The interaction of bacteria and metal surfaces

This review discusses different examples for the interaction of bacteria and metal surfaces based on work reported previously by various authors and work performed by the author with colleagues at other institutions and with his graduate students at CEEL. Traditionally it has been assumed that the interaction of bacteria with metal surfaces always causes increased corrosion rates (“microbiologically influenced corrosion” (MIC)). However, more recently it has been observed that many bacteria can reduce corrosion rates of different metals and alloys in many corrosive environments. For example, it has been found that certain strains of Shewanella can prevent pitting of Al 2024 in artificial seawater, tarnishing of brass and rusting of mild steel. It has been observed that corrosion started again when the biofilm was killed by adding antibiotics. The mechanism of corrosion protection seems to be different for different bacteria since it has been found that the corrosion potential E_corr became more negative in the presence of Shewanella ana and algae, but more positive in the presence of Bacillus subtilis. These findings have been used in an initial study of the bacterial battery in which Shewanella oneidensis MR-1 was added to a cell containing Al 2024 and Cu in a growth medium. It was found that the power output of this cell continuously increased with time. In the microbial fuel cell (MFC) bacteria oxidize the fuel and transfer electrons directly to the anode. In initial studies EIS has been used to characterize the anode, cathode and membrane properties for different operating conditions of a MFC that contained Shewanella oneidensis MR-1. Cell voltage (V)—current density (i) curves were obtained using potentiodynamic sweeps. The current output of a MFC has been monitored for different experimental conditions.     

The polarization behavior of the anode in a microbial fuel cell

Microbial fuel cell (MFC) systems are unique electrochemical devices that employ the catalytic action of bacteria to drive the oxidation of organic compounds. These systems have been suggested as renewable energy sources for small remote devices; however, questions remain about how MFCs can be efficiently optimized for this purpose. Several electrochemical techniques have been employed in this study to elucidate the limiting factors in power production by MFCs. Impedance spectra were collected for the anode and cathode at their open-circuit potential (OCP) before and after all other electrochemical tests. Cell voltage-current curves were obtained using a potential sweep technique and used to determine the maximum power available from the system. Potentiodynamic polarization in two different potential regions was used to determine the exchange current for the reaction occurring at the anode at its OCP and to explore the polarization behavior of the anode and the cathode in a wide potential range. Cyclic voltammetry was used to evaluate the redox activity of the anode. These techniques used in combination showed that the microorganism Shewanella oneidensis MR-1 is solely responsible for the observed decrease of the OCP of the anode, the increased rate of oxidation of lactate, the larger cell voltage and the increased maximum power output of the MFC.     

樊立萍1,*,温越霄1,2

为提高微生物燃料电池(MFC)的废水处理效果和发电性能,制备了一种海藻酸钠-聚季铵盐11/碳毡(SA-PQ-11/CF)阳极,分别以制药废水和糖蜜废水为阳极液,以碳毡为阴极,构建微生物燃料电池(MFC)实验系统,通过扫描电子显微镜(SEM)、电化学阻抗谱(EIS)、循环伏安特性(CV)、化学需氧量(COD)对其性能进行表征。结果显示,SA-PQ-11/CF阳极具有较大的比表面积,MFC的溶液电阻和电荷转移电阻也得到明显降低。阳极液为制药废水时,采用SA-PQ-11/CF阳极的MFC的稳态输出电压和COD去除率分别约为0.22 V和62%,较常规碳毡阳极时分别提高了100%和130%。阳极液为糖蜜废水时,采用SA-PQ-11/CF阳极的MFC的稳态输出电压和COD去除率分别为0.15 V和43%,分别较采用常规碳毡阳极时提高了275%和95%。基于SA-PQ-11的阳极改性能够有效提高MFC的废水处理效果和产电能力。     

Continuous microbial fuel cell using a photoautotrophic cathode and a fermentative anode

A complete microbial fuel cell (MFC) operating under continuous flow conditions and using Chlorella vulgaris at the cathode and Saccharomyces cerevisiae at the anode was investigated for the production of electricity. The MFC was loaded with different resistances to characterise its power capabilities and voltage dynamics. A cell recycle system was also introduced to the cathode to observe the effect of microalgae cell density on steady‐state power production and dynamic voltage profiles. At the maximum microalgae cell density of 2140 mg/L, a maximum power level of 0.6 mW/m² of electrode surface area was achieved. The voltage difference between the cathode and anode decreased as the resistance decreased within the closed circuit, with a maximum open circuit voltage (infinite resistance) of 220 mV. The highest current flow of 1.0 mA/m² of electrode surface area was achieved at an applied resistance of 250 Ω.     

