Fuel cells offer the possibility of zero-emissions electricity generation and increased energy security. We review here the current status of solid oxide (SOFC) and polymer electrolyte membrane (PEMFC) fuel cells. Such solid electrolyte systems obviate the need to contain corrosive liquids and are thus preferred by many developers over alkali, phosphoric acid or molten carbonate fuel cells. Dramatic improvements in power densities have been achieved in both SOFC and PEMFC systems through reduction of the electrolyte thickness and architectural control of the composite electrodes. Current efforts are aimed at reducing SOFC costs by lowering operating temperatures to 500–800 °C, and reducing PEMFC system complexity be developing ‘water-free’ membranes which can also be operated at temperatures slightly above 100 °C.

Fuel cell materials and components

In order to combine the mechanical properties of yttria-stabilised zirconia (ZrO2–3 mol% Y2O3; code Y–ZrO2) with the bioactivity of titania (TiO2), Y–ZrO2–TiO2 green compacts with 0–40 vol.% TiO2 were sintered at 1300, 1400, and 1500 degrees Celsius for 4 h, respectively. The
microstructural features such as grains, pores, and phases were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDX). The mechanical properties such as hardness and toughness were also determined using the methods of Vickers indentation and Knoop indentation. All the composites showed the major tetragonal Y–ZrO2 phase regardless of the content of the added TiO2. However, rutile TiO2 phase was obtained at 1300 degrees Celsius, whereas zirconium titanate (ZrTiO4) phase was found at 1400 and 1500 degrees Celsius. The Y–ZrO2–ZrTiO4 composites sintered at 1500 degrees Celsius showed relatively high hardness (860–1000 kg/mm2) and toughness(4.0–4.5MPam0.5), whereas the Y–ZrO2–TiO2 composites sintered at 1300 degrees Celsius had slightly lower hardness (720–950 kg/mm2) and fracture toughness (3.1–3.3MPam0.5).

Effect of titania addition on yttria-stabilised tetragonalzirconia ceramics sintered at high temperatures

A continuous roll-to-roll manufacturing process is a next-generation process for the environmentally friendly and low-cost mass production of functional printed devices. Unlike paper product printing, a thin plastic web used as a base film in printed electronic devices is exceptionally vulnerable to elastic and thermal deformations owing to its viscoelastic characteristic, which makes the fabrication of highly integrated printed functional devices very challenging. Herein, we review the representative studies regarding the tension applied to the web during the roll-to-roll process and alternatives for compensating web deformation errors. Also, we introduce the development of the theoretical models expressing the dynamics of tension and lateral motion during the web transporting process. We also discuss applicable controllers for compensating the tension and lateral errors and discuss register errors and associated control techniques. Finally, we summarize the mathematical model applied to the internal stress in wound roll and winding tension control techniques, highlighting the idea that defects in the wound roll can be decreased by controlling the winding tension. The review can be helpful in the design of web dynamic control systems in the multi-layer roll-to-roll manufacturing process.

Theories and Control Technologies for Web Handling in the Roll-to-Roll Manufacturing Process

Influence of microwave processing and sintering temperature on the structure and properties of Sr/Zr doped hydroxyapatite

Thermal barrier coatings (TBCs) typically have low thermal conductivity and high resistance to oxidation at elevated temperatures. TBCs are used to protect the turbine blades of aircraft engines op...

Effect of Lanthanum Zirconate on High Temperature Resistance of Thermal Barrier Coatings

Doped and co-doped ceria ceramics are used as electrolyte materials in solid oxide fuel cells. In this work, ceria-based oxides, Ce0.90Gd0.06Y0.02M0.02O2−δ (M = Ca, Fe, La, and Sr) were prepared by conventional as well as microwave processing from the precursors prepared by the mixed oxide method. The consolidated calcined powders in pellet form were sintered in microwave energy at 1400°C for 20 min and in an electric furnace of IR radiation at 1400°C for 6 h. The x-ray diffraction analysis confirmed that all the compositions were crystallized into a cubic fluorite structure. Surface morphology of the sintered products was studied using scanning electron microscopy and the microhardness was investigated using the Vickers hardness test. The comparative results analysis shows that the microwave-sintered samples have uniform grain growth, higher density and higher microhardness than the corresponding conventionally sintered products. The microwave-sintered sample of composition Ce0.90Gd0.06Y0.02Sr0.02O2−δ was found to have the highest microhardness among the four compositions due to its high density and smallest grain size.

