Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials.

In the present work, we have developed a multilayer tape casting and co-sintering process to fabricate large area anode-supported electrolyte film, which is critical for planar type reduced temperature solid oxide fuel cells (SOFCs).

Nickel/yttria-stabilized zirconia (Ni/YSZ), nickel/scandia-stabilized zirconia (Ni/ScSZ) cermets, ScSZ, Ce_0.8Gd_0.2O_1.9 (CGO), and La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)–CGO were used as materials of anode substrate, anode functional layer, electrolyte, interlayer and cathode, respectively. The powders of these functional layers were ball milled with organic additives to form slurries, which were assembled together with the multilayer tape casting procedure to get the green tapes. After dryness, the green tape was co-sintered at 1400 °C for 4 h in air to get the large area anode-supported electrolyte film (thickness ∼ 15 μm). For cells preparation, LSCF–CGO composite cathode was deposited by screen-printing method and sintered at 1100 °C for 3 h. The area-specific resistance (ASR) of the obtained single cell was found to be ∼0.99 Ω cm² at 850 °C with H₂/O₂ as the operating gases, and the maximum power density achieved ∼0.63 W cm⁻². The thickness of the (Zr,Ce)O₂-based solid solution formed at the ScSZ/CGO interface during high temperature sintering was investigated.

The results illustrate that fabrication of anode-supported electrolyte film for planar SOFCs with a CGO interlayer is possible by multilayer tape casting procedure, which is both cost-effective and feasible.

Solid oxide fuel cells (SOFC) are generally considered to be a promising future electricity-generation technology due to their high electrical efficiency. They also display a multi-fuel capability (hydrogen, carbon monoxide, methane, etc.), may play a role in carbon sequestration strategies, and may render the highest electricity generation efficiency in power station design if coupled with a gas turbine. Nevertheless, their development still faces various problems with high-temperature materials, design of cost-effective materials and manufacturing processes, and efficient plant design. This article summarizes world wide efforts in the field of SOFC, presenting an overview of the main SOFC designs and the main developers active in this field. Based on data published in proceedings of international conferences during the last few years, a comparison is made of the results achieved in cell, stack, and system development.

Ammonia is a possible candidate as the fuel for solid oxide fuel cells (SOFCs). In this work, an anode-supported SOFC based on yttrium-stabled zircite (YSZ) thin-film electrolyte was fabricated by a simple dry-pressing process. Directly fueled by commercial liquefied ammonia, the single cell was tested at temperatures from 650 to 850 °C. The maximum power densities were 299 and 526 mW cm⁻² at 750 and 850 °C, respectively, only slightly lower than that fueled by hydrogen. Analysis of open current voltages (OCVs) of the cell indicated the oxidation of ammonia within a SOFC is a two-stage process. Impedance spectra showed the cell fueled by ammonia had the same electrolyte resistances as that fueled by hydrogen, but a little larger interfacial polarization resistances. Further, the performances of the cell were essentially determined by the interfacial resistances under 750 °C.

A simple and cost-effective method for synthesizing yttria-stabilizedzirconia (YSZ) electrolyte membranes is described that is based on a modified dry-pressing process using nanocrystalline powders. The thickness of the YSZ electrolyte membranes was easily controlled by controlling the mass of nanocrystalline YSZ powders. Good adhesion of the dense electrolyte membranes to the anode substrates without cracking or delamination could be readily obtained. The studied single cell possessed much higher open circuit voltage (OCV) and higher output performance than a cell whose electrolyte thick film was made from a traditional dry-pressing method using commercially microcrystalline powders. The good performance in this study was attributable to the successful fabrication of the electrolyte membrane by the uniquely modified dry-pressing process using loose nanocrystalline YSZ powders. The implementation of the modified dry-pressing process using nanocrystalline YSZ powders to fabricate electrolyte membranes exhibits a significant potential to greatly reduce the fabrication cost of solidoxidefuel cells (SOFCs).

Co-tape casting and co-firing of supporting electrode and electrolyte layers could drastically increase productivity and reduce fabrication cost. In this study, Ni-YSZ anode supporting electrode and the YSZ electrolyte with the size of 6.5 cm × 6.5 cm have been successfully fabricated by co-tape casting and co-firing technique. The cell with 1.5 mm anode and 10 μm electrolyte is flat without warping, cracks or delaminations. The power density reaches 661, 856, 1085 mW cm⁻² at 0.7 V and 750, 800 and 850 °C, respectively. The EIS results demonstrate that the cathodic electrochemical resistance is 0.0680 Ω cm², about twice of the anode's which is 0.0359 Ω cm². SEM images show the dense YSZ film had a crack free of surface morphology. The anode and cathode layers are well-adhered to the YSZ electrolyte layer. The La_0.8 Sr_0.2 MnO_3−δ particles do not form a continuous network. Optimization of finer cathodic microstructure and anodic porosity are underway.

Electrolyte films of samaria-doped ceria (SDC,are fabricated onto porous NiO-SDC substrates by a screen printing technique. A cathode layer, consisting ofand 10 wt % SDC, is subsequently screen printed on the electrolyte to form a single cell, which is tested at temperatures from 400 to 600°C. When humidified (3%hydrogen or methane is used as fuel and stationary air as oxidant, the maximum power densities are 188 (or 78) and 397 (or 304) mW/cm² at 500 and 600°C, respectively. Impedance analysis indicates that the performances of the solid oxide fuel cells (SOFCs) below 550°C are determined primarily by the interfacial resistance, implying that the development of catalytically active electrode materials is critical to the successful development of high-performance SOFCs to be operated at temperatures below 600°C. © 2001 The Electrochemical Society. All rights reserved.

