Effects of Pt shell thickness on self-assembly monolayer Pd@Pt core-shell nanocrystals based hydrogen sensing

Fast Hydrogenation and Dehydrogenation of Pt/Pd Bimetal Decorated over Nano-Structured Ag Islands Grown on Alumina Substrates

“…A higher surface to volume ratio-based Ag nanoislands enhances the bimetal capping configuration that makes a percolation pathway that is suitable for higher carrier mobility. It is believed that a hydrogen induced lattice expansion in nanosized catalytic sputtered bimetal may form a shorter conduction pathway for carrier mobility in the transduction process between physisorption to chemisorption on an insular substrate [78,79]. However, maintaining the homogenous nanosized bimetal capping structures is highly challenging, and a catalytic metal nanoislands structure beneath the bimetal structure increases the connection between the metal atoms and enhances the surface conductivity which may enhance the hydrogen induced lattice expansion faster.…”

“…Figure 14a–c illustrate the distribution of electrical permittivity of the Pt/Pd bimetal (10/10 nm) and reveal that a certain applied potential difference on the boundaries of the chamber creates a surface charge density depending on the medium (air, hydrogen) in the chamber inside. A highly dense surface charge density (Figure 14a,b,c) can be observed from the interface of Pt/Pd bimetal as the relative permittivity of Pt/Pd bimetal is much higher (εr=67.88) in comparison to Pt (εr=17.19) and Pd (εr=13.69) [79]. We found a maximum amount of surface charge density for Pt/Pd (10/10 nm) case in air environment and a lowest value in hydrogen environment from all other thickness variation (Supplementary Figure S3).…”

“…Along with faster response, a faster recovery time for S1 sample could be due to the higher grains of the interface that can be used as desorption pathway for hydrogen molecules [67]. In addition with the interfacial grains, an optimized temperature of 120 °C was the best fit of electron scattering process as, Pt has higher absorption rate at 100 °C with fast response but lacks in recovery whereas, Pd has slower absorption rate along with high response magnitude and faster recovery [73,79,80]. Furthermore, catalytic metal alloy of Ag needs a moderate elevated temperature to dissociate the chemisorbed hydrogen molecules [65,66].…”

“…Hydrogen absorption in Pd materials, such as thin films, nanowires, and nanodisks [74,75,76,77,78,79,80], has shown hysteresis and breaking phenomena after a few cycles of hydrogen absorption whereas, the presently studied Pt/Pd@Ag nanoisland structure performed well at the high concentration of 40,000 ppm hydrogen. A negligible hysteresis effect (Figure 15) was due the uniform Pt layer which enhances the passing of hydrogen molecules to interact with Pd/Ag alloy along with an increased clamping effect that reveals a tensile stiffness of a laminate specimen is in inverse relation to the thickness of the specimen [79,80]. Figure 15 illustrates the repeatability of the as fabricated S1 device with a constant response magnitude of 2.3% at a concentration of 10,000 ppm hydrogen at 120 °C.…”

Approaches to Enhancing Gas Sensing Properties: A Review

“…For this structure, the thickness of the shell exerts an apparent influence on the gas sensing properties. Uddin et al [80] synthesized Pd−core/Pt−shell nanotubes structured materials by a facile two step hydrothermal process and further investigated the influences of Pt film thickness on fast response H2 sensing properties. In their experiments, the shell thickness was controlled by various growth periods and the test results suggested that the optimal Pt coverage thickness is ultimately ~ 5−10 nm.…”