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目前,寻找一种可以替代传统化石燃料的可再生能源已成为能源领域的研究热点,绿色、健康、可持续发展是当前环保领域的关键词[1]. 微生物燃料电池( microbial fuel cells,MFCs) 是利用产电微生物(electroactive microorganisms,EABs)将有机污染物中的化学能转化为电能的装置[2]. MFCs 通常由两个电极室组成,在阳极室内,产电菌释放电子和质子,电子经过外电路转移到阴极释放携带的能量,而质子经过离子交换膜转移到阴极[3],在闭环条件下阳极室EABs发生电子转移产生电流,包括直接电子转移(direct electron transfer,DET)和介导电子转移(mediated electron transfer,MET)两种方式将微生物代谢产生的电子转移到阳极上[1]. 但MFCs低功率密度使其难以商业化,因此,优化MFCs的功率密度属于当前的研究热点之一. 在驱动MFCs运行的各种机制中,EABs与阳极之间的细胞外电子传递(extracellular electron transport,EET)成为最重要的机制之一,对EET过程的调控和优化已成为一种常见的策略.
为了提高MFCs的功率密度,研究人员从提高阳极性能、EABs提纯和富集等方面开发了一系列方法来增强阳极与EABs的相互作用,包括使用聚合物涂层和3D阳极材料、结构优化或掺杂导电金属离子、EABs基因工程等[4]. 其中,高性能的阳极材料因具有成本低、制备方法简单、导电性好、生物相容性好,稳定性高等[5]优点成为研究热点. 生物炭材料以稳定性高、易化学改性、成本低、易获得等优点成为公认的阳极材料. 已研究的生物碳材料有松果[6]、天然丝瓜海绵[7]和杏仁壳[8]等. 生物炭阳极材料具有均匀分布的大孔结构,有利于发电微生物的粘附,能避免堵塞问题[9].
已有研究表明,氮可以作为一种元素用于修饰阳极材料,增强产电微生物与电极之间的相互作用[10]. 据报道,He等[11]首次证明向碳纸中注入N+等离子体可以通过降低电荷转移阻力提高生物相容性,从而提高MFCs的发电能力. Wu等[12]使用氮掺杂碳材料,在原子上匹配介导电池外电子转移的扩散氧化还原物种的反应位点,证明氮的贡献. Yu等[13]将氮掺杂碳纳米颗粒引入到MFCs阳极中,证明氮可以促进产电微生物细胞外电子传递过程中黄素的分泌,增强细菌与电极之间的相互作用.
本文从改善阳极材料表面物理化学性质的角度出发,用吐司作为多孔碳前驱体,三聚氰胺为氮源,直接烧制氮掺杂三维碳材料,并将其与不掺杂氮的阳极材料和未改性的商用碳布材料进行比较. 用混合地杆菌Geobacter和希瓦氏菌Shewanella在MFCs中培养后,对其性能进行评价和分析. 三维多孔碳阳极材料与氮元素结合,可以同时提供更大的比表面积、更好的电导率和良好的生物相容性以及适应性强的混合微生物群落,使MFCs具有更好的功率密度,并进一步研究氮在促进EET过程中的作用机制.
氮掺杂多孔碳材料阳极制备及其在微生物燃料电池上的应用
Preparation of nitrogen-doped porous carbon anode and its application in microbial fuel cells
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摘要: 微生物燃料电池(MFCs)作为一种可以替代传统能源的生物电化学系统引起研究者的极大兴趣,其阳极材料的构造是目前的研究热点. 本文从改善阳极材料表面物理化学性质的角度出发,用吐司作为多孔碳前驱体,三聚氰胺为氮源,直接烧制氮掺杂三维碳材料,并与不添加氮源的阳极材料和未改性的商用碳布进行比较. 制备的掺氮NB1000阳极具有较大的比表面积(216.664 m2·g−1)和优良的电导率. 利用Geobacter和Shewanella混合菌落在微生物燃料电池(MFCs)中进行培养和性能评价,NB1000阳极的微生物燃料电池最大面功率密度为3049.714 mW·m−2,电流密度为7.4464 A·m−2,分别是普通碳布阳极的6.54倍和1.54倍. 结果表明,NB1000作阳极的MFCs具有较高的功率密度,主要归因于阳极中引入氮掺杂,促进了产电微生物胞外电子传递过程所需的外膜c型细胞色素OmcA和MtrC的分泌.Abstract: Microbial fuel cells (MFCs), as a bioelectrochemical system that can replace traditional energy sources, have attracted great interest of researchers, and the construction of anode materials is the current research focus. In order to improve the physical and chemical properties of the surface of the anode material, the nitrogen-doped three-dimensional carbon material was directly sintered by using toast as the porous carbon precursor and melamine as the nitrogen source, and compared with the anode material without adding nitrogen source and the unmodified commercial carbon cloth. The nitrogen-doped NB1000 anode has a large specific surface area (216.664 m2·g−1) and excellent conductivity. A mixed Geobacter and Shewanella colony was used to culture and evaluate the performance of MFCs, and the maximum areal power density and current density of the microbial fuel cell with NB1000 anode were 3049.714 mW·m−2 and 7.4464 A·m−2. It is 6.54 times and 1.54 times that of ordinary carbon cloth anode, respectively. The results showed that the high power density of MFCs from NB1000 anode was due to the introduction of nitrogen into the anode, which promoted the secretion of c-type cytochromes OmcA and MtrC in the outer membrane, which were required for the extracellular electron transport process of electrogenic microorganisms.
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图 4 (a)输出电压曲线 (b)极化曲线和功率密度曲线 (c) 电极电位(vs SCE)与电流密度的关系 (d) 生物膜形成后的Nyquist图 (e)图d的Nyquist放大图 (f) 生物膜形成后的拟合欧姆电阻和电荷转移电阻
Figure 4. (a) Output voltage curve (b) Polarization curve and power density curve (c) Relation between electrode potential (VS SCE) and current density (d) Nyquist plot after biofilm formation (e) Nyquist magnification of Figure d (f) fitted ohmic resistance and charge transfer resistance after biofilm formation
图 6 N1000,B1000和CC阳极在有底物条件下的CVs曲线(a),在无底物条件下的CVs曲线(b),稳定培养四个周期后的EIS曲线(c),在底物耗尽后于PBS溶液中的DPV曲线(d)
Figure 6. CVs curves of NB1000, B1000 and CC anodes with substrate (a), CVs curves without substrate (b), EIS curves after four cycles of stable culture (c) ,DPV curves in PBS solution after substrate depletion (d)
表 1 NBs的比表面积
Table 1. Specific surface area of NBs
样品
SamplesNB1100 NB1000 NB9000 NB800 NB700 SBET/(m2·g−1) 61.028 216.664 92.045 82.813 45.634 Note: SBET: the specific surface area. -
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