Advances in Graphene/Graphene Composite Based Microbial Fuel/Electrolysis Cells

The modifications of electrodes using graphene and graphene composites in microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) have been widely applied for enhancing the electrochemical catalytic activity and performance of MFCs and MECs. Graphene as one of advanced materials has shown outstanding features for promoting practical applications of MFCs. This review summarizes the modification methods and characterization methods of graphene and related graphene composites on electrode surfaces in MFCs and MECs. The performance improvements of MFCs and MECs by various graphene related composites have been reviewed, which will provide an efficient guide for selecting suitable graphene material to modify electrodes in MFCs and MECs for improving their performance.     

微生物阳极燃料电池极性反转现象研究

本文在构建出微生物阳极燃料电池系统的基础上,研究了微生物燃料电池极性反转现象. 实验表明,由活性污泥混合菌源接种的微生物阳极在电极表面形成电化学生物膜,但平行构建的微生物阳极燃料电池系统在内阻、输出电压和放电时长等方面存在着不同程度差异. 在串联微生物燃料电池组中,放电操作会导致性能较差的微生物单电池首先出现极性反转. 电极电势测量表明,较高的放电电流使微生物阳极电势迅速正移,导致电池系统出现极性反转. 在室温范围内,温度升高可使MFC承受较高的放电电流,不易发生极化. 燃料物质缺乏时,MFC易发生极性反转,但过高的电流仍能使燃料物质充分的MFC出现极性反转. MFC极性反转会对微生物阳极性能造成影响. 极性反转时间较短(<5 min),对微生物阳极影响不大,但延长极性反转时间,会导致微生物阳极性能下降.     

Effects of different Pt-M (M = Fe,Co, Ni) alloy as cathodic catalyst on the performance of two-chambered microbial fuel cells

For the purpose of reducing the cost and improving the performance of cathodes in microbial fuel cells (MFCs), we prepared Pt/C and Pt-M/C (M = Ni, Co, Fe) electrodes, and characterized them by SEM, XRD and CV. The modified electrodes were used as the cathodes in double-chambered MFCs fed with synthetic medium and molasses sewage respectively. We have found that Pt-M/C catalysts had a better catalytic activity for oxygen reduction than Pt/C in the following order: Pt-Fe/C > Pt-Co/C > Pt-Ni/C > Pt/C. The maximum power density of the MFCs with Pt-M/C cathode was improved by 18–31% compared with the MFC with Pt/C cathode because of the decrease of activation loss in the cathode. This study shows that Pt-M/C catalysts can improve power generation of MFCs without affecting the COD removal and it is proposed that Pt-Fe functions best among the three Pt-M alloys as an efficient and cost-effective catalyst of MFCs.     

Comparative Study of Electrochemical Performance and Microbial Flora in Microbial Fuel Cells by Using Three Kinds of Substrates

This work aimed to investigate the distinct electrochemical performance and microbial flora of microbial fuel cells(MFCs)in relation to different single hazardous fed fuels.Three replicate MFCs were inoculated with the same microbial consortium from a coking wastewater treatment plants wherein ammonium chloride(ammoniiim chlo-ride-fed MFC,N-MFC),phenol(phenol-fed MFC,P-MFC)and potassium sulphide(potassium sulphide-fed MFC,S-MFC)were the sole substrates and main components of real coking wastewater.With initial concentrations of am-monium chloride,phenol and potassium sulphide of 0.75,0.60 and 0.55 g/L,the removal efficiencies reached 95.6%,90.6%and 99.9%,respectively,whereas the peak output power densities totalled 697,324 and 1215 mW/m^2.Micro-bial community analysis showed that the respective addition of substrate substantially altered the microbial community structure of anode biofllm,resulting in changes in relative abundance and emergence of new strains and further affecting the electrochemical properties of MFCs.The chemical oxygen demand(COD)removal efficiency of real coking wastewater,in which,the inoculum was the combined biomass from the three MFCs,reached 82.3%.     

