Development of metal supported solid oxide fuel cells for operation at 500–600 °C

A novel metal-supported solid oxide fuel cell has been developed that is capable of operating at temperatures of 500–600 °C. The rationale behind the materials used to construct this fuel cell type is given, and results are presented from cell testing on hydrogen and reformed natural gas, including durability trials of some 2500 h duration. This new fuel cell variant is shown to be tolerant of carbon monoxide, durable, robust to thermal and redox cycling, and capable of delivering technologically relevant power densities. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Rupture testing as a tool for developing planar solid oxide fuel cell seals

One of the critical issues in designing and fabricating high-performance planar solid oxide fuel cell (pSOFC) stacks is the ability to hermetically seal adjacent metal and ceramic components. In our pSOFC development program, we have designed a testing technique that allows us to screen through the numerous variables involved in developing glass seals. Using this test for example, we have found that the composition of the metal component plays an important role in the strength of the seal. Microstructural analysis of as-sealed specimens revealed that an interfacial reaction zone forms during joining, and it appears that the thickness and composition of this layer are the dominant parameters that control joint strength. In this paper the details of the seal test are reported. The results have proven particularly significant in the development of the next-generation stack design. Supporting microstructural and chemical analyses collected on the test specimens are also presented and used to interpret the seal test results in an effort to identify the necessary steps toward improving glass pSOFC seals. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

An experimental evaluation of the effects of ripple current generated by the power conditioning stage on a proton exchange membrane fuel cell stack

In this article, an impedance model of the proton exchange membrane fuel cell stack (PEMFCS) is proposed. The proposed study employs an equivalent circuit of the PEMFCS derived by the frequency response analysis technique. An equivalent circuit for the PEMFCS is developed to evaluate the effects of ripple currents generated by the power-conditioning unit. The calculated results are then verified by means of experiments using a commercially available PEMFCS. The relationship between ripple current and fuel cell performance, such as power loss and fuel consumption, is investigated. Experimental results show that the ripple current can contribute up to a 6% reduction in the available output power. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

High-temperature electrical testing of a solid oxide fuel cell cathode contact material

The development of high-temperature solid-state devices for energy generation and environmental control applications has advanced remarkably over the past decade. However, there remain a number of technical barriers that still impede widespread commercial application. One of these, for example, is the development of a robust method of conductively joining the mixed-conducting oxide electrodes that lie at the heart of the device to the heat resistant metal interconnect used to transmit power to or from the electrodes and electrochemically active membrane. This study investigated the high-temperature electrical and microstructural characteristics of a series of conductive glass composite paste junctions between two contact materials representative of those used in solid-state electrochemical devices, lanthanum calcium manganate, and 430 stainless steel. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Chemical stability of glass seal interfaces in intermediate temperature solid oxide fuel cells

In intermediate temperature planar solid oxide fuel cell (SOFC) stacks, the interconnect, which is typically made from cost-effective, oxidation-resistant, high-temperature alloys, is typically sealed to the ceramic positive electrode-electrolyte-negative electrode (PEN) by a sealing glass. To maintain the structural stability and minimize the degradation of stack performance, the sealing glass has to be chemically compatible with the PEN and alloy interconnects. In the present study, the chemical compatibility of a barium-calcium-aluminosilicate (BCAS) based glass-ceramic (specifically developed as a sealant in SOFC stacks) with a number of selected oxidation resistant high temperature alloys (and the yttria-stabilized zirconia electrolyte) was evaluated. This paper reports the results of that study, with a particular focus on Crofer22 APU, a new ferritic stainless steel that was developed specifically for SOFC interconnect applications. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Using CrAlN multilayer coatings to improve oxidation resistance of steel interconnects for solid oxide fuel cell stacks

The requirements of low-cost and high-temperature corrosion resistance for bipolar interconnect plates in solid oxide fuel cell stacks has directed attention to the use of metal plates with oxidation resistant coatings. The performance of steel plates with multilayer coatings, consisting of CrN for electrical conductivity and CrAlN for oxidation resistance, was investigated. The coatings were deposited using large area filtered arc deposition technology, and subsequently annealed in air for up to 25 hours at 800 °C. The composition, structure, and morphology of the coated plates were characterized using Rutherford backscattering, nuclear reaction analysis, atomic force microscopy, and transmission electron microscopy techniques. By altering the architecture of the layers within the coatings, the rate of oxidation was reduced by more than an order of magnitude. Electrical resistance was measured at room temperature. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Evaluation of ferritic stainless steel for use as metal interconnects for solid oxide fuel cells

