Humidity Sensor Based on Two-Dimensional SnSe₂/MWCNT Nanohybrids for the Online Monitoring of Human Respiration and a Touchless Positioning Interface

Abstract

Herein, we report the significantly enhanced humidity responsiveness of resistive devices based on two-dimensional SnSe2/MWCNT nanohybrids. The multifunctional humidity sensor was exploited to establish a human–machine interface and for human interactive applications such as breath monitoring and sensing of the humidity of human skin for a touchless positioning interface. The sensor exhibited great potential owing to a high surface-to-volume ratio of SnSe2/MWCNT nanohybrids. The sensor has good linear response over a broad humidity range from 10–70% with fast response and recovery. The sensor shows the humidity responsivity of 0.148 in the humidity range of 10–70% and 0.063 for the humidity range of 75–95%. The maximum current sensitivity of 857% is achieved at 95% relative humidity for SnSe2/MWCNT nanohybrids, which is quite higher than the sensitivity obtained for pristine SnSe2 nanosheets. As a high-performance electronic device, the sensor has extremely low noise level and high recognition power for small humidity variations. The present finding advocates the huge development in humidity monitoring for biomedical, intelligent electronics, and industrial applications.

Charge Redistribution Mechanisms in SnSe2 Surfaces Exposed to Oxidative and Humid Environments and Their Related Influence on Chemical Sensing

“…Definitely, surface oxidation induces an increase in the work function of 0.4 eV, owing to the charge transfer between the substrate and the SnO 2 skin of 0.56 e – per SnO 2 unit. As opposed to previous reports, ,, the pristine SnSe 2 surface is inert to water at room temperature, while the SnO 2 –SnSe 2 heterostructure displays notable sensitivity to humidity.…”

“…Correspondingly, water adsorption on SnSe 2 and SnSe 1.88 surfaces is energetically unfavorable for temperatures above 124 and 264 K, respectively (Figure S11). Hence, we conclude that pristine SnSe 2 is stable in a humid environment and, consequently, is unsuitable for humidity sensing, contrarily to conclusions in refs , , and On the contrary, adsorption of H 2 O on the SnO 2 –SnSe 2 heterostructure (Figure b) is energetically favorable even above room temperature (Figure S11). The values of charge transferred from H 2 O to the SnO 2 skin are 0.43 and 0.30 e – for one and two H 2 O molecules per supercell, respectively.…”

“…In addition, the interaction with water is relevant also for understanding the stability of any other SnSe 2 -based (opto)­electronic device working in ambient humidity, as well as the eventual environmental doping effects in transport properties . Actually, recently different groups have reported that SnSe 2 is extremely sensitive to humid environments, ,, with the possibility of using it in humidity-sensing devices.…”

Chain-ring covalently interconnected cellulose nanofiber/MWCNT aerogel for supercapacitors and sensors

“…20 The more homogeneous the microstructure of the CA, the more efficient its electron transport in combination with the electrolyte since electron conduction needs to be continuous to ensure the performance of the whole device. 21 The variation of the acid–base environment with a neutral reaction environment affects the structure of covalently interconnected fibers; for example, CNF in CAMC-Neu covalently interconnected fibers obtained under neutral reaction conditions tends to agglomerate around MWCNT, while CAMC-Akl covalently interconnected fibers are obtained under alkaline conditions. The CNF in the CAMC-Akl covalently interconnected fibers obtained under alkaline conditions tend to cross-link into a network structure, resulting in a more uniform cross-linked structure of MWCNT.…”

All-cellulose-derived humidity sensor prepared via direct laser writing of conductive and moisture-stable electrodes on TEMPO-oxidized cellulose paper

“…The response and recovery times were defined as the time required to reach 90% of the change in sensor resistance. 1,38 The sensitivity (S) was calculated using the following equation: 17,39…”