Coverage engineering by shell-number-controlled nanoconfinement enables nitric oxide electroreduction in the ppm regime

Electrochemical nitric oxide reduction (NORR) under industrially relevant dilute feeds is fundamentally limited by insufficient interfacial NO coverage and rapid loss of reactive intermediates. Here we introduce quantifiable nanoconfinement as a coverage-regulation strategy for NORR in the ppm regime. Hollow multishelled Cu2O nanoreactors are constructed as a model system, in which shell number defines confinement depth and progressively strengthens confinement by narrowing inter-shell cavities. Under a 1000 ppm NO feed, the three-shell catalyst achieves a Faradaic efficiency of 97.9% and a single-pass NO conversion of 97.3%, which is competitive with systems operating under NO-rich conditions. Finite-element simulations quantitatively show that multishell confinement nonlinearly amplifies intermediate enrichment, increasing local *H and *NH concentrations by over an order of magnitude relative to the single-shell structure while also enhancing local NO coverage. Coverage-dependent density functional theory and transition-state calculations reveal that the confinement-modulated coverage environment reshapes the NORR kinetic and thermodynamic landscape by rebalancing initial *NO hydrogenation and NH3 desorption, defining a favorable coverage window that balances intermediate activation and product release. These findings establish nanoconfinement-enabled coverage engineering for electrocatalysis under dilute feeds. Converting ppm-level NO into ammonia is challenging as reactants and intermediates are easily lost from catalyst surfaces. Here, the authors report quantifiable nanoconfinement as a coverage engineering strategy to nonlinearly enrich these species, improving ppm-level NO electroreduction activity.