Interconnect development for planar solid oxide fuel cells is considered a vital technical area requiring focused research to meet the performance and cost goals. A commercial ferritic stainless steel composition for oxidation resistance properties was investigated by measuring the weight gain due to air exposure at fuel cell operating temperature. A surface treatment process was found to produce a dense, adherent scale and to reduce the oxide scale growth rate significantly. A process was also identified for coating the surface of the alloy to reduce the in-plane resistance and potentially to inhibit chromium oxide evaporation. The combination of treatments provided a very low resistance through the scale. The resistance measured was as low as 10 mΩ-cm² air. The resistance value was stable over several thermal cycles. The treated samples were exposed to a variety of atmospheres that were relevant in fuel cell operation to evaluate changes in scale morphology. Analysis of the scale after such exposure showed the presence of a stable composition. When exposed to a dual atmosphere (air and hydrogen on opposite sides of the metal sheet), however, the scale composition contained a mixture of phases. Additional process modifications are planned to reduce the effect of dual-atmosphere exposure. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory. S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Observations on the structural degradation of silver during simultaneous exposure to oxidizing and reducing environments

The structural stability of silver (Ag) in dual atmosphere exposure conditions, which are representative of solid oxide fuel cell (SOFC) current collector and gas seals, has been examined in the 600–800 °C temperature range. Experiments conducted on Ag tubular sections exposed to flowing H₂-3% H₂O (inside the tube) and air (outside the tube) showed extensive porosity formation along the grain boundaries in the bulk metal. Similar tubular sections, when exposed to air only (both inside and outside the tube), showed no bulk porosity or structural changes. It is postulated that the porosity formation in the bulk metal is related to the formation of gaseous H₂O bubbles due to simultaneous diffusion of hydrogen and oxygen followed by subsequent interaction resulting in the formation of steam. Thermochemical processes that are responsible for structural degradation are presented and discussed. Based on experimental observations, it is concluded that Ag metal may not provide adequate long-term structural stability under a dual-environment condition that is typical of interconnects or gas seals in intermediate temperature SOFCs. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Development of proton conductors using pyrochlore-perovskite phase boundaries

The pyrochlore-perovskite binary systems La₂Zr₂O₇-SrZrO₃ and La₂Zr₂O₇-LaYO₃ were studied as potential high-temperature proton conductors. X-ray diffraction and direct current conductivity measurements were used to develop empirical relationships between structure and conductivity. The solubilities of Sr in La₂Zr₂O₇ and La in SrZrO₃ were low, less than 0.1 mol fraction. The solubility of Zr in LaYO₃ was at least 0.125 mol fraction, and the solubility of Y in La₂Zr₂O₇ was at least 0.25 mol fraction. Y-doped La₂Zr₂O₇ had the highest electrical conductivity, though no composition exceeded σ=3×10⁻⁴ S/cm at the target temperature of 600 °C. The effectiveness of Y as a dopant in La₂Zr₂O₇ was limited because Y substituted for both La on the A-site and Zr on the B-site. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Polarization study on doped lanthanum gallate electrolyte using impedance spectroscopy

Alternating current complex impedance spectroscopy studies were conducted on symmetrical cells of the type [gas, electrode/La_1−x Sr _x Ga_1−y Mg _y O₃ (LSGM) electrolyte/electrode, gas]. The electrode materials were slurry-coated on both sides of the LSGM electrolyte support. The electrodes selected for this investigation are candidate materials for solid oxide fuel cell (SOFC) electrodes. Cathode materials include La_1−x Sr _x MnO₃ (LSM), La_1−x Sr _x Co _y Fe_1−y O₃ (LSCF), a two-phase particulate composite consisting of LSM and doped-lanthanum gallate (LSGM), and LSCF + LSGM. Pt metal electrodes were also used for the purpose of comparison. Anode material investigated was the Ni + Ce_0.85Gd_0.15O₂ composite. The study revealed important details pertaining to the charge-transfer reactions that occur in such electrodes. The information obtained can be used to design electrodes for intermediate temperature SOFCs based on LSGM electrolytes. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Effect of acidic surface functional groups on Cr（VI） removal by activated carbon from aqueous solution

