Effect of cathode electron-receiver on the performance of microbial fuel cells

Performance of cathode electron receivers has direct effect on the voltage and power density of MFC. This paper explored the electrical performance of MFC with potassium permanganate, ferricyanide solution and dissolved oxygen (DO) as cathode electron receivers. The results showed that the internal resistance of MFC with DO depends on catalyst and is higher than that of MFC with potassium permanganate and potassium ferricyanide solution. The maximum volume power density is 4.35 W/m³, and the smallest internal resistance is only about 54 Ω. In case of DO, the internal resistance and power density is different depending on the catalyst and is not too much related to the membranes.     

Effect of coal based pyrolysis gases on the performance of solid oxide direct carbon fuel cells

Solid oxide direct carbon fuel cells (SO-DCFCs) offer a promising way to convert common carbon materials such as coal and biomass to electricity efficiently. It is inevitable that these carbon fuels decompose during SO-DCFCs operation and release pyrolysis gases, which may affect the cell performance and change the anode reaction pathway. In this study, three coals and an activated carbon are used to investigate the role of pyrolysis gases in SO-DCFCs. The cell polarization curve and durability performance are measured for all raw fuels and a pyrolysis pretreated coal at temperatures ranging from 1023 to 1123 K. Mass spectrometry is employed to analyze pyrolysis gases under open circuit operation. The results show that all raw fuels have good electrochemical performance at 1123 K. The cell power density is greatly improved by the presence of pyrolysis gases (mainly H₂ and CO) in the anode chamber. And the cell durability performance is largely dependent on both the amounts of active pyrolysis gases and the carbon gasification reactivity. It is demonstrated that the dominant electrochemical reactions are the electrooxidation of gaseous fuels, namely pyrolysis gases in the initial stage of discharge, then CO produced by carbon gasification. The direct electrooxidation of carbon is less significant than that of gaseous fuels.     

A review on carbon and non-precious metal based cathode catalysts in microbial fuel cells

Microbial fuel cells, an emerging technology has been paid a great attention in recent years, due to its unique advantages in treating wastewater to portable water, together with the generation of useful electricity, with the help of bio-active anodes and electrochemical cathodes, simultaneously. When applying this technology in a practical scale, the indigenous bacteria present in the wastewater catalyze the breakdown of organic matter in the anode compartment, with generation of electrons and in the cathode compartment an oxidant, usually the oxygen present in the air, take the electron and reduce to water (oxygen reduction reaction, ORR). An ideal ORR catalyst should be highly active, durable, scalable, and most importantly it should be cost effective. Generally, platinum-based catalyst is utilized, however, due to the high cost of Pt based catalysts, many cheap, cost effective catalyst have been identified as efficient ORR catalyst. Carbon based catalysts known to possess good electronic conductivity, desirable surface area, high stability, together when doped with heteroatoms and cheap metals is found to remarkably enhance the ORR activity. Although a lot of research has been done in view of developing carbon based cheap, cost-effective catalysts, still their collective information has not been reviewed. In this article we anticipate reviewing various non-precious metal and metal-free catalysts that are synthesized and investigated for MFCs, factors that affect the ORR activity, catalyst designing strategies, membranes utilized for MFCs, together with the cost comparison of non-precious and metal-free catalysts with respect to Pt based catalysts have been summarized. We anticipate that this review could offer researchers an overview of the catalyst developed so far in the literatures and provides a direction to the young researchers.     

Analysis of carbon fiber brush loading in anodes on startup and performance of microbial fuel cells

Flat carbon anodes placed near a cathode in a microbial fuel cell (MFC) are adversely affected by oxygen crossover, but graphite fiber brush anodes placed near the cathode produce high power densities. The impact of the brush size and electrode spacing was examined by varying the distance of the brush end from the cathode and solution conductivity in multiple MFCs. The startup time was increased from 8 ± 1 days with full brushes (all buffer concentrations) to 13 days (50 mM), 14 days (25 mM) and 21 days (8 mM) when 75% of the brush anode was removed. When MFCs were all first acclimated with a full brush, up to 65% of the brush material could be removed without appreciably altering maximum power. Electrochemical impedance spectroscopy (EIS) showed that the main source of internal resistance (IR) was diffusion resistance, which together with solution resistance reached 100 Ω. The IR using EIS compared well with that obtained using the polarization data slope method, indicating no major components of IR were missed. These results show that using full brush anodes avoids adverse effects of oxygen crossover during startup, although brushes are much larger than needed to sustain high power.     

