Platinum Metals Rev., 1990, 34, (3), 130
Palladium Doped Semiconductor Alcohol Sensor
The detection and accurate measurement of the alcohol concentration in breath has been traditionally performed by a fuel cell, with the expired air being oxidised catalytically on a platinum electrode, and the small current generated being amplified (1).
Now Japanese researchers have produced a semiconductor detector which is capable of being used as a breathalyser, and which will selectively ignore other gases (2).
The basis of the detector is a porous alumina substrate, onto which a thick film (about 50 µm) of lanthanum oxide containing indium oxide and palladium was screen printed. Gold electrodes were attached and the whole was then calcined. Indium oxide was chosen as the semiconductor as previous attempts with tin(IV) oxide resulted in an unacceptably high increase in electrical resistance.
The addition of lanthanum oxide improved the sensitivity to ethanol vapour almost 7 fold, even though the electrical resistance and the response time also increased. The further addition of palladium was especially effective, dramatically increasing the sensitivity and shortening the 90% response time to about 35 seconds for 1000 ppm ethanol in air at 300°C.
The device has an “S” shaped response to alcohol gas concentrations between o and 1000 ppm at 300°C, being approximately linear from 0 to 100 ppm, and its selectivity to gases at 300°C, other than ethanol, is only modest.
- 1Platinum Metals Rev., 1974, 18, (3), 91
- 2J. Tamaki, T. Maekawa, S. Matsushima, N. Miura and N. Yamazoe, Chem. Lett. Jpn., 1990, (3), 477