Ion‐Gated Nanoconfinement in Bimetallic Nanorattles Unlocks Enhanced Plasmonic Nitrate Reduction Electrocatalysis

Abstract Nanoconfinement is a powerful strategy to modulate local reaction environments in electrocatalysis, yet direct experimental validation of its impact on multi‐electron transformations remains limited. Here, it is reported that hollow bimetallic Au@AgAu nanorattles serve as proof‐of‐concept tunable electrocatalysts for nitrate reduction (NO ₃ RR). By varying the porosity of Ag‐based shells via controlled galvanic replacement, architectures are constructed in which electric double layer thickness, and thus pore accessibility, can be dynamically modulated and quantified by electrolyte concentration. With increasing ionic strength, a marked enhancement in NO ₃ RR activity is observed, with nanorattles delivering three to fourfold higher mass‐specific currents than solid Au@Ag counterparts, attributable to expanded access to confined interior sites. Plasmonic excitation under visible light further amplifies performance under acidic conditions, highlighting a synergistic interplay between localized surface plasmon resonances and geometric confinement. Density functional theory calculations reveal that alloying and hollowing induce electronic delocalization, favorable charge redistribution, and optimized d‐band energetics. While activity and plasmonic enhancement are attenuated under alkaline conditions, the nanorattles still outperform solid analogues, demonstrating the broad utility of this design. Together, the findings establish a dynamic framework in which engineered porosity, bimetallic composition, and electrolyte‐driven surface accessibility converge to harness nanoconfinement for enhanced electrocatalysis.