Control of dual-chambered microbial fuel cell by anodic potential: Implications with sulfate reducing bacteria

Five dual chamber microbial fuel cell reactors were inoculated with a mixed culture of sulfate-reducing bacteria and fed with artificial wastewater containing lactate and sulfate. A negative poised anode potential enhanced the performance of this fuel cell while a positive poised anode potential or no anode potential had no effect on performance. The effect of this anode potential promoted microbial colonization on the anode surface (biofilm) thereby presenting an effective and successful way for the start-up of a sulfate reducing bacterial microbial fuel cell.     

Modeling the performance of molten carbonate based direct carbon fuel cell anode

A mathematical model is developed to study the performance of a molten carbonate based direct carbon fuel cell anode. The direct carbon fuel cell(DCFC) is a fuel cell which uses solid carbon as fuel and molten carbonate as electrolyte. The model assumes that the 4 electron carbon oxidation reaction is the primary reaction driving the DCFC. However, the 2 electron CO oxidation reaction and the reverse Boudouard reaction is also considered in this model. The model studies the effect of performance parameters on the performance of the DCFC. The effect of the bulk conductivity in the solid phase, the bulk conductivity in the liquid phase, carbon loading and the thickness of the anode layer on the potential and current distribution in the cell is modeled. Model results are compared with experimental data and found to compare well.     

Evaluating the impact of enhanced anode CO tolerance on performance of proton-exchange-membrane fuel cell systems fueled by liquid hydrocarbons

Recent advances in anode electrocatalysts for low-temperature PEM fuel cells are increasing tolerance for CO in the H₂-rich anode stream. This study explores the impact of potential improvements in CO-tolerant electrocatalysts on the system efficiency of low-temperature Nafion-based PEM fuel cell systems operating in conjunction with a hydrocarbon autothermal reformer and a preferential CO oxidation (PROx) reactor for CO clean-up. The incomplete H₂ clean-up by PROx reactors with partial CO removal can present conditions where CO-tolerant anode electrocatalysts significantly improve overall system efficiency. Empirical fuel cell performance models were based upon voltage-current characteristics from single-cell MEA tests at varying CO concentrations with new Pt-Mo alloy reformate-tolerant electrocatalysts tested in conjunction with this study. A system-level model for a liquid-fueled PEM fuel cell system with a 5 kW full power output is used to study the trade-offs between the improved performance with decreased CO concentration and the increased penalties from the air supply to the PROx reactor and associated reduction in H₂ partial pressures to the anode. As CO tolerance is increased over current state-of-the-art Pt alloy catalysts, system efficiencies improve due primarily to higher fuel cell voltages and to a lesser extent to reductions in parasitic loads. Furthermore, increasing CO tolerance of anode electrocatalysts allows for the potential for reduced system costs with minimal efficiency penalty by reducing PROx reactor size through reduced CO conversion requirements.     

A CFD-based model of a planar SOFC for anode flow field design

This study presents a 3D CFD model of a planar SOFC with internal reforming for anode flow field design. The developed model reflects the influence of various factors on fuel cell performance including flow field design and kinetics of chemical and electrochemical reactions. The case study illustrates applications of the CFD model for planar SOFC with different anode flow field designs. Simulation results indicate the importance of the anode flow field design for planar SOFCs. The model is useful for optimization of fuel cell design and operating conditions.     

Effect of gas composition on Ru dissolution and crossover in polymer-electrolyte membrane fuel cells

Pt-Ru-based anodes are commonly used in polymer-electrolyte membrane fuel cells (PEMFCs) to provide improved CO tolerance for reformate fuel applications. However, Ru crossover from the anode to the cathode has been identified as a critical durability problem that has severe performance implications. In the present study, an anode accelerated stress test (AST) was used to simulate potential spikes that occur during fuel cell start-ups and shutdowns to induce Ru crossover. The effects of fuel gas composition, namely hydrogen and carbon dioxide concentrations, on Ru dissolution and crossover were investigated. The cell performance losses were correlated with the degree of Ru crossover as determined by the changes in cathode cyclic voltammetry (CV) characteristics and neutron activation analysis (NAA). It was found that higher hydrogen concentration in the fuel accelerated Ru crossover and that the presence of carbon dioxide hindered Ru crossover. In particular, the injection of 20 vol.% carbon dioxide during potential cycling resulted in very minor Ru crossover, which showed essentially identical performance losses and CV characteristic changes as a fuel cell composed of a Ru-free anode. The experimental results suggest that the Ru species in our Pt-Ru metal oxide catalysts need to go through a reduction step by hydrogen before dissolution. The presence of carbon dioxide may play a role in hindering the reduction step.     

