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Bonyoung KOO,Sunghoon SON,Sokhee JUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
Activated carbon (AC) is an inexpensive catalyst for the oxygen reduction reaction in the air cathode of microbial fuel cells (MFCs). However, since the electrochemical catalytic activity of AC is poor, it is necessary to improve its performance. The metal-organic framework (MOF) is composed of a metal ion and an organic linker. It has high porosity and high electrochemical catalytic activity. Herein, ZIF-67 (cobalt-nitrogen framework) was combined with activated carbon through ultrasonication (U) and solution precipitation (H), which was used to make ZIF-67U and ZIF-67H cathodes, respectively. In maximum power density, ZIF-67U cathode produced 4203 ㎽ m-2, and ZIF-67H did 3881 mW m-2, which is 60% and 48% higher than AC cathode (2625 mW m-2) and 160% and 140% higher than Pt cathode (1614 mW m-2), respectively. Cobalt and nitrogen contents increased in the ZIF catalysts. In atomic nitrogen contents of catalyst surface, pyridine-N was 28% in ZIF-67U and 38% in ZIF-67H, respectively; pyrrole-N was 56% in ZIF-67U and 25% in ZIF-67H, respectively; no nitrogen was detected in AC. These cobalt-nitrogen increased the active site of the oxygen reduction reaction (ORR), improved the reaction rate, and decreased charge transfer impedance. Impedance analysis demonstrated the ZIF-67 addition also decreased the diffusion impedance possibly due to the improved cathode porosity. AC and ZIF-67 were bonded using ultrasonication and tested in the MFC for the first time, producing the highest power ever among the MOFs in the 50-mM phosphate-buffer-saline condition so far.
Evaluation of the Reproducibility of Linear Sweep Voltammetry Tests in Microbial Electrolysis Cells
Bonyoung KOO,Sunghoon SON,Sokhee JUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
Microbial electrolysis cells (MECs) are a promising environmental system performing simultaneous organic waste stream treatment and producing valuable products. Electrode is a key component in a microbial electrolysis cell (MEC) and it needs significant improvement for practical implementation of MEC. For effective development of electrode technology, accurate and reproducible analytical methods are very important. Linear sweep voltammetry (LSV) is an essential analytical method for evaluating electrode performance; however, it has not been firmly established yet in the MEC field. In this study, biological brush (BB), abiotic brush (AB), Pt wire (PtW), stainless steel wire (SSW) and mesh (SSM)) were tested to explore the most suitable counter electrode in different medium conditions. Coefficient of variation (Cv) for Imax of LSV was comparatively analyzed. In BB-anode LSV, SSW (0.48%) and SSM (2.17%) showed higher reproducibility as a counter electrode. Reproducibility of anode LSV test was good in stainless steel wire and mesh as counter electrode. In SSM-cathode LSV, BB (1.76%) and PtW (2.01%) produced more reproducible results. In the Ni-AC-SSM-cathode LSV, PtW (3.54%) and BB (8.81%) produced more reproducible results. It shows electrode used in the operation is an appropriate counter electrode in the acetate-added condition. However, in the absence of acetate, PtW (1.24%) and BB (1.71%) produced more reproducible results in SSM cathode and PtW (0.61%) and SSW (1.21%) did in the Ni-AC-SSM-cathode, showing PtW is an appropriate counter electrode. This is because Pt is not electrochemically polarized as a counter electrode in the cathode LSV test. Reproducibility evaluation results in this study suggest that counter electrodes can be set according to the various conditions in anode and cathode LSV test.
