Application of gas diffusion biocathode in microbial electrosynthesis from carbon dioxide

Area of Science:

• Bioelectrochemistry
• Microbial electrosynthesis
• Carbon dioxide reduction

Background:

• Microbial electrosynthesis (MES) offers a promising route for reducing carbon dioxide (CO2) to multi-carbon compounds.
• Efficient CO2 reduction is hindered by challenges in CO2 dissolution and mass transfer in the electrolyte.
• Gas diffusion electrodes (GDEs) can overcome these limitations by facilitating direct CO2 supply to the biocathode.

Purpose of the Study:

• To investigate the efficacy of a gas diffusion electrode (GDE) in enhancing microbial electrosynthesis (MES) for CO2 reduction.
• To improve the mass transfer of gaseous CO2 to the biocatalyst in an MES reactor.
• To evaluate the production of multi-carbon compounds from CO2 using a GDE-based biocathode.

Main Methods:

• A GDE, comprising a catalyst layer and a hydrophobic gas diffusion layer, was designed and implemented in an MES reactor.
• An enriched inoculum of acetogenic bacteria was used as the biocatalyst.
• The cathode potential was maintained at -1.1 V vs Ag/AgCl to facilitate CO2 reduction.
• Gaseous CO2 (20% and 80% mixtures) was fed through the GDE.

Main Results:

• The GDE facilitated a three-phase interface, ensuring availability of CO2 and reducing equivalents to the biocatalyst.
• Acetate was the primary product, with ethanol and butyrate also detected.
• Average acetate production rates of 32 and 61 mg/L/day were achieved with 20% and 80% CO2 feeds, respectively.
• A maximum acetate production rate of 238 mg/L/day was recorded with a 20% CO2 gas mixture.

Conclusions:

• The developed gas diffusion biocathode effectively supports bioelectrochemical CO2 reduction.
• Enhanced mass transfer of gaseous CO2 was achieved through continuous supply via the GDE.
• This approach shows significant potential for efficient microbial conversion of CO2 into valuable chemicals.