Power Generation and Electrochemical Analysis of Biocathode Microbial Fuel Cell Using Graphite Fibre Brush as Cathode Material

To improve cathodic efficiency and sustainability of microbial fuel cell (MFC), graphite fibre brush (GFB) was examined as cathode material for power production in biocatalysed‐cathode MFC. Following 133‐h mixed culturing of electricity‐producing bacteria, the MFC could generate a reproducible voltage of 0.4 V at external resistance (R_EX) of 100 Ω. Maximum volumetric power density of 68.4 W m^–3 was obtained at a current density of 178.6 A m^–3. Upon aerobic inoculation of electrochemically active bacteria, charge transfer resistance of the cathode was decreased from 188 to 17 Ω as indicated by electrochemical impedance spectroscopy (EIS) analysis. Comparing investigations of different cathode materials demonstrated that biocatalysed GFB had better performance in terms of half‐cell polarisation, power and Coulombic efficiency (CE) over other tested materials. Additionally, pH deviation of electrolyte in anode and cathode was also observed. This study provides a demonstration of GFB used as biocathode material in MFC for more efficient and sustainable electricity recovery from organic substances.     

Electrochemical characteriztion of the bioanode during simultaneous azo dye decolorization and bioelectricity generation in an air-cathode single chambered microbial fuel cell

To achieve high power output based on simultaneously azo dye decolorization using microbial fuel cell (MFC), the bioanode responses during decolorization of a representative azo dye, Congo red, were investigated in an air-cathode single chambered MFC using representative electrochemical techniques. It has been found that the maximum stable voltage output was delayed due to slowly developed anode potential during Congo red decolorization, indicating that the electrons recovered from co-substrate are preferentially transferred to Congo red rather than the bioanode of the MFC and Congo red decolorization is prior to electricity generation. Addition of Congo red had a negligible effect on the Ohmic resistance (R_ohm) of the bioanode, but the charge-transfer resistance (R_c) and the diffusion resistance (R_d) were significantly influenced. The R_c and R_d firstly decreased then increased with increase of Congo red concentration, probably due to the fact that the Congo red and its decolorization products can act as electron shuttle for conveniently electrons transfer from bacteria to the anode at low concentration, but result in accelerated consumption of electrons at high concentration. Cyclic voltammetry results suggested that Congo red was a more favorable electron acceptor than the bioanode of the MFC. Congo red decolorization did not result in a noticeable decrease in peak catalytic current until Congo red concentration up to 900 mg l⁻¹. Long-term decolorization of Congo red resulted in change in catalytic active site of anode biofilm.     

The effect of electrolyte constituents on contact glow discharge electrolysis

Ordinary electrolysis developed spontaneously to contact glow discharge electrolysis (CGDE) at sufficiently high voltage, with glow discharge taking place around a thin platinum anode which was in contact with electrolyte solution. During this transition, the critical voltage (V_D) was an important parameter for the onset of CGDE. The results indicated that V_D decreased with the increasing conductivity and then maintained a certain value. The different dimension and material of cathode had little effect on V_D. When the electrolyte conductivity was 5.0 mS/cm, V_D was hardly affected by electrolyte composition. And the concentrations of H₂O₂ producing in the anolyte were close in different inert electrolyte. However, the concentrations of H₂O₂ in NaCl, NaAc, Na₂CO₃ and NaHCO₃ solution were lower than that in Na₂SO₄ solution. And the concentration of H₂O₂ in the anolyte was also decreased by adding a minute amount of CH₃OH.     