The activated carbon with high surface area was prepared by KOH activation. It was further modified by H2SO4 and HNO3 to introduce more surface functional groups. The pore structure of the activated carbons before and after modification was analyzed based on the nitrogen ad-sorption isotherms. The morphology of those activated carbons was characterized using scanning electronic microscopy (SEM). The surface functional groups were determined by Fourier transform infrared spectroscopy (FTIR). The quantity of those groups was measured by the Boehm titration method. Cr(Ⅵ) removal by the activated carbons from aqueous solution was investigated at different pH values. The results show that compared with H2SO4, HNO3 destructs the original pore of the activated carbon more seriously and induces more acidic surface functional groups on the activated carbon. The pH value of the solution plays a key role in the Cr(Ⅵ) removal. The ability of reducing Cr(Ⅵ) to Cr(Ⅲ) by the activated carbons is relative to the acidic surface functional groups. At higher pH values, the Cr(Ⅵ) removal ratio is im-proved by increasing the acidic surface functional groups of the activated carbons. At lower pH values, however, the acidic surface functional groups almost have no effect on the Cr(Ⅵ) removal by the activated carbon from aqueous solution.     

Temperature dependences of methane elution on a Cu<Subscript>3</Subscript>(BTC)<Subscript>2</Subscript> metal-organic framework

Methane elution from a helium flow was studied on a metal-organic framework Cu₃(BTC)₂ with gas chromatography under temperatures from 20 to 60°C. Specific retention volumes were calculated, and heat of adsorption was determined. The obtained values are characteristic for the microporous adsorbents having relatively large micropores and a low total volume of the micropores. The calculated efficiencies of an adsorbent layer alter slightly and their absolute values are significantly smaller than those of the activated carbons. Efficient kinetic constant has a parabolic dependence on temperature with a minimum at 40°C. Correctness of the developed algorithms to calculate elution constants on adsorbent layers of small length has been confirmed.     

Development of mesopores in active carbons by iron catalyzed carbon hydrogenation

The effect of iron content in the pores of SUA active carbons on the changes in their porous structure in catalyzed hydrogenation of carbon was studied. It was found that preferential development of mesopores occurs during the reaction in adsorbents; increased content of the catalyst results in an increase in the fraction of wide mesopores and the average size of mesopores.     

Analysis of microporous structure of carbon adsorbents in terms of the theory of volume filling of micropores

A methodology of using the theory of filling the volume of micropores when evaluating the porous structure of carbon nanomaterials and adsorbents, as well as describing the adsorption of different species, is considered. Potentialities of the mathematical means of a theory of filling the volume of micropores when differentiating homogeneous and irregular microporous structure of activated carbon, determining the micropores’ parameters (their volume and size), evaluating the degree of heterogeneity of microporous structures, and describing adsorption over wide concentration range are analyzed. The perspectives of this approach, based on the theory of filling the volume of micropores, in the prognosis of the microporous structures’ parameters and the activated carbons’ adsorbability in the process of their synthesis are demonstrated. Original Russian Text ? G.A. Petukhova, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 2, pp. 170–176.     

Effect of acidic surface functional groups on Cr(Ⅵ) removal by activated carbon from aqueous solution

The activated carbon with high surface area was prepared by KOH activation.It was further modified by H2SO4 and HNO3 to introduce more surface functional groups.The pore structure of the activated carbons before and after modification was analyzed based on the nitrogen adsorption isotherms.The morphology of those activated carbons was characterized using scanning electronic microscopy (SEM).The surface functional groups were determined by Fourier transform infrared spectroscopy (FTIR).The quantity of those ...     

