Graphene oxide-mediated polymorphic engineering of In2O3 for boosted NO2 gas sensing performance

Nitrogen dioxide (NO 2 ) is a serious menace to human health and the environment, it is of great practical meaning to develop a fast and accurate gas sensor for monitoring low-concentration NO 2 at near room temperature (RT). Here, the polymorphism of In 2 O 3 was regulated with controllable mixed-phase ratios of hexagonal In 2 O 3 (h-In 2 O 3 ) and cubic In 2 O 3 (c-In 2 O 3 ) via a graphene oxide (GO)-mediated solvothermal approach and annealing treatment. The GO-mediation markedly promoted the formation of h-In 2 O 3 and defect content. The morphology, specific surface area, surface chemical state and activation energy were roundly analyzed. The NO 2 -sensing performance results showed that the sensor based on an 8 wt% GO-mediated In 2 O 3 sample (In 2 O 3 -8) exhibited an ultrahigh response of 1021 towards 1 ppm NO 2 at 30℃, which was 2.3 times higher than that of In 2 O 3 without GO-mediation. At the same time, the response/recovery time of In 2 O 3 -8 was significantly shorter than other sensors. Additionally, the In 2 O 3 -8 sensor possessed good repeatability and long stability. In 2 O 3 -8 with an appropriate GO-mediated content provided a suitable h-In 2 O 3 /c-In 2 O 3 phase junction interface, abundant oxygen vacancies and elevated Fermi energy levels of In 2 O 3 , which activated the surface sites and ultimately enhanced the sensing performance.