GraphTED - graphene nanocomposite materials for thermoelectric devices

The Seebeck effect is a thermoelectric effect whereby a temperature gradient across a material is converted to a voltage,
which can be exploited for power generation. The growing concern over fossil fuels and carbon emissions has led to
detailed reviews of all aspects of energy generation and routes to reduce consumption. Thermoelectric (TE) technology,
utilising the direct conversion of waste heat into electric power, has emerged as a serious contender, particular for
automotive and engine related applications. Thermoelectric power modules employ multiple pairs of n-type and p-type TE
materials. Traditional metallic TE materials (such as Bi2Te3 and PbTe), available for 50 years, are not well suited to high
temperature applications since they are prone to vaporization, surface oxidation, and decomposition. In addition many are
toxic. Si-Ge alloys are also well established, with good TE performance at temperatures up to 1200K but the cost per watt
can be up to 10x that of conventional materials. In the last decade oxide thermoelectrics have emerged as promising TE
candidates, particularly perovskites (n-type) and layered cobaltites (e.g. p-type Ca3Co4O9) because of their flexible
structure, high temperature stability and encouraging ZT values, but they are not yet commercially viable. Thus this
investigation is concerned with improving the thermoelectric properties of oxide thermoelectrics, specifically Strontium
Titanate (n-type) and Bismuth Strontium Cobaltite (p-type).
The conversion efficiency of thermoelectric materials is characterised by the figure of merit ZT (where T is temperature); ZT
should be as high as possible. To maximise the Z value requires a high Seebeck coefficient (S), coupled with small thermal
conductivity and high electrical conductivity. In principle electrical conductivity can be adjusted by changes in cation/anion
composition. The greater challenge is to concurrently reduce thermal conductivity. However in oxide ceramics the lattice
conductivity dominates thermal transport since phonons are the main carriers of heat. This affords the basis for a range of
strategies for reducing heat conduction; essentially microstructural engineering to increase phonon scattering. By
introducing small pieces of graphene into the oxide it is possible to produce composites which have reduced thermal
conductivity and increased electrical conductivity. In this way the ZT characteristics of both Strontium Titanate (n-type) and
Bismuth Strontium Cobaltite (p-type) can be enhanced. We will prepare composites of the two oxides, determine their
structures, their phase content and thermoelectric properties. After validation we will construct thermoelectric modules
using the p-type and n-type composites which will be evaluated in commercially-relevant test environments.

The work will provide a foundation for the development and exploitation of high performance thermoelectric oxide-graphene
composites to generate energy via waste heat. The beneficiaries in the commercial sector are threefold: (i) ceramic
manufacturers who will have new products, (ii) producers of energy management devices who will be able to develop new products for new low and high temperature markets, and (iii) users of thermoelectric modules, such as motor
manufacturers, generating energy from waste heat. Policy makes will benefit from the research by knowledge of
developments of environmentally friendly methods of energy generation and a way to help reduce the use of fossil fuels.
There will be opportunities for museums with exhibits highlighting the principles of thermoelectric power generation and
applications from automobiles to domestic environments. To the wider public there will be environmental benefits of utilising
oxides in place toxic metal thermoelectrics and from the generation of energy from waste heat, leading to improved fuel
consumption for automobiles and economic benefit to individuals and the UK.
The research has the potential to impact the wealth and the economic competitiveness of the UK by the development of
enhanced thermoelectric materials and power modules. For UK companies there will be new opportunities and new
markets in the production of ceramics, the development of energy management systems, and exploitation of energy
generation systems. All companies in the supply chain should become more competitive. With generation of power from
waste heat in the automobile and other sectors there will be improved fuel consumption and the potential for reduction of
imported oil to the UK, giving additional economic benefits. New thermoelectric power modules should be realised within 2-
5 years, bringing benefits to companies in the supply chain within 3-7 years. The wider benefits of effective power
generation and potential reduction of oil consumption should come within 5-10 years.
The researchers working on the project will gain specialist transferable skills in experimental design, materials fabrication,
microstructural and functional property characterisation techniques together with skills in report writing and critical analysis
that will be of great value in future employment.
Non-confidential scientific and technological findings will be disseminated to the academic and industrial communities via
presentations at major international conferences and high impact scientific publications. With our industrial collaborator we
will protect and exploit IP through the University of Manchester Technology Transfer Unit.
Our industrial collaborator ETL (specialist in Energy Management) has the necessary specialist expertise to develop test
modules and evaluate the new materials. The Manchester applicants (R Freer and I Kinloch) have significant experience of
developing and investigating structure-property relationships in functional materials, including thermoelectric materials.
With our industrial collaborators we have the necessary expertise and facilities to successfully undertake the programme of
work.