Sonication‐Assisted Palladium Nanogaps in a Capacitive Structure: A Tunable and Reliable Solution for Sensitive Hydrogen Monitoring

Abstract Pd nanogap hydrogen sensors rapidly and selectively detect H 2 through hydrogenation‐induced volumetric expansion of the Pd lattice. However, this type of resistive sensor faces challenges in ensuring reliability due to the difficulty of precisely controlling nanogaps formed within the potential conduction paths. Herein, a novel H 2 sensor is proposed that utilizes a capacitive mechanism to substantially improve both sensitivity and reliability. Simple ultrasonication is employed to create Pd seed cracks, which evolve into uniform nanogap networks following initial phase transitions (α‐PdH → β‐PdH). In the Pd/PDMS/Doped‐Si system, capacitive response driven by the area change of the upper electrode accurately reflects real‐time nanogap behavior in response to H 2 , producing stable signals within a defined range of values. The initial crack density, adjustable by varying the sonication time, allows for customizable gap sizes and detection ranges, achieving sub‐20 nm gaps and an ultra‐low detection limit of 3 ppm. Repeatability tests using 300 ppm H 2 over 50 cycles demonstrate exceptional durability and signal stability at low concentrations, surpassing previous Pd nanogap sensors. This capacitive sensor provides a reliable and adaptable solution for H 2 detection, marking a significant advancement toward commercializing Pd nanogap sensors.