Palladium Aerogel-Enabled Flexible Hydrogen Sensors: An Insight into Structural Origins of Chemiresistive Performance

Palladium-based chemiresistors exhibit a highly selective and sensitive response to hydrogen gas and are thus promising materials for developing hydrogen gas sensors. As such, several types of palladium-based nanostructures have already been suggested for the fabrication of efficient sensors. Herein, we demonstrate the superior hydrogen gas sensing capabilities of the palladium metal aerogel, a three-dimensional porous nanostructure with a large surface area for maximizing the surficial palladium hydride formation. The aerogel, obtained through facile solution-phase processing, can be directly utilized as a chemiresistor via drop-casting onto a pair of interdigitated electrodes, resulting in 31.7% response toward 3% hydrogen─one of the highest reported for room-temperature palladium-based hydrogen sensors─with rapid response/recovery times of 16 and 20 s, respectively. Additionally, we provide a simple galvanic replacement reaction method to decorate the surface of the palladium aerogel with 0.2 at. % platinum sensitizers to reach a detection limit of 100 ppm. To overcome the engineering challenges of utilizing the brittle metal aerogel, we report the "surface gelation" technique, which successfully induced the heterogeneous growth of the palladium metal aerogel onto a nanofibrous yarn support prepared by dual-nozzle electrospinning. We used this technique to successfully fabricate a flexible room-temperature hydrogen gas sensor for versatile applications.