Au@Pt/Pd Core–Shell Nanoparticle Arrays: Dual-Modal Plasmonic Hydrogen Sensor with Tunable Reversible/Irreversible Sensing Behaviors

An emerging challenge in optical hydrogen sensing is the development of a single platform capable of both reversible detecting low-concentration hydrogen and irreversible signaling under high-concentration conditions. Here, we demonstrate that Au@Pt core-shell nanoparticle arrays (NAs) integrate two distinct mechanisms─reversible hydrogen-induced dielectric constant modulation and irreversible hydrogen-induced aggregation─thereby functioning as a dual-modal plasmonic hydrogen sensor. When exposure to <10% H₂, Au@Pt NAs show a reversible ∼30 nm blue shift of the extinction peak, attributable to the desorption of chemisorbed water that lowers the local dielectric constant. In contrast, exposure to >10% H₂ allows dissociated hydrogen atoms to diffuse into the Pt shell through grain boundaries, inducing lattice expansion and irreversible nanoparticle aggregation. This process leads to a permanent decrease in extinction intensity and a remarkable color change. The critical transition concentration (CTC) between reversible and irreversible modes can be systematically tuned by alloying the Pt shell with Pd. Increasing Pd content lowers the CTC from 10% H₂ (Pt shell) to 1% H₂ (Pt/Pd shell containing 25% Pd), while a higher Pd ratio results in a fully irreversible response. This work establishes a new class of Pt-based plasmonic hydrogen sensor with dual-mode functionality, not only shedding light on its unique sensing mechanism but also broadening the applicability for diverse scenarios.