Study of a Single‐Chamber Solid Oxide Fuel Cell Microstack with V‐Shaped Congener‐Electrode‐Facing Configuration

Single‐chamber solid oxide fuel cell (SC‐SOFC) microstacks with V‐Shaped congener‐electrode‐facing configuration were fabricated and operated successfully in a box‐like stainless steel chamber. Two gas channels with small gas inlets were used to transport the fuel and oxygen to the anodes and cathodes, respectively. The temperature of an anode‐facing‐anode two‐cell stack was higher than that of a cathode‐facing‐cathode two‐cell stack during the test procedure. For a three‐cell stack, the cell in the middle region presented the highest power output. The open circuit voltage (OCV) and maximum power output of the three‐cell stack in a gas mixture of 100 sccm N₂, 120 sccm CH₄, and 80 sccm O₂ were 3.0 V and 413 mW, respectively.     

Design of a reference electrode for high-temperature PEM fuel cells

In this work, we present the design of an external reference electrode for high-temperature PEM fuel cells. The connection between the reference electrode with one of the fuel cell electrodes is realized by an ionic connector. Using the same material for the ionic connection as for the fuel cell membrane gives us the advantage to reach temperatures above 100 °C without destroying the reference electrode. This configuration allows for the separation of the anode and cathode overpotential in a working fuel cell system. In addition to the electrode overpotentials in normal hydrogen/air operation, the influence of CO and CO + H₂O in the anode feed on the fuel cell potentials was investigated. When CO poisons the anode catalyst, not only the anode potential increased, but also the cathode overpotential, due to fewer protons reaching the cathode. By the use of synthetic reformate containing hydrogen, carbon monoxide and water on the anode, fuel cell voltage oscillations were observed at high constant current densities. The reference electrode measurements showed that the fuel cell oscillations were only related to reactions on the anode side influencing the anode overpotential. The cathode potential, in contrast, was only negligibly affected by the oscillations under the applied conditions.     

Evaluation of a Non‐sealed Solid Oxide Fuel Cell Stack with Cells Embedded in Plane Configuration

A non‐sealed solid oxide fuel cell stack with cells embedded in plane configuration was fabricated and operated successfully in a box‐like stainless‐steel chamber. For a two‐cell stack, it demonstrated an open circuit voltage (OCV) of 2.13 V and a maximum power output of 569 mW at the flow rate of 67 sccm CH₄ and 33 sccm O₂. A fuel utilization of 4.16% was obtained. The cell performance was dominated by two different mechanisms, the polarization of the cathode at low current and the concentration polarization of the anode at high current. Finally, a scaled‐up stack with six cells in series generated an OCV of 6.4 V and a maximum power output of 8.18 W.     

Nanostructured palladium-silver coated nickel foam cathode for magnesium-hydrogen peroxide fuel cells

A novel multiscale Pd-Ag catalyzed porous cathode for the magnesium-hydrogen peroxide fuel cell was prepared by electrodeposition of Pd onto Ag coated nickel foam surface from an aqueous solution of palladium chloride. The structure, morphology and composition of the electrodeposited catalyst layer were characterized using SEM, EDS and XPS analysis. Magnesium-hydrogen peroxide fuel cell tests with the Pd-Ag deposited cathode were carried out and compared with the Ag-deposited electrode. The effects of temperature, H₂O₂ flow rate and H₂O₂ concentration on cell performance were investigated, and the electrode stability test was carried out. The Pd-Ag deposited electrode showed higher catalytic activity for the reduction of hydrogen peroxide than that of the Ag-deposited Ni foam cathode, and gave much improved fuel cell performance. The magnesium-hydrogen peroxide fuel cell with nanostructured Pd-Ag coated nickel foam cathode presented a maximum power density of 140 mW cm⁻², but the Mg-H₂O₂ fuel cell with Ag coated Ni foam cathode gave only 110 mW cm⁻² under the same operation condition.     

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.     

