High-Performance, Anode-Supported, Microtubular SOFC Prepared from Single-Step-Fabricated, Dual-Laye
Microtubular solid oxide fuel cells (SOFCs) have been developed in recent years mainly due to their high specific 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 first prepared and presintered to provide mechanical strength to the fuel cell. The electrolyte layer is then deposited and sintered prior to the final 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 flexibility 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 fiber (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-orifice spinneret,passing through an air gap and finally 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 flow 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 μm supported by an asymmetric anode inner layer with 35% fingerlike voids length,
was successfully fabricated using the coextrusion and cosintering process. A single cell that was obtained after deposition of a multilayer cathode onto the dual-layer HF produced the maximum power density of 0.59 W cm − 2 at 570 ° C. [ 6 ] Improvement to the structure of the dual-layer HFs was performed by reducing the electrolyte layer thickness to as thin as 10 μm and the maximum power density of the corresponding cell markedly increased to about 1.11 W cm − 2 at 600 ° C.
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