NiO decorated CeO2 nanostructures as room temperature isopropanol gas sensors

Abstract

Heterostructures developed using CeO₂ show promising peculiarities in the field of metal oxide gas sensors due to the great variations in the resistance during the adsorption and desorption processes. NiO decorated CeO₂ nanostructures (NiO/CeO₂) were synthesized via a facile two-step process. High resolution transmission electron microscopy (HRTEM) results revealed the perfect decoration of NiO on the CeO₂ surface. The porous nature of the NiO/CeO₂ sensor surface was confirmed from scanning electron microscopy (SEM) analysis. Gas sensing studies of pristine CeO₂ and NiO/CeO₂ sensors were performed under room conditions and enhanced gas sensing properties for the NiO/CeO₂ sensor towards isopropanol were observed. Decoration of NiO on the CeO₂ surface develops a built-in potential at the interface of NiO and CeO₂ which played a vital role in the superior sensing performance of the NiO/CeO₂ sensor. Sharp response and recovery times (15 s/19 s) were observed for the NiO/CeO₂ sensor towards 100 ppm isopropanol at room temperature. Long-term stability of the NiO/CeO₂ sensor was also studied and discussed. From all the results it is concluded that the decoration of NiO on the CeO₂ surface could significantly enhance the sensing performance and it has great advantages in designing best performing isopropanol gas sensors.

Fig. 1. Schematic representation of gas sensing measurement circuit.

Fig. 2. XRD patterns of pure CeO₂ nanoparticles and NiO/CeO₂ nanocomposites.

Fig. 3. XPS spectra of (a) NiO/CeO₂, (b) Ni 2p and (c) Ce 3d, and (d) O 1s.

Fig. 4. FESEM images of (a) CeO₂ nanoparticles, (c) NiO/CeO₂ nanocomposites. EDS spectra of (b) pure CeO₂ nanoparticles, and (d) NiO/CeO₂ nanocomposites. (e) SEM micrographs and (f) EDS spectrum of fabricated gas sensor using NiO/CeO₂ nanocomposites. Insets are the particle size distributions.

Fig. 5. (a and b) HRTEM images of NiO/CeO₂ nanocomposites with different magnifications. (c) d-spacing and (d) SAED pattern of NiO/CeO₂ nanocomposites.

Fig. 6. Response and recovery of (a) CeO₂, and (b) NiO/CeO₂ gas sensors towards 100 ppm isopropanol gas at room temperature.

Fig. 7. (a) Response of CeO₂, and NiO/CeO₂ gas sensors towards various concentrations of isopropanol gas at room temperature. (b) Dynamic response and recovery curves of NiO/CeO₂ gas sensor towards isopropanol gas at room temperature.

Fig. 8. (a) Response of NiO/CeO₂ gas sensor versus varying concentrations (1–100 ppm) of test gases at room temperature. (b) Response and recovery times of NiO/CeO₂ gas sensor towards 100 ppm test gases at room temperature.

Fig. 9. (a) Response of CeO₂, and NiO/CeO₂ gas sensors towards 100 ppm test gases at room temperature. (b) The long-term stability of NiO/CeO₂ gas sensor towards 100 ppm isopropanol at room temperature.

Fig. 10. (a) Schematic diagram demonstrating the band gap alignment of NiO/CeO₂. Schematic illustration of the isopropanol gas sensing mechanism of (b) CeO₂ and (c) NiO/CeO₂ gas sensors with surface adsorption and desorption reactions.