Satoshi Mogi

In situ observation of water distribution and behaviour in a polymer electrolyte fuel cell by synchrotron X-ray imaging.

In situ visualization of the distribution and behaviour of water in a polymer electrolyte fuel cell during power generation has been demonstrated using a synchrotron X-ray imaging technique. Images were recorded using a CCD detector combined with a scintillator (Gd(2)O(2)S:Tb) and relay lens system, which were placed at 2.0 m or 2.5 m from the fuel cell. The images were measured continuously before and during power generation, and data on cell performance was recorded. The change of water distribution during power generation was obtained from X-ray images normalized with the initial state of the fuel cell. Compared with other techniques for visualizing the water in fuel cells, this technique enables the water distribution and behaviour in the fuel cell to be visualized during power generation with high spatial resolution. In particular, the effects of the specifications of the gas diffusion layer on the cathode side of the fuel cell on the distribution of water were efficiently identified. This is a very powerful technique for investigating the mechanism of water flow within the fuel cell and the relationship between water behaviour and cell performance.

A passive micro gas regulator for hydrogen flow control

This paper presents the design, fabrication process, experimental characterizations and simulations of a novel passive micro gas regulator. The device is to be used in a miniature fuel cell for portable electronic applications in order to regulate the hydrogen flow feeding the fuel cell from a high-pressure tank. Its structure and working principle are similar to some macroscopic devices. Using MEMS technologies, e.g., deep-RIE etching and multiple wafer bonding, the dimensions of the device have been made less than 8 × 8 × 1 mm3. Moreover, as it is passive, it consumes no power from the fuel cell. Thanks to these two features, it is well suited for portable applications. To our knowledge, this is the first passive micro gas regulator, except those actuated by hydrogels. The experimental characterization shows that the opening and closing are controlled by the released gas pressure. Up to an input pressure of 8 atm, the device has been successfully driven and the leakage has been measured to be below 0.1 sccm nitrogen. Analytical models for the moving part and for the flow rate show a good agreement when compared to the experimental data.

A micro-machined safety valve for power applications with improved sealing

A novel micro-safety valve for portable hydrogen fuel cells has been designed, fabricated and characterized. This device is intended to prevent over-pressure on the hydrogen side of the fuel cell. A careful study of its sealing properties has been conducted under conditions at which it is nearly open. The leakage rate depending on the size of the sealing surface and on the material of the gasket (fluorocarbon and parylene films) has been investigated using hydrogen gas. The experimental results show that small sealing surfaces lead to small leakage rates and that the parylene films are easily damaged, leading to important leakage rates. Moreover, it is shown that the resistance to flow of the device is diminished by reducing the width of the valve nozzle.