The impedance of alkaline manganese cells and their relationship to cell performance. III. Correlation with high-rate pulse discharge capacity

The extent to which the initial impedance characteristics of a batch of LR6 alkaline manganese cells determine their life and therefore capacity during a typical 2 A/10 s pulse discharge regime has been investigated, and the importance of thermodynamic factors have also been considered. It is shown that the potential drop (E-V _pulse) for the initial discharge cycle can be calculated approximately from a knowledge of the initial internal resistance value, and the recovery voltage,V _rec, can be calculated using a simple thermodynamic theory for the homogeneous phase discharge of -MnO₂. During subsequent cycles the polarization of the cathode-can assembly remains approximately constant at 300 mV while that of the anode-separator system increases progressively from 100 mV to >300 mV. The constancy of the former parameter can be attributed to constancy in the cathode contribution to the internal resistance, whereas the changes in the latter can be ascribed to increases in anode resistance polarization and anode concentration polarization. Minimization of cell internal resistance and anode polarization are therefore of primary concern if cell performance is to be maximized.Nomenclature E initial open-circuit voltage - V _pulse cell voltage att=10 s - V _pulse cell voltage att=10 s for the first pulse - V _rec open-circuit voltage at the end of a 50-s recovery period - V total polarization of the cell - V _A anode polarization (anode-separator system) - V _C cathode polarization (cathode-can assembly) - ohmic polarization - _NT charge-transfer polarization - _C concentration polarization - R _i cell internal resistance - R _e electrolyte resistance - R _part ^cath contact resistance between cathode particles or within the particles themselves - R ^cath effective resistance of cathode-can assembly - R _i ^cath contact resistance at the interface between the nickel oxide phase and the cathode (MnO₂ + graphite mixture) - R _phase ^cath resistance of the nickel oxide phase on the surface of the nickel-plated steel positive current collector (cell can) - R ₂ ^cath contact resistance at the interface between the nickel oxide layer on the can surface and the can itself - R high frequency intercept on complex plane impedance diagram - R diameter of the complex plane impedance semicircle - f ^* characteristic frequency at the top of the complex plane semicircle - C effective parallel capacitance in the equivalent circuit for a cell attributed to the cathode-can assembly - c _MnO2 concentration of MnO₂ at any point in the discharge - cMnO ₂ ⁰ maximum MnO₂ concentration at 100% efficiency - c _MnOOH concentration of MnOOH at any point in the discharge - c _MnOOH ⁰ maximum MnOOH concentration at 100% efficiency - proton-electron spatial correlation coefficient - I total current - i _R current through resistanceR - i _c current through capacitor - V _p voltage drop across parallel R-C circuit - A anode - C cathode - obs observed - calc calculated     

The voltage pulse degraded Ti/4H–SiC Schottky diodes studied with I–V and low frequency noise measurements

In this paper we discuss the results obtained after ESD voltage was stress applied to 4H–Silicon Carbide (4H–SiC) Schottky diodes. The Human Body Model (HBM) ESD voltage peaks of 3, 5 and 6 kV were applied to the cathode and anode separately and it was found that the diodes subjected to the cathode stress suffered greater degradation then the ones subjected to the anode stress. The recovery of the I–V characteristics after the stress was observed in the case of diodes subjected to the anode stress. Diode degradations were studied by I–V and low frequency (LF) noise measurements. Optical and electron microscopy inspection revealed the location of the degraded regions. The results of degradation are discussed using the equivalent electrical circuit of degraded diodes.     

Study of direct type ethanol fuel cells: Analysis of anode products and effect of acetaldehyde

The anode products are observed when ethanol fuel is circulated in the direct ethanol fuel cell system using Nafion^® as an electrolyte. The main products are CO₂ and acetaldehyde. I-V characteristics of a direct type fuel cell using ethanol and acetaldehyde as fuels are investigated. Anode and cathode overpotentials are also measured to analyze the characters of the polarization curves obtained for both fuels. The MEA consisted of PtRu anode catalyst. The voltage drops as the concentration of acetaldehyde solution increases. In the case of ethanol solution, the voltage increases as the concentration increases. The anode overpotential increases as the concentration of acetaldehyde increases although the increase of cathode overpotential is smaller than that of anode overpotential. The opposite result is observed for ethanol solutions, i.e., the anode overpotential increases as the concentration of ethanol decreases. This result shows that the voltage drop observed for acetaldehyde solution results from the anode overpotential. Rotating disc electrode (RDE) measurements and polarization curve measurements were also performed to confirm the relation between acetaldehyde concentration and overpotentials. It is supposed that the electrocatalytic oxidation mechanism of acetaldehyde on PtRu catalyst is different from that of ethanol.     

