The effect of relative humidity on the NO2 sensitivity of a SnO2/WO3 heterojunction gas sensor

The sensitivity of a heterojunction sensor, formed between WO3 and 3 wt.% Nd2O3 doped SnO2, to humidity and NO2 has been investigated using forward bias resistance measurements at 300 °C. The sensor showed high sensitivity and a pseudo-linear response to NO2 in the range 0–5 ppm in dry air. The response to variations in relative humidity (RH) was small at RH levels below 40%, with the sensor becoming saturated at higher values of RH. Cross-sensitivity measurements were carried out to assess the influence of RH variations on the sensor response to 2.5 and 5 ppm NO2. Strong interference effects were observed, with the sensitivity of the sensor to NO2 decreasing rapidly as the RH of the atmosphere increased.