Akihiko Momma

Influence of cell configuration on measuring interfacial impedances between a solid electrolyte and an electrode

For AC impedance spectroscopy to measure interfacial impedances between an electrolyte and a working electrode in solid electrolyte cells with three electrodes, the experimental error that is caused by the cell configuration is analyzed using a numerical model. To simulate AC impedance spectra, potential and current distributions in the disk type cells are calculated for various frequencies, and the impedance between the reference electrode and the working electrode is estimated. From the calculation, it is clarified that the difference in the size between the working electrode and the counter electrode can cause the experimental error and the deformation of the impedance spectra from a simple semicircle. The influences of the material properties and the cell configuration on the error and the deformation of the impedance spectrum are discussed.

Performance Evaluation of Anode-supported Planar SOFC with Precisely-simulated Reformate Gases

Performance of a novel simulated-reformate generator was evaluated for testing SOFC cell/stacks performance with ease, no handling of pure carbon monoxide, flexibility for various steam-reforming conditions. Gas composition of synthesized simulated reformate gases with the generator agreed by ± 0.5 mol.% to equilibrium ones for each reforming condition (S/C= 2-3.5, representative fuels such as methane and biodiesel). Furthermore, an anode-supported planar cell was tested with the generator. As long as fuels including biodiesel are reformed in a reformer to equilibrium and SOFC has internal reforming capability, cell performance and DC electrical efficiency would be almost the same at a common S/C despite fuel species. For kerosene reformates, change in S/C (2.0-4.0) affected cell voltages at 80% fuel utilization by ± 10 mV, or approximately ± 1.2%. The gas conversion impedance for the kerosene reformates coincided with calculated values (e.g. 0.25 ± 0.01 Ω cm−2). Therefore, it is concluded that cell performance at various reforming conditions can be evaluated with the generator easily, precisely, and safely without pure CO handling.

Measurement of Solid Oxide Fuel Cell System Flow Rate by Tracer Gas Method

A high-precision method to measure efficiency of fuel cells with a 0.1% margin of error is proposed. This method is principally divided into two procedures: determining the composition of fuel gas to be fed into a fuel cell system and measuring the flow rate of the fuel gas. The composition of the fuel gas is determined by an FTIR (Fourier transform infrared spectrometer) and/or a QMS (quadrapole mass spectrometer) with a built-in sonic nozzle sampling system. The flow rate was measured by the tracer gas method; that is, a given amount of tracer gas, such as one of the noble gases, was introduced into the line of the fuel gas, then, the mixed gas was sampled at the point where the tracer gas had been well mixed, and the concentration of the tracer gas was determined by the QMS. In this paper, a gravimetric calibration method using a highly sensitive balance is also proposed for flow control of the tracer gas. Also proposed are calibration of the FTIR and the QMS to establish the required low uncertainty or high accuracy of the measurement of the efficiency.