【作者】 杨扬；

【导师】 廖强； 叶丁丁；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2016， 博士

【摘要】 微生物燃料电池（MFC）是一种利用细菌的代谢作用,高效处理污水中的有机物同时将其直接转化为电能的绿色能源技术。近年来,MFC的体积逐渐缩小到微纳级别,构成了微流体微生物燃料电池（MMFC）,其作为一种产电设备和在线分析检测技术,在环境监测、生物分析以及微小电源技术方面具有广阔的应用和发展前景,是微流体能源技术的研究热点之一。现阶段的MMFC主要是对大型电池的按比例缩小,受到阳极侧生物膜分布有限、电池运行成本高昂、电池内阻大以及单位成本下产电功率密度低等问题的困扰;与此同时,电池中涉及到的流动和传输现象并未得到深入研究,特别是在流动条件下微小空间内生物膜的成膜特性尚未阐释清楚。针对以上生物膜分布有限和电池功率低下的问题,本文从工程热物理学科中的流体力学和传质理论出发,立足于微流道内阳极生物膜的分布调控,对MMFC内的传输机理和产电特性展开研究。研究内容主要包括:（1）构建了具有单阳极液入口的Y型MMFC,研究了阳极液浓度、阴极液浓度、反应液流量等运行参数对电池性能的影响,并对阳极侧沿流动方向的生物膜分布进行了观察;（2）构建了不同电池构型的MMFC,从缓解扩散混合区域影响的角度出发,构建了具有渐扩流道结构的MMFC,从生物膜分布、阳极侧内阻、电池产电性能等方面研究了改变流道结构对电池性能的影响;从减薄阳极侧边界层的角度出发,构建了具有多阳极液进口的MMFC,与单阳极液进口电池的产电性能进行了对比;通过控制旁路阳极液进口的开关状态分析了增加阳极进口对电池产电性能的作用机理;（3）构建了新型阳极电极和空气自呼吸式MMFC,基于产电菌附着强化思想,构建了一种基于氮掺杂石墨烯气凝胶的新型三维阳极材料,分别从材料化学和生物化学的角度对电极进行了表征,并从生物膜附着、阳极电荷迁移和电池产电方面进行了研究;基于流动简化思想,构建了一种单股流体控制下的空气自呼吸式微流体MFC,研究了所合成催化剂的物理化学特性和电催化特性,并分别在连续流和序批条件下进行电池性能测试。本文主要研究成果如下:1)构建了一种基于石墨电极的Y型结构MMFC,电池性能随着阳极入口燃料浓度和阳极液体积流量的增加而呈现先增加后下降的趋势;在入口燃料浓度化学需氧量为1500 mgL^-1,阳极液流量为10 m L h-1时,输出的最大面积功率密度为618±4 m Wm^-2;对阳极侧表面生物膜形貌的观察发现:产电菌形成的生物膜厚度沿流动方向逐渐减薄,即:流体入口段的生物膜厚度要大于充分发展段的相应厚度;2)构建了基于渐扩、平行、渐缩的三种微流道结构的MMFC,渐扩通道成功避免了扩散混合区的影响,整体上拥有更致密的生物膜分布,同时基于渐扩通道的MMFC在阳极侧电荷迁移阻力最低,其产生的最大面积功率密度为2447.7±38.9m Wm^-2,是基于渐缩通道的MMFC的5.29倍(462.7±17.5 m Wm^-2)和基于平行通道的MMFC的1.24倍(1980.1±27.5 m Wm^-2);3)构建了基于多阳极液进口的MMFC（MMFC-MI）,生物膜在微通道内沿流动方向整体呈致密分布,特别是在三个等间距分布的阳极液入口处,生物膜的分布远远大于单进口MMFC;电池在接种完成后旁路进口关闭状态下MMFC-MI的最大功率密度是打开状态下的85.6%,证实旁路进口的主要作用体现在产电菌富集阶段,而在接种完成后阳极液强化传输的作用相对有限;4)构建了一种基于石墨烯气凝胶（N-GA）的生物阳极材料,其三维结构和含氮官能团有利于强化产电菌在电极内外表面的附着;同时掺杂氮元素后降低了电子从生物膜表面向电极表面的迁移阻力;基于N-GA生物阳极的微型MFC所能达到的体积功率密度为225±12 Wm^-3（正比于腔室体积）和750±40 Wm^-3（正比于阳极体积）;5)构建了一种单股流体控制下的空气自呼吸式MMFC,同时合成了一种含有丰富官能团的氮掺杂石墨烯气凝胶-活性炭（AC@N-GA）氧还原（ORR）催化剂;该催化剂展现了优良的ORR催化性能,电子转移数达到3.92,H₂O₂产率只有4.5%,以AC@N-GA为催化剂的MMFC连续流条件下最大功率密度为1181.4±135.6 Wm^-3,序批条件下最大功率密度为690.2±62.3 Wm^-3,产电性能是相同条件下国际报道MMFC的10倍以上。更多还原

