Development and Evaluation of Gas Diffusion Layer Using Paraffin Wax Carbon for Proton Exchange Membrane Fuel Cells

A gas diffusion layer (GDL) with carbon prepared from paraffin wax was developed for the first time to impart hydrophobicity and porosity for fuel cell application. It is also intended to reduce the non‐functional binder content in the microporous layer and to achieve optimum performance. The topography of the GDL was examined using 3D digital microscope. Membrane electrodes assemblies (MEAs) fabricated with GDLs of paraffin wax carbon (PWC) based microporous layer were evaluated in proton exchange membrane fuel cell between 50 and 100% RH conditions using H₂ and O₂ at ambient pressure. The fuel cell performance of the GDLs fabricated with Pureblack carbon was also evaluated under identical operating conditions for comparison. It was observed that the MEA with GDLs containing PWC showed excellent fuel cell performance at all RH conditions at 80 °C both with H₂/O₂.     

Atmospheric plasma spraying to fabricate metal-supported solid oxide fuel cells with open-channel porous metal support

Metal-supported solid oxide fuel cells (MS-SOFCs) have been fabricated by applying phase-inversion tape-casting and atmospheric plasma spraying (APS). The effect of the binder amount of the phase-inversion slurries on the microstructure development of the 430L stainless steel metal support was investigated. The pore structures, the viscosity of the slurry, porosity and permeability of the as-prepared metal supports are significantly influenced by the amount of the binder. NiO–scandia-stabilized zirconia (ScSZ) anode, ScSZ electrolyte and La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) cathode layers were consecutively deposited on the metal support with an ideal microstructure by APS process. The effect of plasma power of the APS on the microstructure of the electrolyte and cathode was investigated. A dense electrolyte layer and a porous cathode layer were successfully obtained at 40 and 6 kW of the APS plasma power, respectively. MS-SOFCs, with a cell configuration of 430L/Ni-ScSZ/ScSZ/LSCF, achieved a maximum cell power density of 1079 mW cm⁻² at 700°C using humidified H₂ as fuel and ambient air as oxidant. The corresponding ohmic resistance and total resistance of MS-SOFCs was 0.14 and 0.32 Ω cm², respectively. This work demonstrates the feasibility of fabricating high-performance MS-SOFCs with economical and scalable techniques.     

Electrophoretic deposition of ceramic materials for fuel cell applications

La_0.8Sr_0.2Ga_0.875Mg_0.125O_3-x (LSGM), La_0.8Sr_0.2Co_0.2Fe_0.8O_3-δ (LSCF), yttria stabilized zirconia (YSZ) and (Ce_0.8Gd_0.2)O_1.9 (CGO) were electrophoretically deposited on Ni foils and Ni-yttria stabilized zirconia substrates prepared by tape casting. It was demonstrated that the ethyl alcohol–phosphate ester–polyvinyl butyral system is an effective solvent–dispersant–binder system for electrophoretic deposition of these materials. The influence of dispersant, binder and current density on deposition efficiency and deposit morphology was studied. The microstructure of the deposits was examined by electron microscopy. The proposed solvent–dispersant–binder medium for electrophoretic deposition of LSGM, LSCF, YSZ and CGO has important advantages and implications in fuel cell design.     

Sulfonated poly(arylene ether sulfone) as an electrode binder for direct methanol fuel cell

Sulfonated poly(arylene ether sulfone) (sPAES) is synthesized and characterized for the application to the electrode binder for direct methanol fuel cell (DMFC). The effect of sPAES binder in the electrode on the cell performance is studied. The cell based on sPAES binder showed a good adhesion to the sPAES membrane, while Nafion binder is delaminated from the sPAES membrane after supplying the fuel for a prolonged time. The sPAES binder for electrode is found to be more efficient in achieving long-term stability of the cell performance than the conventional Nafion binder.     

