Nanostructured half-Heuslers for thermoelectric waste heat recovery

Thermoelectric materials convert waste heat into useful electric power. Even inefficient thermoelectric power generation recovery can have a substantial impact on UK and global energy consumption because more than half of primary energy is ultimately wasted as heat. So far, thermoelectric generators (TEGs) have been restricted to niche applications, such as powering the Voyager space probes, where durable, reliable and low-maintenance power generation is essential. However, the market for thermoelectric energy harvesters is projected to approach $1bn within a decade.* Potential applications for TEGs include scavenging heat from car exhausts, producing combined heat and power units for use in remote, off-grid locations, and replacing batteries in wearable microelectronic devices. A major limitation has been to develop cheap, efficient TEGs that do not rely on toxic or scarce resources. For example, the most efficient thermoelectric material for automobile heat recovery is currently a compound of toxic lead and scarce tellurium.

In this project, we aim to develop a viable, non-toxic alternative to lead telluride TEGs, using 'Heusler alloys', which combine abundant elements such as titanium, nickel and tin. They also meet the majority of industrial requirements for thermoelectric power generation, having good thermal and mechanical stability, mechanical strength and ease of processing. However, a TEG's thermal conductivity is also critical and optimising the thermal conductivity of Heusler alloys has been problematic. We aim to capitalise on our recent advances in Heusler alloy synthesis and nanostructuring, which currently represents the only UK efforts in this fast-growing field.

The ultimate aim of this proposal is to develop new means of controlling the thermal conductivity of Heusler alloys in order to build a TEG prototype of comparable performance to existing lead telluride devices. Our insight is that there are a variety of alloy phases and intentional defects that can be used to introduce structural texture on the nanoscale, thereby reducing the thermal conductivity. What is exciting is that many of these structures have not previously been studied. A critical aspect is the size and distribution of the texturing, which should be long enough to avoid reducing the material's electrical conductivity but short enough to impede the flow of heat. We will investigate the optimum length-scales for texturing by performing a systematic study of the impact of processing conditions on the HA nanoscale structure. We will use world-leading electron microscopy, neutron scattering facilities and theoretical modelling to probe the atomic-scale structure and dynamics of the new materials in order to optimise the synthesis parameters. We will then use this technical know-how in collaboration with our industrial partner European Thermodynamics Ltd. to build prototype TEG modules.

This collaborative project, involving three academic institutions, national facilities and a UK small business, has substantial potential for impact, with notable prospects for making a contribution to lowering the UK's carbon footprint. It also provides excellent opportunities for knowledge transfer to a vibrant new industry and for high-quality training.

* H. Zervos, "Thermoelectric Energy Harvesting 2014-2024: Devices, Applications, Opportunities," 2014

WHO?

Our principal impact lies in the development of KNOWLEDGE: through the discovery, synthesis and analysis of new nanocomposite Heusler alloys; through the study of alloy stability and dynamics; and by addressing the practical aspects of constructing a viable prototype device.

We aim to develop an energy harvesting technology that will contribute to efforts to reduce the UK's carbon footprint, for example, by improving the fuel efficiency of cars. There is therefore substantial prospect of SOCIETAL IMPACT, both through the development of energy-efficient technologies and through a reduction in the use of scarce and toxic elements.

PEOPLE IMPACT: The training opportunities are substantial, benefitting the 'pipeline' of highly skilled researchers required for our knowledge economy. The research associates working on the project, PhD students working in our groups, and students enrolled on Masters-level and doctoral level taught programmes will benefit from the research. In addition, we identify a number of academic beneficiaries.

ECONOMIC IMPACT: Perhaps the most important impact is via industrial engagement. We are actively collaborating with an industrial SME partner, European Thermodynamics Ltd., with the intention of developing a thermoelectric generator that would be suitable for high-volume production in a market that is not currently covered well in the UK.

HOW?

We will use traditional dissemination activities of publications, workshops and conference contributions to engage with the wider academic community. We have identified specialist conferences with a focus on energy materials, in addition to more general meetings spanning materials, microscopy, etc. These will be augmented by new collaborations, facilitated by visits to other institutions and facilities, inward and outward invited talks, etc.

We will continue to engage with the EPSRC-funded TEMPEST network, which acts as multidisciplinary hub for thermoelectric researchers and industrialists across the UK, and provides an ideal mechanism for maintaining and growing collaborative links with the leading researchers and industrialists in the field.

We will collaborate with our SME partner, European Thermodynamics Ltd., in order to translate our research into the industrial laboratory. The materials discovery and characterisation aspects of our proposal are beyond the capabilities of ETL, making the collaboration of extremely high interest to them. Through this partnership, we will also aim to inform a non-academic, industrial audience by disseminating results at trade shows and in trade magazines.

In accordance with the policy of research-led teaching at the host universities, we will incorporate results into teaching material suitable for postgraduate lecture and laboratory classes. Energy efficiency as a theme is particularly suited to classroom discussion.

We will inform our outreach activities by results derived from the project; as above, the research theme is easy for the public to engage with. The investigators have experience in presenting to the general public, for example, at Science Festivals, and the proposed research will be very accessible to a wide audience. Heriot-Watt will host a dedicated website to disseminate our research aims and non-confidential results to the wider public.

Heriot-Watt University and the University of Glasgow are both signatories of 'EasyAccess IP' (http://www.easyaccessip.org.uk/), a fast-track route for knowledge transfer that aims to develop any commercial benefits of our research for the benefit of the economy and society. We will maintain this approach for any IP generated during the project and will enlist the help of our research and enterprise offices to assist with Knowledge Transfer activities.

We will explore possibilities for follow-on funding including, for example, Knowledge Transfer Partnership funding, should this be appropriate.