Papers by Author: Ruey Yi Lee

Abstract: In this paper, the Taguchi method is employed to systematically optimize the operating parameters of an anode-supported SOFC cell. Effects of cell temperatures (650, 675, and 700°C), fuel flow rates (400, 500, and 600 sccm), and oxidant flow rates (1000, 1500, and 2000 sccm) on electrochemical performance, fuel utilization, and electrical efficiency are investigated. The L₂₇ orthogonal arrays of Taguchi experiments are designed and carried out. The signal-to-noise ratios (S/N) indicate that the electrical efficiency is majorly determined by the hydrogen and air flow rates, while the power output is significantly affected by the operating temperatures. The analysis of variance (ANOVA) reveals that, under the operating temperature at 675°C with hydrogen and air flow rates respectively of 500 and 1500 sccm, the maximum power density is 480 mW/cm², where the overall electrical efficiency and fuel utilization is 51.9% and 86.1%, respectively.

Abstract: Performance testing for a single-cell solid oxide fuel cell (SOFC) stack is carried out to optimize its operating conditions. In this study, the Taguchi method is employed to effectively define the test matrix. The single-cell stack is composed of a 10x10 cm² commercial anode-supported cell, metallic interconnects, current collectors, and glass-ceramic sealant. The major parameters for the experiments include: flow rates of fuel (hydrogen) and oxidant (air) gases, and temperatures. The target indices are the electrical power output, electrical efficiency, and fuel utilization. The fuel flow rates (400, 500, and 600 sccm), air flow rates (1000, 1500, and 2000 sccm) and temperatures (650, 675, and 700°C) are evaluated for different experimental combinations. The results reveal that, the operating temperature is the most crucial factor to the stack performance. The maximum power reaches to 46 W (570 mW/cm²) with a current of 58 A (715 mA/cm²) at test conditions of 700°C and fuel and oxidant flow rates of 600 sccm and 2000 sccm, respectively. As the fuel flow rate decreases to 400 sccm, the electrical efficiency can reach to 53% while the power at 34.6 W (427 mW/cm²) and current 42 A (518 mA/cm²). As the current increases to 44 A (543 mA/cm²), the fuel utilization reaches to 83%, nevertheless concentration polarization is observed in such operating condition.

Abstract: The glass sealant with pre-forming frame structure, used for joining dissimilar materials of planar type SOFC devices, was fabricated by molding process. The flow phenomena during glass molding were investigated by computational modeling. The physical properties of glass sealant fluid were constructed in numerical models. The process parameters, such as mold pressing velocity, initial glass fluid temperature (or viscosity of glass sealant), and initial mold temperature, were examined. As results, the sealants formability could be characterized by molten glass temperature, near the gap between upper and lower molds. If the temperature is greater than its glass transformation temperature Tg, the formability become better, and vice versa. Keywords: solid oxide fuel cells (SOFCs), computational modeling, glass sealant.

Abstract: This paper presents the development of anode substrates of solid oxide fuel cells (SOFCs), prepared by rotating electrode powder-making equipment to improve the efficiency of cells and the coking issue that appears in traditional Ni-YSZ composite anodes when operated with hydrocarbon fuel. Combining the advantage of good electronic conductivity, leading less carbon residue of copper and high temperature oxidation resistance of Cr or Ni, the anode substrate is designed with Cu-Ni and Cu-Cr alloys so that the cells are able to work within the service temperature of 800-1000 C. To optimize the properties of conductivity, less carbon deposition and heat resistance, this research has invented substrates of copper-based dual metal composite alloys which are different from ordinary anode cermet powder made of nickel-ceramic composites. This new anode powder of dual metal alloys is made by rotating electrode powder-making equipment, with the powders being sintered to porous substrates. Experimental results show that the substrate has a good porosity and an electrical conductivity.

Abstract: This study is intended to reduce the difference of thermal expansion coefficient between metallic interconnector and solid electrolyte of SOFC (Solid Oxide Fuel Cell) without sacrificing of electrical conductivity. Fe-Cr alloys have been chosen as candidate materials due to its merit of low cost and high temperature oxidation resistance. Different amount of alloys element and compositions have been varied to optimize the properties by method of alloys design with aid of thermodynamics software Thermal-Cal. Phase diagrams of multi-components alloys have been drawn to predict the possible stable phases formed in the investigated metals. An arc melter and plasma melting furnace were used to melt the investigated alloys. The measurements of thermal expansion coefficients and electrical conductivities are carried out with TMA and ASR resistance instrument. The results indicate that the Fe-10Cr alloy exhibits the smallest thermal expansion coefficient among the alloys, while Fe-16Cr has a lowest electrical resistance .

Abstract: Five oxidized metallic alloys, namely, Crofer22, equivalent ZMG232, stainless steel SS430, SS304 and Inconel718 were subjected to oxidation treatment in hot air environment for various period of time. Then the resulted oxide scale was analyzed by scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and X-ray diffraction (XRD). All the five alloys contain comparable amount of Cr, Mn, Fe, and their surface oxides as analyzed indicate to be Cr2O3 and (Mn, Fe)Cr2O4 spinel compound.