Electricity production by a microbial fuel cell fueled by brewery wastewater and the factors in its membrane deterioration

Electricity production from brewery wastewater using dual-chamber microbial fuel cells (MFCs) with a tin-coated copper mesh in the anode was investigated by changing the hydraulic retention time (HRT). The MFCs were fed with wastewater samples from the inlet (inflow, MFC-1) and outlet (outflow, MFC-2) of an anaerobic digester of a brewery wastewater treatment plant. Both chemical oxygen demand removal and current density were improved by decreasing HRT. The best MFC performance was with an HRT of 0.5 d. The maximum power densities of 8.001 and 1.843 μW/cm2 were obtained from reactors MFC-1 and MFC-2, respectively. Microbial diversity at different condi-tions was studied using PCR-DGGE profiling of 16S rRNA fragments of the microorganisms from the biofilm on the anode electrode. The MFC reactor had mainlyGeobacter,Shewanella, andClostridium species, and some bacteria were easily washed out at lower HRTs. The fouling characteristics of the MFC Nafion membrane and the resulting degradation of MFC performance were examined. The ion exchange capacity, conductivity, and diffusivity of the membrane decreased significantly after foul-ing. The morphology of the Nafion membrane and MFC degradation were studied using scanning electron microscopy and attenuated total reflection-Fourier transform infrared spectroscopy.     

A review on the role of proton exchange membrane on the performance of microbial fuel cell

Proton exchange membranes (PEMs) are the most frequently used separators in microbial fuel cells (MFCs). The role of proton transportation in MFC performance makes PEMs one of the most important components in the cell. The effect of PEMs in MFC performance is commonly determined according to generated power density and coulombic efficiency. Nafion is the commonly used membrane in MFCs, but there are still a number of problems associated with the use of Nafion including oxygen transfer rate, cation transport and accumulation rather than protons, membrane fouling and substrate loss. Moreover, additional problems can also be attributed to the effect of PEMs including internal resistance and pH change in MFCs. Recent developments in PEM performance are attributed to two categories including utilization of other types of membranes and improvements in Nafion by pre‐treatment methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Living and Conducting: Coating Individual Bacterial Cells with In Situ Formed Polypyrrole

Coating individual bacterial cells with conjugated polymers to endow them with more functionalities is highly desirable. Here, we developed an in situ polymerization method to coat polypyrrole on the surface of individual Shewanella oneidensis MR‐1, Escherichia coli, Ochrobacterium anthropic or Streptococcus thermophilus. All of these as‐coated cells from different bacterial species displayed enhanced conductivities without affecting viability, suggesting the generality of our coating method. Because of their excellent conductivity, we employed polypyrrole‐coated Shewanella oneidensis MR‐1 as an anode in microbial fuel cells (MFCs) and found that not only direct contact‐based extracellular electron transfer is dramatically enhanced, but also the viability of bacterial cells in MFCs is improved. Our results indicate that coating individual bacteria with conjugated polymers could be a promising strategy to enhance their performance or enrich them with more functionalities.     

阳极底物对微生物燃料电池处理秸秆水解物性能的影响

以双室微生物燃料电池为反应器,铁氰化钾为阴极液,研究污水处理厂活性污泥菌液和玉米秸秆水解液对MFC的产电性能的影响。结果表明,随着阳极中活性污泥菌液体积（1.5、3.0、4.5、6.0 mL）增加,MFC的产电量逐渐增加,当活性污泥的体积增加至7.5 mL时,产电量开始呈下降趋势;玉米秸秆水解液在底物中的浓度为0、10、15、20、30、40 g/L时,电池的稳定电压分别为54、157、248、208、170、146 mV。当阳极活性污泥菌液体积为6 mL、玉米秸秆水解液浓度为15 g/L时,微生物燃料电池的产电性能最佳,此时MFC的功率密度为54.6 mW/m²,内阻为496 Ω。同时,循环伏安曲线（C-V）和交流阻抗曲线（EIS）测试可知,MFC的电极过程由电荷传递和扩散过程共同控制,反应过程受电子传递控制。     

生物阴极微生物燃料电池

传统微生物燃料电池(microbial fuel cells,MFCs)主要由生物阳极与非生物阴极组成,属于半生物燃料电池,存在化学药剂再生困难、需要铂等贵金属催化及成本高等缺陷。生物阴极则利用微生物参与阴极反应克服了这些缺陷。微生物参与MFCs阴极反应,最初在海底沉积物MFCs中被发现。为了提高空气-生物阴极的产电效率,人们进行了以铁、锰等过渡金属氧化物修饰电极材料的研究。在厌/缺氧环境中,生物阴极可将硝酸盐和硫酸盐等作为最终电子受体。对生物阴极研究的深入为MFCs工业化应用开辟了道路,此外,本文在文献综述的基础上提出了铁锰联合修饰生物阴极材料的可能性。     