High performance cathode based on carbon fiber felt for magnesium-air fuel cells

A series of carbon fiber felt/PTFE based gas diffusion layers (GDL) for Mg-air fuel cells were prepared by a simple method of immersing carbon fiber felt in PTFE suspension. Critical properties of the as-prepared GDL, including the surface morphology, electronic resistivity, porosity and gas permeability, have been characterized to investigate the effect of PTFE suspension concentration and PTFE content on the properties of the GDL. The micrographs indicated that the PTFE was homogenously dispersed on the carbon fiber felts and showed structure with a microporous layer. The as-prepared GDL exhibited good mechanical property, high electronic conductivity, sufficient water repellency and high gas permeability. Compared with the Mg-air fuel cell with a traditional carbon powder based cathode, the performance and the stability of Mg-air fuel cell with the carbon fiber felt based GDL are improved significantly.     

Electrochemical performance of different carbon fuels on a hybrid direct carbon fuel cell

In this work, three processed carbon fuels including activated carbon, carbon black and graphite have been employed to investigate influence of the chemical and physical properties of carbon on the HDCFC performance in different anode atmospheres at 650–800 °C. The results reveal that the electrochemical activity is strongly dependent on crystalline structure, thermal stability and textural properties of carbon fuels. The activated carbon samples demonstrate a better performance with a peak power density of 326 mW cm^?2 in CO₂ at 750 °C, compared to 147 and 59 mW cm^?2 with carbon black and graphite samples, respectively. Compared to the ohmic resistance, the polarization resistance plays a more dominated role in the cell performance. When replacing N₂ by CO₂ purge gas, the power density is the strongly temperature dependent due to the Boudouard reaction.     

Investigation of detailed kinetic scheme performance on modelling of turbulent non-premixed sooting flames

This paper presents the results of an application of a first-order conditional moment closure (CMC) approach coupled with a semi-empirical soot model to investigate the effect of various detailed combustion chemistry schemes on soot formation and destruction in turbulent non-premixed flames.A two-equation soot model representing soot particle nucleation,growth,coagulation and oxidation,was incorporated into the CMC model.The turbulent flow-field of both flames is described using the Favre-averaged fluid-flow equations,applying a standard k-ε turbulence model.A number of five reaction kinetic mechanisms having 50-100 species and 200-1000 elementary reactions called ABF,Miller-Bowman,GRI-Mech3.0,Warnatz,and Qin were employed to study the effect of combustion chemistry schemes on soot predictions.The results showed that of various kinetic schemes being studied,each yields similar accuracy in temperature prediction when compared with experimental data.With respect to soot prediction,the kinetic scheme containing benzene elementary reactions tends to result in a better prediction on soot concentrations in comparison to those contain no benzene elementary reactions.Among five kinetic mechanisms being studied,the Qin combustion scheme mechanism turned to yield the best prediction on both flame temperature and soot levels.     

Investigation of the anode reactions in solid oxide electrolyte based carbon fuel cells

The anode reactions of solid oxide electrolyte based carbon fuel cells (SO-CFCs) are explored by comparing the electrochemical behaviors of SO-CFCs under varying anode carrier gas flow rates (FAr) and at different contact modes. The electrochemical performance of four raw carbon fuels, including a graphitic carbon (GC), two coals (lignite CF and anthracite YQ) and an activated carbon (AC), and their chars is tested to investigate the influence of carbon fuel properties on the cell performance. The results show that CO electro-oxidation and C-CO₂ gasification were main anode reactions. The direct carbon electro-oxidation is insignificant under high F_Ar. Polarization performance of the chars under high F_Ar was similar with that of 5–10% CO. It is also concluded that the cell performance is greatly dependent on the carbon fuel gasification reactivity with CO₂. Thermal pretreated AC displays the best durability performance for its stable and moderate CO₂ gasification rate. Additionally, the coal ash does not affect the cell performance significantly.     