Application of Amorphous Boron Granulated With Hydroxyl‐ Terminated Polybutadiene in Fuel‐Rich Solid Propellant

Amorphous boron powder granulated with HTPB, whose particle diameter could be controlled, was prepared by mechanical mill method. It was found that amorphous boron powder could be granulated with HTPB binder to form B‐HTPB particles, whose median particle diameter (d₅₀) and specific surface area are in the range of 125.0–431.0 µm and 0.02–0.1 m² g⁻¹, respectively. The B‐HTPB particles could be dispersed in the HTPB binder with relatively low viscosity compared with direct addition of amorphous boron powder to the HTPB binder. The experimental results showed that the content of boron particles in a fuel‐rich propellant could be increased by addition of B‐HTPB particles and the combustion characteristics of the fuel‐rich solid propellant could be improved.     

Development of gas diffusion layer using water based carbon slurry for proton exchange membrane fuel cells

The micro-porous layer of gas diffusion layers (GDLs) was fabricated with the carbon slurry dispersed in water containing sodium dodecyl sulfate (SDS), by wire rod coating process. The aqueous carbon slurry with micelle-encapsulation was highly consistent and stable without losing any homogeneity even after adding polytetrafluoroethylene (PTFE) binder for hundreds of hours. The surface morphology, contact angle and pore size distribution of the GDLs were examined using SEM, Goniometer and Hg Porosimeter, respectively. GDLs fabricated with various SDS concentrations were assembled into MEAs and evaluated in a single cell PEMFC under diverse operating relative humidity (RH) conditions using H₂/O₂ and H₂/air as reactants. The peak power density of the single cell using the GDLs with optimum SDS concentration was 1400 and 500 mW cm⁻² with H₂/O₂ and H₂/air at 90% RH, respectively. GDLs were also fabricated with isopropyl alcohol (IPA) based carbon slurry for fuel cell performance comparison. It was found that the composition of the carbon slurry, specifically SDS concentration played a critical role in controlling the pore diameter as well as the corresponding pore volumes of the GDLs.     

In Situ Foaming of Porous (La0.6Sr0.4)0.98 (Co0.2 Fe0.8) O3−δ (LSCF) Cathodes for Solid Oxide Fuel Cell Applications

A binder system containing polyurethane precursors was used to in situ foam (direct foam) a (La_0.6Sr_0.4)_0.98 (Co_0.2 Fe_0.8) O_3?δ (LSCF) composition for solid oxide fuel cell (SOFC) cathode applications. The relation between in situ foaming parameters on the final microstructure and electrochemical properties was characterized by microscopy and electrochemical impedance spectroscopy (EIS), respectively. The optimal porous cathode architecture was formed with a 70 vol% solids loading within a polymer precursor composition with a volume ratio of 8:4:1 (isocyanate: PEG: surfactant) in a terpineol‐based ink vehicle. The resultant microstructure displayed a broad pore size distribution with highly elongated pore structure.     

A 2<Superscript>7-3</Superscript> fractional factorial optimization of polybenzimidazole based membrane electrode assemblies for H<Subscript>2</Subscript>/O<Subscript>2</Subscript> fuel cells

We describe the usefulness of a statistical fractional factorial design to obtain consistent and reproducible behavior of a membrane-electrode-assembly (MEA) based on a phosphoric acid (PA) doped polybenzimidazole (PBI) membrane, which allows a H₂/O₂ fuel cell to operate above 150 °C. Different parameters involved during the MEA fabrication including the catalyst loading, amount of binder, processing conditions like temperature and compaction load and also the amount of carbon in the gas diffusion layers (GDL) have been systematically varied according to a 2^7-3 fractional factorial design and the data thus obtained have been analyzed using Yates’s algorithm. The mean effects estimated in this way suggest the crucial role played by carbon loading in the gas diffusion layer, hot compaction temperature and the binder to catalyst ratio in the catalyst layer for enabling continuous performance. These statistically designed electrodes provide a maximum current density and power density of 1,800 mA cm⁻² and 280 mW cm⁻², respectively, at 160 °C using hydrogen and oxygen under ambient pressure.     

