【作者】 李建海；

【导师】 付玉彬；

【作者基本信息】 中国海洋大学 ， 材料物理与化学， 2010， 硕士

【摘要】 21世纪我们所面临的主要难题之一是能源短缺和环境污染。可再生的生物质能由于不会增加二氧化碳的净排放量而被认识是减缓当前能源与环境危机的途径之一。微生物燃料电池(MFC)是一种可以利用微生物的催化作用通过氧化有机及无机物质产生电能的装置。它是一种利用废水或者其它废弃物产生电能的新技术,具有极大的研究价值和发展空间。海底沉积物微生物燃料电池(BMFC)是MFC的一种特殊形式,在海底环境中运行。BMFC的阳极埋在厌氧的海底沉积物中,通过外电路与上部海水中的阴极相连,海洋沉积物中的有机物质作为电池的“燃料”,海水中的溶解氧充当氧化剂。BMFC具有免维护、连续供应、底物丰富、内阻低、环境友好和造价低廉等优点,因此它非常有希望作为一种能源装置用于驱动在偏远海域工作的低功率监测仪器。但是,目前限制BMFC广泛应用的关键问题是其相对低下的输出功率密度。为了增加BMFC的输出功率密度,在实验室构建了海底沉积物微生物燃料电池的基础上,我们研究了石墨阳极表面化学氧化改性以及电极构型对电池性能的影响。主要研究方案框图见附录,主要结果如下：(1)通过不同的化学氧化方法对石墨电极进行了改性处理,并通过SEM、EDX和吸附实验等表征了改性前后电极表面特性的变化。结果表明：经过化学氧化改性之后,石墨电极比表面积和表面润湿性有明显增加。经过酸性KMnO4、浓HN03和混酸(浓H2SO4和浓HN03)改性后的石墨电极真实表面积分别增加了49%、56%和67%；表面接触角从132°减小为63°、58°和42°。电化学及其它实验表明：石墨电极的化学氧化改性对电池性能的提高有积极影响,可以增加电极的动力学活性。经过酸性KMnO4、浓HN03和混酸(浓H2SO4和浓HN03)改性后,对应BMFC的最高输出功率密度从24.6 mW/m2分别增加到40.6m W/m2、44.4 mW/m2和44.5 mW/m2；电池的表观内阻也对应的从732Ω减小到443Ω、462Ω和482Ω；交换电流密度从1.965×10-3A/m2增加到0.309A/m2、2.586 A/m2和0.893 A/m2。通过涂布法对阳极微生物数量的分析结果表明：以上四种石墨电极表面微生物的细菌密度分别为5509/cm2、16526/cm2、51988/cm2和17559/cm2。这一结果和电极表面荧光显微镜分析结果一致。长期放电实验表明：改性的石墨阳极在电池启动期间表现出较强的抗极化能力,以改性石墨电极作为阳极的BMFCs在长期通电中可以输出更高的电压。经化学氧化改性后,石墨电极表面润湿性的增加、比表面积的增加、表面化学反应活性点的增多、生物相容性的增加(生物相容性的增加是由改性过程中在石墨电极表面引入的含氧官能团引起的)是BMFC性能提高的主要原因。本实验第一次研究了BMFC阳极表面润湿性与其电化学性能之间的关系。化学氧化过程中所用的材料和设备均常见并且价格低廉,并且该方法容易实现工业化。所以化学氧化改性石墨电极是一个提高BMFC性能的理想方法。(2)因为电极的结构对海底沉积物微生物燃料电池(BMFC)的性能有很大的影响,本实验设计了不同形状的石墨电极(柱状、圆盘状、桶状)。由柱状和圆盘状电极组成的BMFC的最高输出功率密度分别为20.2 mW/m2和14.9mW/m2,其电池内阻分别为333Ω和598Ω。内径分别为2.5 cm、1.0 cm、0 cm的石墨桶状电极组成的三个BMFC分别简称为BMFC-Ⅰ、BMFC-Ⅱ和BMFC-Ⅲ。结果表明BMFC-Ⅰ、BMFC-Ⅱ和BMFC-Ⅲ的最高输出功率密度分别为13 mW/m2、11 mW/m2和16 mW/m2,电池内阻分别为435Ω、488Ω和419Ω。BMFC-a(由多孔电极组装而成)和BMFC-b(由平板电极组装而成)的最高输出功率分别为37.6 mW/m2和28.3 mW/m2,内阻分别为203Ω和265Ω。BMFC-A(平板阴极)和BMFC-B(三相阴极)的最高输出功率分别为16.7 mW/m2和25.6 mW/m2,内阻分别为357Ω和268Ω。说明柱状及多孔状的电极结构与圆盘状和桶状的电极结构相比具有更小的内阻和更高的功率密度。阴极的三相界面可以提高BMFC的功率输出密度。该研究结果可以为实际应用中BMFC电极结构的设计提供参考。总之,通过对石墨阳极进行化学氧化改性和优化电极构型都可以在实际应用中进一步提高BMFC的性能。更多还原

【Abstract】 Energy shortage and environment pollution is one of the critical challenges we are facing in 21th century. Renewable bioenergy without a net carbon dioxide emission is viewed as one of the ways to alleviate the current global energy and environment crisis. Microbial fuel cell (MFC) is a device that uses bacteria as the catalysts to oxidize organic and inorganic matter to generate current. It is a new method of producing electric power from wastewater and other waste, and it has great value for further research and development. The benthic sediment microbial fuel cell (BMFC) is a special type of MFC, which operates on the ocean floor. In the BMFC, the anode embedded in anoxic marine sediment is connected to the cathode positioned in overlying sea water by an electrical circuit. The organic matter in the marine sediment serves as the cell "fuel", and the oxygen dissolved in the sea water serves as the oxygenate. The BMFC has many advantages such as maintenance free, supply continuously, rich in substrate, low internal resistance, environmental friendly and low cost etc, so it is very promising to be used as energy installations to supply a wide range of low-power monitoring instruments in the remote marine environment. But the key problem for BMFC is its low output power density at the moment, which prohibits the widespread application of the BMFCs. In order to increase the output power density, on the basis of the BMFC construction in the laboratory, the effect of graphite anode chemical oxidation modification and electrode shape on the performance of the BMFC is studied. The research sketch map is attached in the appendix, and results are as follows:(1) Different chemical oxidation methods are conducted on graphite anodes and the surface properties are characterized by SEM, EDX and adsorption analysis. Results indicate that the specific surface area and surface wettability of the graphite anodes increase obviously after chemical oxidation modification. The true surface area increase by 49%,56% and 67%; the contact angle decrease from 132°to 63°,58°and 42°when the graphite anodes are modified with KMnO4, concentrated HNO3, and the mixed solution of H2SO4/HNO3 respectively.Electrochemical tests and other experiments demonstrate that the chemical oxidation modified graphite anodes have a clear active influence on the system performance and the kinetic activity increase compared with unmodified graphite anode in the BMFCs. The maximum power density (Pm) increase from 24.6 mW/m2 to 40.6 mW/m2,44.4 mW/m2 and 44.5 mW/m2 respectively; the apparent internal resistance of