An enzyme-based microfluidic biofuel cell using vitamin K3-mediated glucose oxidation

Viamin K₃-modified poly-l-lysine (PLL-VK₃) was synthesized and used as the electron transfer mediator during catalytic oxidation of NADH by diaphorase (Dp) at the anode of biofuel cell. PLL-VK₃ and Dp were co-immobilized on an electrode and then coated with NAD⁺-dependent glucose dehydrogenase (GDH). The resulting enzymatic bilayer (abbreviated PLL-VK₃/Dp/GDH) catalyzed glucose oxidation. Addition of carbon black (Ketjenblack, KB) into the bilayer enlarged the effective surface area of the electrode and consequentially increased the catalytic activity. An oxidation current of ca. 2 mA cm⁻² was observed when the electrochemical cell contained a stirred 30 mM glucose, 1.0 mM NAD⁺, pH 7.0 phosphate-buffered electrolyte solution. The performance of glucose/O₂ biofuel cells, constructed as fluidic chips with controllable fuel flow and containing a KB/PLL-VK₃/Dp/GDH-coated anode and an Ag/AgCl or a polydimethylsiloxane-coated Pt cathode, were evaluated. The open circuit voltage of the cell with the PDMS-coated Pt cathode was 0.55 V and its maximum power density was 32 μW cm⁻² at 0.29 V when a pH 7.0-buffered fuel containing 5.0 mM glucose and 1.0 mM NAD⁺ was introduced into the cell at a flow rate of 1.0 mL min⁻¹. The cell's output increased as the flow rate increased. During 18 h of continuous operation of the cell with a load of 100 kΩ, the output current density declined by ca. 50%, probably due to swelling of the enzyme bilayer.     

Dynamic Behavior of a PEM Fuel Cell During Electrochemical CO Oxidation on a PtRu Anode

The dynamic behaviour of a single PEM fuel cell (PEMFC) with a PtRu/C anode catalyst using CO containing H₂ as anode feed was investigated at ambient temperature. The autonomous oscillations of the cell potential were observed during the galvanostatic operation with hydrogen anode feed containing CO up to 1000 ppm. The oscillations were ascribed to the coupling of the adsorption of CO (the poisoning step) and the subsequent electrochemical oxidation of CO (the regeneration step) on the anode catalyst. The oscillations were dependent on the CO concentration of the feed gas and the applied current density. Furthermore, it was found that with CO containing feed gas, the time average power output was remarkably higher under potential oscillatory conditions in the galvanostatic mode than during potentiostatic operation. Accompanying these self-sustained potential oscillations, oscillation patterns of the anode outlet CO concentration were also detected at low current density (<100 mA/cm²). The online measurements of the anode outlet CO concentrations revealed that CO in the anode CO/H₂ feed was partially electrochemically removed during galvanostatic operation. More than 90% CO conversion was obtained at the current densities above 125 mA/cm² with low feed flow rates (100–200 mL/min).     

Self Humidifying Hybrid Anion–Cation Membrane Fuel Cell Operated Under Dry Conditions

Hybrid fuel cells composed of a low‐pH proton conductive membrane in contact with a high‐pH anion conductive membrane were investigated. The effect of relative humidity (RH), ionomer content in the anion‐conductive electrode and the inlet gas flow rates were evaluated. The formation of water at the junction of the anion conductive member and proton conductive membrane is especially interesting because it can self‐humidify the fuel cell when dry gases are used. In situ alternative current (AC) impedance spectroscopy was used as a diagnostic tool to understand the performance limitations under different test conditions. The cell output increased at low RH compared to a traditional proton exchange membrane fuel cell. The cell current under dry conditions was limited by the availability of oxygen in the catalyst sites due to flooding in the electrode layer. The ionomer fraction of the high‐pH cathode plays a significant role in the cell performance. At high gas feed rates, water removal from the electrode layers increased and mitigated the effects of flooding. The hybrid cells were operated at steady‐state operation at 0.58 V and 200 mA cm^–2 using dry H₂/O₂ feeds at 80 °C.     

