High performance hydrogen gas sensors based on PdO-decorated p-type CoV2O6 nanoparticles

P-type spherical-like cobalt vanadate (CoV2O6) nanoparticles were successfully synthesized using an easy and low-cost solution-based process based on ethylene-glycol (EG). Moreover, decoration of nanoparticles with 0−2 wt% palladium oxide (PdO) was achieved using the impregnation method in order to investigate their performance for hydrogen (H2) gas sensing applications. X-Ray Diffraction technique (XRD), Field-Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM) were employed for the structural and morphological characterization. CoV2O6 nanoparticles of spherical-like morphology, highly crystalline triclinic structure with an average diameter of 75–200 nm and PdO crystallites with an average diameter of 5 nm deposited as islands on their surface were obtained. Raman spectrometry confirmed results obtained by the structural analysis, as well as the presence of PdO. Consequently, PdO-decorated CoV2O6 films of 3.5–7 μm thickness were deposited, by the spin-coating technique, onto Al2O3 substrates baring interdigitated Au electrodes. The films were tested against H2 gas (2.500–30.000 ppm) at operating temperatures ranging from 200 to 350 °C in dry air. It was demonstrated that CoV2O6 nanoparticles with an optimum PdO-decorating concentration of 1 wt% exhibited the highest (almost 114) H-sensing response towards 30.000 ppm H2, which was one order of magnitude higher than the undecorated one, as along with a short response time of 17 s, at an optimum operating temperature of 300 °C. In addition, the optimum (1 wt%) PdO- decorated CoV2O6 sensor displayed high H2 selectivity in comparison to NO, NO2, H2S and acetone gases, making PdO-decorated CoV2O6 nanoparticle thick films promising candidates as sensing elements for high performance H2 gas sensors.