La—Ni system porous anode in an alkaline fuel cell

La—Ni system alloys in fine powder form were used to make the hydrogen electrode for an alkaline fuel cell. LaNi₅ electrodes were found to have the highest electrode performance among the La—Ni system electrodes. Using LaNi₅ powder of mean particle size 3.4 μm for the electrode, the limiting current density was 180 mA/cm². However mixing the same size powder (mean particle size 3.4 μm) with powder of mean particle size 40.5 μm in a ratio of 4:1, the limiting current density of the new electrode was 250 mA/cm². The electrode was found to have both relatively fine pores in the range 0.01–0.2 μm and relatively large pores in the ranges 0.5–1 μm and 4–5 μm. Thus, it was found that not only relatively fine pores but relatively large pores had an important effect upon the LaNi₅ electrode characteristics.     

A mathematical model for platinum/ PTFE/porous nickel fuel cell oxygen diffusion electrodes

This paper describes the cylindrical agglomerate model for oxygen/alkali gas diffusion electrodes fabricated from platinum, PTFE and porous nickel. Corrections for the increase in hydroxyl ion concentration with increasing current density have been made to the original model of Brown and Horve. Changes in performance by variation of the bulk structural parameters, e.g. agglomerate radius, porosity and tortuosity, have been studied. Theoretical modes of electrode decay have been explored.List of symbols Transfer coefficient - C Concentration of O₂ in elec trolyte mol cm^–3 - C _i Concentration of O₂ atr = R mol cm^–3 - C _o Concentration of O₂ in electrolyte atr = mol cm^–3 - Diffusion coefficient of O₂ in KOH cm² sec^–1 - Film thickness cm - E Overpotential of the electrode V - F Faraday's constant - i Electrode current density A cm^–2 - i _a Current per agglomerate A - I ₁(Z) First order Bessel function - I ₀(Z) Zero order Bessel function - j Local current density A cm^–2 - j _o Exchange current density A cm^–2 - L Agglomerate length (catalyst thickness) cm - N Number of electrons in rate determining step - N _a Number of agglomerates per cm² of electrode - Potential drop along ag glomerate V - _L Potential drop at L_a V - r Radial direction - R Radius of agglomerate cm - R _o Gas constant - Density of platinum g cm^–3 - S _g Surface area per gram cm² g^–1 - Solubility coefficient of O₂ mol cm^–3 - _m Electrolyte conductivity (ohm cm)^–1 - T Absolute temperature °K - _a Axial tortuosity - Porosity of platinum in the agglomerate - _r Aadial tortuosity of the agglomerate - W Catalyst loading g cm^–2 - x Axial direction     

Scanning electron microscopic studies of porous carbon electrodes used in alkaline fuel cells

Multilayer, polytetrafluoroethylene (PTFE)-bonded gas diffusion-type electrodes were prepared by the rolling method. Changing the electrode structure and manufacturing method improved alkaline fuel cell performance. Activated carbon or carbon black was used as the support material, with platinum as a catalyst and nickel screen as the backing material. Double-layer electrodes possessed both active and diffusion layers on the backing layer. However, the single-layer electrodes had only the active layer on the backing layer. The electrodes were prepared by using different PTFE contents and platinum loadings. In this study the surface photographs of the electrodes were taken with a scanning electron microscope. Elemental analyses of the surface elements were performed by energy dispersive X-ray spectroscopy (EDXS). Electrodes having activated carbon on their surfaces were observed to possess a nonuniform and porous structure. These electrodes showed better performance than electrodes having carbon black, which presented a uniform and nonporous structure.     

Influence of mass transport on the performance of carbon gas-diffusion air electrodes in alkaline solution

The effect of mass transport on the electrochemical behaviour of carbon gas-diffusion air electrodes in alkaline solution was investigated on the basis of ΔE(i) curves. These curves are obtained by subtraction of potential values for an electrode operating with airE _air(i) from potential values for the same electrode operating with pure oxygenE _oxygen(i) at the same current densityi. Three different regions on these curves connected with different modes of mass transport are recognized. A model of the gas-diffusion air electrode which takes into account the diffusion of the gas, diffusion of the dissolved gas, electrochemical reaction and IR drop is used to explain the experimental results.     

