Cathode-driven applications of bio-electrochemical systems (BESs) have the potential to transform CO₂ into value-added chemicals using microorganisms. However, their commercialisation is limited as biocathodes in BESs are characterised by slow start-up and low efficiency. Understanding biosynthesis pathways, electron transfer mechanisms and the effect of operational variables on microbial electrosynthesis (MES) is of fundamental importance to advance these applications of a system that has the capacity to convert CO₂ to organics and is potentially sustainable. In this work, we demonstrate that cathodic potential and inorganic carbon source are keys for the development of a dense and conductive biofilm that ensures high efficiency in the overall system. Applying the cathodic potential of −1.0 V vs. Ag/AgCl and providing only gaseous CO₂ in our system, a dense biofilm dominated by Acetobacterium (ca. 50% of biofilm) was formed. The superior biofilm density was significantly correlated with a higher production yield of organic chemicals, particularly acetate. Together, a significant decrease in the H₂ evolution overpotential (by 200 mV) and abundant nifH genes within the biofilm were observed. This can only be mechanistically explained if intracellular hydrogen production with direct electron uptake from the cathode via nitrogenase within bacterial cells is occurring in addition to the commonly observed extracellular H₂ production. Indeed, the enzymatic activity within the biofilm accelerated the electron transfer. This was evidenced by an increase in the coulombic efficiency (ca. 69%) and a 10-fold decrease in the charge transfer resistance. This is the first report of such a significant decrease in the charge resistance via the development of a highly conductive biofilm during MES. The results highlight the fundamental importance of maintaining a highly active autotrophic Acetobacterium population through feeding CO₂ in gaseous form, which its dominance in the biocathode leads to a higher efficiency of the system.

阴极驱动的生物电化学系统（BES）的应用具有利用微生物将CO ₂转化为增值化学品的潜力。但是，它们的商业化受到限制，因为BES中的生物阴极具有启动速度慢和效率低的特点。了解生物合成途径，电子转移机制以及操作变量对微生物电合成（MES）的影响，对于推进具有转化CO ₂能力的系统的这些应用至关重要。有机物，具有可持续性。在这项工作中，我们证明了阴极电势和无机碳源是开发致密且导电的生物膜的关键，该膜可确保整个系统的高效率。施加-1.0 V，相对于银/氯化银的阴极电势，并提供只有气态CO ₂在我们的系统中，致密的生物膜由主导醋酸杆菌（CA。生物膜的50％）形成。优异的生物膜密度与有机化学品（尤其是醋酸盐）的更高产量有着显着的关联。在一起，H ₂进化超电势（显着降低了200 mV）和丰富的nifH共同降低了观察到生物膜内的基因。如果除了通常观察到的细胞外H ₂产生之外，如果发生细菌细胞内通过氮酶从阴极直接吸收电子的细胞内氢产生，则只能用机械的方式进行解释。实际上，生物膜内的酶促活性加速了电子转移。库仑效率的提高（约69％）和电荷转移电阻的降低10倍证明了这一点。这是关于在MES期间通过形成高导电性生物膜而使充电电阻显着降低的首次报道。结果突出了维持高度活性的自养醋杆菌的根本重要性通过以气态形式喂入CO ₂来增加生物量，其在生物阴极中的优势导致系统效率更高。