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( Huong V. H. Tran ),( Sokhee P. Jung ) 한국폐기물자원순환학회 2022 ISSE 초록집 Vol.2022 No.-
To maximize wastewater treatment and energy production by microbial fuel cells (MFCs), it is important to design the optimal anode arrangement. In this study, four brushes were tested horizontally or vertically to the cathode as the number of the anodes increased from one to four. In the horizontal configuration, adding the anodes greatly reduce electrode resistance and enhanced cell performance, showing four anodes (H4) was the best. In the vertical configuration, two anodes (V2) showed greatest performance and greatest decrease in anode resistance. Compared with one anode, maximum power increased by 59% in H4 and by 18% in V2; anode polarization resistance decreased by 95% in H4 and by 74% in V2; anode impedance decreased by 91% in H2 and by 73% in V2. Cathode resistance was relatively constant, showing adding anodes had negligible effect on it. Because diffusion resistance increases with increasing distance between an anode and a cathode, the vertical anodes should have different diffusion resistance and performances. In this study, adding more anodes vertically decreased cell performance in V3 and V4. However, in a cyclic voltammetry test, current production was substantially increased when the third and the fourth brush anodes were introduced in the both arrangements. Compared with one anode, current production increased by 200% in H4 and by 205% in V4. It shows that the external electrical input relieved diffusion resistance and increased current generation and that installing anodes away from the cathode is a good strategy to increase current production in a system with external power supply such as microbial electrolysis cell. Based on the results, we suggest the following strategy: i) install multiple anodes horizontally along the cathode; ii) install multiple anodes in the second row horizontally along the cathode; iii) install multiple anodes both horizontally and vertically if there is an external power supply.
( Huong V. H. Tran ),( Sokhee P. Jung ) 한국폐기물자원순환학회 2022 ISSE 초록집 Vol.2022 No.-
Activated carbon (AC) is an inexpensive catalyst for oxygen reduction in an air cathode of microbial fuel cells (MFCs). In the AC-based cathode, carbon black (CB) is used as a conductive supporting material. In this study, it was hypothesized cathodic performance would increase if reduced graphene oxide (rGO) replaces CB in an optimum ratio. rGO replaced CB in the four different weight ratios of rGO to CB: 0:30 (rGO0); 5:25 (rGO5); 15:15 (rGO15); 30:0 (rGO30). Maximum power density was the best in rGO15 (2642 mW/㎡) followed by rGO5 (2142 mW/㎡). In the optimum external resistance operation, rGO5 and rGO15 showed similar power (∼1060 mW/㎡), higher than the others. Linear sweep voltammetry, cyclic voltammetry, and impedance spectroscopy also showed that the optimal rGO additions improved cathodic performance and reduced cathodic internal resistance. Due to the flatter and wider shape of rGO and 5 times higher electrical conductivity than CB, the rGO addition improved the cathodic performance, but the complete replacement of CB with rGO decreased the cathodic performance due to the increased thickness and the morphological crack. The optimum rGO addition is a simple and effective method for improving cathodic performance.
( Huong V. H. Tran ),( Sokhee P. Jung ) 한국폐기물자원순환학회 2022 ISSE 초록집 Vol.2022 No.-
For accurate and reproducible MFC experiments, it is important to know when MFCs produce stable cell performance. Herein, four replicate single-chamber MFCs were tested for 17 weeks by using polarization and cyclic voltammetry (CV) tests. The strong MFCs (#2,4,3) showing continuous performance enhancement initially (3<sup>rd</sup>-9<sup>th</sup> week) produced good subsequent performance (9<sup>th</sup>-17<sup>th</sup> week). The weak MFC-1 experienced a performance drop initially and showed bad subsequent performance. All the MFC performance became stable after 9 weeks. The strong MFCs produced power 2.8-3.6 times higher and anode resistance 7.5-23.9 times lower than the weak. However, their cathode resistances were similar. CV results showed anodic current production increased continuously in all MFCs, indicating anode biofilms kept growing; MFC performance did not increase accordingly. Anodic CVs had a typical S-shape curve, but those of MFC-1 showed straight lines from the 9<sup>th</sup> week. The weak MFC-1 showed smaller CV currents and thinner CV curves than those of the strong MFCs. In MFC-1, at the 17<sup>th</sup> week, the anode resistance reduced by 47%, anodic current and cell performance increased. Regression analysis showed anode resistance was a limiting factor of the weak MFC and cathode resistance was that of the strong MFCs. This result suggests one operating principle: improve anodes in weak MFCs and cathodes in strong MFCs to achieve better MFC performance.
Huong V. H. Tran,Eojin Kim,Sokhee P. Jung 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.106 No.-
For accurate and reproducible MFC experiments, it is important to know when MFCs produce stable cellperformance. Herein, four replicate single-chamber MFCs were tested for 17 weeks by using polarizationand cyclic voltammetry (CV) tests. The strong MFCs (#2,4,3) showing continuous performance enhancementinitially (3rd–9th week) produced good subsequent performance (9th–17th week). The weak MFC-1experienced a performance drop initially and showed bad subsequent performance. All the MFC performancebecame stable after 9 weeks. The strong MFCs produced power 2.8–3.6 times higher and anoderesistance 7.5–23.9 times lower than the weak. However, their cathode resistances were similar. CVresults showed anodic current production increased continuously in all MFCs, indicating anode biofilmskept growing;, MFC performance did not increase accordingly. Anodic CVs had a typical S-shape curve,but those of MFC-1 showed straight lines from the 9th week. The weak MFC-1 showed smaller CV currentsand thinner CV curves than those of the strong MFCs. In MFC-1, at the 17th week, the anode resistancereduced by 47%, anodic current and cell performance increased. Regression analysis showed anode resistancewas a limiting factor of the weak MFC and cathode resistance was that of the strong MFCs. Thisresult suggests one operating principle: improve anodes in weak MFCs and cathodes in strong MFCs toachieve better MFC performance.
( Huong V. H. Tran ),( Sokhee P. Jung ) 한국폐기물자원순환학회 2022 ISSE 초록집 Vol.2022 No.-
Microbial fuel cell (MFC) is an innovative environmental and energy system that converts organic wastewater into electrical energy. For practical implementation of MFC as a wastewater treatment process, a number of limitations need to be overcome. Improving cathodic performance is one of major challenges, and introduction of a current collector can be an easy and practical solution. In this study, three types of current collectors made of stainless steel (SS) were tested in a single-chamber cubic MFC. The three current collectors had different contact areas to the cathode (P 1.0 ㎠; PC 4.3 ㎠; PM 6.5 ㎠). The results showed that increasing the contacting area enhanced the power and current generations and coulombic and energy recoveries by mainly decreasing cathodic charge transfer impedance. Application of the SS mesh to the cathode (PM) improved maximum power density, optimum current density and maximum current density by 8.8%, 3.6% and 6.7%, respectively, comparing with P of no SS mesh. The SS mesh decreased cathodic polarization resistance by up to 16%, and cathodic charge transfer impedance by up to 39%, possibly because the SS mesh enhanced electron transport and oxygen reduction reaction. However, application of the SS mesh had little effect on ohmic impedance.
( Huong V. H. Tran ),( Sokhee P. Jung ) 한국폐기물자원순환학회 2022 ISSE 초록집 Vol.2022 No.-
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 mW m<sup>-2</sup>, and ZIF-67H did 3881 mW m<sup>-2</sup>, which is 60% and 48% higher than AC cathode (2625 mW m<sup>-2</sup>) and 160% and 140% higher than Pt cathode (1614 mW m<sup>-2</sup>), 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.