High-performance, anode-supported, microtubular sofc prepared from single-step-fabricated, dual-layer hollow fibers

A high-performance, microtubular solid oxide fuel cell is developed using an improved electrolyte/anode dual-layer hollow fiber fabricated via a novel coextrusion and co-sintering technique. The technique allows control over the porosity of the anode, resulting in an increase in the power output to almost double what has been previously reported

Management and Tillage Infl uence Barley Forage Productivity and Water Use in Dryland Cropping Systems

Annual cereal forages are resilient in water use (WU), water use efficiency (WUE), and weed control compared with grain crops in dryland systems. The combined influence of tillage and management systems on annual cereal forage productivity and WU is not well documented. We conducted a field study for the effects of tillage (no-till and tilled) and management (ecological and conventional) systems on WU and performance of forage barley (Hordeum vulgare L.) and weed biomass in two crop rotations (wheat [Triticum aestivum L.]–forage barley–pea [Pisum sativum L.] and wheat–forage barley–corn [Zea mays L.] –pea) from 2004 to 2010 in eastern Montana. Conventional management included recommended seeding rates, broadcast N fertilization, and short stubble height of wheat. Ecological management included 33% greater seeding rates, banded N fertilization at planting, and taller wheat stubble. Forage barley in ecological management had 28 more plants m–2, 2 cm greater height, 65 more tillers m–2, 606 kg ha–1 greater crop biomass, 3.5 kg ha–1 mm–1greater WUE, and 47% reduction in weed biomass at harvest than in conventional management. Pre-plant and post-harvest soil water contents were similar among tillage and management systems, but barley WU was 13 mm greater in 4-yr than 3-yr rotation. Tillage had little effect on barley performance and WU. Dryland forage barley with higher seeding rate and banded N fertilization in more diversified rotation produced more yield and used water more efficiently than that with conventional seeding rate, broadcast N fertilization, and less diversified rotation in the semiarid northern Great Plains

New fabrication techniques for micro-tubular hollow finer solid oxide fuel cells

A novel combination of phase inversion and electrophoretic deposition was used in the fabrication of anode supported micro tubular (hollow fiber) solid oxide fuel cells (MT-HF-SOFCs). The phase inversion process was used to produce ca. 240 μm thick, highly porous 60 wt. % NiO-40 wt. % yttria-stabilised zirconia (YSZ) hollow fiber anode precursors. The electrophoretic deposition process was then used to apply ca. 40 μm thick, particulate YSZ electrolyte layers onto the unsintered NiO-YSZ HFs from an ethanol suspension at an applied electric field of ca. 0.22 kV cm-1. The YSZ-coated NiO-YSZ HFs were sintered at 1500 oC for twelve hours. Dispersions of YSZ-LSM particles were then painted on top of the electrolyte layer, as ‘graded’ YSZ-LSM porous cathode precursors that were sintered at 1200 oC for three hours. The fabrication process was completed by winding silver wire current collectors spirally round the cathodes and through the lumen of the fibers to enable current collection from the anodes. Single MT-HF-SOFCs delivered peak power densities of 0.20, 0.18 and 0.14 W cm-2 at 800, 750 and 700 oC, respectively, with flow rates of 15 cm3 min-1 H2 (97% H2-3% H2O) and 30 cm3 min-1 of air

Novel fabrication technique of hollow fibre support for micro-tubular solid oxide fuel cells

In this work, a cerium-gadolinium oxide (CGO)/nickel (Ni)-CGO hollow fibre (HF) for micro-tubular solid oxide fuel cells (SOFCs), which consists of a fully gas-tight outer electrolyte layer supported on a porous inner composite anode layer, has been developed via a novel single-step co-extrusion/co-sintering technique, followed by an easy reduction process. After depositing a multi-layers cathode layer and applying current collectors on both anode and cathode, a micro-tubular SOFC is developed with the maximum power densities of 440–1000 W m-2 at 450–580 °C. Efforts have been made in enhancing the performance of the cell by reducing the co-sintering temperature and improving the cathode layer and current collection from inner (anode) wall. The improved cell produces maximum power densities of 3400–6800 W m-2 at 550–600 °C, almost fivefold higher than the previous cell. Further improvement has been carried out by reducing thickness of the electrolyte layer. Uniform and defect-free outer electrolyte layer as thin as 10 µm can be achieved when the extrusion rate of the outer layer is controlled. The highest power output of 11,100 W m-2 is obtained for the cell of 10 µm electrolyte layer at 600 °C. This result further highlights the potential of co-extrusion technique in producing high quality dual-layer HF support for micro-tubular SOFC

