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

In this work, pure and nickel-doped WO 3 films were produced by chemical bath deposition on In-doped SnO 2 (ITO) substrates without annealing process. To synthesize the Ni:WO 3 films, two different types of nickel precursors were used as NiSO 4 and NiCl 2 . The influence of Ni doping using different Ni precursors on the structural, morphological, optical, and gas sensing properties of WO 3 films toward H 2 S gas was investigated in detail. All samples have monoclinic WO 3 polycrystallization where a substitution of Ni 2+ ions with W 6+ mı olmalı ions is detected from the slight shift in x-ray diffraction patterns with the Ni doping process. With nickel chloride source, the synthesized Ni:WO 3 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:WO 3 samples. Ni 2+ ions introduction in WO 3 host lattice has improved H 2 S gas detection capability; however, the biggest positive effect came from the NiSO 4 precursor with increasing solubility and improved growth process. The response to 50 ppb H 2 S gas at room temperature was calculated as 7%, 11%, and 23% for pure WO 3 , NiCl 2 -based Ni:WO 3 , and NiSO 4 -based Ni:WO 3 sensors, respectively. When the gas selectivity property was studied for NiSO 4 -based Ni:WO 3 sensors, they showed more selectivity against H 2 S gas compared to H 2 , benzene, methanol, etc. It is found that precursor type has an incredible impact on the H 2 S, reducing gas sensing properties in doped metal oxide gas sensor applications.