Kent Kammer Hansen

Solid Oxide Fuel Cell

SOFC cell comprising a metallic support 1 ending in a substantially pure electron conducting oxide, an active anode layer 2 consisting of doped ceria, ScYSZ, Ni—Fe alloy, an electrolyte layer 3 consisting of co-doped zirconia based on oxygen ionic conductor, an active cathode layer 5 and a layer of a mixture of LSM and a ferrite as a transition layer 6 to a cathode current collector 7 of single phase LSM. The use of a metallic support instead of a Ni—YSZ anode support increases the mechanical strength of the support and secures redox stability of the support. The porous ferrite stainless steel ends in a pure electron conducting oxide so as to prevent reactivity between the metals in the active anode which tends to dissolve into the ferrite stainless steel causing a detrimental phase shift from ferrite to austenite structure.

Perovskites as Cathodes for Nitric Oxide Reduction

Using cone shaped electrodes, the electrochemical reduction of nitric oxide and oxygen has been investigated by cyclic voltammetry on an oxygen overstoichiometric (La{sub 0.85}Sr{sub 0.15}MnO{sub 3+{delta}}), and an oxygen stoichiometric (La{sub 0.85}Sr{sub 0.15}CoO{sub 3{minus}{delta}}) perovskite over the temperature range 300--500 C. An oxygen ion-conducting 10% gadolinium-doped cerium oxide is used as electrolyte. It is shown that the reduction of nitric oxide proceeds rapidly on La{sub 0.85}Sr{sub 0.15}MnO{sub 3+{delta}} compared to the oxygen reduction while the oxygen reduction on La{sub 0.85}Sr{sub 0.15}CoO{sub 3{minus}{delta}} is faster than the nitric oxide reduction.

Electrochemical reduction of NO and O2 on Cu/CuO

The electrochemical reduction of NO and O2 on a Cu-point electrode covered with a surface layer of CuO is investigated in an electrochemical cell with a gadolinium doped cerium oxide oxygen ion conducting electrolyte in the temperature interval 300–500 ∘C. It is shown that the reduction of NO on CuO is possible at a lower overvoltage than it is in the case of the reduction of O2. The results indicate that the reduction of NO on CuO is not inhibited in the presence of O2 and that the reduction of NO can be selectively performed on a CuO-electrode.

Strontium Titanate-based Composite Anodes for Solid Oxide Fuel Cells

Surfactant-assisted infiltration of Gd-doped ceria (CGO) in Nbdoped SrTiO3 (STN) was investigated as a potential fuel electrode for solid oxide fuel cells (SOFC). An electronically conductive backbone structure of STN was first fabricated at high temperatures and then combined with the mixed conducting and electrochemically active nano-sized CGO phase at low temperatures. Symmetrical cell measurements at open circuit voltage (OCV), showed that the electrochemical activity was maintained or even improved compared to Ni/YSZ fuel electrodes. The novel electrode had an electrode polarization resistance of 0.12 � cm 2 and 0.44 � cm 2 in humidified H2 at 850 oC and 650 oC, respectively. In addition, the ceramic composite electrode was shown to be redox stable. The electrode was actually activated with redox cycles at 650 oC. The ceramic electrode structure thus presents a potential solution to overcome some of the major limitations of the current Ni-YSZ cermet SOFC anodes.

The Effect of a CGO Barrier Layer on the Performance of LSM/YSZ SOFC Cathodes

The solid oxide fuel cell SOFC is a device that converts the chemical energy directly into heat and electricity. The SOFC is traditionally constructed from a strontium-substituted lanthanum manganite/yttria-stabilized zirconia LSM/YSZ composite cathode, a YSZ electrolyte, and a Ni/YSZ composite anode. To lower the operation temperature of the SOFC, new electrode materials are needed, especially on the cathode side. The cathodes that perform better than the traditional LSM/YSZ cathodes are Fe–Co-based perovskites. 1 However, these types of cathodes react with the zirconia-based electrolyte. 2 To use Fe–Co-based perovskite cathodes, a barrier layer between the cathode and the electrolyte is therefore needed to prevent a reaction. Several attempts to use a cerium– gadolinium oxide CGO-based barrier layer have been done. 3-7 It has been shown that a CGO barrier layer prevents the formation of a reaction layer between a Fe–Co-based cathode and a zirconiabased electrolyte. In this study, the effect of a spin-coated CGO barrier layer between the YSZ electrolyte and an LSM/YSZ cathode was studied using electrochemical impedance spectroscopy EIS to investigate the effect of the CGO barrier layer as such. This was possible compared to LSM/YSZ electrodes put directly onto YSZ as strontiumsubstituted lanthanum manganite LSM does not react with YSZ. It is not possible to study the effect of the CGO barrier as such using cobalt-based perovskites as they react with YSZ and, therefore, cannot be put directly onto YSZ. Experimental The LSM25 La0.75Sr0.250.95MnO3+ powder was used as received from Haldor Topsoe A/S. The LSM25 powder was synthesized using drip pyrolysis. The phase purity of the LSM25 powder was confirmed by powder X-ray diffraction. For the synthesis of the LSM25 powder, the following metal nitrates were used: LaNO33·6H2O Alfa Aesar, 99.9% ,S rNO32 Alfa Aesar, 99%, and MnNO32·4H2O Alfa Aesar, 98%. Aqueous solutions of the metal nitrates were made, and the concentrations of these solutions were determined using gravimetry. The YSZ electrolyte powder was also used as received from the supplier Tosoh. Cathode slurries were prepared by mixing LSM25 and YSZ, in a 50 wt % ratio, with a dispersant and a binder and by ballmilling for 24 h. The dispersant was polyvinylpyrrolidone PVP, Sigma Aldrich. The binder was a mixture of Mowital B60H, PVP, dibutylphthalat Merck, and polyethylene glycolMerck .A3 %w/w dispersant and a 2% w/w binder were added to the slurries. The mean particle size of the slurry was 0.9 m. Precursor solutions for CGO were prepared by dissolving CeNO33 Alfa Aesar, 99.5% ,G dNO33 Alfa Aesar, 99.9%, nitric acid, and ethylene glycol in water and by heating the mixture at 80°C. The heating was stopped when the room temperature viscosity of the solution reached 50 mPa s. The room temperature viscosity was determined using a Haake Rheostress 600 rheometer. Spin coating by the CGO precursor solution was performed using a WS-400A-8NPP/lite spin coater from Laurell Technologies. After spin coating, the samples were heat-treated at 550°C for 2 h. To ensure the complete coverage of the tape surfaces, spin coating and heat-treatment were repeated four times. Both surfaces of the tapes were coated. The resulting film had a thickness of 150 nm. Details of the CGO thin-film fabrication can be found in a previous publication. 8 Symmetric cells comprised of porous LSM/YSZ/dense YSZ/porous LSM/YSZ were prepared by spraying, with a spraying robot, on both sides of dense-sintered electrolyte tapes. The following were used as electrolyte tapes: i YSZ tapes and ii CGO thinfilm-coated YSZ tapes. The symmetrical cells with and without a CGO barrier layer were sprayed in one go to make the fabrication of the symmetrical cells as uniform as possible. The symmetrical cells were sintered at 1050°C/2 h. At this sintering temperature, CGO

