P2J-2 Methanol Sensor for Direct Methanol Fuel Cell Using SH-SAW Sensor

A direct methanol fuel cell (DMFC) is one of fuel cells and is expected as a cell for mobile systems. Generation efficiency of the DMFC depends on the concentration of methanol solution, so the methanol sensor is required. As a shear horizontal surface acoustic wave (SH-SAW) sensor detects dielectric constant and conductivity of liquid, we have applied it for methanol sensor in DMFC. First, we calculated SH-SAW propagation characteristics under considering temperature coefficients of the substrate and liquid. The sensitivity increases with increasing the temperature. Then, we measured the methanol solution using the SH-SAW sensor. Measured temperature range was from 25degC to 60degC and concentration range was from 0 to 50% by weight. Linear relationships between the sensor responses and concentration are obtained. Resolution was estimated as 0.1%. Therefore, the SH-SAW sensor can apply as a monitor of the methanol concentration at high temperature. As formic acid is generated in DMFC, influence of it was discussed. Mixture solutions of methanol and formic acid were measured. Using coordinate transformation, it is possible to estimate methanol concentration in mixture solution