Ag/PAMAM树形分子纳米复合材料对PTFE膜性能的影响

以第4.0代端氨基聚酰胺-胺型树形分子(G4.0-NH2PAMAM)为模板制备Ag/PAMAM纳米复合材料(Ag·DENPs), 利用了Ag·DENPs与聚四氟乙烯(PTFE)膜表面的氢键作用,通过超声沉积的方法制备出了PTFE-Ag/PAMAM复合膜.通过研究沉积时间对Ag·DENPs在PTFE膜表面沉积量的影响,得到饱和沉积时间是60min,沉积量约为2.32mg.通过UV-vis光谱和SEM对其化学组成和微观形貌进行了表征.复合膜的水接触角为105.3°,较纯PTFE膜降低了23.6°,显著改善PTFE膜表面亲水性.复合膜对水和牛血清白蛋白的通量比纯PTFE膜低,但傅立叶变换衰减全反射红外光谱(FRR)为88.2%,比纯PTFE膜的35.4%高出了52.8%,且对大肠杆菌及金黄色葡萄球菌具有抑菌作用.表明Ag·DENPs的引入可以改善PTFE的抗污染性及抑菌性.     

Effect of a GDL based on carbon paper or carbon cloth on PEM fuel cell performance

A commercially available GDL based on carbon paper or carbon cloth as a macroporous substrate was characterized by various physical and electrochemical measurements: mercury porosimetry, surface morphology analysis, contact angle measurement, water permeation measurement, polarization techniques, and ac-impedance spectroscopy. SGL 10BB based on carbon paper demonstrated dual pore size distribution and high water flow resistance owing to less permeable macroporous substrate, and more hydrophobic and compact microporous layer, as compared to ELAT-LT-1400 W based on carbon cloth. The membrane-electrode-assembly fabricated using SGL 10BB showed an improved fuel cell performance when air was used as an oxidant. The ac-impedance response indicated that a microporous layer which has high volume of micropores and more hydrophobic property allows oxygen to readily diffuse towards the catalyst layer due to effective water removal from the catalyst layer to the gas flow channel.     

Role of Ag and Cu as an interfacial layer on the electrochemical performance of Ni/Ag/ Co3(PO4)2 and Ni/Cu/Co3(PO4)2 electrodes for hybrid energy storage devices

Hybrid energy storage devices unifying the effect of both batteries (high specific energy) and capacitors (high specific power) have emerged in recent years due to their admirable cyclic stability and charge storage capability. Considerable amount of research has been conducted to optimize the electrode materials capable of showing good electrochemical characteristics. Here, we report the influence of interfacial layer of Ag and Cu on the electrochemical performance of cobalt phosphate electrode. Sputtering of Ag and Cu has been amalgamated to improve the interfacial properties of the current collector. After initial structural and morphological study, detailed electrochemical characterizations have been employed for Ni/Ag/Co₃(PO₄)₂ and Ni/Cu/Co₃(PO₄)₂ have been investigated by utilizing various characterizations. Hybrid device was fabricated using the combination Ni/Ag/Co₃(PO₄)₂ since, Ag possess impressive electrochemical characteristics and electrical conductivity. The fabricated device has achieved the energy density of 65.8 Whkg^?1 and power density of 6012 Wkg^-1 along with the 85.6% retention after 1000 GCD cycles showing the device is stable enough. These results make the hybrid device a potential candidate for supercapattery applications.     

Oxidative conversion of CH4 on Ni and Ag electrode-catalysts in molten carbonate fuel cell reactor

A fuel cell system using molten carbonates of potassium and lithium as electrolyte was applied to the oxidative conversion of methane over Ni and Ag electrodes. A possibility of cogeneration of valuable chemicals, like C₂-hydrocarbons, and electricity in such a system was demonstrated. With CO ₃ ^2– ions (oxygen) transported electrochemically, the rate of formation of C₂-hydrocarbons and selectivity for them on the Ag electrode were found to be greater than those with oxygen premixed to the gase phase.     

High performance wire-shaped supercapacitive electrodes based onactivated carbon fibers core/manganese dioxide shell structures

Micro/nano hierarchical structures with uniformly patterned nanostructures shell and activated internal core are promising for boosting electrochemical performance. Here we report the fabrication of wire-shaped supercapacitive electrodes with manganese dioxide (MnO₂) nanostructures shell integrated onto activated carbon fiber (ACF) core. The ACF core is doped with nitrogen heteroatom and shows good conductivity and hydrophilicity, which endow fast ion and electron transport and high accessibility of electrolyte. The MnO₂ nanostructures shell integrated on the ACF core by electrodeposition method together provide significant pseudocapacitive contribution associated with fast faradaic reactions. The electrochemical performance of the fabricated electrodes was evaluated by cyclic voltammetry, galvanostatic charging/discharging and electrochemical impedance spectroscopy techniques. The integrated wire-shaped electrodes, which boost the synergetic effect of MnO₂ nanostructures and ACF, have excellent current collecting capabilities thus resulting high electrochemical performance (with the specific capacitance of 26.64 mF cm⁻¹ at the current density of 0.1 mA cm⁻¹ and 96% capacitance retention after 8000 charging/discharging cycles at the current density of 1 mA cm⁻¹).     