Ti4O7 supported IrOx for anode reversal tolerance in proton exchange membrane fuel cell

Fuel starvation can occur and cause damage to the cell when proton exchange membrane fuel cells operate under complex working conditions. In this case, carbon corrosion occurs. Oxygen evolution reaction (OER) catalysts can alleviate carbon corrosion by introducing water electrolysis at a lower potential at the anode in fuel shortage. The mixture of hydrogen oxidation reaction (HOR) and unsupported OER catalyst not only reduces the electrolysis efficiency, but also influences the initial performance of the fuel cell. Herein, Ti₄O₇ supported IrO_x is synthesized by utilizing the surfactant-assistant method and serves as reversal tolerant components in the anode. When the cell reverse time is less than 100 min, the cell voltage of the MEA added with IrO_x/Ti₄O₇ has almost no attenuation. Besides, the MEA has a longer reversal time (530 min) than IrO_x (75 min), showing an excellent reversal tolerance. The results of electron microscopy spectroscopy show that IrO_x particles have a good dispersity on the surface of Ti₄O₇ and IrO_x/Ti₄O₇ particles are uniformly dispersed on the anode catalytic layer. After the stability test, the Ti₄O₇ support has little decay, demonstrating a high electrochemical stability. IrO_x/Ti₄O₇ with a high dispersity has a great potential to the application on the reversal tolerance anode of the fuel cell.     

Electrodeposition of PEM fuel cell catalysts by the use of a hydrogen depolarized anode

Up to 30% of the expensive catalyst metal in conventional fuel cell catalysts is not utilized in fuel cells caused by an absence of contact to either the ion conducting, electron conducting or educt phase. This contact can be improved by in situ electrodeposition with a precursor layer which is mostly done in a galvanostatic mode in the literature. In this paper electrochemical deposition with a hydrogen depolarized anode is described and so a potentiostatic electrodeposition under the control of the working-electrode potential and dry working-electrode conditions is enabled. This potentiostatic electrodeposition with a hydrogen depolarized anode significantly increases the performance of the fuel cell.     

High performance of direct methane-fuelled solid oxide fuel cell with samarium modified nickel-based anode

Natural gas is one of the most attractive fuels for solid oxide fuel cell (SOFC), while the anode activity for methane fuel has a great influence on the performance and stability of SOFC. Samarium is a good catalyst promoter for methane reforming. In this work, samarium is used to modify nickel catalyst, which results in small nickel oxide particles. The SmNi-YSZ (yttria-stabilized zirconia) anode has smaller particles and better interfacial contact between nickel and YSZ compared with conventional Ni-YSZ anode. The fine structure of SmNi-YSZ anode results in high activity for electrochemical oxidation of hydrogen and low polarization resistance of the cell. The performance of SmNi-YSZ anode cell with humidified methane as fuel is greatly improved, which is similar to that with hydrogen as fuel. The maximum power densities of SmNi-YSZ anode cell are 1.56 W cm⁻² for humidified hydrogen fuel and 1.54 W cm⁻² for humidified methane fuel at 800 °C. The maximum power density is increased by 221% when samarium is used to modify Ni-YSZ anode for humidified methane fuel at 650 °C. High cell performance results in good stability of SmNi-YSZ anode cell and the cell runs stably for more than 600 min for humidified methane fuel.     

