【作者】 史昕欣；

【导师】 冯玉杰；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2013， 博士

【摘要】 微生物燃料电池（Microbial Fuel Cell，MFC）能够利用产电菌将废水中有机物的化学能直接转化为电能，是21世纪环境工程领域中新兴的水处理研究方向之一。在众多类型的MFC中，空气阴极微生物燃料电池（Air-cathode MicrobialFuel Cell，ACMFC）因其阴极使用空气中的氧气作为氧化剂而具有较高理论电压。然而，ACMFC阴极的氧还原反应需要在铂/碳（Pt/C）的催化下才能顺利进行，昂贵的Pt/C大大增加了ACMFC的成本，这使得ACMFC的研究目前仍停留在小规模的实验室水平上。作为Pt/C的替代，低成本阴极催化剂的研制正在成为ACMFC领域的研究热点。目前催化剂成本的降低往往是以阴极性能下降为代价的。如何在降低ACMFC成本的同时不降低其产电能力是ACMFC研究领域亟待解决的问题。本文围绕“降低ACMFC成本，提高其阴极性能”这一主题，对ACMFC的阴极材料和结构进行了研究，具体内容包括：通过测试单室六面体型ACMFC的功率密度考察了Pd/C和Ru/C的氧还原性能，并与Pt/C进行了对比。结果表明，Pd/C和Ru/C作催化剂时，ACMFC的COD去除率和库伦效率均与Pt/C催化剂相当，ACMFC的最大功率密度分别是Pt/C作催化剂时的90.3%和85.5%，但ACMFC单位成本的产能分别是Pt/C的1.8倍和6倍。为了进一步降低ACMFC的成本，制备了成本低、氧还原催化活性较强、稳定性较好的掺氮碳粉，并将其用作ACMFC阴极催化剂。为了增强掺氮效果，还尝试了在硝酸处理前增加盐酸-热混合预处理的掺氮方法，并对比分析了有无预处理的掺氮碳粉中的含氮量和含氮官能团类型。结果表明，掺氮后，碳粉的催化活性显著提高，ACMFC的最大功率密度提高了1.1倍。预处理有助于增强掺氮效果，使得ACMFC最大功率密度提高了12.4%。发现影响催化活性的关键官能团有：吡啶型氮、吡咯型氮和氮氧化物。尝试通过优化碳粉粒径和掺氮碳粉用量来提高阴极性能，发现碳粉粒径宜为1600nm左右，增大用量能够明显增强ACMFC的产电能力。结果表明，通过混合预处理和硝酸处理后的碳粉可以替代甚至优于Pt/C，采用掺氮碳粉作阴极催化剂后，其ACMFC的最大功率密度为926.0mW·m^-2，与Pt/C(980.6mW·m^-2)相当，但成本可观地降低了78%。此外，掺氮碳粉阴极的过电位仅为Pt/C阴极的一半，其极化损失小。更为重要的是，通过监测30个周期内ACMFC的最大功率密度，发现掺氮碳粉阴极的稳定性明显优于Pt/C阴极，掺氮碳粉阴极ACMFC的最大功率密度几乎不变，而Pt/C阴极ACMFC的最大功率密度下降达13%，且有进一步下降的趋势。通过优化阴极结构来提高ACMFC的产电能力，优化主要针对：催化层的梯度、制备扩散层时的降温方式、碳基层碳粉的灰分和粒径的选择等。结果表明，在不改变催化剂总用量和粘结剂总用量的前提下，将原来的单层催化层改为催化剂和粘结剂用量梯度减少（从阴极液到空气方向）的多层催化层后，ACMFC的功率密度有所提高。在扩散层的制备过程中，快速降温比慢速降温更容易形成有利于氧气扩散的孔隙，使氧气顺利到达催化层参与氧还原反应。碳基层的碳粉粒径存在一个最优值，约为1300nm，此时氧气传质较好。碳粉的灰分越小所制备的碳基层性能越好。在合成低成本催化剂和阴极结构优化的基础上，考察了硫化物对掺氮碳粉催化活性的影响，并与Pt/C催化剂进行了对比。当电解液中含有硫化物时，Pt/C的氧还原催化活性明显降低。ACMFC在Na2S浓度为0.2g·L时的最大功率密度比中性电解液时减少了约21.3%。而掺氮碳粉的催化活性基本不受硫化物的影响，相同Na2S浓度下其ACMFC的最大功率密度比Pt/C高11.4%。当ACMFC阴极受硫化物影响时，使用掺氮碳粉代替Pt/C作为阴极催化剂不仅能大幅降低成本，且能获得更大的电能输出。更多还原