Fabrication and Characterization of Hollow Fibre Micro-tubular Solid Oxide Fuel Cells

Despite three decades of development of solid oxide fuel cells (SOFCs) since the conception of the tubular Siemens–Westinghouse design, no practical alternatives to yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (CGO) electrolytes have been established. However, there have been considerable improvements in the performance of SOFCs, decreasing their specific overall costs, by decreasing operating temperatures, understanding their reaction kinetics, increasing specific surface areas of electrode / electrolyte / reactant three-phase boundaries, establishing new fabrication techniques and employing new geometric designs. So called micro-tubular SOFCs (MT-SOFCs) are one of the most promising geometric designs, though a misnomer, as tube diameters are normally several millimetres, significantly smaller than Siemens–Westinghouse SOFCs with 22 mm tube diameters. This three-year Ph.D. project was aiming to establish the feasibility of, and develop, a novel design of SOFC, fabricated using hollow fibres (HFs) with diameters of hundreds of micrometres, thereby increasing the specific surface area of electrodes, increasing the power output per unit volume/mass, facilitating sealing at high temperatures, and decreasing costs. Collaborators used a spinneret in phase inversion process to produce HFs with non-porous, gas-tight cores and porous outer layers ca. 50-100 μm thick; suspensions of YSZ or CGO particles were used to produce the precursor micro-tubes for electrolyte-supported structures. After sintering the HFs, Ni was deposited electrolessly onto their inner surfaces to form Ni-YSZ anodes, using aqueous nickel (II) solutions and (sodium) hypophosphite (H2PO2-) as the reducing agent. With YSZ electrolyte-supported structures, lanthanum strontium manganite (LSM)-YSZ particles were then coated onto outer surfaces of the HFs to form cathodes; these cells produced only 46-400 W m-2 at 800 oC, compared with ca. 800 W m-2 at 600 oC for CGO-supported cells. Anode-supported structures were also produced using non-conductive, porous NiO-YSZ HFs as anode precursors. YSZ particles were suspended in ethanol and electrophoretically deposited (EPD) onto the external surface of NiO-YSZ HFs, requiring electric fields of ca. 22 kV m-1 between a tubular Cu cathode, placed inside the porous HF precursor, and a tubular platinised titanium mesh anode; this implied they had an effective positive charge. The YSZ-coated NiO-YSZ fibres were then co-sintered at 1500 oC. Mixed (YSZ-LSM) and pure LSM cathode layers, for creating functional layers and enhanced current collector electrodes, were deposited using a paint brush and re-sintered at 1200 oC. The resulting anode-supported HF-MT-SOFCs delivered peak power density of 2 kW m-2 at 800 oC. Collaborators then used a triple orifice spinneret in the phase inversion process to co-extrude CGO/NiO-CGO dual layer-HFs, which were then co-sintered. Dispersions of CGO-LSCF particles were then painted or sprayed onto their outer surfaces, as "graded" LSCF-CGO porous cathode precursors that were then sintered at 1200 oC. HF-MT-SOFC fabrication was completed by winding a silver wire current collector spirally round the cathode. Similar arrangements were used for collecting the current from the HF lumen (anode). The use of functional cathode layers, higher porosity anodes, improved anode and cathode current collectors, and optimizing the thickness of the electrolyte layer and operating parameters, enabled maximum power densities of ca. 25 kW m-2 at ca. 600 oC, believed to be a record for a single MT-SOFC. The effects of electrolyte thickness (100-10 μm), cell length (10-50 mm), and anode morphologies / porosities were also determined. HF-MT-SOFCs were found to be stable to reduction/oxidation and thermal cycling for up to 8 days. Finally, a novel design for stacking individual HF-MT-SOFC in series (voltage scale up) and parallel (current scale up) was studied experimentally; 3 HF-MT-SOFCs in parallel delivered ca. 0.67 W (=3.4 kW m-2) at 7.5 kA m-2, 0.45 V and 600 oC