Effect of primary parameters on the performance of PEM fuel cell

A one-dimensional, steady-state and isothermal model for a proton exchange membrane (PEM) fuel cell has been developed to investigate the effects of various parameters such as the molar fraction of nitrogen gas, relative humidity, temperature, pressure, membrane thickness, anode and cathode stoichiometric flow ratio and the distribution of oxygen in the cathode catalyst while water transfer in membrane is produced by diffusion, pressure gradient and electro-osmotic drag. The most critical problems to overcome in the proton exchange membrane (PEM) fuel cell technology are the water and thermal management. The results show that the cell performance increases as operating pressure and temperature are increased. The performance of cell can decrease by decreasing the relative humidity of inlet gases and increasing the membrane thickness. Increasing the anode and cathode stoichiometric flow ratio can also improve the cell performance. As the oxygen concentration becomes zero in about 8 percent depth of cathode catalyst layer, the thickness of cathode catalyst layer can be reduced 92 percent without any potential loss in output voltage. The cathode activation loss also becomes high by increasing the molar fraction of nitrogen gas. The modeling results agree very well with experimental results.     

Experimental factors that influence carbon monoxide tolerance of high-temperature proton-exchange membrane fuel cells

The poisoning effect of carbon monoxide (CO) on high-temperature proton-exchange membrane fuel cells (PEMFCs) is investigated with respect to CO concentration, operating temperature, fuel feed mode, and anode Pt loading. The loss in cell voltage when CO is added to pure hydrogen anode gas is a function of fuel utilization and anode Pt loading as well as obvious factors such as CO concentration, temperature and current density. The tolerance to CO can be varied significantly using a different experimental design of fuel utilization and anode Pt loading. A difference in cell performance with CO-containing hydrogen is observed when two cells with different flow channel geometries are used, although the two cells show similar cell performance with pure hydrogen. A different combination of fuel utilization, anode Pt loading and flow channel design can cause an order of magnitude difference in CO tolerance under identical experimental conditions of temperature and current density.     

A general electrolyte–electrode-assembly model for the performance characteristics of planar anode-supported solid oxide fuel cells

A general electrode–electrolyte-assembly (EEA) model has been developed, which is valid for different designs of solid oxide fuel cells (SOFCs) operating at different temperatures. In this study, it is applied to analyze the performance characteristics of planar anode-supported SOFCs. One of the novel features of the present model is its treatment of electrodes. An electrode in the present model is composed of two distinct layers referred to as the backing layer and the reaction zone layer. The other important feature of the present model is its flexibility in fuel, having taking into account the reforming and water–gas shift reactions in the anode. The coupled governing equations of species, charge and energy along with the constitutive equations in different layers of the cell are solved using finite volume method. The model can predict all forms of overpotentials and the predicted concentration overpotential is validated with measured data available in literature. It is found that in an anode-supported SOFC, the cathode overpotential is still the largest cell potential loss mechanism, followed by the anode overpotential at low current densities; however, the anode overpotential becomes dominant at high current densities. The cathode and electrolyte overpotentials are not negligible even though their thicknesses are negligible relative to the anode thickness. Even at low fuel utilizations, the anode concentration overpotential becomes significant when chemical reactions (reforming and water–gas shift) in the anode are not considered. A parametric study has also been carried out to examine the effect of various key operating and design parameters on the performance of an anode-supported planar SOFCs.     

Comparative performance analysis of a direct ammonia-fuelled anode supported flat tubular solid oxide fuel cell: A 3D numerical study

Solid oxide fuel cells that are designed in different geometrical structures (planar, tubular, flat-tubular, etc.) are dirt-free, quiet, and efficient cells that run using different fuels including contagions fuels. In this work, the performance of a 3D model of direct ammonia feed anode supported flat-tubular solid oxide fuel cell having six fuel supply channels was developed, investigated, and elucidated numerically in comparison with hydrogen fuels at different operating conditions using COMOSOL Multiphysics. The finding of this study is revealed that the performance of the developed model that is running with direct ammonia is better than hydrogen feed one using the same geometrical dimensions and operating parameters. It is also confirmed that direct ammonia feed anode supported flat-tubular solid oxide fuel cell has outstanding performance over the corresponding anode supported tubular solid oxide fuel cell using the same active cell surface area, gas channel length, and operating conditions. Parametric sweep analyses have been also performed on selected operating parameters and the outcomes revealed that the working temperature and the amount of reactant gases have a powerful impact on cell performance. Thus, ammonia is a green auspicious, and profitable candidate to use as a carbon-neutral fuel for anode supported flat-tubular solid oxide fuel cells in the near future.     

