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 mu m gap interdigitated array (IDA) of gold electrodes behaved as hydrogen 10(-3) sensors. These devices had initial currents on the 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 PdHx 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 Electrodel/Pd/Polyphenol/Electrode 2 junction, and the current increased a remarkable 7-8 orders of magnitude in the presence of >= 1.0% H-2 due to volume expansion upon PdHx formation, which leads to a direct connection between Pd (as PdHx) 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.