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

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.