Influence of NO3 and SO4 on power generation from microbial fuel cells

Potential competition in terms of electron transfer from bacteria to electron acceptors such as nitrate (NO₃) and sulfate (SO₄) or the anode of a microbial fuel cell (MFC) was investigated to determine how alternative electron acceptors would influence power generation in an MFC. The cell voltage was not initially affected when these electron acceptors were introduced into the MFCs. However, the presence of NO₃ decreased the CE of the MFC compared to the injections of SO₄ or control salt (sodium chloride). This suggests that the growth of nitrate-reducing bacteria independent of the microbial populations on the MFC anode were not utilizing the anode as an electron acceptor, rather, they were consuming organic carbon in the anodic chamber of the MFC, resulting in a decrease of the CE of this MFC with no immediate impact on power output. This suggests that the bacterial consortium in the nitrate-MFC still preferred the anode over nitrate as the electron acceptor, although the theoretical reduction voltage of nitrate (+0.74 V) is higher than the reduction voltage in an MFC air cathode (as high as +0.425). These results are useful when considering whether MFC technology can be applied in situ to enhance biodegradation of organic contaminants in the presence of alternative electron acceptors.     

Harnessing of bioelectricity in microbial fuel cell (MFC) employing aerated cathode through anaerobic treatment of chemical wastewater using selectively enriched hydrogen producing mixed consortia

The possibility of bioelectricity generation from anaerobic chemical wastewater treatment was evaluated in a microbial fuel cell (MFC) [dual-chambered; mediator less anode; aerated cathode; plain graphite electrodes] employing selectively enriched hydrogen producing (acidogenic) mixed culture. Performance of MFC was evaluated at two organic/substrate loading rates (OLR) (1.165 Kg COD/m³-day and 1.404 Kg COD/m³-day) in terms of bioelectricity production and wastewater treatment at ambient pressure and temperature under acidophilic microenvironment (pH 5.5) using non-coated plain graphite electrodes (mediatorless anode; air cathode). Experimental data demonstrated the feasibility of in situ bioelectricity generation along with wastewater treatment. The performance of MFC with respect to power generation and wastewater treatment was found to depend on the applied OLR. Maximum voltage of 716 mV (2.84 mA; OLR −1.165 kg COD/m³-day) and 731 mV (2.97 mA; OLR-1.404 kg COD/m³-day) was observed at stable operating conditions. Substrate degradation rate (SDR) of 0.519 Kg COD/m³-day and 0.858 Kg COD/m³-day was observed at two OLRs studied. Maximum power yield (0.73 W/Kg COD_R and 0.49 W Kg/COD_R) and current density (339.87 mA/m² and 355.43 mA/m²) was observed at applied 50 Ω resistance. Fuel cell performance was evaluated employing polarization curve (100 Ω-30 KΩ), Coulombic efficiency (€_cb) and cell potentials along with sustainable power yield at stable phase of fuel cell operation. Designed MFC configuration, adopted operating conditions and used parent inoculum showed positive response.     