【Abstract】 Microbial fuel cells（MFCs）represent a novel green-technology that harness the metabolism of bacteria to convert the organic matters to bio-electricity.Recently,the scale of MFCs has been downsized to form the microsized microbial fuel cells or microfluidic MFCs（MMFCs）.It has been successfully developed as niche power sources and on-line analysis technology.Similar to other microfluidic devices,MMFC has become one of the research spots with the respect of environmental detection,microorganism analysis and power supply.Present MMFCs are basically scaled down the large MFCs and retarded by the insufficient biofilm formation,considerable operation cost,high internal resistance and low power density per capital cost.Meanwhile,the mechanisms of dynamic fluid flow and mass transport in MMFCs are not fully illustrated especially the biofilm formation under the laminar flow in micro-environments.In response to these limitations from the aspect of biofilm-distribution optimization,tremendous experimental studies on characteristics of mass transport and electricity-generation have been carried out according to the theory of engineering thermol physics.The research mainly includes electrode design and cell-structure construction,and details are specifically listed as follows:（1）A graphite-based MMFC is assembled,and the effects of operational parameters are studied including reactant concentrations and volumetric flow rates.The biofilm distribution along flow direction is visualized;（2）MMFCs with different channel structures are constructed.In order to ease the issue of diffusion zone,a MMFC with diverging channel（MMFC-D）is proposed.The effects of channel geometries on biofilm distribution,anodic resistance and power generation are specifically investigated;In order to decrease the thickness of the anodic boundary layer,a MMFC with multiple anolyte inlets（MMFC-MI）is constructed and compared with typical MMFC with one anolyte inlet（MMFC-OI）in biofilm distribution,cell internal resistance and power-generation capacity.The mechanism of multiple inlets is illustrated by controlling the states of extra inlets;（3）A new three-dimensional bio-anode and air-breathing MMFC are proposed.In the view of enhancement of bacterial adhesion on the electrode,a nitrogen-doped graphene aerogel（N-GA）-based bio-anode is synthesized and studied on the sides of material chemistry and bio-chemistry.A MFC equipped with the N-GA electrode is investigated on the bacterial distribution,electron transfer on the anode and power generation;In order to simplify the flow pattern,a single-fluid controlled MMFC with air-breathing cathode is constructed.The oxygen reduction reaction（ORR）catalyst is studied from the aspects of physicochemical and electrochemical characteristics.An air-breathing MMFC with three-dimensional anode is assembled and the property of power generation is tested under continuous-flow and batch modes.The major achievements are listed as follows:1)A graphene-based Y-type MMFC is constructed.It is found the cell performance is initially increased,and then decreased with the increasing of anolyte concentration and volumetric flow rates;a maximum power density of 618±4 mWm^-2 is obtained at the fuel concentration of 1500 mgL^-1（represented by chemical oxygen demand,COD）and at the volumetric flow rate of 10 mL h-1.The biofilm morphologies are visualized by optical microscope.It is found that the thickness of biofilm is gradually decreased along the flow direction.Namely,the thickness of biofilm is higher than those in fully developing zones;2)Three MMFCs with different channel geometries are constructed,respectively are converging channel（MMFC-C）,straight channel（MMFC-S）and diverging channel.Among them,the most densely-packed biofilm and lowest charge transfer resistance are observed in the case of MMFC-D due to the ease of unfavorable mixing zone.MMFC-D delivers the highest areal power density of 2447.7±38.9 mWm^-2,which is 5.29 and 1.24 folds of MMFC-C(462.7±17.5 mWm^-2)and MMFC-S(1980.1±27.5 mWm^-2);3)A MMFC with multiple anodic inlets is proposed.The biofilm distribution in the case of MMFC-MI is more densely packed than that of MMFC-OI especially near three equally-spaced inlets.The maximum power density of MMFC-MI under closed extra inlets is 85.6% of that of opened extra inlets.It indicates the contribution of extra inlets mainly lies in the bacteria-aggregation process rather than the mass transfer enhancement after inoculation;4)A nitrogen doped graphene aerogel bioanode is constructed.The special structure and N-functional groups of N-GA enable the well-distribution of bacterial cells on the electrode.At the same time,nitrogen element could lower the charge transfer resistance between biofilm and electrode.N-GA based MFC delivers a maximum power density of 225 ± 12 Wm^-3（proportional to chamber volume）and 750 ± 40 Wm^-3（proportional to electrode volume）;5)A single-fluid controlled MMFC with air-breathing cathode is proposed.At the cathode side,a nitrogen-doped graphene-activated carbon aerogel（AC@N-GA）catalyst is sythesized and served as the ORR catalyst.AC@N-GA exhibits a superior oxygen reduction property.The number of electron transfer during the ORR process is estimated to 3.92,and the generation rate of H₂O₂ is 4.5%.This microfluidic MFC delivers the highest volumetric power density of 1181.4 ±135.6 Wm^-3 at continuous-flow mode,and 690.2±62.3 Wm^-3 at batch mode.The value of volumetric power density is 10-folds higher than the most-recent reported value.更多还原