Hydrogen switches and sensors fabricated by combining electropolymerization and Pd electrodeposition at microgap electrodes.

Here we describe a simple electrochemical approach to fabricate devices which behave as hydrogen sensors and switches. Devices fabricated by the electrodeposition of Pd directly across a 5 microm gap interdigitated array (IDA) of gold electrodes behaved as "hydrogen sensors". These devices had initial currents on the 10(-3) A level at -0.3 V and exhibited fast and reversible decreases in current in the presence of H(2) concentrations in a N(2) carrier gas with an average detection limit of 400 ppm. The current decrease is due to the formation of the more resistive PdH(x) in the presence of H(2). Devices fabricated by polyphenol electropolymerization on one set of electrodes and Pd electrodeposition on the other set behaved as "hydrogen switches". These devices displayed very low baseline currents of 10-100 pA at -0.3 V due to the presence of polphenol in the Electrode1/Pd/Polyphenol/Electrode 2 junction, and the current increased a remarkable 7-8 orders of magnitude in the presence of > or = 1.0% H(2) due to volume expansion upon PdH(x) formation, which leads to a direct connection between Pd (as PdH(x)) and Electrode 2 through the porous 4-10 nm thick polyphenol insulating film. The response and recovery time for the "hydrogen sensor" ranged from 20 to 60 s while that for the "hydrogen switch" ranged from 10 to >100 s. The response and recovery time generally decreased for the "hydrogen switch" as the number of polyphenol electrochemical cycles decreased.