Effect of Nickel Vacancies on the Room-Temperature NO₂ Sensing Properties of Mesoporous NiO Nanosheets

Abstract

To improve the gas-sensing performance of metal-oxide-semiconductors, the effect of defects on gas-sensing properties has been widely investigated. Nevertheless, although the metal cation defect is the dominative acceptor defect in p-type semiconductors, its effect on the gas-sensing properties remains blank, which leads to a hindrance for further developing p-type semiconductor-based gas sensors. Accordingly, to eleborate the effect of metal cation defects on the sensing properties, mesoporous NiO nanosheets with different amounts of nickel vacancies were prepared by annealing at different temperatures. It was found that the amount of nickel vacancies increased with increasing the annealing temperature. Gas-sensing studies revealed that the NiO with a higher concentration of nickel vacancies exhibited higher sensitivity to NO2 at room temperature. With further increasing the annealing temperature to 600 °C, although the rapid decrease in the specific surface area of the NiO might limit the physisorption of NO2, the NiO could also present a better sensitivity to NO2 due to the abundant nickel vacancies with high activity. Furthermore, an in situ DRIFTS study demonstrated that the number of adsorbed nitrate and nitrite species on NiO surfaces increased with increasing the amount of nickel vacancies, indicating that the nickel vacancies acted as the dominative active sites participating in the gas–solid reaction and then determined the room-temperature sensing properties. According to the defect ionization equation, a hole conduction model was further proposed to decipher the dependency of sensing properties on the metal cation defects. We hope this work could make us better understand the roles of cation defect in the sensing properties, and it could also benefit the improvement of p-type semiconductor-based gas sensors.

The Role of Cation Vacancies in Electrode Materials for Enhanced Electrochemical Energy Storage: Synthesis, Advanced Characterization, and Fundamentals

“…Reproduced with permission. [ 110 ] Copyright 2016, American Chemical Society. Reproduced with permission.…”

“…There are several ways for incorporating cation vacancies and tailoring its content in transition metal oxides/carbides through synthetic approaches, such as replacing the constituent cations or anions with aliovalent substitutes, [ 94–96,104,105 ] equilibration at solutions with different pH values, [ 89,90,99,106,107 ] selective removal of constituent cations, [ 101,102,108 ] thermal annealing in defects inducing atmospheres, [ 109,110 ] and plasma etching. [ 111 ] The characterization of cation vacancies, however, is usually challenging.…”

“…[ 90,95,107 ] Other powerful techniques for detecting cation vacancies in nanomaterials, especially the materials without long‐range order, are extended X‐ray absorption fine structure (EXAFS) [ 77,78,97,105,111 ] and X‐ray pair distribution function (PDF) analysis, [ 89,94,96,106 ] both of which are sensitive to the local structure variations that enable accurate determination of cation vacancies. Additionally, multiple analytical techniques, such as X‐ray photoelectron spectroscopy (XPS), [ 91,105,113 ] nuclear magnetic resonance (NMR), [ 94–96 ] Raman/Fourier transform infrared (FTIR) spectroscopy, [ 104 ] electron paramagnetic resonance (EPR), [ 110 ] photoluminescence (PL), [ 110 ] and positron annihilation spectrometry (PAS), [ 114 ] have also been reported to serve as complementary tools for cation vacancies characterization. Some of these techniques are commonly used together to elucidate the presence and content of cation vacancies, which will give a better understanding of the physical nature of these cation‐deficient nanomaterials.…”

Cu x O self-assembled mesoporous microspheres with effective surface oxygen vacancy and their room temperature NO2 gas sensing performance

“…The response time (t res ), corresponding to the time reaching the 90% steady response and the recovery time (t rec ), corresponding to the time attaining 10% of the initial response, were determined. The t res and t rec upon exposure to 4 ppm NO 2 for the virus-like Cu x O SMMs based sensor were 22 s and 42 s, respectively, which are faster than those observed in the previous study for NO 2 (Table S1, Supplementary information) [17,18,22]. We also measured the response of virus-like Cu x O SMMs based sensor to some typical combustible and toxic gases.…”

“…The sensors based on concave Cu 2 O octahedral nanostructure had good sensing response to NO 2 at 50°C due to their unique concave octahedral-shape [16]. Nickel oxide (NiO) hexagonal nanosheets with micropores present good sensitivity to NO 2 at room temperature due to the abundant nickel vacancies formed in NiO [17]. Tin oxide (SnO 2 ) nanoflower-based sensor exhibited high response toward 200 ppb NO 2 at room temperature due to the oxygen vacancies [18].…”