Title : Maze-structured metal-organic framework (MOFs) used as cathodes in anaerobic digestion microbial electro synthesis systems to enhance the production of acetate and butyrate
Abstract:
The Microbial Electrosynthesis System (MES) represents a promising bioelectrochemical technology for recycling Carbon dioxide (CO2) and producing valuable organic compounds using renewable energy. However, low current densities, limited current efficiency, and poor electron transfer at the biocathode interface present significant bottlenecks for industrial scalability. While MES research has predominantly yielded C2 compounds like acetate, elongating carbon chains to higher-value C4–C8 products remains a critical challenge. Although metal-organic frameworks (MOFs) have emerged as popular electrode catalysts due to their large specific surface area and high porosity, the inferior electroconductivity of monometallic MOFs restricts their electrocatalytic efficiency.
To address these limitations, this study developed a novel, cost-effective, and scalable composite cathode by growing metal-organic framework (MOF)-derived carbon-based bimetallic hybrids (Ni/Co-S) onto carbon felt (Ni/Co-S@CF) via a simple hydrothermal synthesis method. The surface properties, biofilm adhesion, and electrochemical performance of the modified cathode were comprehensively characterized.
Electrochemical assessments demonstrated that the Ni/Co-S@CF cathode achieved higher current density, reduced charge transfer resistance, and an accelerated hydrogen evolution reaction (HER) rate. The positive surface charge, excellent conductive capacity, and high roughness/surface area of the Ni/Co-S matrix significantly enhanced CO absorption and facilitated robust cathodic biofilm attachment via hydrogen bonding and electrostatic interactions. Consequently, this favorable environment promoted rapid biofilm formation and increased the abundance of electrochemically active and acid-producing microorganisms, specifically Acetobacterium and Clostridium.
Over a 14-day operational period, the Ni/Co-S biocathode system significantly boosted bioelectrochemical CO2 reduction to C4 compounds by promoting direct electron transfer and hydrogenotrophic methanogenesis. By the 10th day of operation, the cumulative concentrations of acetate and butyrate reached maximum values of 72.5 mg/L and 64.873 mg/L, respectively. These yields represent a 2-fold increase for acetate and a 1.45-fold increase for butyrate compared to the unmodified control groups. Ultimately, these findings indicate that modifying cathodes with bimetallic MOF derivatives provides a highly efficient strategy to optimize substrate acquisition (CO2) and electron donor delivery (H2), significantly enhancing the conversion efficiency of greenhouse gases into high-value organic acids.
Keywords: Microbial electrosynthesis system; CO2 Biological methanation; Hydrogenotrophic methanogenesis; Direct electron transfer; Bimetallic hybrids (Ni/Co-S).
