Noble Metal-Decorated Nanostructured Zinc Oxide: Strategies to Advance Chemiresistive Hydrogen Gas Sensing.

Hydrogen (H 2 ) is known as the key player in the alternative and renewable energy revolution and henceforth H 2 production, transportation, storage and usage have been a major interest of current research. However, due to severe safety concerns, strategies are indispensable to devise superior H 2 sensors, particularly selective and sensitive H 2 sensors. In this personal account, three specific gas sensing constructs; zinc oxide (ZnO) nanostructures-, noble metal nanoparticles-decorated ZnO- and noble metal nanoparticles-decorated ZnO nanostructures on reduced graphene oxide (rGO)-based H 2 sensors have been demonstrated. The dynamic response and H 2 sensing characteristics of ZnO nanostructures-based H 2 sensors were found to be improved compared to those of pristine ZnO. High-resolution field emission scanning electron microscopy (FESEM) confirmed the flower-like nanostructures that had higher surface area around the nanoscale petals. The mechanism behind the superior sensing characteristics of ZnO nanostructures-based H 2 sensor has been demonstrated. Decoration of ZnO nanostructures with noble metal nanoparticles, particularly platinum (Pt) and gold (Au) was observed to be useful in achieving better H 2 sensing performance compared to that of ZnO nanostructures. The Pt- and Au-decorated ZnO nanostructures followed the well-known "Spill-over" mechanism in enhancing the H 2 sensing characteristics. Abundant free electrons/holes generation and higher conductivity are two important parameters for designing selective and sensitive gas sensors. In this context, a hybrid nanocomposite, rGO-ZnO has been developed and decorated with noble metal nanoparticles, particularly Pt and Au. The ultimate sensing material has been characterized and compared to those of pristine ZnO, ZnO nanostructures and Pt- and Au-decorated ZnO for H 2 gas sensing applications. Such systemic and focus strategies is critical not only for developing efficient H 2 gas sensors but also for better understanding the mechanisms underlying such superior performance.