Hybrid carbon nanostructures consisting of graphene nanoplatelets (GNPs) interspersed with multiwalled carbon nanotubes (MWCNTs) were synthesized by solution phase mixing of their parent aqueous dispersions. To further arrest the aggregation of GNPs, crystalline nanoparticles of a noble metal (Pt) were dispersed in situ by chemical reduction. This ensemble of the metal decorated hybrid structure was solubilized using Nafion and a simple drop casting method was employed to fabricate the sensor. In addition to the remarkable stability and repeatability, the sensor also showed an enhanced sensitivity of ∼17% to a low concentration of 4 vol.% hydrogen in air, at room temperature. The improved sensitivity due to Nafion solubilization could be explained by a dual mechanism of hydrogen dissociation. Variations in the sensor properties with change in hydrogen concentrations and temperature were studied. The kinetics of hydrogen adsorption in the sensor could be well explained by the Avrami-Erofeev model. From the Arrhenius plot of the rate constants, the activation energy was determined to be ∼24 kJ/(mol H). Effect of morphology of the bare hybrid structure was systematically investigated by varying the weight ratios of GNPs and MWCNTs. © 2010 Elsevier Ltd. All rights reserved.