The durability of polyol-synthesized PtRu/C for direct methanol fuel cells

The durability of polyol-synthesized PtRu/C as anode electrocatalyst for direct methanol fuel cells (DMFCs) has been studied by conducting a 2020-h life-test of a single cell discharging at a constant current density of 100 mA cm⁻². Critical fuel cell performance parameters including anode activity, cathode activity and internal resistance are, for the first time, systematically examined at the life-test time of 556, 1093, 1630 and 2020 h. High-resolution transmission electron microscopy and X-ray diffraction (XRD) have also been performed and show that PtRu nanoparticles have agglomerated with the mean particle size increasing from 1.82 to 2.78 nm after the 2020-h life-test. Anode polarization and electrochemical impedance spectroscopy (EIS) show that there exists a stable discharging period where the anode polarization potential is less than 0.363 V versus dynamic hydrogen electrode (DHE). When the anode polarization potential exceeds 0.363 V versus DHE, the performance of the anode degrades dramatically due to the leaching of the unalloyed Ru as indicated by energy dispersive X-ray spectroscopy (EDS) and XRD. This finding provides clues in developing strategies to operate fuel cells achieving maximum lifetime without noticeable performance lose.     

新型平板式固体氧化物燃料电池的开发和性能分析

利用商业数值分析软件和试验获得的电池各部件材料性能数据,改进了用于分析固体氧化物燃料电池(SOFC)单电池内部复杂物理过程的软件包.应用该软件包,得到了设计的新型高效平板式SOFC单电池内部各气体组分浓度、温度、电势、电流及电流密度等参数的分布规律.分析结果表明:在高燃料利用率情况下,阳极内组分扩散引起的浓度极化损失是影响电池性能的重要因素之一.该新型结构电池可有效改善电池的密封性,但其电解质需要较高的最大离子传导率.     

质子交换膜燃料电池建模及水热传输特性分析

针对质子交换膜燃料电池(PEMFC)水管理开展了研究,建立了一维非等温两相流解析模型,研究了不同电流密度、微孔层接触角和不同加湿方案对电池内部水分布和温度分布的影响,提出了更好的进气加湿方案。结果表明:电流密度增大会导致阳极拖干、阴极水淹加剧,导致电池各部分温度上升。因各层材料亲水性不同,在交界面处能观察到液态水阶跃现象。增大微孔层接触角促进阴极液态水反扩散到阳极,一定程度上缓解阳极变干,但过大的接触角可能导致阴极水淹加剧。通过采取"阳极充分加湿、阴极低加湿"的进气加湿方案可以有效提高电池性能,并且能在一定程度改善电池内部受热,提高电池使用寿命。     

Study of the cell reversal process of large area proton exchange membrane fuel cells under fuel starvation

In this research, the fuel starvation phenomena in a single proton exchange membrane fuel cell (PEMFC) are investigated experimentally. The response characteristics of a single cell under the different degrees of fuel starvation are explored. The key parameters (cell voltage, current distribution, cathode and anode potentials, and local interfacial potentials between anode and membrane, etc.) are measured in situ with a specially constructed segmented fuel cell. Experimental results show that during the cell reversal process due to the fuel starvation, the current distribution is extremely uneven, the local high interfacial potential is suffered near the anode outlet, hydrogen and water are oxidized simultaneously in the different regions at the anode, and the carbon corrosion is proved to occur at the anode by analyzing the anode exhaust gas. When the fuel starvation becomes severer, the water electrolysis current gets larger, the local interfacial potential turns higher, and the carbon corrosion near the anode outlet gets more significant. The local interfacial potential near the anode outlet increases from ca. 1.8 to 2.6 V when the hydrogen stoichiometry decreases from 0.91 to 0.55. The producing rate of the carbon dioxide also increases from 18 to 20 ml min⁻¹.     