The vertical distribution of current in a gas-evolving membrane cell

A one-dimensional numerical model to describe gas void fraction and current distribution in five model membrane cell configurations is described in this work. The five models describe ideal (equipotential), upright (top cathode/bottom anode), inverted, u- and n-type electrical connections with anodic chlorine and cathodic hydrogen evolution in each case. In all but the first case the finite resistances of the electrodes are taken into account. The effects of (a) different terminal arrangements, (b) different current densities, (c) different cell heights, (d) different compartment widths, and (e) different overvoltages, have been investigated. For each study the current distribution and anolyte and catholyte void fraction distribution is displayed. The resistive components of the cell voltages are also calculated; the calculated resistive voltage loss varies between extremes of 0.291 V for the ideal cell to 0.377 V for the inverted cell at 3 kA m^–2 and 0.25 m cell height with typical fixed values of other parameters.Nomenclature A cross-sectional area - d bubble diameter - void fraction - _m maximum void fraction - G gas volumetric flow rate - K ratio of conductivities of bubble-free and bubble-filled electrolyte - L liquid volumetric flow rate - electrolyte viscosity - R _AN,R _A resistances of anode, anolyte, membrane - R _M,R _C cathode and catholyte, respectively (see - R _CA resistive network scheme of Fig. 2) - _L, _G liquid and gas phase densities - u ₁ single bubble rise velocity - u _sw bubble swarm rise velocity Paper presented at the 2nd International Symposium on Electrolytic Bubbles organized jointly by the Electrochemical Technology Group of the Society of Chemical Industry and the Electrochemistry Group of the Royal Society of Chemistry and held at Imperial College, London, 31st May and 1st June 1988.     

Studies on promising cell performance with H2SO4 as the catholyte for electrogeneration of Ag2+ from Ag+ in HNO3 anolyte in mediated electrochemical oxidation process

Electrochemical performance of a divided cell with electrogeneration of Ag²⁺ from Ag⁺ in 6 M HNO₃ anolyte has been studied with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte. This work arose because in mediated electrochemical oxidation (MEO) processes with Ag(II)/Ag(I) redox mediator, HNO₃ is generally used as catholyte, which, however, produces NO _x gases in the cathode compartment. The performance of the cell with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte has been compared in terms of (i) the acid concentration in the cathode compartment, (ii) the Ag⁺ to Ag²⁺ conversion efficiency in the anolyte, (iii) the migration of Ag⁺ from anolyte to catholyte across the membrane separator, and (iv) the cell voltage. Studies with various concentrations of H₂SO₄ catholyte have been carried-out, and the cathode surfaces have been analyzed by SEM and EDXA; similarly, the precipitated material collected in the cathode compartment at higher H₂SO₄ concentrations has been analyzed by XRD to understand the underlying processes. The various beneficial effects in using H₂SO₄ as catholyte have been presented. A simple cathode surface renewal method relatively free from Ag deposit has been suggested.     

An improved multi-anode contact glow discharge electrolysis reactor for dye discoloration

To promote treatment efficiency of organic pollutant, an improved multi-anode contact glow discharge reactor was developed for dye discoloration. This paper investigated how and what extent multi-anode contact glow discharge electrolysis (m-CGDE) could improve the discoloration efficiency of Acid Orange 7 (AO). I–V characteristic of m-CGDE was also studied in details. It was found that the critical voltage of m-CGDE was same to that of single anode. The concentration of H₂O₂ in the anolyte and discoloration rates of AO increased with increasing treatment time and anode number. Furthermore, an improved m-CGDE reactor was designed by replacing platinum wire with stainless steel wire. Under the same conditions, multiple stainless steel anodes greatly enhanced the discoloration of AO. The trace amount of iron ion from stainless steel anodes played Fenton-like reaction important role.     

A dual-chamber microbial fuel cell with conductive film-modified anode and cathode and its application for the neutral electro-Fenton process

This study reports on the modification of the anode and the cathode in a dual-chamber microbial fuel cell (MFC) with a polypyrrole (PPy)/anthraquinone-2,6-disulfonate (AQDS) conductive film to boost its performance and the application of the MFC to drive neutral electron-Fenton reactions occurring in the cathode chamber. The MFC equipped with the conductive film-coated anode and cathode delivered the maximum power density of 823 mW cm⁻² that was one order of magnitude larger than that obtained in the MFC with the unmodified electrodes. This was resulted from the enhanced activities of microbial metabolism in the anode and oxygen reduction in the cathode owing to the decoration of both electrodes with the PPy/AQDS composite. The MFC with the modified electrodes resulted in the largest rate of H₂O₂ generation in the cathode chamber by the two-electron reduction of O₂. The increase in the concentration of H₂O₂ was beneficial for the enhancement in the amount of hydroxyl radicals produced by the reaction of H₂O₂ with Fe²⁺, thus allowing an increased oxidative ability of the electro-Fenton process towards the decolorization and mineralization of an azo dye (i.e., Orange II) at pH 7.0.     