Barium Borosilicate Sealing Glasses Synthesized by a Sol–Gel Process: Chemical Interactions with a Stainless Steel and Gas‐Tightness of a SOFC

Several glasses synthesized by sol–gel route and based on the BaO–B₂O₃–X–Al₂O₃–SiO₂ (X = CaO, MgO) glass system have been investigated to evaluate their applicability as sealant for solid oxide fuel cell (SOFC). Chemical interactions with K41X stainless steel and hydrogen‐tightness of these materials were evaluated after operations at high temperatures over 1,000 h in air atmosphere. Formation of a new phase at the steel–glass interface and formation of porosity in the glass were observed and determined as critical problems over mid‐term operations. The role of MgO is important to obtain a gas‐tight sealing. Application of the glass paste without binder addition was performed in order to avoid possible residual porosity related problems. The best glass was finally used as sealant between anodic and cathodic compartments in complete SOFCs operated at 760 and at 800 °C. Open circuit voltages and power densities of the cells were recorded during the first hours of operation.     

Preparation of aluminium lanthanum oxyapatite tapes, La10AlSi5O26.5, by tape casting and reaction sintering

Lanthanum apatite is one of the most promising materials as an electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs) which operate close to 700 °C. Here, we report the preparation and optimization of dense La₁₀AlSi₅O_26.5 tapes obtained by the combination of tape casting technology and reaction sintering. Homogeneous concentrated mixed suspensions of La₂O₃, Al₂O₃ and SiO₂ were prepared in ethanol. The effect of the solid loading, the binder content, ultrasound and the initial particle size of the materials onto the characteristics of the tapes (cracking, composition, microstructure and electrical properties) has been studied. This study paves the way for further improvement in the processing of oxyapatite electrolyte for solid oxide fuel cells.     

Thermal decomposition of fluoropolymers and firing characteristics of priming compositions with fluoropolymers

Many pyrotechnics contain binders, such as nitrocellulose, Viton, and other plastics and elastomers. Most pyrotechnics are prepared by the dispersion of fuel/oxidizer ingredients in a liquid solution, which are then mixed well to form pyrotechnics. The thermal decomposition behavior of a binder is very important to pyrotechnics in a polymer. In this work, the thermal decomposition behaviors of three fluoropolymers have been investigated with differential thermal analysis/thermogravimetry and differential scanning calorimetry. The parameters concerning decomposition have been evaluated with a nonisothermal technique, and a suitable binder is suggested for the Zr/KClO₄ priming mixture. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2054–2059, 2005     

Design and fabrication of photocatalytic coatings with α/β-Bi2O3 and recycled-fly ash for environmental remediation and solar fuel generation

To promote a circular economy, alkali-activated recycled fly ash (AAFA) can be used as an alternative binder for fabricating mortar coatings. The AAFA binder can also be functionalized with photocatalysts for application in environmental remediation. Here, α/β-Bi₂O₃ homojunction photocatalysts were incorporated into AAFA mortar coatings to confer photocatalytic properties for two applications, namely, self-cleaning and solar fuel generation from CO₂ photoconversion. The α/β-Bi₂O₃ homojunctions were prepared using three methods. The homojunctions had a higher proportion of the β-Bi₂O₃ phase compared to α-Bi₂O₃; additionally, they exhibited with a 2D morphology and a bandgap suitable for visible-light activation. X-ray diffraction and energy dispersive spectroscopy analysis of the mortar coatings showed that the inorganic matrix comprised two frameworks based on calcium silicate hydrate and aluminosilicate hydrate, with high porosity. The photocatalytic mortar coatings exhibited self-cleaning activity, with the highest efficiency of 31%. This result was corroborated by total organic carbon analysis, which showed ~15% mineralization. The specimens also showed high activity for CO₂ photoconversion to solar fuels such as formic acid (1932 μmol/g) and methanol (6 μmol/g) under visible light. These results were related to the synergistic effect of the mesoporous framework developed after alkaline activation, more efficient charge transfer in the homojunctions, enhanced CO₂ affinity, and the presence of CaO, MgO, Na₂O, and SiO₂ in the binder. The efficiencies for both applications are comparable to those reported previously. The present approach is potentially applicable not only for minimizing the environmental impact of waste materials by reducing the disposal of fly ash in landfills, but also for producing value-added compounds and reducing the maintenance cost of buildings.     

