Ultra-high selectivity of H2 over CO with a p-n nanojunction based gas sensors and its mechanism

• The P-N nanojunction gas sensors addressed the poor selectivity to mixed gases. • The SMO gas sensors selectively detected H 2 without the cross sensitivity of CO. • The selectivity results were supported by band theory mechanism. The main disadvantage of metal oxide semiconductor sensors is their poor selectivity to different gases having similar (reducing or oxidizing) nature. Taking two strong interference homogeneous gases CO and H 2 as example, it is difficult for the sensor to accurately detect their concentrations when CO and H 2 coexist because of the cross sensitivity between the two homogeneous gases. Thus far, there has been no effective method to selectively detect specific gas without the cross sensitivity of another homogeneous gas. In this paper, the n-SnO 2 /p-Co 3 O 4 composite nanoparticles (NPs) have been prepared for the sensing materials. By means of controlling the p-n nanojunction and holes (h + )-electrons (e − ) concentration, the n-SnO 2 /p-Co 3 O 4 NPs sensor material with the Sn/Co molar ratio of 1:0.15 successfully and selectively detects H 2 without the cross sensitivity of CO. This makes a great breakthrough in solving the poor selectivity. Most important, the mechanism of the excellent selectivity of the sensor to H 2 against CO has been explained based on the series of characterization results. This provides a theoretical guidance and technical solution for solving the problem of poor selectivity of this type of sensors.