Anodic Membranes Research Articles

Calculations of transport phenomena and reaction distribution in a polymer electrolyte membrane fuel cell

The performance of Polymer Electrolyte Membrane fuel cells depends on the design of the cell as well as the operating conditions. The design of the cell influences the complex interaction of activation effects, ohmic losses, and transport limitations, which in turn determines the local current density. Detailed models of the electrochemical reactions and transport phenomena in Polymer Electrolyte Membrane fuel cells can be used to determine the current density distribution for a given fuel cell design and operating conditions. In this work, three-dimensional, multicomponent and multiphase transport calculations are performed using a computational fluid dynamics code. The computational results for a full-scale fuel cell design show that ohmic effects due to drying of polymer electrolyte in the anode catalyst layer and membrane, and transport limitations of air and flooding in the cathode cause the current density to be a maximum near the gas channel inlets where ohmic losses and transport limitations are a minimum. Elsewhere in the cell, increased ohmic losses and transport limitations cause a decrease in current density, and the performance of the fuel cell is significantly lower than that which could be attained if the ohmic losses and transport limitations throughout the cell were the same as those near the gas channel inlets. Thus overall fuel cell design is critical in maximizing unit performance.

High density copper nanowire arrays deposition inside ordered titania pores by electrodeposition

Large area and free-standing TiO 2 films was prepared by ultrasonic splitting and a chemical etching step was used to open the closed bottom end of TiO 2 films and yields a high aspect-ratio anodic titanium oxide membrane open at both ends. Ordered Cu nanowire structures were fabricated by a simple electroplating method inside high aspect-ratio anodic titanium oxide membrane. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the X-ray diffraction (XRD) were employed to characterize the resulting samples. Detailed results and the possible mechanism are presented.

Elimination of a pollution associated with chromic acid during the electro-deposition of Cr(III) using appropriate anodic and membrane materials in a double film bath

A method using trivalent chromium has been used to replace hexavalent chromium for the electro-deposition of chromium. Using a tri-chamber bath system various anodic materials and membranes were evaluated to minimize the production of environmentally and health damaging chromic acid. By measuring the absorbance of Cr(VI) at 640 nm, the results indicate that the use of a titanium plated ruthenium (Ti-Ru) anode produces the least amount of chromic acid byproduct compared to lead-gold alloy and graphite anodes. The concentration of Cr(VI) in the immediate vicinity of the Ti-Ru anode decreased from 0.389 mg/L to 0 during a 40-min deposition period. The use of a Nafion TM quaternary cation exchange membrane portioning the buffer and anode selectively prevented Cr(III) from entering the anode compartment whilst allowing the migration of H + to maintain overall voltaic continuity. It has been demonstrated that the use of a Ti-Ru anode with a Nafion TM membrane can eliminate the production of chromic acid associated with the electro-deposition of chromium plate thereby preventing its health damaging exposure to plant operators and preventing discharge of Cr(VI) into the environment. Addition of a surfactant improved current efficiency by 34.7%.

Controlled growth of branched channels by a factor of 1/√n anodizing voltage?

A novel model, which indicates that the growth of branched channels in anodic alumina oxide membranes is different from what has been reported before, has been established in this communication.

Water Transport and Degradation Analysis in PEMFC by in-situ MRI Visualization

Recent developments in MRI visualization for water transport and degradation analyses in PEMFC are presented. High-resolution MRI experiments were performed for a 117-μm-thick membrane. Partial dehydration of the membrane's anode side was visualized with the increase of current density. Nuclei-labeling MRI was also presented. Results demonstrated its unique potential for direct visualization of the water source on membrane hydration using D2 and D2O. Spatially-resolved NMR was also applied to a degraded membrane. The membrane's cathode side, as measured using 1H-NMR spectra, showed a greater chemical shift.

Aqueous methanol eletrolysis using proton conducting membrane for hydrogen production

In this paper, we present the studies carried out on electrolysis of aqueous methanol for hydrogen production, in a PEM electrolyser consisting of Pt–Ru/C anode, Pt/C cathode and Nafion membrane as the electrolyte. The effect of various parameters such as methanol concentration, cell voltage, temperature, membrane thickness etc. on cell performance was investigated. The results illustrate the attractive features and indicate suitability of aqueous methanol electrolysis for distributed hydrogen production.