An innovative dual fuel cell to capture and collect pure NO X from flue gases

Nitrogen monoxide (NO), a major air pollutant, can be directly used as a precursor for nitrogen fertilizer production as long as it is collected in a pure form. In this study, an innovative dual fuel cell system was designed for the efficient capture and collection of pure NO _X from industrial flue gases as well as for electricity generation. The system consisted of a methanol/ferric-EDTA fuel cell for NO _X capture and a ferrous-EDTA–NO/air fuel cell for captured NO _X collection. In a separation operation, the maximum power densities, which were obtained at pH 2 and 20 °C, were 785 and 1,840 mW m^?2 in FC1 and FC2, respectively, and increased with temperature. The highest overall outputs from FC1 and FC2 were measured at pH 2, a result that is possibly attributable to the redox potential difference between the anolyte and catholyte in the fuel cells. In the combined operation, ferrous-EDTA–NO prepared in the cathode compartment of FC1 was successfully and efficiently converted to ferric-EDTA and NO in the anode compartment of FC2. The present approach was considered advantageous for advanced NO _X reuse technology in the respect that valuable products, such as fertilizer, could be produced.     

A solid state lithium concentration cell with LixV2O5

A solid state lithium concentration cell Li_xV₂O₅/LISICON/Li_0.25V₂O₅ (0.25 x 0.55) was investigated. The open circuit voltage increased monotonously from about 0 mV atx=0.25 to about 270 mV atx=0.55. Cells with variousx-values in the single phase showed similar polarization curves, and their cathode polarizations were slightly larger than the anode polarizations. The cathode potential vs a platinum wire as the third electrode was nearly constant under nitrogen flow, but the anode potential decreased with increase of the lithium content of the sample. During the experiment, Lisicon was satisfactorily stable in contact with Li_xV₂O₅.     

A Photo-electochemical cell with production of hydrogen and oxygen by a cell reaction

A photo-electrochemical cell was demonstrated which had a TiO₂ electrode as an anode, p-GaP as a cathode, and 1 N H₂SO₄ of 1 N NaOH as an electrolyte. The cell reaction was the decomposition of water, ie, oxygen evolution at the anode and hydrogen evolution at the cathode. The open current voltage was 0·58 V for the acid electrolyte and 0·4 V for the base. Deterioration of the cell performance was observed, and this was mainly due to the p-GaP electrode. The deterioration was possibly brought about by a change of surface condition of the p-GaP electrode with working time. Utilization of solar energy was found to be quite limited by the pair of semiconductors chosen.     

MFC-MEC耦合系统产电性能及处理含镉重金属废水的研究

以厌氧活性污泥为阳极菌种,乙酸钠为阳极底物,硫酸铜和重铬酸钾溶液为微生物燃料电池（MFC）阴极液,人工模拟含镉重金属废水为微生物电解池（MEC）阴极液,构建MFC-MEC耦合系统,利用MFC的产电驱动MEC运行,在不消耗外部能源的情况下,实现含镉重金属废水中Cd²⁺的去除。实验研究了MFC反应器容积、MFC堆栈、MEC电极材料、MEC阴极液pH对MFC-MEC耦合系统电性能及含镉重金属废水处理效果的影响。结果表明：MFC反应容积的扩大可以提高其产电性能,但与此同时会造成MFC的内阻升高,随着MFC容积的增加,MEC中Cd²⁺去除率逐渐增加,但同时MFC阴极Cr⁶⁺去除率逐渐下降;MFC堆栈可以提高工作组两端电压,串联时最大输出电压为1509 mV,Cd²⁺去除率为69.3%;以钛板作为MEC电极时,微生物能有效附着在阳极表面,MFC阳极COD去除率为85%,MEC中Cd²⁺去除率为51.5%;MEC阴极液pH在3~5时,有利于含镉重金属废水的处理,Cd²⁺去除率80%以上。经XRD分析,MEC阴极还原产物为CdCO₃。