Copper Oxide Nanorod/Reduced Graphene Oxide Composites for NH3 Sensing

The NH3 sensing performance of copper oxide (CuO) nanorods can be enhanced with reduced graphene oxide (rGO) composites (i.e., CuO:rGO) due to their favorable Fermi level alignments and improved carrier mobility. However, the conductivity and the active sites in CuO:rGO are highly determined by the preparation techniques. Hence, we attempt to unravel the role of different chemical routes (wet chemical synthesis and hydrothermal preparation techniques) on the NH3 sensor device performance of CuO:rGO. Morphological imaging reveals the formation of 1D structures in both preparation techniques, and the role of graphene oxide on the evolution of CuO nanorods is discussed. First-principles calculations probe the interactions between CuO:rGO and NH3, and the structure is optimized for the most stable configuration. The absorption binding energies of the CuO:rGO–NH3 systems are measured to be 1.36 eV, which is much higher than those of the metal–rGO composites. For 50 ppm of NH3, the sensor response is measured to be 3.87 and 6.29 for chemically and hydrothermally synthesized CuO:rGO, respectively. The enhanced response of hydrothermal CuO:rGO is due to the more active sites induced on the CuO nanorod surface by rGO and the favorable band bending at the rGO–CuO interface.