In this work, the compositional optimization in copper oxide/tungsten trioxide (CuO/WO ) composites was systematically studied for hydrogen sulfide (H S) sensing. The response of CuO/WO composites changes from -type to -type as the CuO content decreases. Furthermore, the -type response weakens while the -type response strengthens as the Cu/W molar ratio decreases from 1:0 to 1:10. The optimal Cu/W molar ratio is 1:10, at which the sensor presents the ultrahigh -type response of 1.19 × 10 to 20 ppm H S gas at 40 °C. Once the temperature rises from 40 °C to 250 °C, the CuO/WO (1:1) sensor presents the - response transformation, and the CuO/WO (1:1.5) sensor changes from no response to -type response, because the increased temperature facilitates the Cu-S bonds break and weakens the -type CuO contribution to the total response, such that the CuS bond decomposition by a thermal effect was verified by a Raman analysis. In addition, with a decrease in CuO content, the CuO is transformed from partly to completely converting to CuS, causing the resistance of CuO to decrease from increasing and, hence, a weakening mode of -CuO and -WO to the total response turns to a synergistic mode to it.
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