Fabrication and properties of under-gated triode with CNT emitter for flat lamp

We investigated under-gate type carbon nanotube field emitter arrays (FEAs) for back light unit (BLU) in liquid crystal display (LCD). Gate oxide was formed by wet etching of ITO coated glass substrate instead of depositing SiO₂ on the glass substrate. Wet etching is easier and simpler than depositing and etching thick gate oxide to isolate the gate metal from cathode electrode in triode. To optimize the triode, we simulated the electric field distribution and electron trajectory in triode structures by the SIMION simulator. CNT emitters were formed using screen printing of photosensitive CNT paste. Field-emission characteristics of triode structure were measured. The maximum current density of 92.5 μA/cm² was when the gate and anode voltage was 95 and 2500 V, respectively, at the anode–cathode spacing of 1500 μm.     

PEM fuel cell reaction kinetics in the temperature range of 23-120 °C

The performance of a Nafion 112 based proton exchange membrane (PEM) fuel cell was tested at a temperature range from 23 °C to 120 °C. The fuel cell polarization curves were divided into two different ranges based on current density, namely, <0.4 A/cm² and >0.4 A/cm², respectively. These two ranges were treated separately with respect to electrode kinetics and mass transfer. In the high current density range, a linear increase in membrane electrode assembly (MEA) power density with increasing temperature was observed, indicating the advantages of high temperature operation.Simulation based on electrode reaction kinetic theory, experimental polarization curves, and measured cathodic apparent exchange current densities all gave temperature dependent apparent exchange current densities. Both the calculated partial pressures of O₂ and H₂ gas in the feed streams and the measured electrochemical Pt surface areas (EPSAs) decrease with increasing temperature. They were also used to obtain the intrinsic exchange current densities. A monotonic increase of the intrinsic exchange current densities with increasing temperature in the range of 23-120 °C was observed, suggesting that increasing the temperature does promote intrinsic kinetics of fuel cell reactions.There are two sets of cathode apparent exchange current densities obtained, one set is for the low current density range, and the other is for the high current density range. The different values of cathode current densities in the two current density ranges can be attributed to the different states of the cathode Pt catalyst surface. In the low current density range, the cathode catalyst surface is a Pt/PtO, and in the high current density range, the catalyst surface becomes pure Pt.     

Performance of yttria-stabilized zirconia fuel cell using H2–CO2 gas system and CO–O2 gas system

This paper reports the performance of an yttria-stabilized zirconia fuel cell (YSZ) using five kinds of gas systems. The final target of this research is to establish the combined fuel cell systems which can produce a H₂ fuel and circulate CO₂ gas in the production process of electric power. A large electric power was measured in the H₂–O₂ gas system and the CO–O₂ gas system at 1073 K. The formation process of O²⁻ ions in the endothermic cathodic reaction (1/2O₂+2e⁻→O²⁻) controlled the cell performance in both the gas systems. The electric power of the H₂–CO₂ gas system, which allowed to change CO₂ gas into a CO fuel (H₂+CO₂→H₂O+CO) in the cathode, was 1/31–1/11 of the maximum electric power for the H₂–O₂ gas system. This result is related to the larger endothermic energy for the formation of O²⁻ ions from CO₂ molecules at the cathode (CO₂+2e⁻→CO+O²⁻) than from O₂ molecules. The CO–H₂O gas system and the H₂–H₂O gas system was expected to produce a H₂ fuel in the cathode (CO+H₂O→H₂+CO₂, H₂+H₂O→H₂+H₂O). Although relatively high OCV values (open circuit voltage) were measured in these gas systems, no electric power was measured. At this moment, it was difficult to apply H₂O vapor as an oxidant to the cathodic reaction in a YSZ fuel cell.     

Perovskite SrFe1-xTixO3-δ (x < = 0.1) cathode for low temperature solid oxide fuel cell

Stable and compatible cathode materials are a key factor for realizing the low-temperature (LT, ≤600?°C) operation and practical implementations of solid oxide fuel cells (SOFCs). In this study, perovskite oxides SrFe_1-xTi_xO_3-δ (x?< = 0.1), with various ratios of Ti doping, are prepared by a sol-gel method for cathode material for LT-SOFCs. The structure, morphology and thermo-gravimetric characteristics of the resultant SFT powders are investigated. It is found that the Ti is successfully doped into SrFeO_3-δ to form a single phase cubic perovskite structure and crystal structure of SFT shows better stability than SrFeO_3-δ. The dc electrical conductivity and electrochemical properties of SFT are measured and analysed by four-probe and electrochemical impedance spectra (EIS) measurements, respectively. The obtained SFT exhibits a very low polarization resistance (R_p), .01 Ωcm² at 600?C. The SFT powders using as cathode in fuel cell devices, exhibit maximum power density of 551?mW?cm^?2 with open circuit voltage (OCV) of 1.15?V at 600?C. The good performance of the SFT cathode indicates a high rate of oxygen diffusion through the material at cathode. By enabling operation at low temperatures, SFT cathodes may result in a practical implementation of SOFCs.     

