Ultrahigh humidity tolerance of room-temperature hydrogen sensitive Pt–WO3 porous composite ceramics with ultra-large WO3 grains

Two kinds of WO3 powders with average size of 100 nm and 5 μm have been used to prepare Pt–WO3 porous composite ceramics, whose WO3 grains are around 1 and 5 μm, respectively. The ceramics with 1 μm WO3 grains show a sensitivity of 755 to 0.08% H2 – 20% O2 – N2 in air of 30% relative humidity (RH) at room temperature, but show no response to this concentration of hydrogen in air of 50% RH due to the depression effect of water, which indicate a relatively low humidity tolerance for the ceramics. In contrast, the ceramics with 5 μm WO3 grains show sensitivities of 1200 and 80 to 0.08% H2 – 20% O2 – N2 at room temperature in air of 30% and 50% RH, respectively, and a sensitivity of 8 to 0.02% H2 – 20% O2 – N2 in air of 70% RH, which represent an ultrahigh humidity tolerance. These results clearly demonstrate that the microstructure of room-temperature hydrogen sensitive metal oxide (MOX) materials exerts a decisive influence on their humidity tolerance. Much attention should be paid to MOX materials with large and even ultra-large MOX grains when room-temperature MOX gas sensors with high humidity tolerance are being developed.