Influence of fabrication procedure on the electrochemical performance of Ag/AgCl reference electrodes

The influence of several parameters in the preparation procedure of thermal–electrolytic Ag/AgCl electrodes on the resulting electrode performance has been studied. In particular, we report the effect on electrode performance of subtle variations in the preparation of silver oxide paste used for electrode manufacture, in thermal annealing conditions employed and in the procedure for electrochemically converting a fraction of the electrode from silver to silver chloride. Scanning electron microscopy and electrochemical impedance spectroscopy have been used to study the characteristics of the electrodes produced. This work reveals a correlation between the electrochemical behaviour and surface physical characteristics – in particular electrode porosity. The outputs of this study have positive implications for improving the accuracy and comparability of primary pH measurement.     

PVA/OPD改性膜对微生物燃料电池性能的影响

为提高微生物燃料电池（MFC）的性能，以聚乙烯醇（PVA）为黏合剂，分别以磷钨酸（PWA）和邻苯二胺（OPD）为改性剂，采用溶液浸渍法制备了PVA/PWA和PVA/OPD改性膜并搭载于MFC系统，以SEM、电化学阻抗谱（EIS）、循环伏安法（CV）、吸水率表征了膜的性能，并考察膜改性对MFC产电量和化学需氧量（COD）去除率的影响。结果显示，PVA/PWA和PVA/OPD改性膜均能在一定程度上提升MFC性能，但PVA/OPD改性膜效果更佳。PVA/OPD改性膜的吸水率为14.49%，较常规Nafion 117膜（NF）提高了126.05%。采用PVA/OPD改性膜的MFC在测试周期内的产电量为101.75 J，较采用NF时提高了587.50%；对阿莫西林制药废水的COD去除率为66.2%，较采用NF时提高了48.4%。基于PVA/OPD的膜改性方法对提高MFC的产电性能和废水处理效果有显著作用。     

石墨烯/聚苯胺修饰阳极对微生物燃料电池性能的影响

纳米材料修饰阳极可显著提高微生物燃料电池（MFC）性能,本研究主要探索了石墨烯、聚苯胺和石墨烯/聚苯胺复合修饰电极对MFC产电性能的影响。使用电化学方法电镀石墨烯于碳布表面,进一步通过原位聚合法制备聚苯胺来修饰碳布电极。将修饰电极装载入双室型MFC中,测量其产电性能,并对电极进行表征,测量电化学性能。通过扫描电镜观察到, 碳布能够被修饰上石墨烯和聚苯胺,并且聚苯胺附着于碳纤维或石墨烯薄层表面,形成棒状的纳米结构。产电性能方面,装载石墨烯/聚苯胺修饰电极的MFC最大输出电压最高,达到了（291±22）mV,比装载空白碳布电极的对照组MFC提高了175%以上。石墨烯/聚苯胺电极组MFC的最大输出功率密度同样最高,达到了（653 ± 25）mW·m^-2,为空白碳布对照组的10.5倍。实验结果表明：石墨烯/聚苯胺复合修饰电极可有效利用石墨烯导电性好和聚苯胺生物相容性高的优点,显著提高MFC的产电性能。     

Simulation of influences of layer thicknesses in an alkaline fuel cell

A computational simulation was conducted by using a one-dimensional isothermal model for an alkaline fuel cell (AFC) single cell to investigate influences of the thicknesses of the separator, catalyst layer, and gas-diffusion layer in an AFC. The cell polarizations were predicted at various thicknesses and their influences were also analysed. Thickening the separator layer decreased the limiting current density and increased the slope of the ohmic polarization region. Investigation on the thickness of the anode catalyst layer showed that the optimum thickness varied between 0.04–0.15 mm according to the cell voltage. The thickness of the cathode catalyst layer significantly influenced the cell performance. Also, a limitation of thickness effect in the cathode catalyst layer was observed. This limitation was considered to be caused by the mass transfer resistance of the electrolyte.     

Effect of graphite felt and activated carbon fiber felt on performance of freshwater sediment microbial fuel cell

BACKGROUND: Sediment microbial fuel cells (SMFCs) could be used as power sources and one type of new technology for the removal of organic matters in sediments. Various types of materials have been used as electrodes. Nevertheless, there is still room to improve electrode materials and enhance their effect on the performance of SMFCs. In this work, performances of SMFCs with activated carbon fiber felt (ACFF) and with nitric acid‐treated ACFF were compared with graphite felt (GF) materials. RESULTS: The maximum power density of the SMFC with ACFF electrode was the highest (33.5 ± 1.5 mW m^?2). Nitric acid‐treated GF electrode slightly increased the maximum power density of SMFC, while the nitric acid treated‐ACFF resulted in significant decline in the maximum power density of SMFC. The maximum power density further increased to 74.5 ± 7.5 mW m^?2 in SMFC using GF cathode and ACFF anode. CONCLUSIONS: ACFF as anode can enhance the transport of electrons from the oxidation of organic matter in the sediment, while the output power was found to reduce in SMFC with ACFF cathode. Further efforts are needed to study the formation conditions of the biocathode and new electrode modification technology. Copyright © 2012 Society of Chemical Industry     