Curing temperature effect on smokeless fuel briquettes prepared with molasses and H3PO4

Chars from the co-carbonisation of a low-rank coal and olive stones have been used to prepare environmental acceptable smokeless fuel briquettes. The blend was a mixture of char, molasses and H₃PO₄. This acid was added to favour the polymerisation of the binder. The effect of the curing temperature on the physico-chemical features of the briquettes was studied by Fourier Transform Infrared Spectroscopy and Temperature Programmed Decomposition followed by Mass Spectrometry. The presence of H₃PO₄ as well as the curing process at 200 °C of temperature, contribute to the formation of carboxylic acids which lead to the production of briquettes with adequate mechanical properties.     

Organic binder‐free cathode using FeS2‐MWCNTs composite for thermal batteries

FeS₂ ‐ MWCNTs (Multi‐Walled Carbon NanoTubes) composite without using an organic binder was used as a thin cathode for thermal batteries. A thin cathode with FeS₂ ‐ MWCNTs composite exhibited good mechanical strength without an organic binder. A discharge evaluation of the thin cathode with FeS₂ ‐ MWCNTs composite revealed a discharge capacity 2.3 times that of the pellet type cathode and 1.13 times that of a thin cathode with an organic binder. In addition, the single battery applying a thin cathode with FeS₂ ‐ MWCNTs composite showed a lower total polarization than when applying an organic binder. These results showed that FeS₂ ‐ MWCNTs composite is suitable as a thin cathode for thermal batteries.     

Electrochemical oxidation of boron containing compounds on titanium carbide and its implications to direct fuel cells

Electrochemical oxidation of sodium borohydride (NaBH₄) and ammonia borane (NH₃BH₃) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH₄ as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm⁻² at a load current density of 83 mA cm⁻² is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm⁻² at 105 mA cm⁻² is obtained in the case of AB-based fuel cell at 353 K.     

Enhanced stability of a direct-methane and carbon dioxide protonic ceramic fuel cell with a PrCrO3 based reforming layer

Dry reforming of methane (CH₄ + CO₂ = 2CO + 2H₂) is a very interesting approach both to reduce the overall carbon footprint of the increasing worldwide fossil-based methane consumption as well as to cut emission greenhouse gas of CO₂. Utilizing the produced syngas as fuel directly in protonic ceramic fuel cell can further kill two birds with one stone: obtain power output and high purity CO. However, the drawback of the coking deposition limits the process of the above strategy. Here, we synthesis a Ni-based catalyst with high conversion rates (∼88% for CO₂ and ∼89% for CH₄) and excellent stability (>160 h at 700 °C) proceeded by Ce doping, and further employ it as reforming layer on solid oxide fuel cell. The results demonstrate that the Ce substitution plays an important role for homogenous Ni nanoparticles exsolution, benefiting for the coking resistance of the catalyst then the stability of the cell using CH₄ and CO₂ as fuel directly.     

Effect of Carbon Dioxide and Ammonia on Polymer Electrolyte Membrane Fuel Cell Stack Performance

Proton exchange membrane fuel cell (PEMFC) performance degrades when impurities are present in the anode fuel gas, referred to as catalyst poisoning. This paper investigates the effect of carbon dioxide and ammonia as impurities in the anode gas of the PEMFC, and found that the presence of CO₂ decreases the performance of the fuel cell by up to 10%. The performance loss depends on the CO₂ concentration and the exposure time. The voltage loss is recoverable on passing pure hydrogen gas, indicating that a permanent poisoning of the catalyst layer has not taken place. Exposure of the fuel cell to ammonia beyond 20 ppm, even for a short duration, causes permanent PEMFC failure, probably due to the deterioration of the membrane.     

