Aliovalent Sc and Li co-doping boosts the performance of p-type NiO sensor

Abstract Though p-type NiO possesses excellent catalytic oxidation property toward volatile organic compounds (VOCs), intrinsic low sensitivity of NiO (arising from the hole accumulation layer configuration in ambient air atmosphere sensor) restricts its promising applications in VOCs detection. In this study, Sc and Li were proposed to modulate the (surface) properties of NiO nanosheet-flowers based sensors. At the optimal 2 at.% Sc and 5 at.% Li doping ratio (Ni0.93Sc0.02Li0.05O), the sensitivity to 100 ppm ethanol is 118.4 (105 times higher than that of pure NiO), which is comparable to or even higher than most of reported NiO based sensors. Moreover, Ni0.93Sc0.02Li0.05O sensor exhibits a low detection limit of 10 ppb, excellent repeatability and long-term stability (∼30 % decline of response after 7 months). Apart from regulating the carrier concentration, defect characterizations indicate a noticeable increase of stabilized surface oxygen vacancy (OV) defects and Ni3+ cations by Sc3+ and Li+ co-doping, which greatly facilitate the adsorption of VOCs molecule (revealed by density functional theory calculation) as well as the subsequent VOCs/NiO interfacial charge interaction, thus contribute to the superior sensing performances. This work demonstrates that co-doping offers an effective avenue for boosting the performances of (p-type) oxide sensors.