Geometry-Engineered Pd–Au Plasmonic Nanoarrays: Unveiling Design Principles for High-Performance Hydrogen Sensing

Plasmonic hydrogen sensors based on Pd-Au nanostructures represent a promising platform for safe, label-free hydrogen detection. However, rational design has been hindered by limited control over nanoscale structural parameters and the resulting structure-property relationships. To bridge this gap, we develop a template-assisted evaporation strategy to fabricate highly ordered bilayer Pd-Au nanoarrays with an independently tunable stacking sequence, lateral size, and out-of-plane geometry. We establish stacking order as a critical factor that governs the intrinsic trade-off between sensing sensitivity and response kinetics. Critically, by correlating experimental observations with an extended Gans model, we quantitatively elucidate that the out-of-plane geometry governs the depolarization factors and refractive index sensitivity. Guided by these mechanistic insights, the optimized Pd/Au nanoarrays achieve a substantial localized surface plasmon resonance (LSPR) shift up to 81 nm at 4 vol % H₂ and a detectable shift of 14 nm at 0.5 vol % H₂. This work thus delivers fundamental design principles that advance the rational development of high-performance plasmonic hydrogen sensors.