Ultrasonic radiation to enable improvement of direct methanol fuel cell

To improve DMFC (direct methanol fuel cell) performance, a new method using ultrasonic radiation is proposed and a novel DMFC structure is designed and fabricated in the present paper. Three ultrasonic transducers (piezoelectric transducer, PZT) are integrated in the flow field plate to form the ultrasonic field in the liquid fuel. Ultrasonic frequency, acoustic power, and methanol concentration have been considered as variables in the experiments. With the help of ultrasonic radiation, the maximum output power and limiting current of cell can be independently increased by 30.73% and 40.54%, respectively. The best performance of DMFC is obtained at the condition of ultrasonic radiation (30 kHz and 4 W) fed with 2 M methanol solution, because both its limiting current and output power reach their maximum value simultaneously (222 mA and 33.6 mW, respectively) under this condition. These results conclude that ultrasonic can be an alternative choice for improving the cell performance, and can facilitate a guideline for the optimization of DMFC.     

Fabrication of highly selective PVA-g-GO/SPVA membranes via cross-linking method for direct methanol fuel cells

Organic/inorganic composite membranes were prepared using sulfonated poly(vinyl alcohol) (SPVA), mixed and cross-linked with different amounts of poly(vinyl alcohol)-grafted graphene oxide (PVA-g-GO). The introduction of PVA-g-GO to the membranes not only reduced the methanol permeability but also positively affected the mechanical properties: Increasing the PVA-g-GO content increased the blocking effect of GO. The PVA-g-GO/SPVA membranes were cross-linked with glutaraldehyde, resulting in the formation of cross-linking chains within the matrix, as well as between the matrix and the filler. Therefore, the microstructure of the PVA-g-GO/SPVA cross-linking membrane was different from that of the existing membranes. This structure also reduced the methanol permeability. The composite membranes exhibited proton conductivities ranging from 0.0141 to 0.0319 S/cm at 60 °C, and low methanol permeability ranging from 3.13?×?10^?7 to 1.53?×?10^?7 cm² s^?1 at 25 °C.     

NMR investigation of water and methanol mobility in nanocomposite fuel cell membranes

Water and methanol transport behavior, morphology, and solvent adsorption of filler-free Nafion membrane, Nafion–SiO₂, Nafion–TiO₂, and two Nafion–Zr(HPO₄)₂ composites were investigated using nuclear magnetic resonance methods, including spin-lattice relaxation and pulsed-field-gradient spin-echo diffusion conducted under both variable temperature and variable hydrostatic pressure conditions and scanning electron microscopy analysis. A comparison between water and methanol self-diffusion coefficients reveals that the water mobility is higher than the methanol mobility in all the membranes. Additionally, the inclusion of inorganic fillers improves both the solvent uptakes and the transport properties of the composite membranes relative to filler-free Nafion, with the exception of one of the Nafion–Zr(HPO₄)₂ composite. Nafion–Zr(HPO₄)₂ composites were prepared by two different procedures, in situ and ex situ. Although phosphorus-31 magic-angle spinning nuclear magnetic resonance spectra show the same structures of the particles in both kinds of membranes, the morphology, solvent absorption properties, and solvent mobilities are very different. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur Mer, Sept. 9–15, 2007.     

变压加载对直接甲醇燃料电池阳极性能的影响（英）

为评价直接甲醇燃料电池（DMFC）阳极的稳定性,利用扫描电化学显微镜和常规电化学技术,研究了变压加载过程中DMFC阳极性能的变化。结果表明,在探针扫描过程中,经不同电压加载后的DMFC阳极表面的扫描电流呈相似的锯齿状分布。当阳极加载2 h,随加载电位升高,扫描峰电流的数量减少,对应峰电流的数值则先增大再减小,表明阳极的催化活性处于不均匀分布状态且随加载时间延长和加载电位升高而逐渐降低。在不同加载电位下,随加载时间延长,循环伏安曲线上的正向和反向电流峰先负移再正移,但抗CO性能持续降低。DMFC阳极在0.6 V下分别加载16 h和72 h后,催化剂粒径由3.4 nm分别增大到3.6 nm和4.4 nm。在0.8 V下加载72 h后,Pt/Ru重量比由2.0增加到3.9。变压加载使催化活性的不均匀分布加剧催化剂粒径长大,Ru流失加快,从而导致阳极催化性能衰减。     

