Carbon-based products are crucial to our society, but their production from fossil-based carbon is unsustainable. Production pathways based on the reuse of CO2 will achieve ultimate sustainability. Furthermore, the costs of renewable electricity production are decreasing at such a high rate, that electricity is expected to be the main energy carrier from 2040 onward. Electricity-driven novel processes that convert CO2 into chemicals need to be further developed. Microbial electrosynthesis is a biocathode-driven process in which electroactive microorganisms derive electrons from solid-state electrodes to catalyze the reduction of CO2 or organics and generate valuable extracellular multicarbon reduced products. Microorganisms can be tuned to high-rate and selective product formation. Optimization and upscaling of microbial electrosynthesis to practical, real life applications is dependent upon performance improvement while maintaining low cost. Extensive biofilm development, enhanced electron transfer rate from solid-state electrodes to microorganisms and increased chemical production rate require optimized microbial consortia, efficient reactor designs, and improved cathode materials. This Account is about the development of different electrode materials purposely designed for improved microbial electrosynthesis: NanoWeb-RVC and EPD-3D. Both types of electrodes are biocompatible, highly conductive three-dimensional hierarchical porous structures. Both chemical vapor deposition (CVD) and electrophoretic deposition were used to grow homogeneous and uniform carbon nanotube layers on the honeycomb structure of reticulated vitreous carbon. The high surface area to volume ratio of these electrodes maximizes the available surface area for biofilm development, i.e., enabling an increased catalyst loading. Simultaneously, the nanostructure makes it possible for a continuous electroactive biofilm to be formed, with increased electron transfer rate and high Coulombic efficiencies. Fully autotrophic biofilms from mixed cultures developed on both types of electrodes rely on CO2 as the sole carbon source and the solid-state electrode as the unique energy supply. We present first the synthesis and characteristics of the bare electrodes. We then report the outstanding performance indicators of these novel biocathodes: current densities up to -200 A m-2 and acetate production rates up to 1330 g m-2 day-1, with electron and CO2 recoveries into acetate being very close to 100% for mature biofilms. The performance indicators are still among the highest reported by either purposely designed or commercially available biocathodes. Finally, we made use of the titration and off-gas analysis sensor (TOGA) to elucidate the electron transfer mechanism in these efficient biocathodes. Planktonic cells in the catholyte were found irrelevant for acetate production. We identified the electron transfer to be mediated by biologically induced H2. H2 is not detected in the headspace of the reactors, unless CO2 feeding is interrupted or the cathodes sterilized. Thus, the biofilm is extremely efficient in consuming the generated H2. Finally, we successfully demonstrated the use of a synthetic biogas mixture as a CO2 source. We thus proved the potential of microbial electrosynthesis for the simultaneous upgrading of biogas, while fixating CO2 via the production of acetate.

中文翻译：

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专门设计的分层多孔电极，用于从二氧化碳高速率微生物合成乙酸。

碳基产品对我们的社会至关重要，但是用化石基碳生产它们是不可持续的。基于二氧化碳再利用的生产途径将实现最终的可持续性。此外，可再生电力生产的成本正在以如此高的速度降低，以至于电力有望从2040年开始成为主要的能源载体。由电力驱动的将CO2转化为化学物质的新方法需要进一步开发。微生物电合成是生物阴极驱动的过程，其中电活性微生物从固态电极获取电子以催化CO2或有机物的还原并产生有价值的细胞外多碳还原产物。可以将微生物调整为高速率和选择性的产物形成。微生物电合成在实际生活中的优化和升级取决于性能的提高，同时又保持低成本。生物膜的广泛发展，从固态电极到微生物的电子转移速率的提高以及化学生产速率的提高，需要优化的微生物群落，有效的反应器设计和改进的阴极材料。该帐户涉及专门设计用于改善微生物电合成的不同电极材料的开发：NanoWeb-RVC和EPD-3D。两种类型的电极都是生物相容的，高导电性的三维分层多孔结构。化学气相沉积（CVD）和电泳沉积均用于在网状玻璃碳的蜂窝结构上生长均匀且均匀的碳纳米管层。这些电极的高表面积体积比可最大化生物膜显影的可用表面积，即增加催化剂的负载量。同时，纳米结构使得可以形成连续的电活性生物膜，并具有增加的电子传输速率和高库仑效率。在两种类型的电极上开发的来自混合培养物的完全自养生物膜都依赖于CO2作为唯一的碳源，而固态电极则作为唯一的能源。我们首先介绍裸电极的合成和特征。然后，我们报告了这些新型生物阴极的出色性能指标：电流密度高达-200 A m-2，乙酸盐的生产率高达1330 g m-2 day-1，电子和二氧化碳向乙酸盐中的回收率非常接近100％用于成熟的生物膜。性能指标仍然是专门设计的或商用的生物阴极所报告的最高指标。最后，我们利用滴定和废气分析传感器（TOGA）阐明了这些高效生物阴极中的电子转移机理。发现阴极电解液中的浮游细胞与乙酸盐的产生无关。我们确定了由生物诱导的H2介导的电子转移。除非中断CO2进料或对阴极进行灭菌，否则在反应器的顶部空间中不会检测到H2。从而，生物膜在消耗产生的H2方面非常有效。最后，我们成功地证明了使用合成沼气混合物作为CO2来源。因此，我们证明了微生物电合成在同时升级沼气的同时通过生产乙酸盐固定二氧化碳的潜力。