Preparation and Characterization of BN Nanotubes with Controllable Sizes by Template-aided Synthesis

ABSTRACTIn this study, an efficient approach to prepare high quality BN nanotubes (BNNTs) was developed. BNNTs with specific sizes were prepared by sublimation of ammonia borane complex (BH3NH3) using two kinds of porous alumina anodic membrane template in two independently temperature controlled furnaces in a glovebox filled with N2. The BNNTs with template were nitrided at different temperatures 1300 ∼ 1700 °C in NH3. The BNNTs of 200 – 300 nm wide°60×°m long, and 70 – 80 nm wide°×40 μm long were finally collected after removal of the template by etching of with 40 wt% NaOH solution. The fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) results confirmed the formation of BN from BH3NH3. Ordered arrays of BNNTs were observed by scanning electron microscopy (SEM), and the microstructure of these BNNTs was investigated by transmission electron microscopy (TEM). It was found that the diameters of the BNNTs can be easily controlled by using templates with different pore sizes. The wall thickness of the nanotubes was increased by increasing the sublimation time or the amount of the starting BH3NH3. The crystallinity of BNNTs was improved at higher temperatures (1700 °C) in NH3.

Vapor Infiltration of a Reducing Agent for Facile Synthesis of Mesoporous Pt and Pt-Based Alloys and Its Application for the Preparation of Mesoporous Pt Microrods in Anodic Porous Membranes

Highly ordered mesoporous Pt and Pt-based alloy (Pt−Ru and Pt−Ni) microparticles were deposited from lyotropic liquid crystal (LLC) films containing corresponding metal species via vapor infiltration of a reducing agent of dimethylaminoborane (DMAB). The LLC films with 2D hexagonal symmetry were prepared on flat substrates from diluted surfactant solutions including water, nonionic surfactant, ethanol, and metal species by drop-coating. Low-angle XRD measurements and TEM observations proved that the deposited Pt and Pt-based alloy microparticles have 2D hexagonally ordered mesoporous structures. Moreover, EDS mapping of mesoporous Pt−Ru microparticles indicated that the constituent metals are well-distributed within the mesopore walls. Moreover, we effectively utilized the method to fabricate mesoporous Pt microrods with 100 nm in diameter by using a porous anodic alumina membrane (PAAM) as a hard template. The Pt microrods possess a highly porous nanostructure. Our method utilizing vapor infiltration of ...

Experimental validation of a methanol crossover model in DMFC applications

A design of experiments (DOEs) coupled with a mathematical model was used to quantify the factors affecting methanol crossover in a direct methanol fuel cell (DMFC). The design of experiments examined the effects of temperature, cathode stoichiometry, anode methanol flow rate, clamping force, anode catalyst loading, cathode catalyst loading (CCL), and membrane thickness as a function of current and it also considered the interaction between any two of these factors. The analysis showed that significant factors affecting methanol crossover were temperature, anode catalyst layer thickness, and methanol concentration. The analysis also showed how these variables influence the total methanol crossover in different ways due to the effects on diffusion of methanol through the membrane, electroosmotic drag, and reaction rate of methanol at the anode and cathode. For example, as expected analysis showed that diffusion was significantly affected by the anode and cathode interfacial concentration, by the thickness of the anode catalyst layer and membrane, and by the diffusion coefficient in the membrane. Less obvious was the decrease in methanol crossover at low cathode flow rates were due to the formation of a methanol film at the membrane/cathode catalyst layer interface. The relative proportions of diffusion and electroosmotic drag in the membrane changed significantly with the cell current of the cell.

Basic model for membrane electrode assembly design for direct methanol fuel cells

This research proposes a model that predicts the effect of the anode diffusion layer and membrane properties on the electrochemical performance and methanol crossover of a direct methanol fuel cell (DMFC) membrane electrode assembly (MEA). It is an easily extensible, lumped DMFC model. Parameters used in this design model are experimentally obtainable, and some of the parameters are indicative of material characteristics. The quantification of these material parameters builds up a material database. Model parameters for various membranes and diffusion layers are determined by using various techniques such as polarization, mass balance, electrochemical impedance spectroscopy (EIS), and interpretation of the response of the cell to step changes in current. Since the investigation techniques cover different response times of the DMFC, processes in the cell such as transport, reaction and charge processes can be investigated separately. Properties of single layers of the MEA are systematically varied, and subsequent analysis enables identification of the influence of the layer's properties on the electrochemical performance and methanol crossover. Finally, a case study indicates that the use of a membrane with lower methanol diffusivity and a thicker anode micro-porous layer (MPL) yields MEAs with lower methanol crossover but similar power density.