Steam reforming of liquid hydrocarbon fuels for micro-fuel cells. Pre-reforming of model jet fuels over supported metal catalysts

The present work deals with pre-reforming of logistic hydrocarbon fuel (jet fuel) as a part of an integrated approach to developing an on-board fuel reformer for use in a micro-solid-oxide fuel cell system. The purpose of doing pre-reforming is to ensure carbon-free reformulation of JP-8 jet fuel into hydrogen and carbon monoxide for use in a micro-solid-oxide fuel cell. Several model jet fuels have been tested for the pre-reforming at low temperature (450–550 °C) in a lab-scale reforming reactor. Proper temperature control and pre-mixing of feed fuels and steam have been found to be important for the prevention of coke formation prior to pre-reforming. Both noble metal and base-metal catalysts have been prepared and tested. As compared with an Al₂O₃-supported Ni catalyst, supported Rh catalysts show not only high activity but also high resistance to deactivation due to carbon formation. Removal of residual Cl⁻ from Rh/CeO₂–Al₂O₃ improves the metal dispersion and the pre-reforming activity. The reformates from the current pre-reformer contain mainly CH₄, CO, H₂, in which CH₄ can be further converted to H₂ and CO by subsequent main-reforming.     

RECENT ADVANCES IN CaSO4 OXYGEN CARRIER FOR CHEMICAL-LOOPING COMBUSTION (CLC) PROCESS

Chemical-looping combustion (CLC) is a novel combustion technology with inherent separation of the greenhouse gas CO₂ and low NOx (NO, NO₂, N₂O) emissions. In CLC, the solid oxygen carrier supplies the stoichiometric oxygen needed for CO₂ and water formation, resulting in a free nitrogen mixture. The performance of oxygen carrier is the key to CLC's application. A good oxygen carrier for CLC should readily react with the fuel (fuel reactor) and should be re-oxidized upon being contacted with oxygen (air reactor). In this case, the behavior of CaSO₄ as an oxygen carrier for a CLC process, reacting with gas fuels (e.g., CO, H₂, and CH₄) and solid fuels (e.g., coal and biomass), has been analyzed. The performance of the oxygen carrier can be improved by changing the preparation method or by making mixed oxides. Generally, Al₂O₃, SiO₂, etc., which act a porous support providing a higher surface area for reaction, are used as the inert binder to increase the reactivity, durability, and fluidizability of the oxygen carrier particles. Further, simulation analysis of a CLC process based on CaSO₄ oxygen carrier was also analyzed. Finally, some important tendencies related to CaSO₄ oxygen carrier in CLC technology are put forward.     

Effect of cathode binder IEC on kinetic and transport losses in all-SPEEK MEAs

The effect of ion exchange capacity (IEC) and loading of sulfonated polyether ether ketone (SPEEK) binder on PEFC cathode performance was studied. MEAs were prepared by decal transfer onto a SPEEK membrane (IEC-1.75 mequiv./g). The IEC of SPEEK binder in the MEA cathode was varied between 1.3 and 2.1 mequiv./g. Cathodes prepared with 30 wt.% SPEEK loading had an electrochemically active surface area (ECA) that was 25% lower than a Nafion^® bonded electrode with similar loading. Polarization curves were obtained at 80 °C and 75% RH with hydrogen as fuel and air and oxygen (O₂) as oxidants. Polarization data was analyzed to determine the relative contributions of different sources of polarization, namely membrane ohmic losses, electrode ohmic losses, and mass transport losses in the gas diffusion layer, binder film and electrodes. The electrode ohmic and mass transport losses decreased with increase in SPEEK IEC. However, even for the highest SPEEK IEC, these losses were higher than those obtained in a Nafion^® bonded electrode. This was attributed to the lower proton activity and O₂ permeability in SPEEK. The loading of SPEEK in the electrode was found to influence performance in the activation controlled region, with a loading of 7.5 wt.% giving the highest performance. However, gains in this region were negated at higher current densities due to enhanced ohmic and transport losses and MEAs with all binder loadings between 7.5 and 30 wt.% had similar limiting currents.