Solid gas sensors are widely employed owing to their good stability and excellent gas responses [1]. However, the operating temperature to activate reaction sites of oxide semiconductor is relatively high to widen the applications [2]. As demands of gas sensors have increased in various fields, one of the research issues is to lower the operation temperature to enhance adaptability. To lower sensing temperature of semiconductor oxide sensors from several hundred Celsius to room temperature and to improve the gas selectivity, compositional gradient of catalysts was explored based on the catalyst effects on gas sensing mechanism and performance. Two metals having different catalytic activities were utilized: Platinum (Pt) and palladium (Pd). The thickness of the catalyst layer was kept constant, and only composition (ratio of the components) was changed to investigate the effect of the catalyst composites [3].

In this study, deposition of metal catalysts on ZnO NR gas sensing devices was successfully conducted by the sputter method. Pd and Pt were selected as catalysts to improve the gas sensing behaviors such as gas response, gas response rate, and selectivity. The amount of 1 or 2 % of catalysts was deposited on the gas sensing devices. When metal catalysts were applied, operation temperature of ZnO NR gas sensors was successfully reduced from 300 °C to 100 °C. Moreover, enhancement in gas sensing behaviors was observed with catalysts but degraded gas sensing behavior occurred with large amount of the catalysts. Improvement was resulting from the increase in activate sites and modification of the Fermi energy level. The degradation was primarily due to the blockage of activate sites caused by excessive amounts of catalysts. Catalysts decorated ZnO NR gas sensors can be a candidate for lowered operating temperature with great gas responses.

This research was partially supported by the Korea Institute of Energy Technology Evaluation and Planning (20158520000210) grant funded by the Korea Government Ministry of Trade, Industry and Energy, a grant from a Strategic Research Project (2013-0132) funded by the Korea Institute of Construction Technology, and Auburn University IGP.

[1]     Azad, A. M., et al. Journal of the Electrochemical Society 139.12 (1992): 3690-3704..

[2]     Morrison, S. Roy. Sensors and actuators 12.4 (1987): 425-440..

[3] Müller G, Friedberger A, Kreisl P, Ahlers S, Schulz O, Becker T. Thin Solid Films. 2003;436(1):34-45.