Solid neutral red/Nafion conductive layer on carbon felt electrode enhances acetate production from CO2 and energy efficiency in microbial electrosynthesis system

Housing of electrosynthetic biofilms using a roll-up carbon veil electrode increases CO2 conversion and faradaic efficiency in microbial electrosynthesis cells

Electrode-driven microbial electron transfer enables the conversion of CO2 into multi-carbon compounds. The electrosynthetic biofilms grow slowly on the surface and are highly susceptible to operational influences, such as hydrodynamic shear stress. In this study, a cylindrical roll-up carbon felt electrode was developed as a novel strategy to protect biofilms from shear stress within the reactor. The fabricated electrode allowed hydrogen bubble formation inside the structure, which enabled microbes to uptake hydrogen and convert CO2 to multi-carbon organic compounds. The roll-up electrode exhibited faster start-up and biofilm formation than the conventional linear shape carbon felt. The acetate yield and cathodic faradaic efficiency increased by 80% and 34%, respectively, and the bioelectrochemical stability was improved significantly. The roll-up structure increased biofilm development per unit electrode surface by three to five-fold. The roll-up configuration improved biofilm formation on the electrode, which enhanced the performance of microbial electrosynthesis-based CO2 valorization.

Facial Synthesis, Stability, and Interaction of Ti3C2Tx@PC Composites for High-Performance Biocathode Microbial Electrosynthesis Systems

Developing high-performance biocathodes remain one of the most challenging aspects of the microbial electrosynthesis (MES) system and the primary factor limiting its output. Herein, a hollow porous carbon (PC) fabricated with MXenes coated over an electrode was developed for MES systems to facilitate the direct delivery of CO2 to microorganisms colonized. The result highlighted that MXene@PC (Ti3C2Tx@PC) has a surface area of 434 m2/g. The Ti3C2Tx@PC MES cycle shows that in cycle 4 and cycle 5, the values are -309.2 and -352.3. Cyclic voltammetry showed that the coated electrode current response (mA) increased from -4.5 to -20.2. The substantial redox peaks of Ti3C2Tx@PC biofilms are displayed at -741, -516, and -427 mV vs Ag/AgCl, suggesting an enhanced electron transfer owing to the Ti3C2Tx@PC complex coating. Additionally, more active sites enhanced mass transfer and microbial development, resulting in a 46% rise in butyrate compared to the uncoated control. These findings demonstrate the value of PC modification as a method for MES-based product selection.

Citrate Synthase Overexpression of Pseudomonas putida Increases Succinate Production from Acetate in Microaerobic Cultivation

Acetate is an end-product of anaerobic biodegradation and one of the major metabolites of microbial fermentation and lingo-cellulosic hydrolysate. Recently, acetate has been highlighted as a feedstock to produce value-added chemicals. This study examined acetate conversion to succinate by citrate synthase (gltA)-overexpressed Pseudomonas putida under microaerobic conditions. The acetate metabolism is initiated with the gltA enzyme, which converts acetyl-CoA to citrate. gltA-overexpressing P. putida (gltA-KT) showed an ∼50% improvement in succinate production compared to the wild type. Under the optimal pH of 7.5, the accumulation of succinate (4.73 ± 0.6 mM in 36 h) was ∼400% higher than that of the wild type. Overall, gltA overexpression alone resulted in 9.5% of the maximum theoretical yield in a minimal medium with acetate as the sole carbon source. This result shows that citrate synthase is important in acetate conversion to succinate by P. putida under microaerobic conditions.

Role of microbial electrosynthesis system in CO2 capture and conversion: a recent advancement toward cathode development

Microbial electrosynthesis (MES) is an emerging electrochemical technology currently being researched as a CO₂ sequestration method to address climate change. MES can convert CO₂ from pollution or waste materials into various carbon compounds with low energy requirements using electrogenic microbes as biocatalysts. However, the critical component in this technology, the cathode, still needs to perform more effectively than other conventional CO₂ reduction methods because of poor selectivity, complex metabolism pathways of microbes, and high material cost. These characteristics lead to the weak interactions of microbes and cathode electrocatalytic activities. These approaches range from cathode modification using conventional engineering approaches to new fabrication methods. Aside from cathode development, the operating procedure also plays a critical function and strategy to optimize electrosynthesis production in reducing operating costs, such as hybridization and integration of MES. If this technology could be realized, it would offer a new way to utilize excess CO₂ from industries and generate profitable commodities in the future to replace fossil fuel-derived products. In recent years, several potential approaches have been tested and studied to boost the capabilities of CO₂-reducing bio-cathodes regarding surface morphology, current density, and biocompatibility, which would be further elaborated. This compilation aims to showcase that the achievements of MES have significantly improved and the future direction this is going with some recommendations. Highlights - MES approach in carbon sequestration using the biotic component.- The role of microbes as biocatalysts in MES and their metabolic pathways are discussed.- Methods and materials used to modify biocathode for enhancing CO₂ reduction are presented.

Construction of Cupriavidus necator displayed with superoxide dismutases for enhanced growth in bioelectrochemical systems

It is of great significance to utilize CO2 as feedstock to synthesize biobased products, particularly single cell protein (SCP) as the alternative food and feed. Bioelectrochemical system (BES) driven by clean electric energy has been regarded as a promising way for Cupriavidus necator to produce SCP from CO2 directly. At present, the key problem of culturing C. necator in BES is that reactive oxygen species (ROS) generated in cathode chamber are harmful to bacterial growth. Therefore, it is necessary to find a solution to mitigate the negative effect of ROS. In this study, we constructed a number of C. necator strains displayed with superoxide dismutase (SOD), which allowed the decomposition of superoxide anion radical. The effects of promoters and signal peptides on the cell surface displayed SOD were analyzed. The proteins displayed on the surface were further verified by the fluorescence experiment. Finally, the growth of C. necator CMS incorporating a pBAD-SOD-E-tag-IgAβ plasmid could achieve 4.9 ± 1.0 of OD600 by 7 days, equivalent to 1.7 ± 0.3 g/L dry cell weight (DCW), and the production rate was 0.24 ± 0.04 g/L/d DCW, around 2.7-fold increase than the original C. necator CMS (1.8 ± 0.3 of OD600). This study can provide an effective and novel strategy of cultivating strains for the production of CO2-derived SCP or other chemicals in BES.