【Abstract】 Taking advantage of bacterium consuming the organics in the wastewater,microbial fuel cell （MFC） directly converts the bioenergy to electricity and it isbecoming a new research direction in the field of environmenetal engineering.Among many different types of MFC, air-cathode microbial fuel cell （ACMFC）provides relatively high theoretical cell voltage because it uses the oxygen in the airas the cathodic catalyst for oxygen reduction reaction （ORR）. However, theexpensive platinum （Pt）, which serves as the indispensable ORR catalyst incathodes, dramatically increases the cost of ACMFCs. The relative research onACMFCs is still limited to the laboratory scale. Many low-cost substitutes for Pthave been developed and the cost of ACMFCs is indeed reduced, however, at thecost of degrading the electricity generation capacity. Reducing the cost of ACMFCwhile keeping its high electricity generation capacity is becoming an urgentproblem to be solved in the field of research on ACMFC.Focusing the goal of reducing cost and improving cathodic performance ofACMFCs, cathodic materials and structure was studied, with the detailed contentsas below:Catalytic activities of Pd/C and Ru/C for ORR were investigated by testingpower densities of a single-chamber hexahedral ACMFC and comparison with Pt/Cwas made as well. Results showed that Pd/C and Ru/C were both equivalent to Pt/Cin terms of columbic efficiencies and COD removal rates of ACMFCs and theirmaximum power densities （MPDs） were respectively90.3%and85.5%of that ofPt/C. The amount of electricity generation per cost for Pd/C and Ru/C wererespectively1.8times and6times as that for Pt/C.Low-cost nitrogen-doped carbon powders （NDCP） with high catalytic activityfor ORR and good stability were prepared and used as the cathodic catalyst ofACMFCs. In order to further improve the effect of the nitrogen-doped treatment, ahybrid pretreatment was introduced consisting of hydrochloric acid immersion andheat treatment. The nitrogen content and the types of key nitrogen functional groupwere compared in NDCPs with and without the hybrid pretreatment. Results showedthat the catalytic activity of NDCP （without the pretreatment） was1.1times as that of untreated carbon powders. The pretreatment can obviously enhance the N-dopedeffect, with the corresponding maximum power density of ACMFC increased by12.4%. Three key N-functional groups were found to be pyridinic-type nitrogen,pyrrolic-like nitrogen and chemisorbed nitrogen oxide. The grain sizes of carbonpowders and the dosage of catalysts were optimized in order to improve thecathodic performance. Reuslts showed that the grain size of1600nm was preferredand increasing the dose of NDCP could considerably improve the MPD of ACMFC.The final conclusion achieved was that the prepared NDCP （with the pretreatment）was competent enough to replace the expensive Pt/C. The MPD of the ACMFCbased on NDCP was almost equal to that of ACMFC based on Pt/C, i.e.926.0mW·m^-2for NDCP vs.980.6mW·m^-2for Pt/C, while the cost of ACMFCs wasreduced by78%. Moreover, the NDCP cathode processed much smaller polarizationloss, which was only half of that of Pt/C cathode. More importantly, NDCP showedmuch higher long-term stability than Pt/C. The MPD of ACMFC based on NDCPnearly remained unchanged after running30periods. By contrast, the MPD ofACMFC based on Pt/C decreased by as much as13%and tended to decreasefurther.Optimizations of cathodic structure was conducted in terms of the gradient ofcatalytic layer, the cooling rate when preparing diffusion layer, ash content andgrain sizes of carbon powders of the carbon base layer, and so on. Results showedthat the MPD of ACMFCs was increased by keeping the total dose of catalysts andbinder both constant while changing the single catalyst laer to the gradient multiplecatalytic layers in which the amount of catalysts gradually decreased along thedirection from the cathodic electrolyte to the outside air. The cathodic performancealso benefited from the rapid cooling when preparing the diffusion layer, becausethe developed pore passage was easier for oxygen to pass and then reach thecatalytic layer completing ORR reaction. There existed an optimum grain size,around1000mesh, for carbon powders in the carbon base layer. The lower the ashcontent was, the better the performance of ACMFCs.Based on the previous prepared low-cost NDCP catalyst and the optimizedcathodic structure, the effect of sulfide on the catalytic activity of NDCP wasstudied and compared with Pt/C. Results showed that existence of sulfide greatlydecreased the activity of Pt/C. When concentration of Na2S solution was0.2g/L, theMPD of ACMFC with Pt/C cathode was reduced by21.3%as compared to the neutral electrolyte. By contrast, NDCP cathodes nearly disregard the existence ofsulfide and the corresponding MPD of ACMFC larger than that of Pt/C by11.4%under the same concentration of Na2S. With such NDCP cathodes, not only the costof ACMFCs can be substantially reduced, but larger electricity output can be alsoachieved when ACMFCs operated in the presence of sulfide.更多还原