Novel boron-nitrogen coordinated polymers as next-generation n-type thermoelectric materials

Despite the high interest in new, greener energy sources, we are not using our current energy sources efficiently: the amount of waste heat generated in the UK in 2019 equals approximately 10% of the national electricity demand in the same year. In addition to finding new energy sources, recycling unused energy, especially waste heat which is attributed to the majority of the energy loss, is also vital for a more sustainable world in the future. Thermoelectric generators can capture the waste heat and convert it to electricity, hence their importance in contributing to sustainability has been highlighted in recent years. Organic thermoelectric generators, which are built up with organic polymeric p-type and n-type thermoelectric material couples, are more favoured over conventional heavy-metal materials concerning sustainability. Although many good p-type thermoelectric materials are established, a lack of good n-type materials lags the development of organic thermoelectric generators. This is because good n-type materials require low-lying HOMO/LUMO energies and narrow band gaps for effective charge transfers and decent air stabilities. So far only a few groups of compounds meet the criteria. This project will work on a new group of n-type organic thermoelectric materials: boron-nitrogen coordinated polymers. The B-N coordination unit has been applied in several families of electronic materials as an effective way to boost up the electron affinities but has almost not been exploited in the thermoelectric field. Introducing the B-N coordination unit to organic thermoelectric materials may allow us to discover more high-performance n-type thermoelectric materials.This project aims to develop conjugated polymers bearing boron units within the structures that are either novel or yet to be studied as n-type thermoelectric materials. In general, the identified targets will be synthesised, characterised and made into thin films. Intrinsic thermoelectric properties will be measured to determine if targets display good n-type performance. When possible, the developed materials will be paired up with commercially available, high-performance p-type thermoelectric materials, such as PEDOT:PSS, to build proof-of-concept thermoelectric generators to showcase energy harvesting abilities. Approaches towards the targets will be the following four routes, with target novelties and technical difficulties gradually increasing from Route 1 to Route 4:

Route 1: Thermoelectric performance of known boron-nitrogen based polymers. Initially published n-type B-N coordinated polymers that have been exploited in fields other than thermoelectric materials but show promising properties (e.g. low-lying frontier orbitals, narrow band gaps) that fit the requirements for good n-type thermoelectric materials will be trialled.

Route 2: B-N decoration on known n-type thermoelectric polymers. This route will focus on known examples of n-type thermoelectric polymers and discover the extent of enhancement on the n-type thermoelectric performance by incorporating B-N coordination units into the structures.

Route 3: Optimisation on developed targets. Optimisation methods like adding electron-withdrawing groups and extending the length of sidechains are commonly used on n-type thermoelectric materials. Therefore, this route will further optimise the compounds developed from Route 1 and 2 to maximise their performance. Computational calculations (e.g. DFT) will evaluate the design, particularly the HOMO/LUMO levels, before targets are synthesised.

Route 4: Polymers bearing other coordination units. In addition to B-N coordination, other types of coordination units, such as B-O, might do a better job than B-N in n-type thermoelectric materials. Likewise, calculations in silico will be done as a proof of concept before synthesis.

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.