Decoration of Ag nanoparticles on reduced graphene oxide and their application to gas sensors

We fabricated functionalized RGO that demonstrates excellent sensitivity to H₂S gas. The functionalization process used GO suspensions mixed with AgNO₃, NaOH, and DI water. X-ray diffraction (XRD) and transmission electron microscopy indicated that the functionalizing structures were composed of cubic Ag and silver oxide (Ag_xO_y) phases. Nanoparticles and nanorods with a cubic Ag phase were attached to the surface of the RGO. Raman spectra revealed that the structural disorder of the functionalized RGO was higher than that of pristine GO. The decrease of resistance by the introduction of H₂S gas indicated that the functionalized RGO was an n-type sensor. Accordingly, we suggested that the n-type Ag_xO_y, whose presence was confirmed by XRD, should be a main current path for the sensor. A H₂S gas sensing test revealed that the sensor response at 50 ppm was about 1.65. With respect to H₂S sensing mechanisms, we propose that the following four reasons could explain the significant enhanced sensitivity by the functionalization: (i) reduction of the conduction volume by the conduction through the Ag_xO_y structure rather than RGO, (ii) generation of silver sulfide structures, (iii) generation of an n-Ag_xO_y/p-RGO heterointerface, and (iv) larger surface area of Ag/Ag_xO_y structures. The Ag catalyst is not only the source of the Ag_xO_y, but also provides the spillover effect.