A New Strategy for Humidity Independent Oxide Chemiresistors: Dynamic Self‐Refreshing of In₂O₃ Sensing Surface Assisted by Layer‐by‐Layer Coated CeO₂ Nanoclusters

Abstract

The humidity dependence of the gas sensing characteristics of metal oxide semiconductors has been one of the greatest obstacles for gas sensor applications during the last five decades because ambient humidity dynamically changes with the environmental conditions. Herein, a new and novel strategy is reported to eliminate the humidity dependence of the gas sensing characteristics of oxide chemiresistors via dynamic self-refreshing of the sensing surface affected by water vapor chemisorption. The sensor resistance and gas response of pure In2 O3 hollow spheres significantly change and deteriorate in humid atmospheres. In contrast, the humidity dependence becomes negligible when an optimal concentration of CeO2 nanoclusters is uniformly loaded onto In2 O3 hollow spheres via layer-by-layer (LBL) assembly. Moreover, In2 O3 sensors LBL-coated with CeO2 nanoclusters show fast response/recovery, low detection limit (500 ppb), and high selectivity to acetone even in highly humid conditions (relative humidity 80%). The mechanism underlying the dynamic refreshing of the In2 O3 sensing surfaces regardless of humidity variation is investigated in relation to the role of CeO2 and the chemical interaction among CeO2 , In2 O3 , and water vapor. This strategy can be widely used to design high performance gas sensors including disease diagnosis via breath analysis and pollutant monitoring.

Gas Sensors Based on Chemi-Resistive Hybrid Functional Nanomaterials

“…For CP-based chemi-resistive heterojunctions, unsatisfied sensitivity (response) and long-term stability will be two challenging issues for researchers. Obvious advantages of heterojunction-type chemi-resistive hybrids-based gas sensor can be summarized as: (1) higher sensitivity due to manipulations of the potential energy barrier formed by band bending of different components (e.g., Fe 2 O 3 /TiO 2 tube-like quasi-1D nanostructures (n-n) [114], n-ZnO/p-CoPc [119], and n-SnO 2 /p-Cu 2 O [120] core-sheath NRs); (2) improved selectivity to some gases (e.g., CuO-SnO 2 p-n nanowires to H 2 S [67]); (3) promising, although limited so far, to anti-interference gas (e.g., CeO 2 -In 2 O 3 hollow spheres with anti-humidity properties [113]); (4) avoiding UV-introduced ozone and performance degradation (for example, when narrow-band guest material hybrids with semi-conductive host materials, e.g., CdS-ZnO [123,124], ZnO-CdS [125], CdSe-ZnO [126], the room operation temperature can be achieved by the visible-light-driven gas sensing). The representative works are summarized in Table 4.…”

“…Although excellent advances in both e-nose system and chemi-resistive sensory unit have been reached in the field during the last few years, there is still room for improvements. Below is a summary of the main rules for improving the performance of hybrid material-based gas sensors (details see the summary paragraph of each section): For sensors based on heterojunctions (potential energy barrier manipulation), the more uniform and the larger the contact area of heterojunctions and charge transfer hybrids, the higher the response, resulting in faster speed/ lower operating temperature, e.g., Fe 2 O 3 /TiO 2 tube-like quasi-1D nanostructures (n-n) [114], n-ZnO/p-CoPc [119], CeO 2 -In 2 O 3 hollow spheres with anti-humidity properties [113], and CdS-ZnO [123,124].…”

“…TEM images and dynamic sensing transients of Ce-In 2 O 3 hollow spheres exposed to 0.5-20 ppm of acetone at 450 °C in dry (red) and RH 80% (blue). Reproduced with permission[113].Copyright 2016, Wiley-VCH. b TEM image of 1D Fe 2 O 3 /TiO 2 tube-like nanostructures.…”

Metal-Organic Framework Templated Synthesis of Ultrasmall Catalyst Loaded ZnO/ZnCo2O4 Hollow Spheres for Enhanced Gas Sensing Properties

“…The baseline resistance of Pd-ZnO/ZnCo 2 O 4 HSs was increased at a higher humidity (Fig. S5b), because the adsorption of water vapor can donate the electrons to the sensing layers41 and these electrons are recombined with hole in the ZnCo 2 O 4 . Therefore, the hole accumulation layers decreased, leading to the decrease in the sensing properties (Fig.…”

In-Situ Growth and Characterization of Indium Tin Oxide Nanocrystal Rods

“…Nanostructured ITO [8] has many new applications because of its unique surface [9] and quantum effects [10]. Nanometer-scale structured ITO material has a high specific surface area and can be applied in cells [11] and gas sensors [12,13]; it has also demonstrated gas sensitivity in the field of environmental sensitive exploration [14,15]. Although many other transparent conducting oxide thin-films have been developed to replace ITO film [16,17], ITO films are still the most widely used in commercial applications.…”