Electron compensation in p-type 3DOM NiO by Sn doping for enhanced formaldehyde sensing performance

Abstract

Formaldehyde is a common air pollutant. In this paper, a formaldehyde sensor with a high response is fabricated based on Sn-doped three dimensionally ordered macroporous (3DOM) NiO. The sensing performances of Sn-doped 3DOM NiO for formaldehyde are investigated and the possible sensing mechanism is proposed. The results indicate that Sn doping can effectively improve the gas sensing properties of NiO. 10 at% Sn-doped 3DOM NiO exhibits the highest response (∼145) to 100 ppm formaldehyde at 225 °C, which is nearly 85 times higher than that of the pure one. With the increase of the doping concentration, the surface area of the samples increases gradually, which can provide more active sites for gas adsorption and enhance the sensing response. Moreover, the significant improvement of the response to formaldehyde can be explained by the electronic compensation mechanism. Free electrons are generated to compensate for the substitution of Sn⁴⁺ into Ni²⁺ sites, which decreases the hole concentration in NiO. In addition, the free electrons contribute to the formation of adsorbed oxygen, which is beneficial for the improvement of the formaldehyde sensing performance.