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When hydrocarbons are used as a fuel in solid oxide fuel cells (SOFCs), internal steam reforming increases the energy conversion efficiency and simplifies the system, including the balance-of-plant. However, conventional nickel–yttria stabilized zirconia (Ni–YSZ) anodes are prone to deterioration at high temperatures and high humidity. This paper focuses on effects in anode microstructure on performance and durability of microtubular SOFCs. The evaluations were conducted under high steam content and internal methane reforming conditions using Ni–YSZ anodes using acrylic resin and graphite pore formers. The initial cell performance was almost identical to that of SOFCs with anodes using acrylic resin and graphite pore formers in 40% H2–3% H2O at 700 °C. However, the anode using acrylic resin deteriorated rapidly in 40% H2–30% H2O over a period of 28 h. Furthermore, it generated almost no electric power by internal steam reforming of methane. The local oxidation of nickel particles was observed at the interface between the electrolyte and the deteriorated anodes. The anode using graphite pore former provided stable power generation in 40% H2–30% H2O, and was able to generate power in 10% CH4–30% H2O. The pore formers strongly affect fuel diffusivity in the SOFC anodes, which is an important factor in stable internal steam reforming of methane. Keywords: Solid oxide fuel cell (SOFC), Nickel–yttria stabilized zirconia (Ni–YSZ) anode, Internal steam reforming, Pore former, AC impedance

A microtubular solid oxide fuel cell (SOFC) with an anode functional layer (AFL) consisting of NiO–Sc stabilized zirconia (ScSZ) between the electrolyte (ScSZ) and the anode (NiO–Y stabilized zirconia) has been fabricated and evaluated at low fuel supplement condition of H2, 6 mL min−1 per electrode area of 1 cm2, in order to discuss the effect of the AFL on the fuel cell energy efficiency. The effect of the AFL has clearly seen in the improvement of the power density as well as fuel utilization, resulting in the improvement of the energy efficiency. The performance of the cell simply improves from 0.27 to 0.45 W cm−2, and 0.35 to 0.52 W cm−2 when the anode functional layer is introduced, and the energy efficiency reached 41 and 47% (LHV) at 650 and 700 °C, respectively using diluted hydrogen as a fuel. Keywords: Anode, Functional layer, SOFC, Fuel cell

We report the world smallest tubular solid oxide fuel cell – needle-type micro SOFCs applicable to micro power devices. The anode-supported cell was prepared using cost effective, conventional extrusion and dip-coating techniques. The diameter of the needle-type cell is 0.4 mm, consisting of NiO-Gd doped Ceria (GDC) for anode (under 100 μm thick), GDC for electrolyte (8 μm thick), and (La, Sr) (Co, Fe)O3 – GDC for cathode. The cell performances of 80, 160 and 300 mW cm−2 at 450 °C, 500 °C, and 550 °C, respectively, were obtained using a simple current collection method with wet H2 fuel. Impedance analysis indicated that the SOFC has a potential to be improved by optimizing the current collection method. Bundle concept using the SOFCs with the packing density of 100 cells in 1 cm3 was also proposed. Keywords: SOFC, Micro-tubular, Low temperature, Ceria, Anode-supported

Micro-tubular solid-oxide fuel cell consisting of a 10-μm thick (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 (ScSZ) electrolyte on a support NiO/(ScSZ) anode (1.8 mm diameter, 200 μm wall thickness) with a Ce0.8Gd0.2O1.9 (GDC) buffer-layer and a La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)/GDC functional cathode has been developed for intermediate temperature operation. The functional cathode was in situ formed by impregnating the well-dispersed nano-Ag particles into the porous LSCF/GDC layer using a citrate method. The cells yielded maximum power densities of 1.06 W cm−2 (1.43 A cm−2, 0.74 V), 0.98 W cm−2 (1.78 A cm−2, 0.55 V) and 0.49 W cm−2 (1.44 A cm−2, 0.34 V), at 650, 600 and 550 °C, respectively. Keywords: Solid-oxide fuel cells, Micro-tubular, Impregnation, Electrochemically catalytic Ag, Power performance

Publisher Summary A typical Solid oxide fuel cell (SOFC) consists of doped zirconia for an electrolyte, Ni cermet for an anode and doped lanthanum manganite for a cathode, and it has shown its long-term stability over 20,000 h operation as well as high power output up to 2 W/cm2 at 800°C. SOFCs have been recognized as a keystone of the future energy economy, and the development of SOFC systems has been an important issue in recent years. This chapter discusses development of micro tubular SOFCs, summarizes recent development of fabrication/integration technology for micro tubular SOFCs, and examines characteristics of micro tubular SOFCs. High-performance SOFCs lies in the design of the cell/bundle/stack and novel fabrication technology that can realize optimized electrode structures. By using recent development of fabrication/integration technology for micro tubular SOFCs with diameters of 0.8–2.0 mm in diameter operable at at/under 550°C are fabricated. Characterization of micro tubular SOFC is discussed in detail, including current collecting loss due to the dimension of the cell. For practical realization of the micro tubular SOFC system, further investigations of the tubular cells and the bundles are necessary to gain the knowledge necessary for understanding the following issues: stack design (manifold design); thermal distribution in the stack and thermal management (simulation); gas pressure loss in the stack/system and optimization of gas flow; fuel utilization; current collecting loss from the cathode matrix; and sealing technology.