阴极电子受体对微生物燃料电池性能的影响

以双室型微生物燃料电池为试验装置,比较铁氰化钾、重铬酸钾、高锰酸钾作为阴极电子受体时微生物燃料电池的电压和功率输出。结果表明,高锰酸钾与重铬酸钾混合电子受体对微生物燃料电池性能的提高没有显著效果,不如两者的单独表现;高锰酸钾对应的最高输出电压可达1 160 mV,但很不稳定,会很快下降到600 mV左右,在实际应用中有一定障碍;在酸性条件(pH=3.0)下,重铬酸钾的开路电压为1 081.2 mV,最大输出功率密度为35.1 W/m3,电池内阻为170.27Ω,而且表现稳定,是理想的阴极电子受体。     

Effects of periodically alternating temperatures on performance of single-chamber microbial fuel cells

Practical applications of microbial fuel cells (MFCs) for wastewater treatment are usually operated over a wide range of temperature, especially day–night temperature difference. Here, MFCs at alternating temperatures were compared with those at constant temperatures. MFCs at 6/18 °C reached a steady-state voltage of 0.41 ± 0.05 V at 6 °C and 0.36 ± 0.04 V at 18 °C, which were lower than that of MFCs at 18/30 °C (0.42 ± 0.01 V at 18 °C and 0.47 ± 0.02 V at 30 °C). MFCs at 18/30 °C produced the highest power density of 2169 ± 82 mW m⁻² at 30 °C, even higher than that of MFCs at constant temperature 30 °C. Moreover, MFCs at 6/18 °C and 18/30 °C obtained a comparable coulombic efficiencies (94.6 ± 5.2%, 83.2 ± 4.1%, respectively) compared with MFCs at constant temperatures (86.3 ± 7.3% at 18 °C and 84.1 ± 5.5% at 30 °C). These results demonstrate that MFCs could be successfully adapted for use under day–night temperature difference conditions.     

Effect of hydrogen producing mixed culture on performance of microbial fuel cells

This study examined the influence of H₂-producing mixed cultures on improving power generation using air-cathode microbial fuel cells (MFCs) inoculated with heat-treated anaerobic sludge. The MFCs installed with graphite brush anode generated higher power than the MFCs with carbon cloth anode, regardless heat treatment of anaerobic sludge. When the graphite brush anode-MFCs were inoculated selectively with H₂-producing bacteria by heat treatment, power production was not improved (about 490 mW/m²) in batch mode operation, but for slightly increased in carbon cloth anode-MFCs (from 0.16 to 2.0 mW/m²). Although H⁺/H₂ produced from H₂-producing bacteria can contribute to the performance of MFCs, suspended biomass did not affect the power density or potential, but the Coulombic efficiency (CE) increased. A batch test shows that propionate and acetate were used effectively for electricity generation, whereas butyrate made a minor contribution. H₂-producing mixed cultures do not affect the improvement in power generation and seed sludge, regardless of the pretreatment, can be used directly for the MFC performance.     

Novel multi walled carbon nanotube based nitrogen impregnated Co and Fe cathode catalysts for improved microbial fuel cell performance

For application in a microbial fuel cell (MFC), transition metal and nitrogen co-doped nanocarbon catalysts were synthesised by pyrolysis of multi-walled carbon nanotubes (MWCNTs) in the presence of iron- or cobalt chloride and nitrogen source. For the physicochemical characterisation of the catalysts, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) was used. The results obtained by rotating disk electrode (RDE) method showed an extraordinary electrocatalytic activity of these catalysts towards oxygen reduction reaction (ORR) in neutral media, which was also confirmed by the MFC results. The Co-N-CNT and Fe-N-CNT cathode catalysts exhibited maximum power density of 5.1 W m^?3 and 6 W m^?3, respectively. Higher ORR activity and improved electric output in the MFC could be attributed to the formation of the active nitrogen-metal centers. All findings suggest that these materials can be used as potential cathode catalysts for ORR in MFC to replace expensive noble-metal based materials.     

