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A more efficient way to convert CO2 into chemicals via MER

By Gerald Ondrey |

Microbial electrochemical reduction (MER) of CO2 into value-added chemicals is a potential way to curb greenhouse gas (GHG) emissions. MER uses chemolithoautotrophs, which are microbes found in the deep sea, in caves and in hydrothermal vents. These bacteria get their energy by oxidizing inorganic compounds and reducing CO2 into organic compounds. Typically, MER reactors use planar cathodes with microbes growing as a biofilm on the surface of the cathode, and supply CO2 by bubbling the gas into the solution. However, such systems have poor efficiencies due to the low solubility of CO2 in water and the small surface area of the cathode.

Now, an alternative design is being developed by the research group of professor Pascal Saikaly, associate professor of Environmental Science and Engineering at King Abdullah University of Science and Technology (KAUST; Thuwai, Saudia Arabia; https://kaust.edu.sa). In this new design, the cathode is made of porous nickel hollow-fibers (Ni-PHFs). In a microbial electrosynthesis (MES) reactor (diagram), the CO2 is pumped through the pores of Ni-PHFs and delivered directly to the biofilm chemolithotrophs growing on the surface of Ni-PHFs. Initial studies showed a 77% conversion efficiency for CO2 to methane by methanogens when CO2 is delivered through the pores of Ni-PHFs, compared to 3% when bubbling CO2 into the solution, according to the study published in a recent issue of Advanced Functional Materials. In a follow-up study, published in the Journal of Materials Chemistry A, the group showed that by modifying the Ni-PHFs with carbon nanotubes (CNTs), an 11-fold increase in CO2 adsorption capability was achieved, along with a 76% reduction of cathode electron-transfer resistance, which nearly doubled the production of acetate (HAc) from CO2 using Sporomusa ovata.

CO2 into chemicals

So far, “we have demonstrated the new design at lab-scale, since this was a proof-of-concept,” says Saikaly. “We are currently working on developing easier approaches to make conductive and porous cylindrical electrodes for large-scale applications. Also, at the same time we are exploring alternative anode materials (photoanodes) to reduce the cost of operation,” explains Saikaly. “These systems are currently being operated using a power source. Ultimately, we can couple this process with renewable energy sources, such as sun or wind,” he says.

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