Electronic and Mechanical Antagonist Effects in Resistive Hydrogen Sensors Based on Pd@Au Core-Shell Nanoparticle Assemblies Prepared by Langmuir-Blodgett

Pd@Au core-shell nanoparticles, synthesized with a good control of the shell thickness, can be assembled by a simple Langmuir-Blodgett method as 2D assembles and transferred onto glass chips to fabricate H-2 resistive sensors. Thanks to the specific reactivity of palladium toward hydrogen leading to the reversible conversion of palladium as palladium hydride, these core-shell nanoparticle layers can be used to detect hydrogen in extended H-2 concentration ranges. Fabricated sensors show attractive sensing performances including high signal amplitudes, good specificity toward hydrogen, and short response and recovery times. Depending on the Pd shell thickness and H-2 concentration, distinct response types are observed, either resistive or conductive. These responses, in terms of amplitude and sign, strongly depend on the balanced contribution of two antagonist mechanical and electronic effects, promoted by the palladium hydride formation under H-2 atmosphere. By using the percolation theory and simple data modeling, these Pd thickness-dependent contributions are decorrelated, and the sensing mechanisms are described.