Fabrication and operation of flow‐through tubular SOFCs for electric power and synthesis gas cogeneration from methane

Flow‐through type tubular solid oxide fuel cells were successfully fabricated and operated with a single‐chamber configuration for realizing the simultaneous generation of electric power and synthesis gas from methane by integrating a downstream catalyst into the fuel cell reactor. A new operation mode, which completely eliminated the gas diffusion between cathode side and anode side, is proposed. The cell showed high open‐circuit voltages of 1.02–1.08 V at the furnace temperature range of 650–800°C when operating on CH₄‐O₂ gas mixture at a molar ratio of 2:1. A peak power density of approximately 300 mW cm^?2 and a maximum power output of 1.5 W were achieved for a single cell with an effective cathode geometric surface area of 5.4 cm² at the furnace temperature of 750°C. The in‐situ initialization of the cell using CH₄‐O₂ gas mixture was also realized via applying an effective catalyst into the tubular cell. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1036–1044, 2014     

Realising a reference electrode in a polymer electrolyte fuel cell by laser ablation

This work presents a new concept for realising a reference electrode configuration in a PEM fuel cell by means of laser ablation. The laser beam is used to evaporate a small part of the electrode of a catalyst-coated membrane (CCM) to isolate the reference electrode from the active catalyst layer. This method enables the simultaneous ablation of the electrodes on both sides of the CCM because the membrane is transparent for the laser beam. Therefore, a smooth electrode edge without electrode misalignment can be realised. A test fuel cell was constructed which together with the ablated CCM enables the separation of the total cell losses during operation into the cathode, anode and membrane overpotentials in PEFC as well as in DMFC mode. The methanol tolerance of a selenium-modified ruthenium-based catalyst (RuSe _x ) was investigated under real fuel cell conditions by measuring polarisation curves, electrochemical impedance spectroscopy (EIS) and current interrupt measurements (CI).     

Performance of a direct methanol fuel cell

The performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) is reported. The fuel cell utilizes a vaporized aqueous methanol fuel at a porous Pt–Ru–carbon catalyst anode. The effect of oxygen pressure, methanol/water vapour temperature and methanol concentration on the cell voltage and power output is described. A problem with the operation of the fuel cell with Nafion® proton conducting membranes is that of methanol crossover from the anode to the cathode through the polymer membrane. This causes a mixed potential at the cathode, can result in cathode flooding and represents a loss in fuel efficiency. To evaluate cell performance mathematical models are developed to predict the cell voltage, current density response of the fuel cell.     

Improved electrochemical CO removal via potential oscillations in serially connected PEM fuel cells with PtRu anodes

The polarization performance of two PEM fuel cells (with anode PtRu/C catalyst) connected either in parallel or serial, was compared to the performance of a single PEM fuel cell in galvanostatic operation using CO-free H₂ or 200 ppm CO-containing H₂ stream as anode feed at ambient temperature. Spontaneous potential oscillations were observed experimentally for the coupled configuration with two cells connected in serial or parallel using CO-containing H₂ feed at various current densities applied. The potential oscillations are ascribed by the dynamic CO adsorption and subsequent electrochemical CO oxidation on the anode. The measured anode outlet CO concentration was found to decrease with the order: single cell > parallel cells > serial cells at various current densities and anodic flow rates. The low anode outlet CO concentration (<10 ppm) at high current densities applied showed that CO in the anode feed was removed efficiently by the electrochemical CO oxidation occurring on the PtRu anode. The anode outlet CO concentration decreased as follows: a single cell > the parallel cells > the serial cells at broad range of current densities and anodic flow rates. The highest CO conversion and the highest average power output at equal hydrogen recovery degree were obtained with serially coupled fuel cells.     

