Palladium-Gold Alloy Nanowire-Structured Interface for Hydrogen Sensing.

Abstract

Understanding how the detailed nanoscale structure governs the interfacial interactions and reactivities is key to the exploration of nanostructured chemical sensors. We describe herein novel findings of an investigation of a palladium-gold alloy nanowire interface for hydrogen sensing. A dielectrophoretic growth pathway was utilized for controllable fabrication of the alloyed nanowires with minimum branching structures on a microelectrode device using controlled ratios of palladium and gold precursors in a two-step mechanism, a nucleation process initiated at a lower alternating current (AC) frequency followed by a growth process at a higher frequency up to 15 MHz. The nanowires showed a reduced branching propensity and highly oriented 1D feature, with the bimetallic composition scaling linearly with the frequency. The nanowires exhibited excellent responses to hydrogen in concentrations as low as 0.5 % by volume. The hydrogen-response characteristic represents an optimized balance of the gold-induced lattice expansion of palladium and hydrogen adsorption-induced phase and stress changes, a new insight into the sensing mechanism of the alloy nanowire. The mechanistic sensing details are also discussed in correlation with the growth mechanism, which provides a new insight into the synergy of the bimetallic composition of the alloy nanowires for the enhanced sensitivity for the detection of hydrogen.