generation for buildings.

Relevance to nanotechnology

The chemical reaction used to generate electricity is controlled through a metal catalyst particles (usually platinum), which are attached to a semi-permeable membrane. To complete the circuit and generate current, one of the chemical reactants becomes charged by the platinum catalyst, travels through the membrane and reacts with the second chemical reactant. Nanotechnology has the potential to address two issues with this technology: catalyst particle size and membrane composition.

Platinum is a rare metal. The quantity of metals used can be significantly reduced by decreasing the size of the particles. This reduction in particle size increases the efficiency of the catalyst. It is therefore a challenge for material scientists to develop nanofabrication techniques to produce well defined nanoscale platinum particles. There are also attempts to address this situation by using alternative catalysts.

There is a significant opportunity to develop more reliable and cheaper membranes. There are problems with pollutants in the chemical fuel sources degrading the efficiency of the fuel cells. Advanced membranes could be used to remove these impurities. These membranes could be tailored to more efficiently transport the reactants through the fuel cell. There have been claims that SW/MWCNTs or fullerenes could efficiently perform this role.

Potential benefits

Fuel cells may lead to an increase in the battery life of electronic devices.

Potential applications in vehicles include:

Greater efficiency than internal combustion engine.
Zero harmful emissions are generated using these devices which will lead to improved air quality in cities.
CHP is a potential method for improved energy efficient generation in distributed systems.

Current risks

Compared to conventional combustion or batteries, fuel cells are prohibitively expensive.
One of the main uses for fuel cells is in hydrogen-powered cars. Development of the hydrogen economy has a significant list of problems. Although hydrogen fuel cells only emit water, currently the only commercially available method of producing hydrogen is from non-renewable resources.
Other fuels for use in fuel cells generate CO2, therefore unless the fuel sources are renewable there will be an environmental impact of using these devices.
There are concerns that there are not enough platinum reserves to satisfy a large scale adoption of fuel cells.
Fuel cells are sensitive to degradation through poisoning, therefore effective methods of prolonging their life are required.

A 1.1.6Hydrogen generation

Overview

Current hydrogen generation methods are limited to either water splitting using electrolysis which is inefficient and requires electricity from either renewable or non-renewable sources or natural gas steam reformation which generates CO2 and uses non-renewable feedstocks. To be a renewable and clean feedstock, it is likely that hydrogen generation will need to be achieved using electrolysis with electricity from a renewable source. Systems using solar power are being developed, however attention to the electrodes is also prudent to improve overall efficiencies.

Relevance to nanotechnology

In a similar theme to fuel cell research, the use of nanostructured components is effective at catalysing water electrolysis to form hydrogen and oxygen. The high surface area and reactivity of nanostructured materials improves the electrolysis process and therefore the overall efficiency of hydrogen generation. In addition to platinum, several other nanostructured metals and alloys are being developed to effectively split water into hydrogen and oxygen.

Potential benefits

The generation of renewable hydrogen could reduce issues with energy storage and remove our reliance on fossil fuel powered cars. If implemented on a large scale this technology, combined with fuel cells, could significantly contribute to solving the UK energy demand problem. There are small integrated solar units being developed to provide hydrogen for small applications, such as remote farms. There have been studies investigating the generation of hydrogen from wind power which generates significantly less CO2 than steam reformation.