Biohybrid Materials for Improved Electron Transfer in Bioelectrochemical Systems

随着全球人口的持续增长，能源需求也随之激增，导致环境中二氧化碳水平急剧上升。为了促进经济发展，同时减少环境风险，必须采用可持续技术。生物电化学系统（BES）是利用微生物回收二氧化碳的独特方法。BES可以将低成本的基材（如废物）转化为能源和增值产品，从而成为向循环经济过渡的宝贵工具。微生物电合成（MES）涉及将二氧化碳厌氧还原成有机产物。MES需要外部电源作为二氧化碳减排的热力学驱动力，并提供了一种有吸引力的替代方案，可以生产多种资源，如氢气、醋酸盐和生物聚合物。然而，BES系统的效率目前还无法与传统燃料电池竞争。为了实现经济可行性，必须解决几个瓶颈，包括能源效率和成本。电极是BES的重要组成部分，因为它为生物膜的形成提供了表面。生物膜内的细胞外电子转移（EET）是通过被称为“纳米线”的导电表面蛋白来促进的。然而，细菌和电极界面的不良表面相互作用限制了电子传递，导致能量转换效率低，并将BES限制在原型中。非生物和生物表面之间的不相容性预计会导致电子传递不良。合成材料可以破坏细菌的天然电子传递链途径，抑制细菌的代谢活性。蛋白质纳米线的多血红素结构成分与电极中紧密排列的金属结构成分之间存在不匹配，从而增加了阻抗。如果电极表面存在不利的生长条件，则细菌和电极之间的接触也不足。因此，必须开发新型电极，在不影响成本的情况下无缝集成生物和非生物组件。缓解限制的一个策略是开发生物混合系统。生物杂化电极，也称为“活电极”，是一种将活成分（即细菌）与合成材料相结合的混合系统。细胞生长必须维持在电极界面，而不抑制材料的导电性，以维持EET。Cupriaviadus necator H16 （C. necator）是一种革兰氏阴性细菌，能够氧化许多底物并利用二氧化碳作为其唯一的碳源。因此，它是一个很有前途的候选者，可以通过MES使二氧化碳增值，从而产生一系列多用途的增值产品。生物混合电极的成功开发有望成为BES可扩展性和经济可行性的关键时刻。本研究旨在开发一种新型的生物杂化电极，以改善生物电化学系统中非生物和生物界面之间的电子传递动力学。这种生物杂化电极将由一种生物相容性丙烯酸酯聚合物制成，并设计成导电的。电导率不应损害电极的生物相容性，以维持生物膜的形成。作为概念验证，生物杂交电极的性能将在MES中通过监测Cupriavidus necator H16从二氧化碳中合成细胞内聚羟基丁酸盐（PHB）来验证。

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.