Effects of polytetrafluoroethylene or polyimide coating on H2 sensing properties of anodized TiO2 films equipped with Pd–Pt electrodes

Abstract

Diode-type H 2 sensors based on anodically oxidized TiO 2 thin films equipped with Pd-Pt electrodes (Pd-Pt/T-TiO 2 , T-TiO 2 represents the TiO 2 thin film fabricated by the anodization of the pre-oxidized Ti plate at 600°C for 1 h in air) have been fabricated, and the effects of the polymer coating on the Pd-Pt/T-TiO 2 sensor to humidity and oxygen partial pressure on the sensing properties to 500~8,000 ppm H 2 under dry and wet atmospheres have been investigated in this study. The films tested were polytetrafluoroethylene (PTFE), polyimide (PI) film and heterogeneously laminated layers of these two polymer films, and the sensors fabricated were referred to as P-n/Pd-Pt/T-TiO 2 or P 1 -n/P 2 -n/Pd-Pt/T-TiO 2 (P, P 1 and P 2 : PTFE or PI, n: polymer concentration of the coating solution (wt%)). The H 2 response of almost all sensors in wet air was larger than that in dry air, while the PTFE-n/Pd-Pt/T-TiO 2 and PI-n/PTFE-n/Pd-Pt/T-TiO 2 sensors showed only a slight enhancement in the H 2 response by introduction of moisture, in comparison with the Pd-Pt/T-TiO 2 or PI-n/Pd-Pt/T-TiO 2 sensors.On the other hand, the H 2 response of all sensors in N 2 was not affected by humidity. The PI-10/Pd-Pt/T-TiO 2 sensor showed the largest H 2 response in air at 250°C as well as N 2 among the all sensors tested; the response of the sensors in dry air and dry N 2 were ca. 3.1 × 10-4 A and ca. 4.7 × 10 -2 A, respectively, where the sensor current in H 2 atmosphere was regarded as sensor response, since that in the atmosphere without H 2 was extremely small.In addition, the H 2 response of the Pd-Pt/T-TiO 2 , PTFE-20/Pd-Pt/T-TiO 2 and PI-20/Pd-Pt/T-TiO 2 sensors were almost proportional to the H 2 concentration in a lower concentration range (500~2,000 ppm) in both dry and wet air, while it tended to saturate at a higher concentration range, especially for the PI-20/Pd-Pt/T-TiO 2 sensor in wet air. On the other hand, the sensor response to H 2 is well proportional to the logarithm of H 2 concentration in both dry and wet N 2 in the whole concentration range. Thus, the direct coating of the PTFE-n film on the Pd-Pt/T-TiO 2 sensors reduced the effect of humidity on the H 2 response 3 and the direct coating of the PI-n film on the Pd-Pt/T-TiO 2 sensors was effective for enhancing the H 2 response.

Moisture Insensitive PMMA Coated Pt-AlGaN/GaN Diode Hydrogen Sensor and Its Thermal Stability

“…Hydrophobicity of the polymer film is one of important factors in the water-blocking behavior of PMMA thin film. 21,34 The contact angles of 150 nm PMMA on Pt, and Pt itself, for water were 75…”

“…21 Yamato et al reported the mitigation of humidity effect and improved hydrogen sensing characteristics of anodized TiO 2 Schottky diode using polytetrafluoroethylene or polyimide coating. 34 At 25…”

Protective applications of vacuum-deposited perfluoropolymer films

“…All of the layers are deposited by vacuum deposition [30]. The similar type of sensor with PTFE protective film was developed in India [31] and in Japan [32], but they are used for electrical detection of changes occurred in the multilayered film in hydrogen presence. The sensors made in Japan use a multilayered structure: in the case of PI-10/PTFE-10/Pd-Pt/T-TiO 2 sensor, the additional coating of PI-10 on the PTFE increased the magnitude of wet air/dry air sensor response at temperatures lower than 200 °C, in comparison with that of Pd-Pt/T-TiO 2 , leading to the enhancement of the interference from humidity on the H 2 response.…”

Anodized nanoporous WO3Schottky contact structures for hydrogen and ethanol sensing

“…The same trend of response and recovery times for other nanoporous metal oxide gas sensors has been reported where the recovery time is generally longer than the response time upon exposure to various analyte concentrations. 41,64 As the concentration of the gas analyte increases, a faster response is demonstrated. Conversely, the recovery time increases as the gas analyte concentration increases.…”