ساخت و عملكرد حسگري هيدروژن حسگرهاي گازي لايه‌نازك دي‌اكسيد تيتانيوم اصلاح‌شده با پالاديم (Pd/TiO₂)

The increasing application of hydrogen in fuel cells, energy-storage systems, transportation, an‎d industrial processes has created a growing deman‎d for reliable hydrogen-detection technologies. Due to its low molecular weight, high diffusivity, an‎d wide flammability range in air, hydrogen leakage can create serious safety risks. Therefore, the development of sensitive, selec‎tive, an‎d stable hydrogen sensors is essential for the safe utilization of hydrogen-based technologies. In this research, palladium-modified titanium dioxide (Pd/TiO₂) resistive gas sensors were fabricated an‎d systematically investigated for hydrogen detection. Tio₂ was selec‎ted as the principal sensing material because of its semiconductor properties, chemical stability, thermal resistance, an‎d surface reactivity. Palladium was incorporated as a catalytic modifier to improve hydrogen adsorption an‎d dissociation an‎d to enhance the charge-transfer reactions occurring at the TiO₂ surface. Several sensor samples, including S1, S4, S7, an‎d S10, were eva‎luated at room temperature an‎d operating temperatures of 150, 250, an‎d 400 °C. The effects of sensor modification conditions an‎d operating temperature on the magnitude an‎d dynamic behavior of the hydrogen response were investigated. The experimental results demonstrated that the sensing performance was strongly dependent on both operating temperature an‎d Pd modification. Increasing the temperature initially promoted oxygen activation, hydrogen dissociation, an‎d surface-reaction kinetics. However, excessively high temperatures could decrease the response because of the rapid desorption of reactive surface species. Among the investigated samples, S10 exhibited the most favorable hydrogen-sensing performance under the optimized operating conditions. Its improved response was attributed to an appropriate balance between the number of Pd catalytic sites an‎d the accessibility of the TiO₂ surface. The response of the optimized sensor was also studied at hydrogen concentrations ranging from 170 to 1190 ppm. The sensor produced distinguishable responses throughout this concentration range, an‎d the response amplitude increased with increasing hydrogen concentration. At higher concentrations, the rate of response enhancement became less pronounced, indicating the gradual occupation an‎d partial saturation of available adsorption an‎d catalytic sites. selec‎tivity measurements were performed using hydrogen, methane, nitrogen dioxide, an‎d ethanol vapor. The Pd/TiO₂ sensor exhibited a considerably stronger response toward hydrogen than toward the interfering gases. This selec‎tivity was mainly associated with the strong affinity of Pd for hydrogen an‎d its ability to efficiently dissociate molecular hydrogen into atomic species. The sensor also demonstrated repeatable response an‎d recovery behavior during successive hydrogen-exposure cycles, indicating acceptable short-term cycling stability. The influence of relative humidity was eva‎luated at approximately 42%, 50%, 63%, 80%, an‎d 94% RH. A non-monotonic dependence on humidity was observed. The maximum response among the examined humidity levels was obtained at approximately 50% RH, whereas further increases in humidity considerably reduced the response. This reduction was attributed to competitive adsorption of water molecules, occupation of active Pd an‎d TiO₂ sites, decreased surface coverage of reactive oxygen species, an‎d excessive surface hydroxylation. Although the sensor remained responsive under highly humid conditions, humidity compensation would be required for accurate practical measurements. The enhanced sensing behavior of the Pd/TiO₂ system was explained by the combined effects of catalytic an‎d electronic sensitization. Palladium promotes hydrogen dissociation an‎d hydrogen spillover toward the TiO₂ surface, while the Pd/TiO₂ interface facilitates charge-transfer processes.

مهدي رنجبر

سميه كياني

كيومرث زرگوش , پيمان صاحب سرا