Effect of humidity on the gas sensing property of the tetrapod-shaped ZnO nanopowder sensor

The testing chamber humidity and the storage circumstance humidity effects on the tetrapod-shaped ZnO nanopowder (named as T-ZnO) thick film sensors were investigated by measuring the resistance and sensitivity. The resistance increases gradually with increasing relative humidity (RH) in a range of 32%–75% RH in testing chamber, while in a range of 75%–96% RH, decreases gradually with the increase of RH. The sensitivity to ethanol 100 ppm in testing chambers with different humidity is in the order of 50% RH > of 75% RH > of 32% RH > of 96% RH. The sensitivity change in the storage circumstance with different RH is similar to the change in testing chamber with different RH. The stability of T-ZnO sensor is influenced evidently by the storage circumstance humidity. The water vapour in the tetrapod-shaped ZnO nanopowders was investigated by thermogravimetric analysis (TGA). The testing gas and the reactant adsorbed in the sensitive film were characterized by infrared spectrum (IR). The explanation of the observed effects was given and the mechanism of interaction of the ZnO sensing layer with H2O was proposed.