Abstract
Solid Oxide Fuel Cell (SOFC) is an energy conversion device that converse chemical energy into electric energy directly, it is got more attention in the world because of high efficiency and environment-friendly. Reducing operating temperature is the focus of recent studies and fabricating thin, fully electrolyte layer is a main approach. It is difficult to fabricate thin(<30μm) coating with fine grain microstructure by Atmospheric Plasma Spray(APS) because the dimension of powder is between 10~100μm, so Suspension Plasma Spray(SPS) is developed. Suspension is injected into plasma jet，dense and thin coating with fine grain microstructure is fabricated, which could decrease the working temperature of SOFC.
A method for fabricating composed electrode of solid oxide fuel cell (SOFC) on silicon substrate by atmospheric and suspension plasma spray is presented. Anode and cathode layers are deposited by atmospheric plasma spraying (APS) using dry powder feedstock; Electrolyte layer is deposited by suspension plasma spraying (SPS). The main researches contain five aspects as follow:
1) Confect highly dispersing and stable suspension which can not only avoid particles clogging nozzle, but also ensure the equality of electrolyte layer. The parameters of confecting suspension include PH, dispersant and solid loading of the suspension. The best parameters of YSZ aqueous suspensions are as follows: 20% solid loading, PH at 10,0.39(wt %) dispersant related to the weight of solid particles, with analyzing sediment height and viscosity of different suspension.
2) Research suspension penetration within plasma jet, related parameters and the influence of suspension penetration within plasma jet by Mechanical injection. Suspension penetration within plasma jet, in the form of mechanical injection, is monitored by a CCD camera; related parameters including spray power, spray current and injection pressure are analyzed. The quality of plasma flow is best on condition of 0.25MPa injection pressure,0.3mm diameter single-fluid nozzle, 600A spray current and 33Kw spray power.
3) Research the influence of spray distance on electrolyte microstructure, deposition efficiency and porosity by SPS. Results show that spray distance is the most important parameter. High deposition efficiency (0.25μm /Pass) is acquired on condition of 33Kw spray power, 600A spray current and 60mm spray distance.
4) Research the approach of improving porosity of anode layer and cathode layer,including spray angle, spray speed and pore-forming agent. Results show that the porosity of anode layer is 28.7% in new parameters compared with 19.4% in old parameters; the porosity of cathode layer is 32.6% in new parameters compared with 20.3% in old parameters.
5) The electrode layers are characterized in terms of microstructure and components by means of SEM and EDAX. Results show that this method can manufacture SOFC composed electrode; thickness of anode layer, electrolyte layer and cathode layer is 20, 25 and 40μm and suspension plasma spray achieves a thin (25μm), fine grain (2~4μm) and dense (porosity of 2.15%) electrolyte layer of SOFC.
Keywords: solid oxide fuel cell; atmospheric and suspension plasma spray;composed electrode; microstructure
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