Cost-effective fabrication of polycrystalline TiO2 with tunable n/p response for selective hydrogen monitoring

Abstract

In this report, we demonstrate a simple and cost-effective strategy to prepare polycrystalline rutile TiO2 based gas sensors with tunable n/p type conductivity inversion depending on gas concentration, operating temperature and applied voltage. The effect of surface modification by Ag and Ni thin film on structural, morphological and gas sensor characteristics is studied in detail. The sensors show excellent sensing performance in terms of sensitivity (~25% for 0.1 vol. % H2 diluted in technical air), selectivity (selectivity factor for 0.1 vol. % H2 is about ~24 against NH3, CH4, NO2 and ~8 for CO), stability (both long-term and short-term) and reaction times (~0.7 min for 0.1 vol. % H2). The aforementioned performance is recorded at 300 °C with applied voltage of 0.1 V. Excluding the power consumption of sensor heater-5 watt), this applied voltage 0.1 V can reduce the power-10 watt. We found a critical point, defined with threshold-concentration (CTh), threshold-temperature (TTh) and criticalvoltage (VC), at which the conductivity inverses from one kind to another, something intriguing to novel sensing phenomena that can be exploited to tailor the selectivity of the sensors. A physical-chemical sensing model is presented to understand the aforesaid peculiar occurrence.

Sol-gel Synthesis of TiO2 With p-Type Response to Hydrogen Gas at Elevated Temperature

“…This reaction reduces the thickness of space charge region (depletion layer) resulting an increase of surface conduction electron density [e − ] and thus the increased electronic conductivity, see Equation (4). Usually, titanium dioxide exhibits an n-type response to hydrogen, but some factors lead to a p-type transition, such as impurities, temperature, applied electric field, and gas concentration (Li et al, 2009;Haidry et al, 2018). However, contradicting with , in this work the transition point and the influencing factors leading to transition were not found.…”

“…According to the author's best knowledge, in the temperature range of 300-500 • C, pure n-type semiconductors might also show p-type response, which is resulted due to the formation of inversion layer on the surface (Li et al, 2009;Haidry et al, 2018).…”

The critical role of hydroxyl groups in water vapor sensing of graphene oxide

“…[39][40][41][42][43][44][45][46][47] However, we strongly believe that the mentioned s res and s rec values in the present case do not represent the actual surface reaction but are rather given by the gas mixing process of the designed sensor test experiment, as already described elsewhere. 48 This was already proven by the breath analysis experiment shown in Fig. 4(d).…”

Detection of Semi-volatile Plasticizers as a Signature of Early Electrical Fire

“…Similar to the TGS-822, the nanofiber sensor also exhibited resistance reduction when exposed to the reducing gases of DOP and 2-EH, suggesting n-type semiconductor mechanism. Following this mechanism, the reducing gas reacts with the oxygen anion adsorbed on the surface of the semiconductor, resulting in a decrease of the resistance (Haidry et al, 2018). As shown in Figure 6, the maximum response reached 41 and 26 for 100 ppm DOP and 2-EH, respectively, much larger than those for the TGS sensor (Yi et al, 2019).…”