变压加载对直接甲醇燃料电池阳极性能的影响（英）

为评价直接甲醇燃料电池（DMFC）阳极的稳定性,利用扫描电化学显微镜和常规电化学技术,研究了变压加载过程中DMFC阳极性能的变化。结果表明,在探针扫描过程中,经不同电压加载后的DMFC阳极表面的扫描电流呈相似的锯齿状分布。当阳极加载2 h,随加载电位升高,扫描峰电流的数量减少,对应峰电流的数值则先增大再减小,表明阳极的催化活性处于不均匀分布状态且随加载时间延长和加载电位升高而逐渐降低。在不同加载电位下,随加载时间延长,循环伏安曲线上的正向和反向电流峰先负移再正移,但抗CO性能持续降低。DMFC阳极在0.6 V下分别加载16 h和72 h后,催化剂粒径由3.4 nm分别增大到3.6 nm和4.4 nm。在0.8 V下加载72 h后,Pt/Ru重量比由2.0增加到3.9。变压加载使催化活性的不均匀分布加剧催化剂粒径长大,Ru流失加快,从而导致阳极催化性能衰减。     

A comprehensive review on recent material development of passive direct methanol fuel cell

Direct methanol fuel cells (DMFCs) within all types of fuel cells are the most viable alternative to lithium-ion batteries in the portable application and recently attracted much attention. This study reviews on passive DMFC material development with emphasis on to the performance activity, cost, durability and stability aspect. This paper has reported the basic desirable characteristics of each component with their material development. This paper has reviewed all possible materials of passive DMFC component, which can make the passive DMFC compact and feasible energy source in the future.     

Novel cross-linked membrane for direct methanol fuel cell application: sulfonated poly(ether ether nitrile)s

In order to reduce water uptake, swelling ratio, and methanol permeability in sulfonated proton exchange membranes (PEM), novel-sulfonated aromatic poly(ether ether nitrile)s-bearing pendant propenyl groups had been synthesized by direct copolymerization method. All the results showed that the propenyl groups were suitable cross-linkable groups, and that this method was an effective way to overcome the drawbacks of sulfonated polymers at high ion exchange capacity (IEC) values. By cross-linking, the water uptake, swelling ratio, and methanol diffusion could be restricted owing to the formation of compact network structure. For example, CSPEN-60 membranes showed the proton conductivity of 0.072 S cm^?1 at 80 °C, while the swelling ratios and water uptake (17.9 and 60.7 %) were much lower than that of the SPEN-60 membrane (60.8 and 295.2 %). Meanwhile, a 1.1 × 10^?7 cm² s^?1 of methanol diffusion was obtained which was much lower than that of Nafion 117 (14.1 × 10^?7 cm² s^?1). Although the proton conductivity of the CSPEN-60 membranes is lower than that of the SPEN-60 membrane, the selectivity is much higher. The CSPEN-60 membrane exhibited the highest selectivity among the tested membranes, about 5.8 times higher compared with that of Nafion117.     

Complexed sol-gel synthesis of improved Pt-Ru-Os-based anode electro-catalysts for direct methanol fuel cells

A high specific surface area (SSA) Pt-Ru-Os-based anode catalyst synthesized by a novel complexed sol-gel (CSG) process shows better catalytic activity in comparison to pure equi-atomic compositions of Pt-Ru anode catalysts synthesized by similar sol-gel processes. A homogeneous amorphous gel was successfully synthesized by complexing platinum(II) acetylacetonate, ruthenium(III) acetylacetonate and osmium(III) chloride with tetramethylammonium hydroxide (TMAH) used as a complexing agent. Phase-pure Pt(Ru,Os) and Pt(Ru) solid solutions possessing high specific surface area (∼110-120 m²/g) were successfully synthesized by controlled removal of carbonaceous species present in the as-prepared precursor generated from the CSG process. This has been successfully achieved by precise thermal treatments of the precursor using controlled oxidizing atmospheres. Results indicate that the nano-crystalline Pt(Ru,Os) solid solution of nominal composition 50 at%-Pt-40 at% Ru-10 at% Os possesses good chemical homogeneity, and reveals excellent catalytic activity, thus demonstrating the potential of the novel CSG process for synthesizing high-performance Pt-Ru-Os-based catalysts for direct methanol fuel cells.     

Experimental studying of the effect of active area on the performance of passive direct methanol fuel cell

This work experimentally studies the effect of the size and shape of active area on the performance of passive direct methanol fuel cell. The obtained results show that the cell performance strongly depends on the size and shape of active area. Experimental results of this study also demonstrate that the cell performance improves with an increase in the size of active area. Increasing the size of active area also leads to a lower internal resistance, lower OCV, and higher operating temperature. Furthermore, it was found that the smallest active area (4 cm²) produced the longest stable discharging voltage (about 16.5 h). This study also reveals that the square active area has the best performance and the highest power density compared to the rectangular and circular active areas. Finally, the results prove that the place of applying the clamping force is an important parameter that should be considered in the cell design.     

