Metal impregnated granular activated carbon cathodes for microbial electrosynthesis of organic fatty acids
Tuominen, Markus (2023)
2023
Bioteknologian ja biolääketieteen tekniikan maisteriohjelma - Master's Programme in Biotechnology and Biomedical Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2023-12-18
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-2023121510900
https://urn.fi/URN:NBN:fi:tuni-2023121510900
Tiivistelmä
Bioelectrochemical systems have emerged as an intriguing method to produce volatile fatty acids such as acetate by microbial electrosynthesis (MES). With the utilization of acetogens, CO2 can be reduced into acetate by supplying the microbes with electrons via an electric current. The electrodes play a key role in this process as the current-yielding redox reactions, such as hydrogen formation, take place and are catalyzed on their surfaces. Unfortunately, the inefficiency of the overall process hinders its attractiveness for large-scale industrial utilization. For MES, the lack of electron or hydrogen supply is often a significant bottleneck for the production rates.
The aim of this study was to investigate the effects of electrode surface modifications with catalytic metals to enhance hydrogen evolution reaction and to test the feasibility of such electrodes for the MES of acetate. Granular activated carbon (GAC) was used as the electrode material as such or impregnated with copper and nickel. The electrocatalytic properties of the impregnated GAC were then compared to that of unimpregnated GAC. Abiotic characterization was first performed to measure the rates of abiotic hydrogen evolution at a cathode potential of -0.85 V vs. Ag/AgCl reference electrode. Two biological batches were then conducted, and the acetate formation rates were measured at a constant potential of -0.85 V vs. Ag/AgCl.
While the unimpregnated granules caused no notable hydrogen accumulation, the average rate of hydrogen evolution was 0.025 L/h with copper and 0.049 L/h with nickel impregnated granules in abiotic experiments. The metal-impregnated granules also consistently led to more negative currents than the unimpregnated granules, which led to increased H2 production and consequently increased acetate production. The measured acetate productivities in biological experiments were 109 mg/L/d for unimpregnated granules, 254 mg/L/d for copper impregnated granules and 206 mg/L/d mM for nickel impregnated granules at best.
These results imply that the metal modifications indeed improve the electrodes’ electrocatalytic properties, which can be observed from increased abiotic hydrogen evolution and biological acetate formation rates. In these experimental conditions, copper-impregnated electrodes proved to be more efficient in MES of acetate than the nickel-impregnated electrodes. However, the fact that highest abiotic hydrogen producing GAC (impregnated with Ni) did not yield the highest acetate production might suggest that there are still some unidentified factors affecting the overall process. Such factors could be biological hydrogen evolution or the fact that in other literature, copper itself has been related to abiotic reduction of CO2 into acetate, although in different operational conditions. Despite the results achieved here, further research should be conducted to identify other potential factors affecting the process and to evaluate the most feasible modification metals in terms of electrocatalytic efficiency, electrode integrity and cost-efficiency.
The aim of this study was to investigate the effects of electrode surface modifications with catalytic metals to enhance hydrogen evolution reaction and to test the feasibility of such electrodes for the MES of acetate. Granular activated carbon (GAC) was used as the electrode material as such or impregnated with copper and nickel. The electrocatalytic properties of the impregnated GAC were then compared to that of unimpregnated GAC. Abiotic characterization was first performed to measure the rates of abiotic hydrogen evolution at a cathode potential of -0.85 V vs. Ag/AgCl reference electrode. Two biological batches were then conducted, and the acetate formation rates were measured at a constant potential of -0.85 V vs. Ag/AgCl.
While the unimpregnated granules caused no notable hydrogen accumulation, the average rate of hydrogen evolution was 0.025 L/h with copper and 0.049 L/h with nickel impregnated granules in abiotic experiments. The metal-impregnated granules also consistently led to more negative currents than the unimpregnated granules, which led to increased H2 production and consequently increased acetate production. The measured acetate productivities in biological experiments were 109 mg/L/d for unimpregnated granules, 254 mg/L/d for copper impregnated granules and 206 mg/L/d mM for nickel impregnated granules at best.
These results imply that the metal modifications indeed improve the electrodes’ electrocatalytic properties, which can be observed from increased abiotic hydrogen evolution and biological acetate formation rates. In these experimental conditions, copper-impregnated electrodes proved to be more efficient in MES of acetate than the nickel-impregnated electrodes. However, the fact that highest abiotic hydrogen producing GAC (impregnated with Ni) did not yield the highest acetate production might suggest that there are still some unidentified factors affecting the overall process. Such factors could be biological hydrogen evolution or the fact that in other literature, copper itself has been related to abiotic reduction of CO2 into acetate, although in different operational conditions. Despite the results achieved here, further research should be conducted to identify other potential factors affecting the process and to evaluate the most feasible modification metals in terms of electrocatalytic efficiency, electrode integrity and cost-efficiency.