Q2. What are the future works in "Hydrogen gas sensor based on mesoporous in2o3 with fast response/recovery and ppb level detection limit" ?
In the future work, the authors will further explore the different ways for the isolation of the heating source and measurement unit.
Q3. What was used to study the chemical binding of In2O3?
X-ray photoelectron spectroscope (XPS, Kratos Axis-Ultra DLD with Mg Ka radiation) was used to study the chemical binding of In2O3.
Q4. What types of sensors have been developed over the past decades?
Over the past decades, various types of hydrogen gas sensors have been developed,including semiconductor [1, 2], thermoelectrics [3, 4] optical [5-8] and surfaceacoustic wave [9, 10] sensors.
Q5. What are the sensing mechanisms of hydrogen gas sensors?
The sensing mechanisms of these sensors are based mainly on chemical reactionsbetween hydrogen with the negatively charged oxygen species on the surfaces ofmetal oxide sensing materials [33].
Q6. Why does the sensor show a high response value?
Due to lots of chemisorbed oxygen ions adsorbed on thesurfaces of mesoporous In2O3, the sensor shows high response values, e.g., with a value of 43.8 to 2000 ppm of hydrogen.
Q7. What is the problem for the successful application of this technology?
Because the optimum working temperature of the hydrogen sensor based on mesoporous In2O3 is 260 oC, the potential problem for the successful application of this technology is that heating is needed during the sensing process.
Q8. Why does the sensor show fast response and recovery times?
Because the mesoporous structures of the In2O3 are beneficial to the adsorption and desorption of hydrogen, the sensor shows fast response and recoveryspeeds.
Q9. What is the reaction reaction of the mesoporous In2O3 based?
After it is exposed to hydrogen at a working temperature above 200 oC, the hydrogen molecules are absorbed and reacted with the oxygen species of O− on the surfaces of In2O3 to release free electrons (see chemical reaction equation (5)) [36].
Q10. What was used to check the band gap of the samples?
Diffuse reflectance spectra (DRS) of the powders wereobtained to check the band-gaps of samples using a UV-2101 Shimadzu apparatuswith BaSO4 as a reference.
Q11. What are the advantages of the semiconductor sensors?
Among them, the semiconductor sensors are simple,inexpensive, highly sensitive, and can be easily integrated with microelectronicdevices.
Q12. What was the sensitivity of the hydrogengas sensor?
The hydrogengas sensor based on the mesoporous In2O3 showed high sensitivity, fast response and recovery, and detection limit of ppb level.
Q13. Why does the sensor exhibit a high response value to hydrogen?
Because of the mesoporous structuresand large specific surface area of the In2O3, and also lots of chemisorbed oxygen ions on its surfaces, the sensor exhibits fast response/recovery and a high response value tohydrogen, as shown in Fig.
Q14. What are the fastest response/recovery rates for hydrogen sensing materials?
Some of them have fastresponse/recovery rates for hydrogen sensing, such as those based on a-MoO3 nanowires [27] and p-TiO2 thin film [25], but their response values are low and their detection limits are normally higher than ppm level.
Q15. What is the importance of detection of traces of hydrogen gas?
detection of traces of hydrogengas is essential to mitigate the danger of explosion caused by leaks of hydrogenduring its production, storage, transportation and usage.
Q16. What is the detection limit of the sensor?
For a low concentration of 0.01 ppm, thesensor sill shows an obvious response value of 1.2, indicating that the sensor has alow detection limit of 10 ppb.
Q17. What are the requirements for the in2O3 based hydrogen sensors?
In2O3 based hydrogen gas sensors with fast response/recovery, high response and low level detection limit are urgently needed.
Q18. What are the advantages of adding metal oxides to the sensors?
many ofthese hydrogen sensing materials have been further modified by adding/doping withnoble metal nanoparticles or metal ions to enhance their sensing properties [37-40],especially for improving their response/recovery speeds.
Q19. What is the detection limit of the hydrogen gas sensor?
Compared with other hydrogen gas sensors based on pure metal oxides in theliterature [31, 32] listed in Table 1, the hydrogen gas sensor in this study shows notonly faster response/recovery times, but also a lower detection limit.
Q20. How can the authors calculate the optical band-gap of In2O3?
The opticalband-gap (Eg) can be calculated by extrapolating the linear section of the curve to F(R)= 0 (see the inset of Fig. 3a as an example).