the BMFCs decrease from 732Ωto 443Ω,462Ωand 482Ωrespectively; the exchange current density increase from 1.965×10-3 A/m2 to 0.309 A/m2,2.586 A/m2 and 0.893 A/m2 respectively when the anodes are modified by acidic KMnO4, concentrated HNO3, and the mixed solution of H2SO4/HNO3.The quantitative analysis of bacteria by the method of plating indicates that:The bacterial density of anodes unmodified, modified with KMnO4, HNO3, and H2SO4/HNO3 are 5509/cm2,16526/cm2,51988/cm2, and 17559/cm2 respectively. The result is consistent to the fluorescence images.The long time discharge experiments indicate that modified anodes of BMFCs demonstrated a very good capability of anti-polarization in the start-up phase. The BMFCs with a modified anode output higher voltage than the BMFC with unmodified anode in the long time discharge.The increase of the cell performance may be due to the enhancement in anode surface wettability, increase in anode specific surface area, increase in active site for chemical reaction on the electrode surface, or by an increase in the biocompatibility by introducing the oxygen-containing functional groups on the anodes surface. The relationship between the anode surface wettability and the electrochemistry performance is studied in the BMFC.The materials and equipments used in the chemical oxidation modification of the graphite anodes are all low cost and common, and this method is suitable for the industrialization. Therefore, the chemical oxidation modification of the graphite anode is an ideal method to enhance the performance of the BMFCs.(2) As the electrode structure has a great effect on the performance of the BMFC, several graphite electrodes with different shapes (column, plane disk and tubular shape for example) are designed in this study. The maximum power density (Pm) of BMFC-column and BMFC-disk are 20.2 mW/m2 and 14.9 mW/m2 respectively, and the internal resistances are 333Ωand 598Ωrespectively. Three cells are composed of three different sizes of graphite tubes, and their internal diameters of these electrodes are 2.5 cm (called it BMFC-I for short); 1.0 cm (BMFC-II) and 0 cm (column shape for comparison, BMFC-III) respectively. Test results show that the Pm of BMFC-I, BMFC-Ⅱand BMFC-Ⅲare 13 mW/m2,11 mW/m2and 16 mW/m2 respectively, and their internal resistances are 435Ω,488Ω. and 419Ωrespectively. The Pm of BMFC-a (composed of porous electrode) and BMFC-b (composed of plane electrode) are 37.6 mW/m2 and 28.3 mW/m2 respectively, and the internal resistances are 203Ωand 265Ωrespectively. The Pm of BMFC-A (composed of plane cathode) and BMFC-B (composed of three-phase cathode) are 16.7 mW/m2 and 25.6 mW/m2 respectively, and the internal resistance are 357Ωand 268Ωrespectively.Results show that the column and porous structure electrode has a lower internal resistance and higher power density than the disk and tubular structure electrode. The three-phase in the cathode can enhance the performance of the BMFC. Results of the research can be utilized to design BMFC structure in practical application.So the performance of the BMFC can be further enhanced by the ways of anode chemical oxidation modification or optimization of electrode shape. Energy shortage and environment pollution is one of the critical challenges we are facing in 21th century. Renewable bioenergy without a net carbon dioxide emission is viewed as one of the ways to alleviate the current global energy and environment crisis. Microbial fuel cell (MFC) is a device that uses bacteria as the catalysts to oxidize organic and inorganic matter to generate current. It is a new method of producing electric power from wastewater and other waste, and it has great value for further research and development. The benthic sediment microbial fuel cell (BMFC) is a special type of MFC, which operates on the ocean floor. In the BMFC, the anode embedded in anoxic marine sediment is connected to the cathode positioned in overlying sea water by an electrical circuit. The organic matter in the marine sediment serves as the cell "fuel", and the oxygen dissolved in the sea water serves as the oxygenate. The BMFC has many advantages such as maintenance free, supply continuously, rich in substrate, low internal resistance, environmental friendly and low cost etc, so it is very promising to be used as energy installations to supply a wide range of low-power monitoring instruments in the remote marine environment. But the key problem for BMFC is its low output power density at the