Microscopic characterizations of membrane electrode assemblies prepared under different hot-pressing conditions

The durability of the membrane electrode assembly (MEA) for direct methanol fuel cells (DMFCs) is one of the most critical issues to be addressed before widespread commercialization of the DMFC technology. In this work, we investigated the effect of the hot-pressing duration on the performance and durability of the MEA prepared by hot-pressing technique. It was found that the 60-min hot pressing at 135 °C under the pressure of 4.0 MPa yielded a significantly improved MEA durability than did the 3-min hot pressing (a typical duration in practice) under the same condition, but no substantial difference was found in the cell performance of the MEAs prepared with the two different hot-pressing durations. The reason why the hot-pressing duration had no significant effect on cell performance is explained based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) characterizations of the changes in the physiochemical properties of MEAs and their constituent components, including the anode, cathode and Nafion membrane, before and after hot pressing with different durations.

Silver-Plated Electrospun Fibrous Anode for Glucose Alkaline Fuel Cells

This investigation is part of an effort to develop a low cost glucose-fueled fuel cell for portable devices. Electrospinning, a method that can produce high surface-to-volume ratio membranes, was used to fabricate micrometer-size polycaprolactone (PCL) fibrous electrocatalytic anode membranes for the oxidation of glucose in an alkaline fuel cell. The membranes were coated with silver using the electroless plating method that covered the whole surface of the fibers and gave the mat electrical conductivity and catalytic capability to oxidize glucose. The plated PCL membranes served as anodes in a fuel cell supplied with glucose and KOH electrolyte. With a mean plated fiber diameter membrane, the cell produced an open circuit voltage (OCV) of and a peak power density of . For a fiber membrane, the OCV was and the was . For comparison, a pure silver foil anode was placed in the same cell under the same conditions. In this case the OCV was and the reached . The experimental results indicate that the electrical performance of the fuel cell is proportional to the surface area of the fibrous anodes.

The Biflow: An instrument for transfer‐loop mediated, continuous, preparative‐scale isoelectric trapping separations

The Biflow, a new isoelectric trapping instrument was designed to obtain a narrow DeltapI fraction from a complex feed in one step. The Biflow contains two identical separation units, each unit houses: an anode and cathode compartment, an anodic and cathodic membrane, an anodic and cathodic separation compartment, and a separation membrane. The separation units are connected to independent power supplies. The anodic membranes in Units 1 and 2 typically buffer at the same pH value and so do the cathodic membranes. The separation membranes in Units 1 and 2 buffer at different pH values, these determine the pI range (DeltapI) of the product. The cathodic separation compartments in Units 1 and 2 contain the feed and harvest streams. The two anodic separation compartments, connected through an electrically insulating air gap, form the transfer loop through which the transfer stream is recirculated between Units 1 and 2. Ampholytic components in the feed, with pI values lower than the pH of the buffering membrane in Unit 1, pass into the transfer stream and are shuttled into Unit 2. In Unit 2, components in the transfer stream which have pI values higher than the pH of the buffering membrane in Unit 2, pass into the harvest stream. This double transfer of the target component, oppositely directed, guarantees the complete exclusion of products outside the desired DeltapI range from the harvest stream. The utility of the Biflow unit was demonstrated by isolating carnosine from a mixture of UV-absorbing ampholytes and ovalbumin isoforms as well as 4.4 <pI <4.5 and 5.4 <pI <5.5 minor constituents from chicken egg white.

Fabrication of Polystyrene/Gold Nanotubes and Nanostructure-Controlled Growthof Aluminate

Direct adsorption of gold nanoparticles in the inner of alumina template and following immersion of polystyrene (PS) dichloromethane solution in the template resulted in the fabrication of composite nanotubes of PS and gold nanoparticles. Several methods have been used to characterize the tubular structure. Nanostructured sodium aluminates were formed when the anodic alumina oxide membrane was dissolved by the sodium hydroxide. A "flower" shape was found after etching the template while the synthesis process was recorded as function of a time. The results demonstrate that the shape and size of the aluminates nanostructure can be controlled by etching time and the pore diameter of the alumina membrane.

Nanoscale membrane electrode assemblies based on porous anodic alumina for hydrogen–oxygen fuel cell

In this paper, we demonstrate that nanoscale membrane electrode assemblies, functioning in a H2/O2 fuel cell, can be fabricated by impregnation of anodic alumina porous membranes with Nafion® and phosphotungstic acid. Porous anodic alumina is potentially a promising material for thin-film micro power sources because of its ability to be manipulated in micro-machining operations. Alumina membranes (Whatman, 50 μm thick, and pore diameters of 200 nm) impregnated with the proton conductor were characterized by means of scanning electron microscopy, X-ray diffraction, and thermal analysis. The electrochemical characterization of the membrane electrode assemblies was carried out by recording the polarization curves of a hydrogen–oxygen 5 cm2 fuel cell working at low temperatures (25 ÷ 80 °C) in humid atmosphere. Our assemblies realized with alumina membranes filled with phosphotungstic acid and Nafion® reach respectively the peak powers of 20 and 4 mW/cm2 at room temperature using hydrogen and oxygen as fuel and oxidizer.

