Abstract
A high long-term stability is crucial for room-temperature gas-sensitive metal oxide semiconductors (MOSs) to find practical applications. A series of Pd-SnO2 mixtures with 2, 5, and 10 wt% Pd separately were prepared from SnO2 and Pd powders. Through pressing and sintering, Pd-SnO2 composite nanoceramics have been successfully prepared from the mixtures, which show responses of 50, 100, and 60 to 0.04% CO-20% O2-N2 at room temperature for samples of 2, 5, and 10 wt% Pd, respectively. The room-temperature CO-sensing characteristics were degraded obviously after dozens of days’ aging for all samples. For samples of 5 wt% Pd, the response to CO was decreased by a factor of 4 after 20 days of aging. Fortunately, some rather mild heat treatments will quite effectively reactivate those aged samples. Heat treatment at 150 °C for 15 min in air tripled the response to CO for a 20 days-aged sample of 5 wt% Pd. It is proposed that the deposition of impurity gases in air on Pd in Pd-SnO2 composite nanoceramics has resulted in the observed aging, while their desorption from Pd through mild heat treatments leads to the reactivation. More studies on aging and reactivation of room-temperature gas sensitive MOSs should be conducted to achieve high long-term stability for room-temperature MOS gas sensors.
Highlights
CO is a highly dangerous gas and can be formed unintentionally in our ambient environments
It can be seen that most strong peaks are from rutile SnO2 phase, and some peaks from metallic Pd can be observed
This is in agreement with a previous paper, which shows that metallic Pd is formed for the system of Pd-SnO2 when it is heat treated at temperatures above 900 ◦ C [15]
Summary
CO is a highly dangerous gas and can be formed unintentionally in our ambient environments. Electrochemical gas sensors have the drawbacks of short life and high cross sensitivity with other gases. MOS gas sensors are highly attractive with high sensitivity, long life, and low cost. These gas sensors can only operate at high temperatures (around 400 ◦ C), which is energy consuming and dangerous [3,4,5,6,7,8]. Wang et al invented a high temperature mixed potential CO gas sensor for on-site combustion control, and these porous NiO sensors were able to detect a low CO range of 0–100 ppm at 1000 ◦ C [11]. Wang et al obtained Pt/SnO2 nanostructures through microwave-assisted hydrothermal synthesis with strong and quick responses 100 ppm CO at 225 ◦ C [12]
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