Investigation of oxygen reduction on activated carbon electrodes in alkaline solution

Oxygen reduction has been studied on gas diffusion electrodes made from various kinds of activated carbon materials. The potentiodynamic method was used to study the electrochemical behavior of the reduction reaction, while nitrogen gas adsorption and powder X-ray diffraction were used to determine the pore size distribution and the crystal structure of the carbon material, respectively. The relationship between the catalytic activity of activated carbon and the surface content of edge orientation was discussed. The specific catalytic activity of activated carbon is determined by the percentage of the edge orientation on the surface. The higher the content of the edge plane, the lower the oxygen reduction overpotential. The reduction overpotential is also related to the effective surface area, which determines the local current density.     

Effect of cerium oxide nanoparticles coating on the electrodes of benthic microbial fuel cell

Benthic microbial fuel cell is a power source for low-power devices. For enhancement of power, Cerium oxide (CeO₂) nanoparticles (NPs) were coated on anode and cathode electrodes and compared separately. CeO₂ NPs were synthesized by hydrothermal method and characterized by Dynamic light scattering. Polyvinylidene fluoride and graphite powder were used as a conductive matrix for binding CeO₂ NPs. Coated electrodes were characterized by physical and electrochemical analysis. Maximum power densities generated by CeO₂ coated cathode and anode were 60 and 43 mW/m³ respectively; whereas conductive matrix only produced 14 mW/m³. Results demonstrated that CeO₂ at cathode performed better than at anode. NPs show their effectiveness as an oxygen reduction reaction catalyst in the sea water.     

Effect of compression on the performance of a HT-PEM fuel cell

This paper shows by thorough electrochemical investigation that (1) the performances of high-temperature polymer electrolyte fuel cell membrane electrode assemblies of three suppliers are differently affected by compressive forces. (2) Membrane thickness reduction by compressive pressure takes place less than expected. (3) A contact pressure cycling experiment is a useful tool to distinguish the impact of compression on the contact resistances bipolar plate/gas diffusion layer (GDL) and GDL/catalytic layer. A detailed visual insight into the structural effects of compressive forces on membrane and gas diffusion electrode (GDE) is obtained by micro-computed X-ray tomography (μ-CT). μ-CT imaging confirms that membrane and GDEs undergo severe mechanical stress resulting in performance differences. Irreversible GDL deformation behavior and pinhole formation by GDL fiber penetration into the membrane could be observed.     

Effect of carbon paper substrate of the gas diffusion layer on the performance of proton exchange membrane fuel cell

Gas diffusion layers (GDLs) were fabricated using non-woven carbon paper substrates with various thicknesses developed by Hollingsworth & Vose Co. Highly consistent carbon slurry containing Pureblack carbon and vapor grown carbon fiber (3:1 ratio) with 25 wt.% Teflon was prepared by using a dispersion agent, Novec-7300 in isopropyl alcohol. Micro-porous layer was coated by using a fully automated Coatema coating tool with a uniform carbon loading of 2.6-3 mg cm⁻² using carbon slurry. The surface morphology, contact angle and pore size distribution of the GDLs were examined using SEM, Goniometer and Hg Porosimeter, respectively. Various cathode GDLs assembled into MEAs were evaluated in a single cell PEMFC under various operating relative humidity (RH) conditions using H₂/O₂ and H₂/air as reactants. The peak power density of the single cell using the optimum carbon paper substrate thickness was about 1400 and 700 mW cm⁻² with H₂/O₂ and H₂/air at 60% RH, respectively. It was found that the pore diameter as well as the corresponding pore volumes of the GDLs played a key role in exhibiting the optimum fuel cell performance.     

Study of the performance of secondary alkaline pasted zinc electrodes

Calcium zincate was prepared by a chemical coprecipitation method and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical performance of pasted zinc electrodes with bismuth and calcium additives was investigated by the charge–discharge method. The addition of metallic bismuth powder improves the discharge performance of zinc electrodes due to the formation of an electronic conduction matrix. The calcium-containing zinc electrodes showed higher discharge capacity, less shape change and longer cycle lifetime. Moreover, zinc electrodes using calcium zincate as active material show better electrochemical performance than those with the physical mixture of zinc oxide and calcium hydroxide.