moment, which prohibits the widespread application of the BMFCs. In order to increase the output power density, on the basis of the BMFC construction in the laboratory, the effect of graphite anode chemical oxidation modification and electrode shape on the performance of the BMFC is studied. The research sketch map is attached in the appendix, and results are as follows:(1) Different chemical oxidation methods are conducted on graphite anodes and the surface properties are characterized by SEM, EDX and adsorption analysis. Results indicate that the specific surface area and surface wettability of the graphite anodes increase obviously after chemical oxidation modification. The true surface area increase by 49%,56% and 67%; the contact angle decrease from 132°to 63°,58°and 42°when the graphite anodes are modified with KMnO4, concentrated HNO3, and the mixed solution of H2SO4/HNO3 respectively.Electrochemical tests and other experiments demonstrate that the chemical oxidation modified graphite anodes have a clear active influence on the system performance and the kinetic activity increase compared with unmodified graphite anode in the BMFCs. The maximum power density (Pm) increase from 24.6 mW/m2 to 40.6 mW/m2,44.4 mW/m2 and 44.5 mW/m2 respectively; the apparent internal resistance of the BMFCs decrease from 732Ωto 443Ω,462Ωand 482Ωrespectively; the exchange current density increase from 1.965×10-3 A/m2 to 0.309 A/m2,2.586 A/m2 and 0.893 A/m2 respectively when the anodes are modified by acidic KMnO4, concentrated HNO3, and the mixed solution of H2SO4/HNO3.The quantitative analysis of bacteria by the method of plating indicates that:The bacterial density of anodes unmodified, modified with KMnO4, HNO3, and H2SO4/HNO3 are 5509/cm2,16526/cm2,51988/cm2, and 17559/cm2 respectively. The result is consistent to the fluorescence images.The long time discharge experiments indicate that modified anodes of BMFCs demonstrated a very good capability of anti-polarization in the start-up phase. The BMFCs with a modified anode output higher voltage than the BMFC with unmodified anode in the long time discharge.The increase of the cell performance may be due to the enhancement in anode surface wettability, increase in anode specific surface area, increase in active site for chemical reaction on the electrode surface, or by an increase in the biocompatibility by introducing the oxygen-containing functional groups on the anodes surface. The relationship between the anode surface wettability and the electrochemistry performance is studied in the BMFC.The materials and equipments used in the chemical oxidation modification of the graphite anodes are all low cost and common, and this method is suitable for the industrialization. Therefore, the chemical oxidation modification of the graphite anode is an ideal method to enhance the performance of the BMFCs.(2) As the electrode structure has a great effect on the performance of the BMFC, several graphite electrodes with different shapes (column, plane disk and tubular shape for example) are designed in this study. The maximum power density (Pm) of BMFC-column and BMFC-disk are 20.2 mW/m2 and 14.9 mW/m2 respectively, and the internal resistances are 333Ωand 598Ωrespectively. Three cells are composed of three different sizes of graphite tubes, and their internal diameters of these electrodes are 2.5 cm (called it BMFC-I for short); 1.0 cm (BMFC-II) and 0 cm (column shape for comparison, BMFC-III) respectively. Test results show that the Pm of BMFC-I, BMFC-Ⅱand BMFC-Ⅲare 13 mW/m2,11 mW/m2and 16 mW/m2 respectively, and their internal resistances are 435Ω,488Ω. and 419Ωrespectively. The Pm of BMFC-a (composed of porous electrode) and BMFC-b (composed of plane electrode) are 37.6 mW/m2 and 28.3 mW/m2 respectively, and the internal resistances are 203Ωand 265Ωrespectively. The Pm of BMFC-A (composed of plane cathode) and BMFC-B (composed of three-phase cathode) are 16.7 mW/m2 and 25.6 mW/m2 respectively, and the internal resistance are 357Ωand 268Ωrespectively.Results show that the column and porous structure electrode has a lower internal resistance and higher power density than the disk and tubular structure electrode. The three-phase in the cathode can enhance the performance of the BMFC. Results of the research can be utilized to design BMFC structure in practical application.So the performance of the BMFC can be further enhanced by the ways of anode chemical oxidation modification or optimization of electrode shape.更多还原