Comparison of hydrogen detection by WOx/SiC and Pt/WOx/SiC structures using amperometric and potentiometric modes of measurement

Hydrogen sensors were fabricated with a well-known structure, formed by depositing WO,, films (with or without an additional Pt overlayer) onto SiC substrates. These sensors differed in terms of the morphology and nanostructure of the WOx films, which were pulsed laser deposited (PLD) under varying conditions. The sensory characteristics of WOx/SiC and Pt/WOx/SiC samples were analyzed using conventional current-voltage measurements. In addition, the possibility of detecting an electrical signal in these structures without applying an external voltage (EMF-powered mode) was investigated. The sensor response strongly depended on the qualifies of the metal oxide film, including its strength, uniformity, continuity, and adhesion to the SiC substrate. Optimization of the PLD allowed the formation of triclinic WOx < 3 and monoclinic W18049 films with relatively good quality. The current measured at 300 degrees C by the amperometric method for the WOx/SiC sensors increased by 15 times (up to 24 mu A at a voltage of 0.5 V) when 2% H-2 was added to air. For the Pt/WOx/SiC sensors, the current increased by up to 100 times. The highest response to 2% H-2 in the potentiometric mode of measurement was found for the WOx/SiC sensor containing W18O49 film. The EMF-initiated voltage increased by > 27 times. The highest voltage detected for an external load of 1 k Omega was similar to 400 mu V. The N film deposition markedly worsened the sensory properties of Pt/WOx/SiC structures measured by the EMF-powered mode. Possible mechanisms of the appearance of the EMF in the prepared structures are considered.