Sub-ppm H2S sensing by tubular ZnO-Co3O4 nanofibers

•Cobalt containing electrospun ZnO nanofibers acquire a tubular structure.•Walls of the tubes are formed by agglomerated wurtzite Zn1-yCoyO nanoparticles.•Spinel ZnxCo3-xO4 nanoparticles are located on the outer surface of Zn1-yCoyO tubes.•Tuning of sensor properties is based on change in the ZnO acidity cobalt doping.•Removal of p – n junction provides excellent selectivity of ZnO-CoOx in H2S sensing. Tubular ZnO – Co3O4 nanofibers were co-electrospun from polymer solution containing zinc and cobalt acetates. Phase composition, cobalt electronic state and element distribution in the fibers were investigated by XRD, SEM, HRTEM, HAADF-STEM with EDX mapping, and XPS. Bare ZnO has high selective sensitivity to NO and NO2, while ZnO-Co3O4 composites demonstrate selective sensitivity to H2S in dry and humid air. This effect is discussed in terms of transformation of cobalt oxides into cobalt sulfides and change in the acidity of ZnO oxide surface upon cobalt doping. Reduction in response and recovery time is attributed to the formation of a tubular structure facilitating gas transport through the sensitive layer.