( Bonyoung Koo ),( Sokhee P. Jung ) 한국폐기물자원순환학회 2022 ISSE 초록집 Vol.2022 No.-
Although MFC has many applications, the most promising application is in wastewater treatment. MFC can be grafted into a sewage treatment plant to remove the remaining organic matter and generate energy for the operation of the sewage treatment plant. Many studies have been carried out to improve the performance of these MFCs, and they have shown the potential for commercialization of MFCs, such as showing results of grafting them with actual sewage treatment plants. The current research trend of MFC scale-up is as follows. i) development of electrodes and membranes with high economy and performance to reduce high cost, ii) development of materials resistant to contamination, corrosion and clogging for long-term operation, iii) connection of multiple modules to minimize losses Scale up in the form of a stack. However, there are still a number of obstacles that prevent scale-up. The main obstacles are high cost, low power generation due to internal losses, durability and removal of contaminants. Therefore, it is important to develop efficient electrodes and ion membranes and increase the actual wastewater treatment efficiency in order to reduce the high cost and internal losses. Looking at the results of MFC scale-up studies so far, it has been shown that stack configuration can achieve high performance by reducing internal losses, is cheaper than scaling up a single reactor, and has high pollutant handling capacity. Suggested research strategies for scale-up for future practical use are as follows. First, by using a stack type reactor, secondly by using a reactor without an ion film to reduce internal resistance and cost, thirdly by using a microbial anode as the ultimate catalyst for durability and sustainability, and finally by increasing the processing efficiency. It is to achieve high treatment efficiency through pre-treatment and post-treatment by grafting other sewage treatment processes to increase it.
Bonyoung KOO,Sunghoon SON,Sokhee JUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
Microbial fuel cell (MFC) is an innovative environmental and energy system that converts biomass energy in wastewater into electrical energy and purify wastewater by using a microbial electrochemical reaction. For the practical implementation of MFC as a next-generation wastewater treatment process, MFC performance should be enhanced far more than the current level. Characterizations of the electrochemistry of MFC is very important in developing bio-electrochemical energy producing wastewater treatment process. Compared to the development of MFC technology, however, understanding of its electrochemical characterization is still insufficient. The main reason is that its electrochemical analysis is very difficult due to the complex nature of the anode biofilm, which is a key to generating electricity. In this experiment, the influence of the measurement potential of impedance and the scanning rate for polarization curve on the MFC electrochemistry was investigated. The experiment was performed after stabilizing the system for accurate measurement. Unlike the previous batch tests showing the lowest anodic impedance at -400 ㎷ vs. Ag/AgCl, the anodic impedance decreased and the current production increased as the anode potential increased up to +5.7 mV vs. Ag/AgCl in the continuous flow MFC. The polarization curves were produced at two scanning rates (1 and 0.1 ㎷/s) in a continuous mode, and those electrochemical data were comparatively analyzed. The rapid scan rate has the advantage of being able to collect data in a short time, but the measured data differs from the performance value when operating the MFC with a constant external resistance. When it is difficult to maintain a steady state for a long time in an MFC, it will be possible to produce polarization curves in a short time with a faster scanning rate. When performance analysis is needed, the comparative analysis would be possible among the data at different conditions through extrapolation.
Recent Trends of Oxygen Reduction Catalysts in Microbial Fuel Cells
( Bonyoung Koo ),( Sokhee P. Jung ) 한국폐기물자원순환학회 2022 ISSE 초록집 Vol.2022 No.-
Microbial fuel cell (MFC) is a system being developed for a next-generation energy-producing wastewater treatment process that treats wastewater and recovers energy. Because an MFC cathode performing oxygen reduction is a bottleneck in performance enhancement, significant improvement of the cathode performance is necessary for the practical implementation of MFC system. The most ideal oxygen reduction catalyst is known as platinum. However, platinum is expensive and not long-lasting, making it difficult to apply to a real application. For this reason, a lot of research has been conducted on development of cathode catalysts in the MFC field. One of the important goals of MFC technology is an energy-independent or energy-supplied wastewater treatment process. Considering the size of the wastewater treatment plant and the characteristics of the wastewater, the ideal cathode catalyst for this should have high durability and high economic efficiency in long-term operation. Summarizing the research results so far, the activated carbon-based catalyst is considered to be the most promising ORR catalyst for the practical use of MFC. The 1,210 mW/$ achieved by the activated carbon catalyst mixed with CB is the highest cost-performance ratio in the studies reported to date. It is necessary to study electrochemical mechanisms and materials to improve the performance and durability of activated carbon catalysts, and research for mass production of electrodes is needed.