Synthesis of CuO microstructures with controlled shape and size and their exposed facets induced enhanced ethanol sensing performance

Ethanol-sensitive sensors were fabricated using various CuO microstructures with controlled size and shape. For the materials preparation, Cu2O microstructures were first synthesized by a facile wet chemical reaction and then were oxidized into CuO under air conditions. Hexahedron-, octahedron-, decahedron- and flower-shaped CuO microstructures were obtained. The particle size of CuO decahedrons can be tailored from 1.27 to 2.23 μm by simply adjusting the amount of glucose. Gas sensing properties of various CuO microstructures were also compared. It is interesting that the gas response of the CuO decahedron samples increased with increasing the particle size. The one with the maximum average particle size (2.23 μm) has gas responses ≥3 times larger than the one with the minimum average particle size (1.27 μm), toward 5 to 100 ppm ethanol vapor. It was found that the gas response of the CuO microstructures increased with the increase of the exposure extent of the low index (111¯) facet relative to high index (202¯) facet. This phenomenon was also observed in the gas sensing tests of CuO microstructures with lower crystal quality and different shape. The enhanced gas response may be attributed to the higher exposure extent of the (111¯) facet with highly activity. In addition, the crystal quality, surface defect density and shape also play important roles in the gas sensing performance.