Abstract
Microbial electrosynthesis (MES) is a promising technology to convert CO2 into value-added chemicals. Enhancing the interactions between biofilms and electrodes is the key of bioelectrochemical systems (BES). In this work, we studied the conversion of CO2 by MES in reactors equipped with novel gas diffusion electrodes (GDEs) modified with a polyaniline (PANI) polymer binary doped with H2SO4 and ammonium lauryl sulfate. The enhanced conductive and hydrophilic properties of the polymer increased the biocompatibility of the PANI-modified GDEs compared to the non-modified carbon GDEs. This increased biocompatibility resulted in faster start-up and higher bioproduction of volatile fatty acids (VFAs) such as acetate and butyrate. Up to 4400 ppm acetate was produced in PANI-modified reactors after 24 days of operation, compared to 408 ppm in reactors equipped with non-modified GDEs. A maximum acetate concentration of 7500 ppm (production rate of 554.8 ± 267.5 ppm day−1) was reached in reactors equipped with PANI-GDEs. After 60 days, apart from acetate, 245 ppm butyrate was produced in reactors equipped with the electrodes modified with PANI, while less than 60 ppm was produced with non-modified GDEs. SEM analysis revealed the development of biofilms on both modified and non-modified electrodes, but the images also suggest differences in compositions.
Highlights
In light of the on-going climate crisis and of the accumulation of greenhouse gases (GHGs) such as CO2 in the atmosphere, efforts have been undertaken globally towards developing technologies for carbon capture and storage (CCS) and carbon capture and utilisation (CCU) [18]
A higher activity towards hydrogen evolution reaction (HER) is expected to be beneficial for microbial electrosynthesis (MES) as it was shown that H2-mediated electron transfer (MET) is the most likely mechanism for CO2 conversion in bioelectrochemical systems [23,47,58]
Acetobacterium is known for dominating bacterial communities of most acetate-producing MES systems inoculated with environmental samples, which is in agreement with the results presented here [2,38,39,43,44,46]
Summary
In light of the on-going climate crisis and of the accumulation of greenhouse gases (GHGs) such as CO2 in the atmosphere, efforts have been undertaken globally towards developing technologies for carbon capture and storage (CCS) and carbon capture and utilisation (CCU) [18]. Despite being a major contributor to global warming, CO2 is a potential resource as a building block for more valuable organic molecules, especially when using microorganisms as catalysts [55] In this context, technologies such as gas fermentation and microbial electrosynthesis (MES) are attractive, with the required reducing power coming from a gaseous stream or in solution in the former case, or from renewable energies in the latter [15,55]. We studied the impact of the utilisation of carbon-based GDEs modified with PANI doped with H2SO4 and ammonium lauryl sulfate on the CO2 conversion by MES, especially in terms of start-up time and bio-production. Physico-chemical and electrochemical properties of the electrodes prior to and after the MES experiment were evaluated, and the concentrations of the main volatile fatty acids produced were followed
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