Methanol Sensor Using Shear Horizontal Surface Acoustic Wave Device for Direct Methanol Fuel Cell

Abstract

A liquid-phase sensor is realized that uses a shear horizontal surface acoustic wave (SH-SAW) device. The advantage of using an SH-SAW sensor is the simultaneous detection of liquid properties, such as density, viscosity, permittivity, and conductivity. In this study, the SH-SAW sensor is applied as a methanol (MeOH) sensor for a direct methanol fuel cell (DMFC). As the generation efficiency of the DMFC depends on the methanol concentration, the monitoring of MeOH concentration is needed. The SH-SAW sensor is applied to the MeOH sensor to measure the electrical properties. The efficiency of the DMFC is also influenced by materials contained in the fluid. If a component of the SH-SAW sensor is eluted into the fuel, the SH-SAW sensor cannot be used in the DMFC. The SH-SAW sensor was dipped into the fuel at 80 °C and it was found that the concentration of eluted components from the SH-SAW sensor was low and that the efficiency was not influenced by such components. Then, the temperature characteristics of the SH-SAW sensor with various MeOH solutions were measured. The maximum operating temperature of the DMFC is 80 °C and the minimum temperature depends on the place of installation. In this work, the minimum temperature is assumed to be -5 °C. Thus, the SH-SAW sensor must measure the MeOH concentration from -5 to 80 °C without malfunction. The results indicate that the MeOH concentration can be measured when the temperature is lower than 60 °C. If the temperature is higher than 60 °C, bubbles are generated on the sensor surface and the sensor is influenced by them. A liquid flow system was demonstrated to reduce the influence of bubbles.