A microfluidic microbial fuel cell array that supports long-term multiplexed analyses of electricigens

Microbial fuel cells (MFCs) are green energy technologies that exploit microbial metabolism to generate electricity. The widespread implementation of MFC technologies has been stymied by their high cost and limited power. MFC arrays in which device configurations or microbial consortia can be screened have generated significant interest because of their potential for defining aspects that will improve performance featuring high throughput characteristics. However, current miniature MFCs and MFC array systems do not support long-term studies that mimic field conditions, and hence, have limitations in fully characterizing and understanding MFC performances in varieties of conditions. Here, we describe an MFC array device that incorporates microfluidic technology to enable continuous long-term analysis of MFC performance at high throughput utilizing periodic anolyte/catholyte replenishment. The system showed 360% higher power output and 700% longer operating time when compared to MFC arrays without catholyte replenishment. We further demonstrate the utility of the system by reporting its successful use in screening microbial consortia collected from geographically diverse environments for communities that support enhanced MFC performance. Taken together, this work demonstrates that anolyte/catholyte replenishment can significantly improve the long-term performance of microfabricated MFC arrays, and support the characterization of diverse microbial consortia.     

Nanostructured Graphene/TiO2 Hybrids as High‐Performance Anodes for Microbial Fuel Cells

A new nanostructured graphene/TiO₂ (G/TiO₂) hybrid was synthesized by a facile microwave‐assisted solvothermal process in which amorphous TiO₂ was assembled on graphene in situ. The resulting G/TiO₂ hybrids were characterized by XRD, SEM, TEM, Raman spectroscopy, and N₂ adsorption/desorption analysis. The electrochemical properties of the hybrids as anode materials for Shewanella‐inoculated microbial fuel cells (MFCs) were studied for the first time, and they proved to be effective in improving MFC performance. The significantly improved bacterial attachment and extracellular electron‐transfer efficiency could be attributed to the high specific surface area, active groups, large pore volume, and excellent conductivity of the nanostructured G/TiO₂ hybrid, and this suggests that it could be a promising candidate for high‐performance MFCs.     

电极面积对老龄垃圾渗滤液为底物的微生物燃料电池性能影响

构建生物阴极型双室微生物燃料电池,处理老龄垃圾渗滤液。研究了阳极与阴极面积比值对微生物燃料电池产电能力和对老龄垃圾渗滤液处理效果的影响。结果表明,阳极与阴极面积比为1:2、2:2、2:1的3组生物阴极型微生物燃料电池输出电压分别为408、452、396mV,最大电功率密度分别为145.73、237.65、136.50mW/m³,内阻分别为350、200、400Ω,COD的去除率分别为21.18%、20.20%、22.31%。3组微生物燃料电池运行30d后,垃圾渗滤液中氨氮、硝酸盐氮、亚硝酸盐氮浓度均下降,其中,氨氮去除率分别为80.88%、73.61%和66.17%,其去除效果与产电性能相关。     

Hierarchical micro/nano structures of carbon composites as anodes for microbial fuel cells

We demonstrate the utility of hierarchical micro/nano structures of electrically conductive carbon composites as anodes for microbial fuel cells (MFCs). To construct the hierarchical structures, carbon nanotubes (CNTs) were directly grown on micro-porous graphite felts at high densities. Using the CNT-modified felts as anodes, power outputs from MFCs were increased ～7 fold compared to those with bare graphite-felt anodes. We also show that this power improvement is sustainable even in MFCs operated with naturally occurring microbial communities. These results suggest the wide utility of the hierarchical micro/nano structures of conductive carbon composites for bio-electrochemical processes.     

Enhance cathodic capacitance to eliminate power overshoot in microbial fuel cells

Journal of Solid State Electrochemistry - Power overshoot that presents in the power curves of microbial fuel cells (MFCs) is one of the main reasons for the deterioration of MFC performance over...     

