Direct confirmation of confinement effects by NiO confined in helical SnO2 nanocoils and its application in sensors

Abstract

Confinement effects in space-confined catalysts are attracting attention due to their advantages, like size control, unique nanoscale chemical environments and designable nature of the active sites. There are rarely works on the direct confirmation of confinement effects because of restrictions of nanoscale confined space. Herein, we report the fabrication of a novel structure that is composed of NiO nanoparticles confined in SnO₂ nanocoils (I-NiSnNCs) via atomic layer deposition (ALD). The I-NiSnNCs displayed higher sensing performance towards hydrogen than the NiO–SnO₂ film, NiO outside NiSnNC and NiO both outside and inside NiSnNC sensors. The I-NiSnNC sensor shows a response to about 7 to 50 ppm H₂ with a 2.4 s response time and 4.2 s recovery time at 260 °C and excellent repeatability. The synergistic effect of interfacial sites is attributed to the reaction between adsorbed H on NiO and adsorbed O at interfacial active sites. The “funneling effect” formed because the enrichment effect of hydrogen on the NiO surface is higher than that of the gas state as the adsorbed H quickly reacts at interfacial active sites. The enrichment effects of H₂ lead to high sensing performance to H₂, and the high reactivity of H₂ at interfacial active sites leading to rapid transfer of electrons is responsible for the high response/recovery performance. The gas sensor offers a new way to directly confirm the confinement effect. And the confinement effects in return give a novel way to design sensing materials.