Layered Oxides Thermoelectrics for High Temperature Waste heat Recovery

Energy demand is growing and our society faces a challenge to find sustainable sources with minimal environmental impact. Existing technologies such as solar, wind and geothermal have been deployed and effort to improve their physical and cost effectiveness is ongoing. Another source of renewable energy available which has not been harvested to its full potential so far is "waste" heat. It arises from a variety of sources, from household boiler to large scale power plant, and a striking example is the conventional combustion engine in which 60 % of the energy produced is lost in the form of heat. The possibility to design a semiconductor device made of p-n junctions which when exposed to a temperature gradient will output electrical power is an attractive solution for the automotive industry to improve fuel efficiency, lower the carbon foot print and end-user costs. This device, called a thermoelectric generator has been successfully used for aero-spatial application or in its converse form as Peltier cooler, contributes to all component of the energy trilemma. The major barrier for a widespread dissemination of this technology as energy harvester is the high raw material costs and a lack of material for high temperature operation.

This research will investigate new classes of inorganic oxide composed of earth abundant elements presenting electrical and thermal properties suitable for integration in a high temperature thermoelectric generator. Efficient thermoelectric materials possess high electrical conductivity and low thermal conductivity which, in a standard semiconductor picture, are antagonistic properties. Focusing on the high temperature spectrum, oxides materials will display the chemical stability required for the device to function reliably. Since the majority of these materials are electrically insulating, the concept is based on identifying structure patterns that have hidden electronic lattice which could act as conducting channel. Similar concept has been successfully applied on layered oxides where only competitive p-type thermoelectric materials where produced. The project aims to explore the possibility to use the strong correlation between electronic, thermal and magnetic lattice to circumvent the limitations encountered in this class of materials and expand our understanding of this complex compounds.

A specific objective of the project is to prepare poly- and single crystalline layered oxides derived from the trirutile structure, measure the high temperature conductivity and thermopower and optimise the thermoelectric property using chemical doping to obtain both p and n type compounds. The layered structures of the proposed compounds are conducive to exotic magnetic properties and more complex phenomena such as Nernst-Ettinghausen effect and spin Seebeck effect will be investigated.

Advanced functional materials are key elements of modern technologies and a clear materials gap hinders the development of high temperature thermoelectric generators. Consideration of chemical stability, efficiency and raw material sustainability is vital for the possible translation from compound discovery to operational devices. The materials produced in this project aim to address this bottleneck and a specific application in the automotive sector is targeted. The main impact objective is their integration in waste heat harvesting devices on automotive exhaust.

Interaction with the complete industrial chain of supply from raw material supplier to original equipment manufacturer is targeted to raise the technology readiness level of this technology and to achieve long term impact. Support from companies with expertise in ceramic processing (Morgan Advanced Materials), thermoelectric modules testing and modelling (European Thermodynamics Ltd), exhaust manufacturing (Unipart) has been gained indicating the industry interest in this technology and highlighting the timeliness of the project.

Key milestones in the project will be the trigger for interaction with the relevant partners creating a feedback loop between academic and industrial research accelerating advances. To deliver efficient exchange, the University of Liverpool is part of the Knowledge Centre for Materials Chemistry, which will provide engagement with the industry and seek new partners during the program as well as disseminate the research outputs in other relevant Knowledge Transfer Network communities.

The specialised used of thermoelectric devices has so far not attracted as much promotion as other renewable energy systems to the general public. The concept behind this technology, where waste heat is transformed into electricity, is core to the education of the wider society in building a sustainable energy consumption and generation for the future.