•A method of combining chemical vapor deposition (CVD) and ultrasonic spray pyrolysis (USP) was applied to deposit SiO2/Al2O3 composite membrane in-situ on the Pt-modified ZnO sensing film. And membranes of different Si/Al ratios could adjust the oxygen diffusion.•The sensors acquire high H2 responses under 10,000 ppm and 50 ppm oxygen concentration.•The recovery time was evaluated with a method which allowed us to observe the continuous change in resistance intuitively.•Pt-modified ZnO exhibits low response to H2 in high oxygen concentration and high response in low oxygen concentration. This shows the high oxygen activity of Pt-modified ZnO, which is contrary to the traditional idea.•A high throughput gas testing network was used to test the sensing properties of several sensors at the same time.Utilizing sensor to detect H2 under different oxygen concentrations is essential in monitoring status of nuclear weapon. A membrane covering on a sensing film could influence the diffusion of oxygen, thus changing the sensing performance of a metal oxide (MOX) gas sensor. In this research, silica and alumina (SiO2/Al2O3) composite membranes were deposited in-situ on Pt-modified ZnO by combining chemical vapor deposition (CVD) and ultrasonic spray pyrolysis (USP) methods Through adjusting the ratio of silicon to aluminum (Si/Al), the composition of membranes, the diffusion rate of oxygen and H2 sensing property under different oxygen concentrations were regulated. With the decrease of the Si/Al ratio, the H2 responses of the sensors increased first and decreased then under high (10,000 ppm) oxygen concentration. While under low (50 ppm) oxygen concentration, the H2 responses of the sensors went down first and rose then. The sensors covered with membranes of high Si/Al ratio exhibited aerobic H2 sensing property. Meanwhile, sensors deposited with membranes of low Si/Al ratio or without membrane showed anaerobic H2 sensing property. This study contributes to further understanding of the influence of oxygen diffusion on MOX sensing properties.

CO sensor based on metal oxide has been developed for a long time. Although the gas sensitive response of sensor is greatly improved already, the poor selectivity and interference immunity limit the application. To achieve the purpose of fast identification of CO by a single sensing film, the optical modulation method is first proposed and applied herein. This method allows us to be capable of obtaining the characteristic parameters, the photoresponse and the photogenerated carrier lifetime, based on the optical modulation spectra. According to the characteristic parameters, CO can be successfully distinguished from the other gases, including H2, ethyl alcohol and acetic acid. The results show that the optical modulation provides an effective method for fast and accurately identifying gas species and opens up a way to investigate the selectivity of the MOX sensors.

Metal oxide used as resistive gas sensor has been known for a long time and the resistance variation is related to the gas around sensor. This behavior can be rationalized by the model of oxygen ionization, which has relation to the oxygen adsorption. One special phenomenon that the irreversible R-T curves of metal oxide gas sensor under programmed temperature cycle appears repeatedly in previous reports. However the classical adsorption isobar cannot explain it perfectly. Herein a series of experiments were designed to reveal the laws of the irreversible R-T curves. Moreover the proper adsorption potential energy curves and the adsorption isobar for oxygen adsorption were proposed to better illustrate the mechanisms. Based on the above theory, we found a way to obtain the surface state filled with abundant chemisorbed oxygen. For pure SnO2, it can maintain at least 27 min within the 5% decrease of resistance. Simultaneously the gas sensing behavior was investigated at room temperature. It will contribute to more thoroughly understand the characteristic of metal oxide gas sensor.

A novel headspace integrated E-nose based on metal oxide gas sensor arrays is reported. And its performance to distinguish six groups of Chinese medical herbs which might be mixed easily by appearance is presented. The headspace integrated E-nose is mainly consisted of gas sensing module, signal procession module and human-machine interaction module. The E-nose, integrated with an innovative headspace diffusion sampling way, has a compact structure with an approximate size of Φ 48 × 100 mm. For the characteristics of the small size and the headspace diffusion sampling way, it is suitable for on-site volatiles analysis in food and raw material detection. Temperature modulation technology was combined with pattern recognition analysis to enhance the selectivity of the E-nose. Principal components analysis and Sammon mapping were used in the feature extraction, while the sample was discriminated by Fisher discriminant analysis. The correct classification rate of the headspace integrated E-nose for discriminating thirteen species of herbs is 100%, which shows the potential application of the E-nose for on-site volatiles analysis.

In this work, a smart platform was reported with an ability to rapidly screen the gas sensing properties of metal oxide gas sensors which were loaded on a single material chip with a capability of 36 sensor films. Among the SnO2-based material sensitized with various catalysts (Mo, Pd, Cd, Mn, Pt, Y, La, Ce, Pr, Sm, Gd) in different concentrations, a significant enhancement of sensing performance was observed for the film with surface functionalized La. To intrinsically investigate its sensitization mechanism, the changes in microstructure and surface valence of the SnO2-based materials were characterized by XRD, SEM, XPS, PL, HRTEM and EDX. It is demonstrated that the hydrated lanthanum chloride transformed to La2O3 with an intermediate of LaOCl during the sintering process of the samples. Thus, the sensitization mechanism of La2O3 can be concluded into two items: (1) numerous of oxygen vacancies are newly created on the SnO2 surface through the LaOCl to La2O3 transformation resulted in the enhancement of gas-sensing properties; (2) the chemisorbed peroxide O22− on La2O3 surface has the ability to cause an H-abstraction reaction with hydrocarbon, which may account for the decrease of optimum temperature toward formaldehyde.