Materials Discovery in Charge Transfer Complexes for Thermoelectricity

Thermoelectric devices are electronic chips that turn differences in heat into electricity and vice versa. Most people will have never heard of thermoelectric (TE) devices as they are used very little. Practical TE devices could generate green electricity and make refrigeration less polluting. This cant happen currently as room temperature thermoelectric materials are either too expensive or too inefficient. A 1.4% efficient TE material applied to the 40C waste steam generated by all UK thermal power plants in 2021 could have generated 5TWh of electricity per year, enough for 2 million, 8% of all, UK homes at a wholesale value of £900M per year (UK average price June 22 June 23). Organic TE materials are likely to reduce the cost of TE devices due to their atom abundance and low energy processing. Both negative and positive type (like the ends on a battery) TE materials are needed to make devices. Organic p-type materials have seen good progress, but n-types are much rarer, have lower performance, and are easily decomposed by oxidation in air. A recent discovery of a family of metal halide organic complexes with a generic structure M(II)Br2(Haloaniline)2 has reported high (2000-3900 S cm-1) electrical conductivity and power factors, a measure of TE performance (1500 3700 W m1 K2) an order of magnitude greater than the research benchmark of PEDOT:PSS polymer 200 W m1 K2.This new family's constituent atoms are all earth-abundant, comprised of Cu, Zn, Br, I, C and N.Currently, the processing solvent is toxic, but there is potential for developing safer and less environmentally harmful solvent methods. Crucially, this family reports high stability in air and water for year timescales experimentally and theoretically. And maximum operating temperatures between 100 - 200C and good performance one-fifth to half as good as the best materials available.
This class of materials is underexplored as TE materials, and many questions about how to boost their performance remain. This project will help to develop methods for their production, discover new materials in the family and explore methods for tailoring their performance. The early goal will be to replicate the leading research results via vacuum drying. If this method reliably gives films that can be analysed, then a library of different organic molecules with different halide substituents and Pi-conjugated systems will be developed. These experiments will help us understand the molecule's effect on how we can make the materials better. If data generation is fast and reliable, the use of artificial intelligence could help us improve the materials. If the vacuum drying technique does not provide reliable deposition of high-quality films, then alternative drying methods will be investigated. Hot substrates to evaporate off the solvent, using a solvent that washes away the solvent but leaves the materials in place. Ambient temperature washing is favourable as it avoids thermal stress and has lower energy requirements. Cosolvent techniques may give finer control of the crystallisation. Once films are produced, they will be validated for homogeneity and thickness with Optical microscopy, Electron microscopy, and profilometry. The composition of the deposited films will be determined by grazing incidence x-ray diffraction. Previous studies have not included structural measurements of the cast films, only materials derived by mechanochemistry and crystallisation. Analysis of the cast film will reveal any differences. If possible, the materials will be cast onto the silicon nitride measurement chips of a thin film analyser. This system can give basic thermoelectric characterisation. This system's speed and high reliability will reduce uncertainty and time per sample compared to conventional measurements. If this system is unsuitable, methods will be developed using silica slides with thermally evaporated conductive tracks for 4 terminal measurements.

This CDT will deliver impact aligned to the following agendas:

People
A2P will provide over 60 PhD graduates with the skill sets required to deliver innovative sustainable products and processes into the UK chemicals manufacturing industry. A2P will inspire and develop leaders who will:
- understand the needs of industrial end-users;
- embed sustainability across a range of sectors; and
- catalyse the transition to a more productive and resilient UK economy.

Economy
A2P will promote a step change towards a circular economy that embraces resilience and efficiency in terms of atoms and energy. The benefits of adopting more sustainable design principles and smarter production are clear. For example, the global production of active pharmaceutical ingredients (APIs) has been estimated at 65,000-100,000 tonnes per annum. The scale of associated waste is > 10 million tonnes per annum with a disposal cost of more than £15 billion. Consequently, even a modest efficiency increase by applying new, more sustainable chemical processes would deliver substantial economic savings and environmental wins. A2P will seek and deliver systematic gains across all sectors of the chemicals manufacturing industry. Our goals of providing cross-scale training in chemical sciences with economic and life- cycle awareness will drive uptake of sustainable best practice in UK industry, leading to improved economic competitiveness.

Knowledge
This CDT will deliver significant new knowledge in the development of more sustainable processes and products. It will integrate the philosophy of sustainability with catalysis, synthetic methodology, process engineering, and scale-up. Critical concepts such as energy/resource efficiency, life cycle analysis, recycling, and sustainability metrics will become seamlessly joined to what is considered a 'normal' approach to new molecular products. This knowledge and experience will be shared through publications, conferences and other engagement activities. A2P partners will provide efficient routes to market ensuring the efficient translation and transferal of new technologies is realised, ensuring impact is achieved.

Society
The chemistry-using industries manufacture a rich portfolio of products that are critical in maintaining a high quality of life in the UK. A2P will provide highly trained people and new knowledge to develop smarter, better products, whilst increasing the efficiency and sustainability of chemicals manufacture.
To amplify the impacts of our CDT, effective public engagement and technology transfer will become crucially important. As a general comment, 'sustainability' styled research is often regarded in a positive light by society, however, the science that underpins its effective implementation is often poorly appreciated. The University of Nottingham has developed an effective communication portfolio (with dedicated outreach staff) to tackle this issue. In addition to more traditional routes of scientific communication and dissemination, A2P will develop a portfolio of engagement and outreach activities including blogs, webpages, public outreach events, and contribution of material to our award-winning YouTube channel, www.periodicvideos.com.

A2P will build on our successful Sustainable Chemicals and Processes Industry Forum (SCIF), which will provide entry to networks with a wide range of chemical science end-users (spanning multinationals through to speciality SMEs), policy makers and regulators. We will share new scientific developments and best practice with leaders in these areas, to help realise the full impact of our CDT. Annual showcase events will provide a forum where knowledge may be disseminated to partners, we will broaden these events to include participants from thematically linked CDTs from across the UK, we will build on our track record of delivering hi-impact inter-CDT events with complementary centres hosted by the Universities of Bath and Bristol.