The overshoot phenomenon as a function of internal resistance in microbial fuel cells

A method for assessing the performance of microbial fuel cells (MFCs) is the polarisation sweep where different external resistances are applied at set intervals (sample rates). The resulting power curves often exhibit an overshoot where both power and current decrease concomitantly. To investigate these phenomena, small-scale (1 mL volume) MFCs operated in continuous flow were subjected to polarisation sweeps under various conditions. At shorter sample rates the overshoot was more exaggerated and power generation was overestimated; sampling at 30 s produced 23% higher maximum power than at 3 min. MFCs with an immature anodic biofilm (5 days) exhibited a double overshoot effect, which disappeared after a sufficient adjustment period (5 weeks). Mature MFCs were subject to overshoot when the anode was fed weak (1 mM acetate) feedstock with low conductivity (<100 μS) but not when fed with a higher concentration (20 mM acetate) feedstock with high conductivity (>1500 μS). MFCs developed in a pH neutral environment produced overshoot after the anode had been exposed to acidic (pH 3) conditions for 24 h. In contrast, changes to the cathode both in terms of pH and varying catholyte conductivity, although affecting power output did not result in overshoot suggesting that this is an anodic phenomenon.     

微生物燃料电池电极材料研究进展

微生物燃料电池以微生物为催化剂将化学能直接转化成电能,可用于废水处理并产生电能,是一种极具应用前景的生物电化学技术. 本文综述了近年来微生物燃料电池电极材料的制备、功能修饰及表面构建等的研究进展,着重介绍了炭基纳米材料的微结构与成分对微生物燃料电池性能的影响,并分析了微生物燃料电池电极材料现存的主要问题,以期不久的将来微生物燃料电池能付之实用.     

Graphene/Fe3O4 Nanocomposites as Efficient Anodes to Boost the Lifetime and Current Output of Microbial Fuel Cells

The enhancement of microbial activity and electrocatalysis through the design of new anode materials is essential to develop microbial fuel cells (MFCs) with longer lifetimes and higher output. In this research, a novel anode material, graphene/Fe₃O₄ (G/Fe₃O₄) composite, has been designed for Shewanella ‐inoculated MFCs. Because the Shewanella species could bind to Fe₃O₄ with high affinity and their growth could be supported by Fe₃O₄, the bacterial cells attached quickly onto the anode surface and their long‐term activity improved. As a result, MFCs with reduced startup time and improved stability were obtained. Additionally, the introduction of graphene not only provided a large surface area for bacterial attachment, but also offered high electrical conductivity to facilitate extracellular electron transfer (EET). The results showed that the current and power densities of a G/Fe₃O₄ anode were much higher than those of each individual component as an anode.     

微生物燃料电池

微生物燃料电池 (Microbial Fuel Cells,MFCs) 是一种利用微生物作为催化剂,将燃料中的化学能直接转化为电能的装置。本文首先简要介绍了MFCs 的发展简史和基本原理,针对MFCs 产电性能低的现状,分别从产电微生物、电池结构、质子交换膜(PEM)、电极以及电解液等方面着重综述了近几年有关提高MFCs 产电性能的研究进展。最后介绍了关于MFCs 的另一些有趣的研究方向：植物MFCs,生物阴极MFCs,以及污水脱氮和有毒废水处理。     

Bioenergetics and extracellular electron transfer in microbial fuel cells and microbial corrosion

Bioenergetics can be used to analyze the theoretical voltage output of a microbial fuel cell (MFC) and the thermodynamic driving force in microbiologically influenced corrosion (MIC). MFCs involve both inward and outward extracellular electron transfer (EET), whereas only inward EET is behind EET–MIC caused by an electroactive biofilm's harvest of energy from a metal. EET is often rate-limiting, and it is an important process in microbial energy metabolism. EET is critical to the understanding of MFCs and EET–MIC bioelectrochemical processes. Many advances have been made in the past decade on EET by MFC and MIC researchers. Gene manipulations have been used to improve EET in MFCs, leading to enhanced energy output. They have also been used to elucidate the EET processes for better understanding of EET–MIC, which aids in MIC analysis and decision-making of biocide treatment and its efficacy assessment. Researchers are starting to integrate EET knowledge from both fields.     

阳极电势对Geobacter sulfurreducens产电性能的影响

以产电模式菌Geobacter sulfurreducens为研究对象接种两瓶型微生物燃料电池(MFC)阳极室, 利用恒电位仪控制阳极电势, 考察了7种电势条件下MFC的启动期、最大功率密度和阳极生物量的变化情况. 研究结果表明, 当阳极电势为-250, -100和50 mV(vs. SCE)时, MFC启动较快, CV曲线和极化曲线表明, 在这3种电势条件下, MFC产电性能增强, 其中阳极电势为-100 mV时, MFC最大功率密度为1.67 W/m³, 比固定外阻条件下启动的MFC最大功率密度提高了5倍. 控制合适的阳极电势可以使阳极生物量提高2.5~3倍.