Hydrogen sensor based on WO3 subnano-clusters and Pt co-loaded on ZrO2

Pt and WO3 co-loaded ZrO2 equipped with a pair of interdigital Au electrodes has been tested as a H2 gas sensor. The resistance R estimated from the intersection of the semi-circle with the real axis in a complex-impedance plot was used as a sensing signal. H2 addition in a gas decreased the resistance. Pt–WO3/ZrO2 showed a higher response magnitude to H2 than WO3/ZrO2 and Pt/ZrO2. The sensor was found to respond consistently and rapidly to change in concentration of H2 in the oxygen rich and moist gas mixture at 120–150 °C. The conductivity of the device varied almost linearly with the H2 concentration from 0.25 to 1.25%. The rate constants (k) of Pt–WO3/ZrO2 for the response and recovery transients were 10 and 53 times higher than those of Pt/WO3, respectively. The response magnitude of Pt–WO3/ZrO2 to H2 was not markedly affected by changing the water vapor concentration from 1.0 to 3.4% and O2 concentration from 5 to 20%. The effect of WO3 loading of the Pt–WO3/ZrO2-based sensor combined with STEM and UV–vis results indicates that subnano-sized polytungstate clusters on the zirconia surface play an important role in the conductivity increase by H2 adsorption, which can be due to an increase in the number of acidic Hδ+ species on the polytungstate surface.