Electronic structure and oxygen vacancy tuning of Co & Ni co-doped W18O49 nanourchins for efficient TEA gas sensing

Inducing oxygen vacancies in metal oxides by dual doping metal ions is the key to modulating their electronic structure and designing highly sensitive noble metal-free materials for detecting hazardous toxic gases. This study reports nickel (Ni) and cobalt (Co) co-doping in W18O49 crystal lattices leads to electronic structure modulation and generates oxygen vacancies to highly activate the redox capability and catalytic efficacy of the urchin-like W18O49 sensor toward triethylamine (TEA) gas species. The electronic structure modulations and physisorption interactions between TEA molecules and W18O49 and/or Co&Ni co-doped W18O49 nanourchins were calculated by density functional theory (DFT). The experimental results and DFT calculations confirmed more significant charge transfers due to bandgap excitation and reactivity of TEA with Co&Ni co-doped W18O49 verifying their strong binding interactions. Electrons move from lattice oxygen to surface O2 molecules through co-doped cations-induced oxygen vacancies, which provide active sites and form surface superoxide and peroxide species incorporated into the sensing materials surface. Benefiting from the high specific surface area, abundant active sites, and faster electron/charge transport capability, the optimized 2 %Ni-doped W18O49, and 1 %Co&2%Ni co-doped W18O49 nanourchins exhibited excellent sensitivity towards TEA gas molecules. The sensing response of Co&Ni-W18O49 (Ra/Rg = 156) is higher than Ni-W18O49 (Ra/Rg = 114) and W18O49 (Ra/Rg = 76) at 250 °C, fast response/recovery (16/13), and superior selectivity. The XRD and XPS results combining the DFT calculations verify the improved sensitivity due to the synergistic modulation of electronic structure, which paws a friendly strategy for enriching the free electronics to design cost-effective gas sensors.