Enhanced response and selectivity of H₂S sensing through controlled Ni doping into ZnO nanorods by using single metal organic precursors

We report on enhancing the selectivity and response of room (23 °C) and high temperature H₂S gas sensing through controlled Ni doping (0–10 at%) into ZnO nanorods (NRs) grown with a facile solution growth method using a single hybrid bimetallic metal-organic precursor (nickel/zinc acetylacetonate). The morphology, microstructure, surface chemistry and photoluminescence properties of the as-grown NRs are extensively examined. The gas sensing results are discussed in terms of doping concentration, operating temperature, gas type, gas concentrations and relative humidity. The optimal response toward 100 ppm of H₂S reaches 3.1 at 23 °C and increases to 45.3 at 200 °C for 8 at% Ni-doped ZnO NR sensors, where the corresponding response/recovery time at 23 °C and 200 °C also reaches 76/160 and 48/60 s, respectively. The same sensor exhibits high H₂S selectivity over other gases, including CH₄, CH₃OH and C₂H₅OH. The enhancement of gas sensing is attributed to increasing the number of active sites for adsorption of oxygen and target gases on the surface through incorporation of Ni³⁺ over Ni²⁺ ions. At 23 °C, the sensing mechanism is related to the formation of a 7 nm-thick ZnS layer over the NRs through reactions between H₂S and adsorbed oxygen.