Preparation and Extraordinary Room-Temperature CO Sensing Capabilities of Pd–SnO₂ Composite Nanoceramics

Abstract

Pd-SnO2 composite nanoceramics have been prepared from SnO2 and Pd nanoparticles through traditional pressing and sintering. Their responses to CO at room temperature are found to depend greatly on the content of Pd. For those samples with 1.0 and 5.0 mol% Pd, their resistance increases dramatically upon being exposed to CO in air; while for samples of 0.2 mol% Pd, their resistance decreases greatly upon being exposed to CO in air, and extraordinary room-temperature CO sensing capabilities, including high sensitivities around 15, short response time of 20 s and recovery time of 60 s for 100 ppm CO in air, a high selectivity against H2, have been observed for them. X-ray photoelectron spectroscopy analyses showed that Pd2+ was formed in samples of 1 mol% Pd, while both Pd2+ and Pd4+ were formed in samples of 0.2 mol% Pd. It is proposed that for Pd-SnO2 composite nanoceramics, Pd2+ is responsible for CO-induced increase while Pd4+ is responsible for CO-induced decrease in resistance.

Aging Behavior and Heat Treatment for Room-Temperature CO-Sensitive Pd-SnO2 Composite Nanoceramics

“…It is clear that these three kinds of samples all show strong and stable responses to CO at room temperature, with both especially quick response and recovery speeds. As a matter of fact, similar results were also obtained for Pd-SnO 2 composite nanoceramics in some previous investigations [14,15]. It is worthy to note that SnO 2 -based gas sensors usually show responses to multiple reducing gases.…”

“…Many pores of quite different size and shape can be observed. As a matter of fact, there were no sintering shrinkages in the diameter of the pellets, which is due to a unique sintering behavior of SnO 2 nanoparticles [14,15]. In a previous investigation, no sintering shrinkage was observed even for pressed pellets of SnO 2 nanoparticles sintered at 1200 • C [23].…”

“…The mixtures were stirred at 800 rpm for 4 h on a magnetic stirrer, dried in an oven at 100 • C for 15 h. The obtained dry powders were ground for 30 min, then deionized water was added as a binder and pellets with a diameter of about 10 mm and a thickness of 1.5 mm were pressed from the powders through a hydraulic press at about 3 MPa. Finally, the pellets were sintered at 950 • C in air for 2 h. A pair of rectangular Au electrodes was formed on a major surface of sintered pellets through direct current (DC) magnetron sputtering for gas-sensing measurement, as described in some previous papers [14,15].…”

“…In 2015, Pan et al developed an ultra-sensitive room-temperature CO sensor using zinc oxide nanocombs, whose peak sensitivities to 250 ppm and 500 ppm CO are as high as 7.22 and 8.93, respectively [13]. In 2018, Wang et al prepared palladium(Pd)-SnO 2 composite nanoceramics with highly attractive room-temperature CO-sensing capabilities, including high sensitivities around 15, short response time of 20 s and recovery time of 60 s for 100 ppm CO in air [14]. In 2019, it was further revealed that the formation of Pd 4+ in Pd-SnO 2 composite nanoceramics is responsible for the observed room temperature CO-sensing capability [15].…”

“…Though several kinds of room-temperature CO sensors have been prepared and studied [13][14][15][16][20][21][22], there have been no reports on the long-term stability of room-temperature CO sensors based on MOSs in the literature up to date. In particular, an impressive roomtemperature CO-sensing capability has been obtained for Pd-SnO 2 composite nanoceramics, whose Pd content has been revealed to have an intriguing effect on the formation of the room-temperature CO-sensing capability [14,15]. As bulk materials prepared through pressing and sintering, these composite nanoceramics are more promising for practical applications than low-dimensional nanostructured MOSs in robustness and mass production.…”