Synthesis and Characterization of Novel Sulfur-Functionalized Silica Gels as Mercury Adsorbents

This paper describes the synthesis, functionalization, and characterization of silica gels as mercury adsorbents. The synthesis was carried out according to the modified Stöber method using tetraethyl orthosilicate [TEOS], 3-mercaptopropyl trimethoxysilane [MPTMS] and bis(triethoxysilylpropyl) tetrasulfide [BTEPST] as precursors. The functionalization was carried out via co-condensation and impregnation methods using MPTMS, BTESPT, elemental sulfur [ES], and carbon disulfide [CS₂] as sulfur ligands. The choice of the sulfur ligands as precursors and functionalization agents was due to the existence of sulfur active groups in their molecular structures which were expected to have high affinity toward Hg(II) ions. The synthesized adsorbents were characterized by using scanning electron microscope, fourier transform infrared spectrophotometer, nitrogen adsorption/desorption, and energy dispersive X-ray diffractometer. The batch Hg(II) adsorption experiments were employed to evaluate the Hg(II) adsorption performances of the synthesized adsorbents under different pH values. The results revealed that the highest Hg(II) adsorption capacity was obtained for the SG-MPTMS(10) which was 47.83 mg/g at pH 8.5. In general, the existence of sulfur functional groups, especially MPTMS in the silica matrices, gave a significant enhancement of Hg(II) adsorption capacity and the sulfur functionalization via co-condensation method, which is potential as a superior approach in the mercury adsorbent synthesis.     

Dosierung von Schadgasen mit Hilfe von Lochblenden – Ein Verfahren zur Korrosionsprüfung an Edelmetallwerkstoffen der Elektrotechnik

Proportioning of noxious gases through hole type diaphragms – A method for testing the corrosion resistance of nobel metal materials for electrical engineering Corrosion testing of nobel metal base materials for weak current engineering requires laboratory proportioning methods enabling the usually occurring noxious gases (such as hydrogen sulfide, sulfurdioxide or nitrogen oxides) to be added to a carrier gas stream in concentrations between appr. 10 ppb and 10 ppm. The authors present a method suitable for corrosion applications; this method is based on hole diaphragms used in the so called critical flow range. This method utilizes the phenomenon that – if the pressure difference across the diaphragm is sufficiently high – the gas flow rate in the narrowest cross section of the diaphragm hole will approach the velocity of sound, which, however, will not be exceeded even if the pressure difference is further increases. The diaphragms used were gold foils having hole diameters between 10 and 100 microns so that with a two-step dilution concentrations between 0.1 ppm and > 100 ppm could be obtained. This proportioning mecanism is of simple design and, because of the absence of moving or fragile parts, rather robust. The concentrations of the noxious gases may be held constant for a long time; the method prooves also successful when compared to other known metering methods. It appears therefore perfectly sutied to incorporation in the planned testing standards DIN 40 046, parts 36 and 37.     

Physicochemical properties of palladium adsorbents as catalysts in liquid-phase hydrogenation

The structure and physicochemical properties of palladium catalysts used in liquid-phase hydrogenation processes were studied with the use of adsorption, calorimetric, thermogravimetry, and temperature-programmed reduction techniques. The specific surface areas and average sizes and volume of pores of the adsorbents were determined. The palladium on activated carbon catalysts was found to possess a complex porous structure, whereas palladium on combined alumina and coal carrier catalysts is an adsorbent with a nonporous structure. The concentration of the applied metal and the nature of a support have a significant impact on the physicochemical properties of palladium catalysts.     

STUDY ON THE PROPERTIES OF DIFFERENT ACTIVATED CARBON FIBERS AND THEIR ADSORPTION CHARACTERISTICS FOR FORMALDEHYDE

1. IntroductionOne of the undesirable features of the modern day world is the widespread coatami-nation associated with the release of a large number of chemicals into the environment.At presellt, people paid more and more attention to indoor air pollution than ever be-cause people almost spend their 8ty90% time in rooms everyday. FOrmaldehyde and otheraldehydes are main pollutans in indoor air. Formaldel1yde is a kind of poison. Highconceatrated formaldehyde can cause a 8eries of symptoms su…     

Hydrogen (H<Subscript>2</Subscript>) Adsorption in Model Carbon Adsorbents with Slitlike Micropores

The Dubinin theory of volume filling of micropores and the linearity of adsorption isosteres were used to calculate the adsorption of hydrogen on model microporous adsorbents with slitlike pores. In calculating, the model adsorbents were considered the micropores of which were formed through a progressive removal of one, two, and so on to seven layers of hexagonal carbon in a graphite crystalline structure, while the micropore sizes varied within a range from 0.5 to 2.5 nm. The integral energy of adsorption was evaluated for the model structures and most of industrial carbon adsorbents. The obtained results were compared with experimental data. Dependences of the gravimetric density of hydrogen on temperature and pressure were analyzed.