Adsorption-semiconductor hydrogen sensors based on nanosized tin dioxide with cobalt oxide additives

Co-doped SnO2-based sensor materials with various cobalt contents were synthesized via the ethylene glycol supported sol–gel method. Electrical resistance, sensor response to hydrogen and catalytic activity towards hydrogen oxidation were studied as a function of cobalt doping and were shown to correlate, exhibiting maxima corresponding to the sensor material with 0.2 wt% Co. It was concluded that there are two major reasons leading to the obtained result. First, the formation of active edge sites between promoter particles (cobalt oxide) and tin dioxide surface, with the assumption that such bordering regions are favorable for oxygen chemisorption. Thus, a change in cobalt concentration in sensor materials can cause a change in a chemisorbed oxygen concentration and, hence the correlation between cobalt content and such parameters as electric resistance, sensor response and catalytic activity of corresponding materials. The second reason is the size of the tin dioxide grains. It was found that addition of small amount of cobalt content to the nanosized sensor material led to drastic increase in the resistance of the sensor and hence it's response because of “electronic sensitization” effect.