Insight into graphite oxidation in a NiO-based hybrid direct carbon fuel cell

A direct carbon fuel cell is an electricity generation device using solid carbon as a fuel directly with no reforming process. In this study, three-carbon fuels, graphitic carbon (GC), carbon black (CB), and biomass carbon (BC) are tested as the fuel to investigate the influence of carbon fuel properties on the cell performance in HDCFC with a traditional nickel oxide as the anode. Either an electrolyte-supported cell with a thin nickel oxide anode or an anode-supported cell with a thick nickel oxide anode is used to evaluate the electrochemical reactivity of carbon samples. These three-carbon fuels are characterised on the crystal structure, particle size, composition, and surface property. It is found that GC shows excellent cell performance on thin nickel oxide anode. However, it displays relatively slow electrochemical reactivity on the thick anode due to its great extent of carbon oxidation. BC shows good initial cell performance but fast degradation of the cell performance, as much more hydrogen is released at the beginning of the cell test. The anode reactions of HDCFCs are explored by the in-situ gas analysis in open circuits and under current load conditions. It is observed that GC produces the highest amount of CO among these three fuels, suggesting that carbon oxidation is the dominant electrochemical process in HDCFCs after a certain time when most of the hydrogen is released from the pyrolysis process.     

Corrosion of anode current collectors in molten carbonate fuel cells

Corrosion of metallic parts is one of the life-time limiting factors in the molten carbonate fuel cell. In the reducing environment at the anode side of the cell, the corrosion agent is water. As anode current collector, a widely used material is nickel clad on stainless steel since nickel is stable in anode environment, but a cheaper material is desired to reduce the cost of the fuel cell stack. When using the material as current collector one important factor is a low resistance of the oxide layer formed between the electrode and the current collector in order not to decrease the cell efficiency. In this study, some candidates for anode current collectors have been tested in single cell molten carbonate fuel cells and the resistance of the oxide layer has been measured. Afterwards, the current collector was analysed in scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). The results show that the resistances of the formed oxide layers give a small potential drop compared to that of the cathode current collector.     

Identifying in operando changes in membrane hydration in polymer electrolyte membrane fuel cells using synchrotron X-ray radiography

The cost of the polymer electrolyte membrane (PEM) fuel cell must undergo significant reductions before the widespread adoption of PEM fuel cell powered automotive drivetrains can be achieved. Eliminating the need for active anode humidification is one strategy for reducing the cost and system size of the PEM fuel cell. In this study, we investigated the impact of anode gas inlet relative humidity (RH) on membrane hydration and the associated electrochemical performance of the PEM fuel cell. The anode gas inlet RH was varied to study the impact on fuel cell potential, during which simultaneous in operando visualizations were performed using synchrotron X-ray radiography, and electrochemical impedance spectroscopy was used to gain an understanding of the membrane hydration and water dynamics. The thickness of a Nafion^® N115 membrane expanded by up to 26 μm (20% of nominal thickness) compared to the manufacturer specification, as a result of changes in membrane hydration. Through this work, we present the utility of synchrotron X-ray radiography for tracking changes in membrane hydration of an operating PEM fuel cell.     

Improving dynamic performance of proton-exchange membrane fuel cell system using time delay control

Transient behaviour is a key parameter for the vehicular application of proton-exchange membrane (PEM) fuel cell. The goal of this presentation is to construct better control technology to increase the dynamic performance of a PEM fuel cell. The PEM fuel cell model comprises a compressor, an injection pump, a humidifier, a cooler, inlet and outlet manifolds, and a membrane-electrode assembly. The model includes the dynamic states of current, voltage, relative humidity, stoichiometry of air and hydrogen, cathode and anode pressures, cathode and anode mass flow rates, and power. Anode recirculation is also included with the injection pump, as well as anode purging, for preventing anode flooding. A steady-state, isothermal analytical fuel cell model is constructed to analyze the mass transfer and water transportation in the membrane. In order to prevent the starvation of air and flooding in a PEM fuel cell, time delay control is suggested to regulate the optimum stoichiometry of oxygen and hydrogen, even when there are dynamical fluctuations of the required PEM fuel cell power. To prove the dynamical performance improvement of the present method, feed-forward control and Linear Quadratic Gaussian (LQG) control with a state estimator are compared. Matlab/Simulink simulation is performed to validate the proposed methodology to increase the dynamic performance of a PEM fuel cell system.