Ultrathin Palladium Nanowires for Fast and Hysteresis-Free H₂Sensing

One-dimensional nanomaterials are of great interest for gas-sensing applications due to their high surface-to-volume ratio and effective electron transport pathways. Palladium nanowires (PdNWs) form hydrides at room temperature, altering their electrical resistance and making them useful in H2 sensors. Reducing the PdNW diameter would improve sensor sensitivity and response speed, but conventional lithography cannot fabricate PdNWs <10 nm in diameter and is relatively expensive. We report the colloidal solvothermal synthesis of ultrathin PdNWs (diameter <5 nm). UV-ozone treatment was used to degrade surface ligands on the PdNWs before fabricating a sensor by simple drop-casting. The sensor showed a response of 1.7% and response and recovery times of 3.4 and 11 s to 1% H2 in air. It displayed hysteresis-free behavior and was stable under repeated exposure to 1% H2 in air while maintaining high selectivity for H2 relative to CO, CO2, and CH4. We attribute the observed fast response and recovery times and outstanding stability to a combination of factors, including ultrathin nanowire diameter, the formation of nanowire networks, and the presence of highly catalytically active facets on the surface that combine to make this one of the fastest reported chemiresistive Pd-based sensors for room-temperature detection of H2.