Investigation of H2S gas sensing performance of Ni:WO3 films at room temperature: nickel precursor effect

In this work, pure and nickel-doped WO3 films were produced by chemical bath deposition on In-doped SnO2 (ITO) substrates without annealing process. To synthesize the Ni:WO3 films, two different types of nickel precursors were used as NiSO4 and NiCl2. The influence of Ni doping using different Ni precursors on the structural, morphological, optical, and gas sensing properties of WO3 films toward H2S gas was investigated in detail. All samples have monoclinic WO3 polycrystallization where a substitution of Ni2+ ions with W6+ mi olmali ions is detected from the slight shift in x-ray diffraction patterns with the Ni doping process. With nickel chloride source, the synthesized Ni:WO3 samples exhibit nano-ball shapes with different dimensions on the film surfaces. Optical band gap energy severely decreases with nickel doping due to increasing oxygen vacancies, especially when nickel chloride is used as a precursor source in Ni:WO3 samples. Ni2+ ions introduction in WO3 host lattice has improved H2S gas detection capability; however, the biggest positive effect came from the NiSO4 precursor with increasing solubility and improved growth process. The response to 50 ppb H2S gas at room temperature was calculated as 7%, 11%, and 23% for pure WO3, NiCl2-based Ni:WO3, and NiSO4-based Ni:WO3 sensors, respectively. When the gas selectivity property was studied for NiSO4-based Ni:WO3 sensors, they showed more selectivity against H2S gas compared to H-2, benzene, methanol, etc. It is found that precursor type has an incredible impact on the H2S, reducing gas sensing properties in doped metal oxide gas sensor applications.