Preparation and characterization of carbon-related materials supports for catalysts of direct methanol fuel cells

In this work, two types of carbon materials such as CBs and GNFs were treated by a fluorination in order to study the effect of surface modification. The carbon-supported platinum (Pt) and ruthenium (Ru) catalysts were prepared using two types of carbon materials to check the influence of the fluorinated carbon supports on the activity of catalysts. The crystalline characteristics of the carbon-supported catalysts were determined by XRD method. Electrochemical properties of the electrocatalysts were analyzed by cyclic voltammetry (CV) experiments. When fluorinated GNFs were used as catalyst supports, the current density obtained in fuel cell was greater than that of CBs-supported catalyst; meaning GNFs-supported catalysts had a higher performance relative to CBs-supported catalysts. These results were supported with the CV results that showed the greater activity for PtRu at higher potentials.     

The modification of anode material for direct borohydride fuel cell

The direct borohydride fuel cell (DBFC) is a promising device that converts chemical energy into electricity by electrochemical reactions. This type of power source is technically more simple than traditional fuel cells, because it does not require any hydrogen container and noble metals. Hydrogen evolution during hydrolysis can be inhibited by modification of anode materials. Extensive studies are focused on various specific electrocatalysts and their impact on oxidation and hydrolysis of borohydride. The aim of the study is to determine the effect of anode material composition using borohydride as a fuel. In order to enhance the utilization of borohydride fuel, AB₅-type alloy (LaMnNi_3.55Al_0.30Mn_0.40Co_0.75) was modified by adding Si or two kinds of carbon materials using the ball milling method. The most proper electrolyte was selected. The physical and electrochemical properties of anode materials were evaluated by scanning electron microscopy (SEM), cyclic voltammetry, chronopotentiometric measurements and electrochemical impedance spectroscopy. Studies showed that graphite was the best additive to anode material due to its density, compact structure and improvement of conductivity.

     

PVdF-HFP membranes for fuel cell applications: effects of doping agents and coating on the membrane’s properties

Poly(vinylidene fluoride-co-hexafluoropropene)–hexafluoropropylene (PVdF-HFP; M _n, 130,000)-based membranes were prepared by means of phase inversion technique by coagulating with water and MeOH and then doping with H₃PO₄ and H₂SO₄. In order to improve the electrochemical properties of the PVdF-HFP membranes, coagulated membranes were also coated with polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PSEBS) and sulfonated with chlorosulfonic acid in the second stage. The effects of the type of coagulant, coagulation time, doping agents, coating, and sulfonation on the membrane properties were investigated. Membranes were thermally stable up to 400 °C. The conductivity values were measured to be between 1.10E???01 and 6.00E???03 mS/cm for uncoated samples. The proton conductivity value of the PSEBS-coated and sulfonated membrane was increased from 6.00E???03 to 92.1 mS/cm. Water uptake values varied from 0 to 38 % for uncoated samples and from 11.5 to 65.2 % for coated samples. Chemical degradation of PVdF-HFP membranes was investigated via Fenton test. All membranes were found to be chemically stable. Morphology of the membranes was examined by scanning electron microscopy. Different membrane morphologies were observed, depending on different membrane preparation procedures.     

Preparation of durable nanocatalyzed MEA for PEM fuel cell applications

Novel nanocatalyzed membrane electrode assembly (MEA) with high performance and durability for polymer electrolyte membrane fuel cell application is prepared by modifying nonequilibrium impregnation–reduction method. The electrochemical and physical properties of nanocatalyzed MEA have been examined using various techniques such as cyclic voltammetry, impedance spectroscopy, scanning electron microscopy, and X-ray diffraction studies. The lifetime of the nanocatalyzed MEA is studied and compared with that of the conventional one. It is observed that the performance and durability of nanocatalyzed MEA are better than the conventional one. In addition, the influence of supported carbon corrosion in MEA durability has been studied.     

