Biohybrid Materials for Improved Electron Transfer in Bioelectrochemical Systems

As the global population continues to grow, there has been a corresponding surge in energy demand, leading to a sharp rise in environmental CO2 levels. To facilitate economic progress whilst mitigating environmental risks, it is imperative to adopt sustainable technologies. Bioelectrochemical systems (BES) are unique approaches to recycling CO2 using microorganisms. BES can convert low-cost substrates, such as waste, into energy and value-added products, thereby emerging as a valuable tool for transitioning towards a circular economy. Microbial electrosynthesis (MES) involves the anaerobic reduction of CO2 into organic products. MES requires an external power source as the thermodynamic driving force for CO2 reduction and offers an attractive alternative to produce a versatile range of resources, such as hydrogen, acetate, and biopolymers. However, the efficiency of BES systems cannot currently compete with traditional fuel cells. Several bottlenecks, including energy efficiency and costs, must be addressed to achieve economic viability.The electrode is a crucial component of BES as it provides the surface for biofilm formation. Extracellular electron transfer (EET) within the biofilm is facilitated through conductive surface proteins called "nanowires". However, poor surface interactions at the bacteria and electrode interface limit electron transport, resulting in low energy conversion efficiencies and confining BES to prototypes. The incompatibility between abiotic and biotic surfaces is predicted to give rise to poor electron transfer. Synthetic materials can disrupt bacteria's natural electron transport chain (ETC) pathway and inhibit metabolic activity. A mismatch exists between the multiheme structural components of protein nanowires and those of close-packed metallic structures in electrodes, thereby increasing impedance. There is also insufficient contact between the bacteria and the electrode if unfavourable growth conditions are present at the electrode surface. Therefore, novel electrodes must be developed to seamlessly integrate biotic and abiotic components without compromising costs.
A strategy to mitigate limitations is to develop biohybrid systems. A biohybrid electrode, also known as a "living electrode", is a hybrid system that integrates living components, i.e., bacteria, with synthetic materials. Cell growth must be sustained at the electrode interface without inhibiting material conductivity to sustain EET. Cupriaviadus necator H16 (C. necator) is a gram-negative bacterium capable of oxidising many substrates and utilising CO2 as its sole carbon source. It is, therefore, a promising candidate for valorising CO2 to yield a versatile array of value-added products through MES. The successful development of a biohybrid electrode is anticipated to be a pivotal moment for BES's scalability and economic viability.This study aims to develop a novel biohybrid electrode to improve the electron transfer kinetics between abiotic and biotic interfaces in bioelectrochemical systems. The biohybrid electrode will be made from a biocompatible acrylate polymer and engineered to be conductive. The conductivity should not compromise the biocompatibility of the electrode in order to maintain biofilm formation. As a proof of concept, the performance of the biohybrid electrode will be validated in an MES by monitoring the biosynthesis of intracellular polyhydroxybutyrate (PHB) from CO2 using Cupriavidus necator H16.

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.