Research On Electricity Production Enhanced By Designing Of Efficient Electrode And Interface In Microbial Fuel Cells

Energy shortage and environmental pollution have become more serious day by day. Microbial fuel cell（MFC） could treat wastewater and generate electricity simultaneously through transfering of biomass to electricity by the bacteria metabolism, which provides a new stratagy for solving the water pollution and energy shortage issues. However, the lower power generation limites the practical application of MFC. On the cathode, the oxygen is the ideal electron acceptor due to its property of easy to get and green, however, the slow kinetic sluggishness of cathodic oxygen reduction reaction（ORR） need high efficient catalyst to accelerate the reaction. Moreover, the anode of MFC determines the amount of biamss and the efficiency of extracellular electron transition（EET）, which is important for the power output of MFC.For the major problems existing in MFC, this research was mianly based on the triple-phase boundary of elctrode. To improve the performance of MFC, the cheap stainless stell mesh（SSM） was used as electricity collector in place of carbon cloth in air-cathode, cost-efficient nano-hybid and 3D ORR electrocatlysts were devolped, and the triple-phase boundary properties of electrode were adjusted through binders and construction of air-cathode. Furthermore, a 3D capacitor anode was consturcted to increase the amount of biomass and EET efficiency, which improved the power density and performance of MFC.Ag-WC/C was synthesized and used as ORR electrocatalyst, which shown highly active for electrocatalysis of oxygen reduction in p H-neutral electrolyte. With the nanometres-scale synergistic effects of carbon, tungsten carbide and silver nanoparticles, the ORR on Ag-WC/C nanohybrid could take place through the overall four-electron pathway. The Ag-WC/C catalyst could achieve a comparable magnitude of power density to commercial Pt/C catalyst in microbial fuel cell. This study gives a demonstration of platinum-alternative high-efficiency and cost-effective ORR electrocatalyst for more sustainable electricity generation from biomass materials in MFC. Furthermore, noble-metal-free 3D porous Co NC catalysts were derived from metal organic frameworks through direct carbonization at high temperature. The carbonization temperature affected the efficient surface area, content and types of doped nitrogen, which further affected the ORR activities of Co NC catalysts and performance of MFC with Co NC. The large surface area, microporous nature and the involvement of nitrogen-coordinated cobalt species of Co NC. These properties enable the efficient ORR by increasing the active sites and enhancing mass transfer of oxygen and protons at “water-flooding” three-phase boundary where ORR occurs. The maximum power density of 1665 m W/m2 was achieved for the optimized Co NC pyrolyzed at 900 °C, which is 39.8% higher than that of 1191 m W/m2 for commercial Pt/C catalyst in the single-chamber MFC. The MOF derived catalysts provides a novel route to prepare cost-effective and platinum-free electrocatalysts for ORR in neutral electrolyte and microbial fuel cells.The stainless stell mesh（SSM） was used as electricity collector in place of carbon cloth in air-cathode. The conductivity, ORR charactristics and performance of gas-diffusion electrode were consist with the concent of polytetrafluoroethylene（PTFE）, the optimal concent of PTFE was 20 wt%. The cost of the SSM e lectrode was only 61% of the cost of carbon cloth electrode. So the used of SSM could improve the performace and reduce the cost of cathode and MFC.Ethylenediamine tetraacetic acid（EDTA） was investigated as binder to construct air-cathode in place of commercial Nafion solution. The electrochemical results showed that EDTA enhanced proton transfer from phosphate ions, decreased the charge-transfer resistance and enhanced the interfacial oxygen reduction reaction on the cathode. The MFC with cathode of 0.02 mol/L-EDTA binder produced a maximum power density 42 % higher than that of commercial Nafion binder（5 wt%）. Moreover, the study fabricated a new type of binder-free gas diffusion electrode made of cobalt oxide（Co₃O₄） micro-particles directly grown on SSM. By performing various electrochemical analysis, the SSM/Co₃O₄ hybrid electrode demonstrated improved performances in terms of electrocatalytic activity, selectivity of 4-electron reduction way, durability and economics toward ORR in p H-neutral solution, in comparison with conventional carbon supported platinum catalyst. The MFC with SSM/Co₃O₄ gas-diffusion electrode had a comparable power density of 17.8 W /m3, and the cell voltage of MFC decreased by only 1.6% after a 45 days operation, indicating a well durability of SSM/Co₃O₄.Based on the research on the interface of cathode, three-dimensional structured pseudo-capacitive anode was created by in-situ deposition of Mn O₂ on carbon electrode through redox reaction of permanganate and carbon, which could improved the performance of MFC. The applied of CP-Mn O₂ shorted the start-up of MFC compared with the unmodified CP anode. The maximum power density of MFC with CP-Mn O₂ increased with the capacition of the anode. The highest power density of MFC with CP-Mn O₂-24 was 603.7 m W/m2, which was 7.98 higher than that of MFC with the unmodified CP anode. The improved performance of MFC with CP-Mn O₂ was mainly due to both increased surface area through 3D sturcture of Mn O₂ and local density of exoelectrogenic biofilm and effective interfacial shuttling of electron transfer facilitated by pseudo-capacitive Mn O₂.