NOx conversion on LSM15-CGO10 cell stacks with BaO impregnation

The electrochemical conversion of NOx on non-impregnated and BaO-impregnated LSM15-CGO10 (La0.85Sr0.15MnO3–Ce0.9Gd0.1O1.95) porous cell stacks has been investigated, and extensive impedance analysis have been performed to identify the effect of the BaO on the electrode processes. The investigation was conducted in the temperature range 300–500 °C, a polarisation range from 3 V to 9 V and in atmospheres containing 1000 ppm NO, 1000 ppm NO + 10% O2 and 10% O2. On the non-impregnated cell stacks no NOx conversion was observed under any of the investigated conditions. However, BaO impregnation greatly enhanced the NOx conversion and at 400 °C and 9 V polarisation a BaO-impregnated cell stack showed 60% NOx conversion into N2 with 8% current efficiency in 1000 ppm NO + 10% O2. This demonstrates high NOx conversion can be achieved on an entirely ceramic cell without expensive noble metals. Furthermore the NOx conversion and current efficiency was shown to be strongly dependent on temperature and polarisation. The impedance analysis revealed that the BaO-impregnation increased the overall activity of the cell stacks, but also changed the adsorption state of NOx on the electrodes; whether the increased activity or the changed adsorption state is mainly responsible for the improved NOx conversion remains unknown.

Diffuse Reflectance Infrared Fourier Transform Study of NOx Adsorption on CGO10 Impregnated with K2O or BaO

In the present work diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy is applied to study the adsorption of NO(x) at 300-500 °C in different atmospheres on gadolinium-doped ceria (CGO), an important material in electrodes investigated for electrochemical NO(x) removal. Furthermore, the effect on the NO(x) adsorption when adding K(2)O or BaO to the CGO is investigated. The DRIFT study shows mainly the presence of nitrate species at 500 °C, whereas at lower temperature a diversity of adsorbed NO(x) species exists on the CGO. The presence of O(2) is shown to have a strong effect on the adsorption of NO, but no effect on the adsorption of NO(2). Addition of K(2)O and BaO dramatically affects the NO(x) adsorption and the results also show that the adsorbed NO(x) species are mobile and capable of changing adsorption state in the investigated temperature range.

Gd0.6Sr0.4Fe0.8Co0.2O3 − δ : A Novel Type of SOFC Cathode

The fabrication and electrochemical activity of a type of solid oxide fuel cell (SOFC) cathode is described in this paper. In search of new cathodes a Gd 0.6 (Sr 0.4 Fe 0.8 Co 0.2 O 3-δ compound was synthesized using the glycine-nitrate method. It turned out that this was a two-phase compound consisting of two perovskite phases, a cubic and an orthorhombic phase, as shown by Rietveld refinements. These two phases were synthesized and a cone-shaped electrode study was undertaken. It was shown that the composite cathode had an electrochemical activity superior to that of the two single-phase perovskites, indicating that the unique microstructure of this type of cathode is essential for achieving high electrochemical activity toward the reduction of oxygen in a SOFC.

NOx selective catalytic reduction (SCR) on self-supported V–W-doped TiO2 nanofibers

Electrospun V–W–TiO2 catalysts, resulting in a solid solution of V and W in the anatase phase, are prepared as nonwoven nanofibers for NOx selective catalytic reduction (SCR). Preliminary catalytic characterization indicates their superior NOx conversion efficiency to the-state-of-the-art material. A novel concept of a self-supported, ultra-compact, and lightweight nanofibrous SCR-reactor is defined.

Optimization of an electrochemical cell with an adsorption layer for NOx removal

The structure of a multilayer electrochemical cell with an adsorption layer was optimized by removing an yttria-stabilized zirconia cover layer. It was found that the NOx removal properties of the electrochemical cell were dramatically enhanced through the optimization, especially under conditions of low voltage, intermediate temperature, and high O2 concentration. The pronounced increase in activity and selectivity for NOx decomposition after removing the ytrria-stabilized zirconia cover layer was attributed to the extensive release of selective reaction sites for NOx species and a strong promotion for NOx reduction from the interaction of the directly connected adsorption layer with both the Pt and catalytic layers. The optimized electrochemical cell may provide a promising solution for NOx emission control.