Studies on electrodeposition of Fe-W alloys for fuel cell applications

Electrodeposition of Fe-W alloy has been carried out from acidic triammonium citrate (TAC) complex bath solution. The deposit is characterised by XRD, SEM, EDAX, XPS and polarization techniques. The alloys are amorphous and become partially crystalline on heat treatment. The composition (Fe/W) of elements in the coating and their oxidation states vary from the surface to the bulk of the material. The coatings exhibit as novel electrode material with low over voltage and good corrosion resistance for anodic oxidation of methanol in H₂SO₄ medium. The anodic peak current, a measure of oxidation reaction rate is considerably high on Fe-W alloy when compared to pure Fe and also the relative surface area of Fe by alloying it with W found to increase by 1200-fold.     

Neutrons for fuel cell membranes: Structure, sorption and transport properties

A molecular level understanding of structure and transport properties in fuel cell ionomer membranes is essential for designing new electrolytes with improved performance. Scattering techniques are suited tools for this purpose. In particular, neutron scattering, which has been extensively used in hydrogen-containing systems, is well adapted to investigate water-dependent complex polymeric morphologies. We report Small-Angle Neutron Scattering (SANS) studies on different types of fuel cell polymers: perfluorinated, radiation-grafted and sulfonated polyphosphazene membranes. We show that contrast variation methods can be efficiently employed to provide new insights on membrane microstructure and reveal ionic condensation effects. Neutrons have been used also as non-intrusive diagnosis tool to probe water properties and distribution inside membranes. Recently, in-situ neutronography and SANS experiments on operating fuel cells have been reported. In-plane cartography of water distribution at the surface of bipolar plates and water profiles across membrane thickness have been obtained and studied as a function of operating conditions. The last section of the article is devoted to the use of Quasi-Elastic Neutron Scattering to study water dynamics at molecular scale. We show that analysis with an appropriate sophisticated diffusion model allows to extract diffusion coefficients, characteristic times and length-scales of molecular motions. This quantitative information is fruitfully integrated in multi-scale modelling and usefully compared with numerical simulations. QENS also permits to compare alternative polymers and relate dynamical properties to chemical composition and membrane nanostructure.     

A high-throughput search for direct methanol fuel cell anode electrocatalysts of type PtxBiyPbz

We used a high-throughput method to screen for direct methanol fuel cell anode electrocatalysts in the Pt-Bi-Pb system. Previous studies showed that PtBi and PtPb (both NiAs structure type) were active electrocatalysts for the oxidation of formic acid, but only PtPb was active in oxidizing methanol. We synthesized thin films with continuous composition spreads of the three elements by magnetron sputtering at deposition temperatures from ambient to 510 °C. A fluorescence method was then used to identify compositions that were active toward methanol oxidation. Only films deposited between temperatures of 160 and 400 °C showed electrocatalytic activity. The areas that were active for methanol oxidation showed predominantly the NiAs structure type according to XRD, with optimal activity for compositions near PtBi_0.01Pb_0.53.     

Proton conduction in oxyacid salts at intermediate temperatures for fuel cell applications

Materials that are proton conducting at intermediate temperatures are of prime importance for fuel cell applications. For example, by lowering the operating temperature of a solid oxide fuel cell the severe material problems encountered at high temperatures may be avoided while fast kinetics at the electrodes may still be obtained. In this article a number of proton conducting solid materials based on oxyacid salts are discussed, materials with and without structural protons, as well as composites. Paper presented at the 97th Xiangshan Science Conference on New Solid State Fuel Cells, Xiangshan, Beijing, China, June 14–17, 1998.     

Modelling soot emission from a direct injection diesel engine fuelled with diesel–methanol dual fuel

The objective of this paper is to develop a soot model for multi-dimensional simulations of diesel–methanol dual-fuel engines to predict engine-out soot emissions. To the two-step soot model a special term, based on experimental study and analysis, is appended to the soot formation rate to account for the effect of methanol. The results of engine-out soot emissions predicted by the models were compared with experimental data and it is shown that the existing model predicts well for diesel engines, whereas the proposed model predicts well for both diesel and dual-fuel engines especially for the large fractional methanol flow rates. The results suggest that the soot model must be modified for the dual-fuel combustion mode.     

Angle-dependent THz tomography – characterization of thin ceramic oxide films for fuel cell applications

A time-resolved THz tomography system for the incidence-angle-dependent three-dimensional characterization of layered structures is presented. The capabilities of the developed system are demonstrated on multi-layer ceramic samples used for solid oxide fuel cells (SOFC). Appropriate methods for determining unknown refractive indices are discussed. It is shown how the angle of incidence of a THz imaging system has a significant influence on measured signals. This fact can be exploited especially in Brewster-angle configurations to enhance the capabilities of any THz tomography system. Data evaluation algorithms are presented. Received: 8 June 2000 / Revised version: 13 September 2000 / Published online: 10 January 2001