Sol-gel Synthesis of TiO2 With p-Type Response to Hydrogen Gas at Elevated Temperature

Lijuan Xie,Zhe Wang,Linchao Sun,Azhar Ali Haidry,Zhong Li,Qawareer Fatima,Zhengjun Yao,Baoxia Dong

doi:10.3389/fmats.2019.00096

Abstract

Titanium dioxide is considered as one of the potential candidates for high-temperature gas sensing applications due to its excellent sensitivity and stability. However, its practical use as a gas sensor under elevated conditions is limited on account of its selectivity and insufficient understanding of response conversion from n- to p-type. To this context, the present work is intended to prepare and understand the p-type response of anatase TiO2 toward H2 gas (20-1000 ppm) at elevated temperature (500 C). Sol-gel route is adopted to facilely synthesize powders containing pure and chromium (1-10 at.%) doped TiO2 nanoparticles, which are then brushed onto substrates with already patterned inter-digitated platinum electrodes. In this work, even, the undoped TiO2 samples showed p-type gas sensing response, which then decreased with Cr doping. However, in comparison to previously reported work, the sensing characteristics of all sensors is improved. For instance, 5 at.% Cr-TiO2 showed high response (152.65), fast response and recovery (142/123s) time, and good selectivity to hydrogen against monoxide and methane. Despite better response values, the TiO2 based samples show instability and drift in baseline resistance; such issues were not observed for Cr-doped TiO2 samples (3 at.%). The powders were further analyzed by XRD, SEM, TEM and XPS to understand the basic characteristics, p-type response and stability. Further, a plausible sensing mechanism is discussed on basis of results obtained from aforementioned techniques.

Highlights

Expected to be widely used energy source in the near future, hydrogen has gained increasing attention as one of the cleanest energy sources
The chromium acetate with different atomic contents (1, 3, 5, 10 at.%) and 3 ml DI water were dissolved in 25 ml ethanol in another flask
On the basis of the reports (Gonullu et al, 2015), it can be explained by the formation electric stress produced as a result of Cr replacing Ti4+ in TiO2 lattice

Summary

Introduction

Expected to be widely used energy source in the near future, hydrogen has gained increasing attention as one of the cleanest energy sources. Its use in practical applications is limited because, during production, storage, transportation and use, H2 can effortlessly leak out as the atomic distance between the centers of two hydrogen atoms in H2 molecules is very small (∼1.06 Å). Explosion caused by hydrogen leakage presents a major threat to human and the environment (Haidry et al, 2012; Hermawan et al, 2018; Li et al, 2018). From this perspective, Cr-TiO2 Gas Sensor it is utmost important to monitor hydrogen in production plants, pipelines, storage tanks, refilling stations and automotive vehicles, at high temperature. One of the main challenges in hydrogen sensor working at high temperature is to aim higher sensitivity, selectivity, faster response time with excellent stability

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Conclusion