Biohybrid Materials for Improved Electron Transfer in Bioelectrochemical Systems

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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.