An anode-supported yttria-stabilized zirconia (YSZ) electrolyte was fabricated using tape casting and co-sintering techniques for use in a solid oxide fuel cell (SOFC). Nickel/YSZ, lanthanum strontium manganite (La_0.85Sr_0.15MnO₃) and 8 mol% Y₂O₃–ZrO₂ were used for the anode, the cathode and the electrolyte, respectively. The anode-supported electrolyte was prepared with a tape casting technique followed by hot pressing lamination. Co-sintering between the anode and the electrolyte was applied at 1350 °C under pressurized conditions to fabricate the anode-supported electrolyte of the unit cell. Scanning electron microscopy (SEM) revealed the crack-free and dense structure of the electrolyte in the unit cell. The open circuit voltage (OCV) of the unit cell was 1.08 V at 750 °C, indicating negligible leakage of fuel through the electrolyte layer. The active layer was applied to the interface between the anode and the electrolyte layer to increase the three-phase boundary, the electrochemical reaction site of the anode. The unit cell having an active layer exhibits good performance due to the drastic reduction of polarization resistance.

A co-tape casting technique was applied to fabricate electrolyte/anode for solid oxide fuel cells. YSZ and NiO–YSZ powders are raw materials for electrolyte and anode, respectively. Through adjusting the Polyvinyl Butyral (PVB) amount in slurry, the co-sintering temperature for electrolyte/anode could be dropped. After being co-sintered at 1400 °C for 5 h, the half-cells with dense electrolytes and large three phase boundaries were obtained. The improved unit cell exhibited a maximum power density of 589 mW cm⁻² at 800 °C. At the voltage of 0.7 V, the current densities of the cell reached 667 mA cm⁻². When the electrolyte and the anode were cast within one step and sintered together at 1250 °C for 5 h and the thickness of electrolyte was controlled exactly at 20 μm, the open-circuit voltage (OCV) of the cell could reach 1.11 V at 800 °C and the maximum power densities were 739, 950 and 1222 mW cm⁻² at 750, 800 and 850 °C, respectively, with H₂ as the fuel under a flow rate of 50 sccm and the cathode exposed to the stationary air. Under the voltage of 0.7 V, the current densities of cell were 875, 1126 and 1501 mA cm⁻², respectively. These are attributed to the large anode three phase boundaries and uniform electrolyte obtained under the lower sintering temperature. The electrochemical characteristics of the cells were investigated and discussed.

During operation solid oxide fuel cells are stressed by temperature gradients and various internal and external mechanical loads, which must be withstood. This work deals with the optimization of the strength of as-sintered anode supported half-cells by imposing changes to production parameters, such as powder milling and sintering temperature. The strength was measured with the ball-on-ring method, and analyzed with a large displacement finite element model. Weibull statistics were used to describe the distribution of strengths. The influence on the Weibull strength of the many different processing parameters was found to be quantifiable in terms of cell porosity to a large extent. The results were validated with an independent set of measurements of strength and stiffness by uniaxial tension and the impulse excitation technique, respectively. For application of the finding in relation to the SOFC technology a mathematical frame to determine the optimal porosity of a SOFC system is presented.

The infiltration (impregnation) of nanoscale particles, forming connected networks, into solid oxide fuel cell electrodes, has been shown to lead to considerable benefit in performance. Porous electrode skeletons (backbones), consisting of electrolyte material such as YSZ, when infiltrated, delivered results comparable to those of the standard Ni-YSZ and LSM-YSZ electrode configurations. Additionally, the performances of both single component mixed ionic electron conductor and of composite electrodes have been significantly enhanced by the connected nanoscale particle networks formed by infiltration.

As the anode of a solid oxide fuel cell, Ni/YSZ cermet material was investigated. We measured the power output, IR resistance and polarization resistance as a function of the Ni/YSZ volume ratio. IR resistance decreased as the Ni/YSZ ratio was increased. The linear relationship between IR resistance and the reciprocal values of the nickel surface area indicates that the contact resistance between the electrolyte and the anode dominated IR resistance. On the other hand, polarization resistance increased as the Ni/YSZ ratio was increased. Analysis of AC impedance plots indicated that polarization resistance contributed to the number of reaction sites which were ascribed to the triple boundary layer. Moreover, the boundary between nickel particles and zirconia particles in the anode worked as the triple boundary layer. Furthermore, we proposed the double layer anode, which consisted of the interfacial layer and the bulk layer. A cell with a double layer anode exhibited high performance. The interfacial layer and the bulk layer had a strong effect on IR resistance and polarization resistance, respectively.

Thin wall thickness (0.25–0.35 mm) tubes, as tubular electrolytes of solid oxide fuel cells, were successfully fabricated from yttria stabilised zirconia (YSZ) by way of extrusion. Water-based additives and organic additives were studied. An economic and practical process was developed to achieve smooth, linear, and dense ceramic tubes with 2.7–2.8 mm diameter. The microstructures of the selected tubes were examined. This paper describes the fabrication procedure, formulations and optimisation parameters for successfully extruding thin YSZ tubes.