Catalytic Membrane Sensors. A Thin Film Modified H2Resistive Sensor for Multi-Molecular Detection

Abstract

A so-called “catalytic membrane sensor” (CMS) is being developed to impart selectivity and reactivity to the surface of an existing sensor by modifying it with a series of thin films. The proposed “sandwich-type” modification involves deposition of a catalyst layer between two size selective sol-gel layers on a Pd/Ni resistive H₂ sensor. The role of the catalyst is to convert organic materials to H₂ and organic by-products by a dehydrogenation mechanism. The roles of the membranes are to impart chemical specificity by molecular sieving of the analyte and the converted product streams as well as to control access to the underlying Pd/Ni sensor. The “sandwich” modification will mediate the sensor response and avoid potential poisoning effects. Ultimately, an array of these CMS elements encompassing different catalysts and membranes will further enable improvements in selectivity and specificity via pattern recognition methodologies. This report details the synthesis of the various thin film solutions (i.e., catalyst precursors, sol-gel solution), the generation of the catalyst through ion-exchange, a comparison of the double alkoxide versus standard catalyst precursors, and the processing required to generate a CMS. This paper also details the novel and surprising experimental data concerning the increased selectivity and durability observed for the sol-gel modified H₂ gas sensing resistors. The utility of the CMS component as a multi-molecular detector will be reported later.