Methane (CH4) sensitivity of zinc oxide (ZnO) thin film has been studied in the present work. The sensor element comprises of a chemically fabricated ZnO semiconducting layer and a layer of palladium (Pd) as catalyst. The catalyst layer was formed on the surface of semiconducting ZnO following a wet chemical process from palladium chloride (PdCl2) solution. Fundamental features of a sensor element e.g. sensitivity, response time and recovery process has been studied. The effect of operating temperature on performance of the sensor material has been investigated and a choice of optimum temperature was made at around 200oC. The sensor element exhibited reasonable sensitivity of about 86% at this temperature in presence of 1 vol% methane (CH4) in air.
This work presents the studies on the electrochemical process of thin palladium layers formation onto electrodeposited cobalt coatings. The suggested methodology consists of the preparation of thick and smooth cobalt substrate via galvanostatic electrodeposition. Cobalt coatings were prepared under different cathodic current density conditions from acidic bath containing cobalt sulphate and addition of boric acid. Obtained cobalt layers were analyzed by x-ray diffraction to determine their phase composition. Freshly prepared cobalt coatings were modificated by the galvanic displacement method in PdCl2 solution, to obtain smooth and compact Pd layer. The comparison of electrocatalytic properties of Co coatings with Co/Pd ones enabled to determine the influence of Palladium presence in cathodic deposits on the hydrogen evolution process.
A layered sensor structure of metal-free phthalocyanine H2Pc (~160 nm) with a very thin film of palladium (Pd ~20 nm) on the top, has been studied for hydrogen gas-sensing application at relatively low temperatures of about 30°C and about 40°C. The layered structure was obtained by vacuum deposition (first the phthalocyanine Pc and than the Pd film) onto a LiNbO3Y- cut Z-propagating substrate, making use of the Surface Acoustic Wave method, and additionally (in this same technological processes) onto a glass substrate with a planar microelectrode array for simultaneous monitoring of the planar resistance of the layered structure. In such a layered structure we can detect hydrogen in a medium concentration range (from 0.5 to 3% in air) even at about 30°C. At elevated temperature up to about 40°C the differential frequency increases proportionally (almost linearly) to the hydrogen concentration and the response reaches its steady state very quickly. The response times are about 18 s at the lowest 0.5% hydrogen concentration to about 42 s at 4% (defined as reaching 100% of the steady state). In the case of the investigated layered structure a very good correlation has been observed between the two utilized methods - the frequency changes in the SAW method correlate quite well with the decreases of the layered structure resistance.