Long-term effect of carbon nanotubes on electrochemical properties and microbial community of electrochemically active biofilms in microbial fuel cells

Carbon nanotubes (CNTs) have been widely exploited to improve anodic performance, but information is needed on their long-term stability for improvement. Herein, we prepared a novel CNTs-modified graphite felt (CNTs-GF) by a simple and scalable process and evaluated its long-term performance using anaerobic sludge as inoculum. the MFC with CNTs-GF yielded a sustained enhancement of power output, increasing from 1.93 ± 0.09 W m^?2 after 1 month to 2.10 ± 0.05 W m^?2 after 3 months and reaching 2.00 ± 0.10 W m^?2 after 13 month, indicating the enhancement in electricity generation by the CNTs was not declined over one year. However, the bare GF showed a declining tendency of performance during 13 months. The long-term enhancement can be explained by the facts that the CNTs-GF was beneficial to electrochemically active biofilms (EABs) growth and interacted better with EABs and increased the extracellular electron transfer. Community analysis showed an increase in Geobacter in response to CNTs modification. These results demonstrated that CNTs modification could sustain a superior long-term enhancement in MFC performance.     

Investigation of fin based oxygen supply modules on the performance of air-breathing polymer electrolyte membrane fuel cells

In an effort to identify an optimized performing top-layer for air-breathing polymer electrolyte membrane (ABPEM) fuel cells, the following strategies were employed to evaluate thin-fin and duct top-layer arrangements: polarization testing, electrochemical impedance spectroscopy testing, Schlieren imaging, and infrared imaging. The duct arrangement was tested under a vertical configuration, while the thin-fin top-layer was tested for both horizontal and vertical orientations. The two top-layers under consideration were introduced and tested at temperatures ranging from room temperature to 50 °C. To maintain the fuel cell temperature at the desired testing conditions, an external heater was used. Additionally, the fuel cell itself was designed to have a large thermal mass, in order to minimize self-heating temperature fluctuations resulting from the electrochemical reactions. From the experiments, it was found that vertical configurations for both top-layers show similar performance. However, the performance of the horizontal configuration is the least efficient due to water droplet formation on the Gas Deficient Layer (GDL) and impeded airflow by the large cathode plate. It is concluded that, due to thin-fin top-layer’s simplicity in design and suitability to a variety of configurations and temperatures, the thin-fin design presents a potentially effective solution as a top-layer for ABPEM fuel cells among the prototypes.     

Impact of salinity on cathode catalyst performance in microbial fuel cells (MFCs)

Several alternative cathode catalysts have been proposed for microbial fuel cells (MFCs), but effects of salinity (sodium chloride) on catalyst performance, separate from those of conductivity on internal resistance, have not been previously examined. Three different types of cathode materials were tested here with increasingly saline solutions using single-chamber, air-cathode MFCs. The best MFC performance was obtained using a Co catalyst (cobalt tetramethoxyphenyl porphyrin; CoTMPP), with power increasing by 24 ± 1% to 1062 ± 9 mW/m² (normalized to the projected cathode surface area) when 250 mM NaCl (final conductivity of 31.3 mS/cm) was added (initial conductivity of 7.5 mS/cm). This power density was 25 ± 1% higher than that achieved with Pt on carbon cloth, and 27 ± 1% more than that produced using an activated carbon/nickel mesh (AC) cathode in the highest salinity solution. Linear sweep voltammetry (LSV) was used to separate changes in performance due to solution conductivity from those produced by reductions in ohmic resistance with the higher conductivity solutions. The potential of the cathode with CoTMPP increased by 17–20 mV in LSVs when the NaCl addition was increased from 0 to 250 mM independent of solution conductivity changes. Increases in current were observed with salinity increases in LSVs for AC, but not for Pt cathodes. Cathodes with CoTMPP had increased catalytic activity at higher salt concentrations in cyclic voltammograms compared to Pt and AC. These results suggest that special consideration should be given to the type of catalyst used with more saline wastewaters. While Pt oxygen reduction activity is reduced, CoTMPP cathode performance will be improved at higher salt concentrations expected for wastewaters containing seawater.     

