Density functional theory study of NO ₂ -sensing mechanisms of pure and Ti-doped WO ₃ (002) surfaces

Abstract

Density functional theory (DFT) calculations are employed to explore the NO 2 -sensing mechanisms of pure and Ti-doped WO 3 (002) surfaces. When Ti is doped into the WO 3 surface, two substitution models are considered: substitution of Ti for W 6c and substitution of Ti for W 5c . The results reveal that substitution of Ti for 5-fold W forms a stable doping structure, and doping induces some new electronic states in the band gap, which may lead to changes in the surface properties. Four top adsorption models of NO 2 on pure and Ti-doped WO 3 (002) surfaces are investigated: adsorptions on 5-fold W (Ti), on 6-fold W, on bridging oxygen, and on plane oxygen. The most stable and likely NO 2 adsorption structures are both N-end oriented to the surface bridge oxygen O 1c site. By comparing the adsorption energy and the electronic population, it is found that Ti doping can enhance the adsorption of NO 2 , which theoretically proves the experimental observation that Ti doping can greatly increase the WO 3 gas sensor sensitivity to NO 2 gas.

First-Principles Study of H₂ Dissociative Adsorption Reactions on WO₃ Surfaces

“…The most favorable ad- Considering that O1c has a free bond and is also the outermost atom, this result is reasonable and also suggested by other calculations related with WO3 surfaces. 30,32 Our results also theoretically prove that two H atoms prefer to be adsorbed on one O1c atom forming H2O rather than on two separate O1c atoms forming hydroxyl groups, which is consistent with the experimental phenomenon. 11,33 The formation of H2O reduces the surface energies significantly and may play a key role in the adsorption structure stabilization.…”

A DFT study on WO3 nanowires with different orientations for NO2 sensing application

“…Ultimately, N atom was chosen to connect to the surface since it is easier for N to coordinate with W and O atoms, consistent with the cases in references [20,35]. Fig.…”

“…Oison et al [19] illustrated the microscopic mechanism of O 3 and CO sensing on WO 3 surface by highlighting the role of the oxidation of CO and the reduction of O 3 on the value of the resistivity of WO 3 gas sensor. Our group has previously used DFT calculations to investigate adsorption of NO 2 on bulk WO 3 (0 0 2) surface [20]. Recently, we investigated the effect of NO 2 adsorption on the electronic structure and electron population of [0 1 0]-oriented W 18 O 49 nanowire employing DFT method [21].…”

Characterization of Tungsten Oxide Thin Films Produced by Spark Ablation for NO2 Gas Sensing

“…This increases the thickness of the depletion layer, thereby increasing the resistance of the films. Although the interaction mechanisms are not fully understood, recent density functional theory calculations 15,16 indicate that the Fermi level of the energy band of tungsten oxide shifts toward higher energies, inducing changes in their resistance, upon adsorption of NO 2 molecules. 16 WO x nanoparticles and nanomaterials can be synthesized by a number of liquid-phase and gas-phase methods.…”

“…Although the interaction mechanisms are not fully understood, recent density functional theory calculations 15,16 indicate that the Fermi level of the energy band of tungsten oxide shifts toward higher energies, inducing changes in their resistance, upon adsorption of NO 2 molecules. 16 WO x nanoparticles and nanomaterials can be synthesized by a number of liquid-phase and gas-phase methods. 17−20 Among those, synthesizing nanoparticle building blocks by spark ablation in the gas phase has many advantages.…”