Nicolas Droushiotis

High‐Performance, Anode‐Supported, Microtubular SOFC Prepared from Single‐Step‐Fabricated, Dual‐Layer Hollow Fibers

Microtubular solid oxide fuel cells (SOFCs) have been developed in recent years mainly due to their high specifi c surface area and fast thermal cycling. Previously, the fabrication of microtubular SOFCs was achieved through multiple-step processes. [ 1–3 ] A support layer, for example an anode support, is fi rst prepared and presintered to provide mechanical strength to the fuel cell. The electrolyte layer is then deposited and sintered prior to the fi nal coating of the cathode layer. Each step involves at least one high-temperature heat treatment, making the cell fabrication time-consuming and costly, with unstable control over cell quality. For a more economical fabrication of microtubular SOFCs with reliability and fl exibility in quality control, an advanced dry-jet wet-extrusion technique, i.e., a phase inversion-based coextrusion process, was developed. Using this technique, an electrolyte/electrode (either anode or cathode) dual-layer hollow fi ber (HF) can be formed in a single step. Generally, the electrolyte and electrode materials are separately mixed with solvent, polymer binder, and additives to form the outer and inner layer spinning suspensions, respectively, before being simultaneously coextruded through a triple-orifi ce spinneret, passing through an air gap and fi nally into a non-solvent external coagulation bath. In the mean time, a stream of nonsolvent internal coagulant is supplied through the central bore of the spinneret. The thickness of the two layers is largely determined by the design of the spinneret and can be adjusted by the corresponding extrusion rate, while the macrostructure or morphology of the prepared HF precursor can be controlled by adjusting coextrusion parameters such as suspension viscosity, air gap, and fl ow rate of internal coagulant. The dual-layer HF precursor obtained is then co-sintered once at high temperature to remove the polymer binder and form a bounding between the ceramic materials. In previous work, [ 4–6 ] a dual-layer HF support for microtubular SOFCs, which consisted of an electrolyte outer layer of approximately 80 μ m supported by an asymmetric anode inner layer with 35% fi ngerlike voids length, was successfully fabricated using the coextrusion and cosintering process. A single cell that was obtained after deposition

Co-Extrusion / Phase Inversion / Co-Sintering for Fabrication of Hollow Fiber Solid Oxide Fuel Cells

We have used a co-extrusion / phase inversion process, followed by co-sintering and then NiO reduction with hydrogen, to fabricate anode (Ni-CGO) / cerium-gadolinium oxide electrolyte (CGO) dual-layer hollow fibers (HFs) with inner diameters < 1 mm. This is the first time such dual-layer fibers have been produced as components of SOFCs, thereby decreasing the number of fabrication steps compared with single layer extrusion, while ensuring a gas-tight electrolyte layer of controlled thickness (ca. 60-80 μm). A La0.6Sr0.4Fe0.8Co0.2O3 (LSCF)-CGO cathode ca. 100 μm thick was deposited using slurry coating. Preliminary measurements of the performance of the dual-layer microtubular HF-SOFCs were made with hydrogen flowing at 5 cm min and air at 40 cm min, achieving maximum power densities of 420 W m, 800 W m and 1000 W m at 450C, 550C and 580C, respectively. A proposed stack design shows how these microtubular SOFCs could be connected in parallel to increase currents and in series for scaling up voltages, aiming at the design of practical stacks.