集胞藻PCC-6803催化的光合微生物燃料电池性能研究

以集胞藻PCC-6803(Synechocystis PCC-6803)为阳极催化剂搭建直接利用太阳能的双室H-型光合微生物燃料电池(PMFC),通过极化曲线法、交流阻抗法、循环伏安法等电化学方法,开展电极面积比、质子交换膜、内阻等因素对光合微生物燃料电池产电的影响研究。试验结果显示:在PMFC运转过程中,其输出功率稳定,且达到的最大功率密度为72.3 mW/m2;阴阳极面积大小对PMFC产电性能没有显著影响,说明双室光合微生物燃料电池中,质子交换膜传递质子的速率较慢,限制了PMFC发电效能的提高。PMFC启动后,随着生物膜的增长,其欧姆内阻、极化内阻、总内阻都呈现下降的趋势,且欧姆内阻下降的速率小于极化内阻,从而使欧姆内阻占总内阻的比率变大,进一步说明质子交换膜传递质子的速率是限制PMFC发电的关键因素。     

Detailed chemical kinetic models for the low-temperature combustion of hydrocarbons with application to gasoline and diesel fuel surrogates

This paper presents a review of gas-phase detailed kinetic models developed to simulate the low-temperature oxidation and autoignition of gasoline and diesel fuel components (alkanes, ethers, esters, alkenes, cycloalkanes, aromatics, including from four atoms of carbon) and of mixtures of several of them, which have been proposed as surrogates. The recently proposed models are summarized, as well as the experimental results available for their validation. A comparison between the major models in terms of considered elementary steps and associated rate constants is also proposed.     

Effects of chlorides on the performance of proton exchange membrane fuel cells

This paper investigates the effects of cathode gases containing chloride ions on the proton exchange membrane fuel cell (PEMFC) performance. Chloride solutions are vaporized using an ultrasonic oscillator and mixed with oxygen/air. The salt concentration of the mixed gas in the cathode is set by varying the concentration of the chloride solution. Five-hour tests show that an increase in the concentration of sodium chloride did not significantly affect the cell performance of the PEMFC. It is found that variations in the concentration of chloride do not show significant influence on the cell performance at low current density operating condition. However, for high current density operating conditions and high calcium chloride concentrations, the chloride ion appears to have a considerable effect on cell performance. Experimental results of 108-h tests indicate that the fuel cell operating with air containing calcium chloride has a performance decay rate of 3.446 mV h⁻¹ under the operating condition of current density at 1 A/cm². From the measurements of the I-V polarization curves, it appears that the presence of calcium chloride in the cathode fuel gas affects the cell performance more than sodium chloride does.     

Platinum decorated aligned carbon nanotubes: Electrocatalyst for improved performance of proton exchange membrane fuel cells

This study aims to improve the performance of proton exchange membrane fuel cells (PEMFCs) using carbon nanotubes as scaffolds to support nanocatalyst for power generation over prolonged time periods, compared to the current designs. The carbon nanotubes are prepared using chemical vapor deposition and decorated by platinum nanoparticles (Pt-NPs) using an amphiphilic approach. The PEMFC devices are then constructed using these aligned carbon nanotubes (ACNTs) decorated with Pt-NPs as the cathode. The electrochemical analyses of the PEMFC devices indicate the maximum power density reaches to 860 mW cm⁻² and current density reaches 3200 mA cm⁻² at 0.2 V, respectively, when O₂ is introduced into cathode. Importantly, the Pt usage was decreased to less than 0.2 mg cm⁻², determined by X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy as complimentary tools. Electron microscopic analyses are employed to understand the morphology of Pt-ACNT catalyst (with diameter of 4-15 nm and length from 8 to 20 μm), which affects PEMFC performance and durability. The Pt-ACNT arrays exhibit unique alignment, which allows for rapid gas diffusion and chemisorption on the catalyst surfaces.