Novel catalytic gas sensors based on functionalized nanoparticle layers

A thermal hydrogen gas sensor with a new type of catalytic layer based on films made of dodecylamine (DDA) capped platinum nanoparticles (DDA capped PtNPs) is presented here. These nanoparticles – prepared by a colloidal synthetic approach – offer, due to their ligand shell, a higher stability and a better adhesion to substrates and show lower agglomeration. Working principle of the sensing elements, consisting of two thermopiles and a central heater placed on a silicon nitride membrane, is the thermoelectric effect. By deposition of the ligand capped nanoparticles on the heated junction of one thermopile, hydrogen can be detected due to a change of the thermopile thermovoltage resulting from the reaction heat released during catalytic H2 oxidation. A second thermopile was used as a reference element. In order to determine the influence of the organic ligands on the sensor activity, unprotected platinum nanoparticles (unprotected PtNPs) were also used as catalyst. Both approaches, the uncovered and functionalized platinum nanoparticles, have been characterized and exposed to different hydrogen concentrations. Results point towards a strong agglomeration of unprotected nanoparticles resulting in low output signals, whereas for the ligand capped nanoparticles a linear and reproducible output signal with a sensitivity up to 6.4 mV/1000 ppm hydrogen was observed.