Nitric Oxide Detector Based on WO₃-1wt%In₂O₃-1wt%Nb₂O₅ with State-of-the-Art Selectivity and ppb-Level Sensitivity

Abstract

Fast, sensitive, and precise detection of nitric oxide (NO) is critical to many applications in environmental monitoring and early disease diagnosis via respiratory testing. An effective detection system requires a sensor to detect NO gas at the parts per billion (ppb) level, and this system should possess a high degree of anti-interference selectivity. To achieve these targets, a series of gas sensor thin films based on intrinsic WO3, one-additive-doped WO3 (prepared by doping In2O3 or Nb2O5), and two-additive-doped WO3 (synthesized by doping with In2O3 and Nb2O5) oxides were successfully grown. By analyzing the properties of sensitivity, selectivity, responsiveness, and recovery time of the gas sensors, we found that WO3-1wt%In2O3-1wt%Nb2O5 has overwhelming advantages over intrinsic WO3, WO3-In2O3, and WO3-Nb2O5. A sensing response value of 2.4 was observed for NO concentrations as low as 20 ppb from the WO3-1wt%In2O3-1wt%Nb2O5 sensor. With 100 ppb NO gas, the WO3-1wt%In2O3-1wt%Nb2O5 sensor achieved a high response of 56.1 at 70 °C, which is a state-of-the-art performance for NO detection at low working temperature settings. WO3-1wt%In2O3-1wt%Nb2O5 also yields significantly improved selectivity and stability over intrinsic WO3, WO3-In2O3, and WO3-Nb2O5. Studies on the sensing mechanism show that the grain size, rather than the n–n heterostructure effect, plays a dominant role in the observed results. By decreasing the grain size so that it is close to the thickness of the space-charge layer, the sensing response is enhanced. Although room remains to further improve the sensing properties, the performance of WO3-1wt%In2O3-1wt%Nb2O5 is sufficient for implementation in low-content NO detection devices.

Liquid Metal-Based Epidermal Flexible Sensor for Wireless Breath Monitoring and Diagnosis Enabled by Highly Sensitive SnS 2 Nanosheets

“…The device exhibited a 197% sensitivity to 200 ppb with a response time of 223 s and easily recovered its initial resistance once we had stopped injecting NO. In contrast to most other NO sensors, our LM-based electrode performed rather well at low concentrations and could detect NO levels as low as 15 ppb with a sensitivity of 8.7% [45][46][47][48][49][50][51][52][53][54]. The sensitivity of our sensor exhibits a strong linear correlation with the gas concentration (Figure 3(c), R 2 = 0:95).…”

Observation of Switchable Dual-Conductive Channels and Related Nitric Oxide Gas-Sensing Properties in the N-rGO/ZnO Heterogeneous Structure

“…Equations 1−8 show some details regarding those physical and chemical processes. 52 According to the previous studies, those active oxygen species that are adsorbed on the surface of a semiconductor oxide are dependent on T w . When T w is below 150 °C, the dominant adsorbed oxygen species is O 2(ads) − (eq 1).…”

“…It is very similar to the doped WO 3 materials previously studied in detail. 52 The energy of gas molecules at 90 °C is sufficient to overcome the activation energy barriers of the adsorption process and redox reactions, 54,62 then, a higher temperature may result in a heavy desorption process and reduce the total number of adsorbed molecules. In addition, from the redox reactions described using eqs 6 and 7, at a high T w , the electrons start to move back to the material from NO molecules, which also decreases the sensitivity.…”

“…Each process can greatly affect the sensitive characteristics of the sensors. Equations – show some details regarding those physical and chemical processes . According to the previous studies, those active oxygen species that are adsorbed on the surface of a semiconductor oxide are dependent on T w .…”

A Low-Temperature Micro Hotplate Gas Sensor Based on AlN Ceramic for Effective Detection of Low Concentration NO2

“…As an ideal gas sensing material, In 2 O 3 has good development prospects for low temperature gas sensing detection of oxidizing gases, like NO 2 [15,16]. To improve the NO 2 gas sensing performance of In 2 O 3 -based materials, a lot of dopants and catalysts have been exploited and their role in NO 2 sensing behavior has been investigated [17,18]. Among these dopants and catalysts, Nb is mainly employed to improve the conductivity and stability of metal oxides [17,19,20,21], and Pt is used to enhance the sensing response and selectivity of sensors [11,18,22].…”