Humidity-Independent Gas Sensors Using Pr-Doped In₂O₃ Macroporous Spheres: Role of Cyclic Pr³⁺/Pr⁴⁺ Redox Reactions in Suppression of Water-Poisoning Effect

Abstract

Pure and 3–12 at. % Pr-doped In2O3 macroporous spheres were fabricated by ultrasonic spray pyrolysis and their acetone-sensing characteristics under dry and humid conditions were investigated to design humidity-independent gas sensors. The 12 at. % Pr-doped In2O3 sensor exhibited approximately the same acetone responses and sensor resistances at 450 °C regardless of the humidity variation, whereas the pure In2O3 exhibited significant deterioration in gas-sensing characteristics upon the change in the atmosphere, from dry to humid (relative humidity: 80%). Moreover, the 12 at. % Pr-doped In2O3 sensor exhibited a high response to acetone with negligible cross responses to interfering gases (NH3, CO, benzene, toluene, NO2, and H2) under the highly humid atmosphere. The mechanism for the humidity-immune gas-sensing characteristics was investigated by X-ray photoelectron and diffuse reflectance infrared Fourier transform spectroscopies together with the phenomenological gas-sensing results and discussed in relation with Pr3+/Pr4+ redox pairs, regenerative oxygen adsorption, and scavenging of hydroxyl groups.

Surface Functionalized Sensors for Humidity‐Independent Gas Detection

“…Although these strategies were effective in suppressing the humidity‐dependent gas‐sensing characteristics, their use was usually accompanied by unintended side effects, such as response deterioration, selectivity alteration and resistance variation. For example, species such as NiO, [7] CuO, [8] and Al [9] can be used to capture hydroxyls and supply oxygen adsorption sites, and surface modification using noble metal (Pd [10] or Pr [11] ) particles to catalyse the removal of hydroxyls can improve robustness to humidity. However, these methods suffer from limitations including poor performance in the low humidity range (0–20 RH%).…”

Platinum-Supported Cerium-Doped Indium Oxide for Highly Sensitive Triethylamine Gas Sensing with Good Antihumidity

“…This phenomenon may be attributed to the competitive reaction of H 2 O with adsorbed oxygen species and other reducing gases, which generates OH on the surface and releases electrons to the materials, resulting in a significant change in gas response. , The introduction of cerium can improve the humidity independence due to its reversible redox cycle properties (Ce 3+ /Ce 4+ redox pairs). , The typical antihumidity mechanism of the 1% Pt/Ce 12 In is summarized by the following eqs – …”

“…Among various gas-sensing materials, metal-oxide semiconductors (MOSs) exhibit superior performance due to their advantages including chemical and physical properties, low cost, facile preparation, and long-term stability, which have gained wide acceptance in the field of breath analysis in medical diagnosis, air quality monitoring, food safety inspection, and other industrial areas. , MOS gas-sensitive materials can be classified as p-type and n-type, such as In 2 O 3 , , SnO 2 , , LaFeO 3 , , WO 3 , , and Cu 2 O, according to their resistance responses to oxidizing or reducing gases. As a typical n-type MOS, In 2 O 3 , with a wide band gap of 3.55–3.75 eV, has been used to detect many gases including H 2 S, NO 2 , acetone, and formaldehyde .…”

Highly conjugated three-dimensional van der Waals heterostructure-based nanocomposite films for ultrahigh-responsive TEA gas sensors at room temperature

“…To this end, researchers have explored many methods, such as adjusting the sensing response temperature, changing the types of the adsorbed oxygen, loading or doping elements, or metal oxides with strong humidity adsorption, such as Rh, Sb, NiO, and CuO, to protect the sensitive layer so as to improve the humidity resistance of the MOS sensors. [5][6][7][8][9][10] However, most of the MOS-based sensing materials have poor response and selectivity to low concentration gas, which makes a challenging issue for the design of a reasonable gas sensor.…”