Effect of Dopants and Sintering Method on the Properties of Ceria-Based Electrolytes for IT-SOFCs Applications

Zirconia-based ceramic oxides Zr0.90Y0.06Ce0.02X0.02O2−δ (X = Ca, Fe, La, Sr, and Mg) were prepared by conventional and microwave processing. The precursors of Zr0.90Y0.06Ce0.02X0.02O2−δ (X = Ca, Fe, La, Sr, and Mg) were prepared by a mixed oxide method and were calcined at 600°C in an electric furnace. The powders were consolidated in pellet form and sintered in a conventional electric furnace at 1400°C for 6 h and compared using microwave energy at 1400°C for 20 min. The structure and microstructure of sintered products obtained by both methods were studied by x-ray diffraction and scanning electron microscopy. Their density and microhardness were also compared. The electrical conductivities of these samples were studied using alternating current impedance spectroscopy. The analysis of the products obtained by microwave aand conventional methods shows that the microwave sintered samples have uniform grain growth, higher density, higher microhardness and higher electrical conductivity than the corresponding conventionally sintered products. The microwave sintered sample of composition Zr0.90Y0.06Ce0.02Ca0.02O2−δ was found to have the highest density and microhardness, as well as the highest electrical conductivity among all of the microwave and conventionally sintered products.

The Influence of Various Dopants and Sintering Techniques on the Properties of the Yttria-Ceria-Zirconia System As an Electrolyte for Solid Oxide Fuel Cells

Besides YSZ (yttria stabilized zirconia) as an appropriate anode material, YZT (titania doped YSZ) is emerging as a material of interest. The undoped YSZ and the doped YSZ i.e. 5 mol % YZT, are synthesized by conventional as well as microwave processing techniques, from the precursors prepared by mixed oxide method and subsequently characterized for a comparative analysis by XRD, Raman spectroscopy, FTIR, SEM and Vickers hardness test to investigate the crystal structure, structural changes taking place during the processing, the surface morphology and the micro hardness of sintered products. Whereas earlier, others have processed the same compositions conventionally, in the present investigation, microwave energy has been exploited for sintering YZT composites. Notable density, phase stabilization, grain growth, hardness and density are observed for microwave sintered products.

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Comparative Analysis of Yttria Stabilized Zirconia (YSZ) and Titania Doped YSZ (YZT) Sintered by two Different Routes: Conventional and Microwave Processing

The aim of the present study is to investigate the effect of microwave energy on the structural and electrical properties of yttria-stabilized zirconia (YSZ) electrolyte for solid oxide fuel cells (SOFC). Five different compositions of Zr1−x
 Y
 x
 O2−x/2 (x = 0.06–0.14) were prepared by a co-precipitation method and were then sintered by microwave as well as conventional heating at 1400°C for 20 min and 240 min, respectively. The structural and electrical properties of the samples sintered by both the methods were compared. The x-ray diffraction (XRD) results revealed that YSZ samples sintered by both methods had either a tetragonal crystal structure or a cubic structure depending on its composition. Almost the same degree of densification as well as conductivity of same order was found from impedance analysis for both microwave- and conventionally sintered YSZ products, which showed that microwave sintering is the better alternative for material processing in terms of saving energy and time without compromising the product quality.

Structural and Electrical Analysis of Microwave Processed YSZ Electrolytes for SOFC Prepared by Co-precipitation Method

In this work, the effect of microwave sintering on the properties of scandia doped zirconia (10 mol% scandia in zirconia) was investigated. The sample was prepared by mixed oxide method and the sin...

Payal Sharma

Papers

Effect of Dopants and Sintering Method on the Properties of Ceria-Based Electrolytes for IT-SOFCs Applications

The Influence of Various Dopants and Sintering Techniques on the Properties of the Yttria-Ceria-Zirconia System As an Electrolyte for Solid Oxide Fuel Cells

Comparative Analysis of Yttria Stabilized Zirconia (YSZ) and Titania Doped YSZ (YZT) Sintered by two Different Routes: Conventional and Microwave Processing

Structural and Electrical Analysis of Microwave Processed YSZ Electrolytes for SOFC Prepared by Co-precipitation Method

Effect of Microwave Sintering on the Properties of Zirconia Based Ceramic Electrolytes for Solid Oxide Fuel Cells