Oxygen Defects in Nanostructured Metal‐Oxide Gas Sensors: Recent Advances and Challenges^†

Abstract

Defect engineering has been the most promising strategy to modulate the surface microstructure and electronic structure of the metal oxides, which will govern the efficiency of a given oxide for the applications in heterogeneous catalysis, energy storage and conversion fields, and gas sensing. This review summarizes recent research advances on understanding the role of oxygen vacancies of the metal oxides in gas sensing. First, different strategies for oxygen vacancy productions are summarized and compared. Then, the proper characterization techniques for oxygen vacancy are introduced. Importantly, the structure-activity relationships between vacancy engineering and gas sensing ability are further illustrated coupling the experimental results and theoretical studies. Finally, the key challenges and prospects regarding defect engineering in gas sensing are highlighted. Wenjie Ding (left) obtained his bachelor degree from Beijing Forestry University in 2018. Currently, he is pursuing his master degree under the supervision of Associate Professor Jiajia Liu in Beijing Instituted of Technology, China. His current research interests mainly focus on the synthesis of nanomaterials for the application of gas sensing. Dr. Jiajia Liu (middle) received her PhD degree in 2010 from Department of Chemical & Biomolecular Engineering of National University of Singapore, Singapore. Currently, she is Associate Professor in School of Materials and Engineering, Beijing Institute of Technology, China. Her current research interest is the development of metal oxide nanostructures and their applications in sensor, catalysis, and optoelectronics. Jiatao Zhang (right) was born in 1975. He earned his PhD from the Department of Chemistry, Tsinghua University, in 2006. Currently, he is Xu Teli Professor in the School of Materials and Engineering, BIT. He was awarded the Excellent Young Scientist foundation of NSFC in 2013. He also serves as the director of Beijing Key Laboratory of Construction-Tailorable Advanced Functional Materials and Green Applications. His current research interest is inorganic chemistry of semiconductor-based hybrid nanostructures with novel optical, electronic properties for the applications in energy conversion and storage, catalysis, optoelectronics and biology.

In situ observation of highly oxidized Ru species in Ru/CeO2 catalyst under propane oxidation

“…Indeed, in the recent work of Aitbekova et al, 61 the redispersion of Ru NPs on the ceria surface induced by annealing in oxygen at 230 C was demonstrated. It is possible that the single Ru atoms on the ceria surface, accompanied by oxygen This journal is © The Royal Society of Chemistry 2022 chemisorption occurring on metal oxides, 62,63 may have a slightly different oxidation state than the ruthenium atoms in RuO 4 . Another explanation could be the modication of the electronic structure (so-called the size effect) of the small-size RuO 4 clusters (or single Ru 8+ ions), or even the band bending effects arising from the interaction of two oxides with different bandgaps.…”

Enhanced acetic acid sensing of MOF-derived α-Fe2O3/ZrO2 arising from phase junction and defects

“…Defect engineering is mainly used in the gas detection of metal oxide gas sensors such as ZnO, TiO 2 , SnO 2 , In 2 O 3 , WO 3 , CuO and Fe 2 O 3 . 15–17 Defects ( e.g. , grain boundaries, cation vacancies and dopants) would generate intermediate bands, thus regulating the carrier concentration; 18 more notably, electron-deficient defects as active sites contribute to adsorbing and activating gas molecules.…”

“…Defect engineering is mainly used in the gas detection of metal oxide gas sensors such as ZnO, TiO 2 , SnO 2 , In 2 O 3 , WO 3 , CuO and Fe 2 O 3 . [15][16][17] Defects (e.g., grain boundaries, cation vacancies and dopants) would generate intermediate bands, thus regulating the carrier concentration; 18 more notably, electron-deficient defects as active sites contribute to adsorbing and activating gas molecules. 19 Besides, the construction of heterojunctions at the interface of MOs can promote carrier transfer due to differences in band gap structures, and consequently increase the carrier concentrations on the MO surfaces (e.g., p-Co 3 O 4 /n-In 2 O 3 , n-TiO 2 /n-SnO 2 and p-CuO/p-NiO).…”

Significant role of defect‐induced surface energy in water splitting to generate electricity by nickel ferrite hydroelectric cell

“…Oxygen vacancies have a crucial role in the chemical and physical properties of any metal oxides 1‐4 . For the adsorption of any gas or liquid on the surface of metal oxides, surface cation and oxygen vacancy pair (M +δ –Vo ‐δ ) are the predominant reactive sites 5 .…”

“…Oxygen vacancies have a crucial role in the chemical and physical properties of any metal oxides. [1][2][3][4] For the adsorption of any gas or liquid on the surface of metal oxides, surface cation and oxygen vacancy pair (M +δ -Vo -δ ) are the predominant reactive sites. 5 Among metal oxides, ferrites are the most versatile materials used in various gas sensing applications due to heterogeneous ionic sites on the surface.…”