PH transients during salt removal in isoelectric trapping separations: A curse revisited

The pH transients that occur during isoelectric trapping separations as a result of the removal of nonampholytic ionic components have been re-examined. Salts containing strong electrolyte anions and cations, both with equal and dissimilar mobilities, have been studied using anodic and cathodic buffering membranes whose pH values were both equidistant and nonequidistant from pH 7. The direction and magnitude of the pH transient (acidic or basic) was found to depend on both the mobilities of the anion and cation (mu(anion)/mu(cation)) and the pH difference between pH 7 and the pH of the buffering membranes (|pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)|). When |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)| = 1, mu(anion)/mu(cation)<1 leads to an acidic pH transient, mu(anion)/mu(cation) = 1 eliminates the pH transient and mu(anion)/mu(cation)>1 leads to a basic pH transient. When mu(anion)/mu(cation) = 1, |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)|<1 leads to a basic pH transient, |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)| = 1 eliminates the pH transient and |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)|>1 leads to an acidic pH transient. By selecting appropriate anodic and cathodic buffering membranes to adjust the |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)| value, pH transients caused by dissimilar anion and cation mobilities can be avoided.

A Monolithic Hybrid Direct Methanol Fuel Cell

A monolithic hybrid direct methanol fuel cell (DMFC) with a novel configuration is proposed in an effort to reduce the weight and size of the conventional hybrid fuel cell system. A modified DMFC with a layer of hydrous ruthenium dioxide (RuO 2 ·xH 2 O) sandwiched between the anode catalyst layer and membrane has been used to demonstrate the principle of the monolithic hybrid DMFC. Experimental results indicate that the RuO 2 .xH 2 O layer is equivalent to a resistive-capacitive transmission line and functions similar to a capacitor in parallel with the anode electrode. The improvement in dynamic response of the modified DMFC has been experimentally confirmed under square current pulse operating.

Water Management by Material Design and Engineering for PEM Fuel Cells

PEMFCs depend on proper water management to obtain high power density and energy efficiency. Traditionally, water management has been addressed by system design and engineering. That is, by adding processes to the basic PEMFC system to provide humidification to the anode and to remove water from the cathode. This approach adds significant complexities and costs and reduces the overall efficiency of the PEMFC system. Development of new materials and better understanding of the functions of these materials have led to a paradigm shift as to how water management can be implemented in a PEMFC system. In this new paradigm, materials with the right properties will be used in the membrane and electrode assemblies such that zero net water transport across the membrane is achieved. Once this goal is attained the next goal will be to achieve optimal anode and cathode gas humidification and membrane hydration with zero-external- system-water requirement.

A novel supercapacitor-fuel cell hybrid cell

A monolithic hybrid fuel cell (MHFC) with a novel configuration was proposed in an effort to improve the fuel cell performance during instantaneous power changes. A modified direct methanol fuel cell (DMFC) with a layer of hydrous ruthenium dioxide (RuO 2· xH 2O) sandwiched between the anode catalyst layer and membrane was used to demonstrate the principle of the MHFC. Experimental results indicate that the RuO 2· xH 2O layer is equivalent to a resistor-capacitor transmission line and functions similar to a capacitor in parallel with the anode electrode. The improvement in dynamic response of the MHFC was experimentally confirmed under step current change and square current pulse operating. The ionic conductivity of the RuO 2· xH 2O layer was also obtained.

Electrical Properties of Hydrous Ruthenium Dioxide in Direct Methanol Fuel Cells

The electrical properties of hydrous ruthenium oxide (RuO2.xH2O) have been investigated in a modified direct methanol fuel cell (DMFC). The configuration of the modified DMFC involves a RuO2.xH2O layer sandwiched between anode catalyst layer and membrane. The experiments on polarization curves and electrochemical impedance spectra of the modified DMFC have been carried out to obtain the ionic resistance and capacitance of the RuO2.xH2O layer. Further numerical simulation study based on an electrical circuit model indicates that the RuO2.xH2O layer in the modified DMFC is equivalent to a resistive-capacitive transmission line and functions similar to a capacitor in parallel with the anode electrode. The improvement in the dynamic response of the modified DMFC has been experimentally confirmed in square current pulse operating condition. Finally, a novel monolithic hybrid DMFC has been proposed and discussed.