Electrochemical performance of low-temperature solid oxide fuel cells running on syngas from pyrolytic urban sludge

Low temperature solid oxide fuel cells (SOFCs) that efficiently utilize widely available hydrocarbon resources are highly desirable for cost reduction and durability purposes. In this work, SOFCs consisting of highly ionic conductive ceria-carbonate composite electrolytes and lithiated transition metal oxide symmetric electrodes are assembled and their electrochemical performances at reduced temperature (≤650 °C) are investigated using syngas fuel (44.65% H₂, 10.19% CH_4, 2.01% CO and the balanced CO₂) derived from pyrolytic urban sludge. The cell gives a peak power output of 127 mW cm^?2 at 600 °C and shows a relatively stable operation for 11 hours under constant voltage operational conditions. Though the composite electrode presents a moderately high polarization resistance toward CH₄ and CO oxidation and the electrochemical performance is highly correlated with the microstructure of ceria-carbonate electrolyte, it is interesting to see that a higher concentration of methane is obtained after the fuel cell reaction, which may suggest an alternative approach to realize the power and chemical co-generation within such a SOFC reactor. Finally, the symmetric electrode shows high resistance toward carbon deposition, possibly due to its high alkaline nature.     

Performance improvement of a micro borohydride fuel cell operating at ambient conditions

In this study, aqueous borohydride solutions were employed to fuel a micro cell. Electrochemical performance of the micro borohydride fuel cell was tested at ambient conditions without any auxiliary facilities. Electrochemical impedance spectroscopy (EIS) analyses were performed to characterize the cell performance. Both anion and cation exchange membranes were tried to separate the fuel from the cathode. Membrane properties were found to be a decisive factor for cell performance. A maximum power density of 40 mW/cm² at room temperature was achieved when the Nafion NRE211 membrane was used. Hydrogen evolution at the anode side resulted from the competitive hydrolysis reaction influenced cell performance by obstructing transfer of the electrolyte. The cell also demonstrated promising performance even when an Ag cathode was used.     

液相进样直接甲醇燃料电池性能研究

报道了用研制的Pt-Ru/C催化剂, 采用特殊工艺制备了膜电极, 并组装了直接甲醇质子交换膜单电池系统。考察了电极扩散层制备方法、催化剂层中催化剂、Teflon-C以及Nafion液的用量等电极制备工艺条件以及空气作为氧化剂对单电池性能的影响。结果表明：采用刷涂法制备电极扩散层比喷涂法好,催化剂层中催化剂的优化含量为0.6mg·cm-2,Teflon-C、Nafion液的最佳用量分别为0.3 mg·cm-2、0.5 mg·cm-2。当工作温度为80℃时,输出电压为0.3V,氧气作为阴极气体的输出电流密度为36mA·cm-2;而空气作为阴极气体的输出电流密度为22.5mA·cm-2。膜电极有效面积为9cm2的的液相进样直接甲醇/氧气燃料电池三电池电堆的最大功率为0.285W,此时输出电压为0.7V,输出电流为0.407A;而液相进样直接甲醇/空气三电池电堆的输出电压为0.635V,输出电流为0.252A时,最大功率为0.160W。     

质子交换膜燃料电池电源系统停机特性及控制策略

质子交换膜燃料电池(PEMFC)电源系统在停机后,燃料电池开路高电压被认为是造成电池性能下降和寿命缩短的重要因素。这主要是因为PEMFC电源系统停机后,燃料电池处于开路状态,阳极侧残留的氢气和阴极侧的空气发生电化学反应,电池电压为开路高电压且维持在开路电压的时间比较长,这容易引起催化剂碳载体发生氧化,使分布在载体上的铂(Pt)颗粒脱落,造成燃料电池性能衰减以及寿命缩短。以最大程度缩短停机后开路高电压的时间和加快阳极侧残留氢气的消耗速度为目标,提出了一种PEMFC电源系统的停机策略,通过实验分别研究了直接停机和停机策略停机对PEMFC输出特性的影响。以该停机控制策略为基础,通过实验验证了该停机策略的有效性,为提出保护性的PEMFC电源系统停机控制策略提供了参考性指导。