Stability and Sensing Enhancement by Nanocubic CeO₂ with {100} Polar Facets on Graphene for NO₂ at Room Temperature

Metal oxides with a polar surface interact strongly with polar NO2 molecules, thus facilitating sensitive detection of NO2. In this work, the composites comprising graphene and cubic CeO2 nanoparticles with the {100} polar surface are prepared by a hydrothermal technique, and they exhibit fast response, excellent selectivity, stable recovery, and sensitive detection with a low detection limitation of 1 ppm for NO2 at room temperature. According to the first-principle calculations, the adsorption energy of NO2 on the CeO2{100} polar surface is the most negative corresponding to the strongest interactions between them. The formation energy of oxygen vacancies (Ov) on the {100} polar plane is also negative, and the abundant Ov facilitates the adsorption of NO2. The internal electric field near the polar surface promotes the charge separation and accelerates the charge exchange between NO2 and the composites. In addition, graphene promotes electron transfer at the interface and improves the stability of the CeO2{100} polar surface. The composites of graphene and metal oxides with a polar surface are excellent for NO2 detection, and the discovery reveals a new sensing strategy.