Effects of surface modification with platinum and ruthenium on temperature and humidity dependence of SnO2-based CO gas sensors

A significant improvement in temperature and humidity dependence of SnO2-based CO gas sensors has been achieved by a novel surface modification with platinum group metal. The surface modification method consists of impregnation of the sensor element into a dilute metal salt solution containing platinum and/or ruthenium for only a few seconds followed by heating it at 600°C for 5 min. The sensor surface modified by this simple procedure markedly decreases the sensorʹs sensitivity to variations in temperature and humidity, and the effect is more enhanced by the surface modification with a combination of both metals than by that with either of them, individually. Moreover, surface modifications using sulfuric acid and thiourea solutions, which were revealed in our previous work to enhance long-term stability of the sensor, further improve the sensing property and stabilize it for long-term operation under the conditions that temperature and humidity change.