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Micro-tubular 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 micro-tubular SOFC was achieved through multiple-step processes. [1][2][3] A support layer, for example anode-support, is first prepared and pre-sintered to provide mechanical strength to the fuel cell. The electrolyte layer is then deposited and sintered prior to the final coating of 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 micro-tubular SOFC with reliability and flexibility in quality control, an advanced dry-jet wet extrusion technique, i.e. a phase-inversion-based coextrusion process, is developed. Using this technique, a dual-layer electrolyte/electrode (either anode or cathode) hollow fibre (HF) can be formed in a single step. Generally, the electrolyte and electrode materials are separately mixed with solvent and polymer binder to form the outer and inner layer spinning suspensions, respectively, before simultaneously co-extruded 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 non-solvent internal coagulant is supplied through the central bore of the spinneret. Thickness of the two layers are 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 1 Submitted to by adjusting co-extrusion parameters such as suspension viscosity, air gap, flow rate of internal coagulant, etc. The obtained dual-layer HF precursor is finally co-sintered once at high temperature as a procedure to remove polymer binder and form bounding between the ceramic materials. In our previous work, [4][5][6] a dual-layer HF support for micro-tubular SOFC, which consists of an electrolyte outer layer of approximately 80 µm supported by an asymmetric anode inner layer with 35 % finger-like voids length, was successfully fabricated using the co-extrusion/co-sintering process. A single cell that obtained after deposition of a multi-layer cathode onto the dual-layer HF produced the maximum power density of 0.59 W cm -2 at 570 o C.[6] Improvement on the structure of the dual-layer HFs was further 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 o C. [7] Although this result has proved the potential of the dual-layer HF as a promising support for micro-tubular SOFC, the value of powder density was still slightly lower than the ramextruded anode-supported cell with similar electrolyte thickness and highly porous anode (about 1.29 W cm -2 at 600 o C).[8] One of the possible major reasons for the lower power output is the less effectiv...

A double laser Doppler electrophoresis apparatus has been used to study the effects of bubble size, pH, type and concentration of electrolytes and electric field strength, on the electrophoretic mobilities of electrolytically generated oxygen and hydrogen bubbles in aqueous electrolyte solutions. The pH dependence of the (very large) bubbles' electrophoretic mobilities implied the presence of an isoelectric point between pH 2 and 3 and their (negative) mobilities increased in magnitude with increasing bubble diameter, in the experimentally accessible range of about 60-100 pm. The apparent negative charge of the bubbles in the surfactant-free electrolyte solutions was ascribed to preferential adsorption of O Hions. The pH-dependent mean charge density was estimated as ca. -18 pC rn-, at pH 6.9 by addition of sufficient cationic surfactant (DoTAB) of known adsorption isotherm, to bring the bubble electrophoretic mobility to zero. Although very small, this was similar to the value of ca. -10 pC rn-, derived from the diameter dependence of the electrophoretic mobilities in surfactant-free NaClO, solutions assuming charge polarisation to the extent of greatly diminishing the electrophoretic drag. The very high mobilities enabled complementary experiments involving holding the bubbles stationary against gravity with an applied field, which is seldom possible for solid particles with the same density difference to the suspending liquid; the resulting mobilities were comparable to those obtained with laser Doppler anemometry. The high mobilities were ascribed to polarisation of adsorbed charge at the mobile gas/liquid interface decreasing the electrophoretic drag. Extrapolation to zero applied field gave a finite, though very small mobility, which may be ascribable to hydrodynamic charge polarisation.