<p>Electrochemical nitrate reduction to ammonia offers a sustainable route for wastewater remediation and fertilizer production. However, the prevailing hydrogen-atom-mediated pathway often suffers from low selectivity owing to competing hydrogen evolution. Here we show that nanoconfinement can fundamentally redirect the reaction pathway towards a highly efficient proton-coupled electron transfer process. We constructed a catalyst comprising CuCo alloy nanoparticles embedded within carbon nanotubes via flash joule heating. This architecture achieves an ammonia yield of 2.23 mg h⁻¹cm⁻² with 93.8% Faradaic efficiency, surpassing non-confined counterparts. Mechanistic studies reveal that the nanoconfined microenvironment restructures the interfacial hydrogen-bond network to create a water-deficient, nitrate-enriched interface that suppresses water dissociation and facilitates direct proton shuttling. The system demonstrates robust stability in treating real wastewater, with technoeconomic and life-cycle analyses confirming its viability. This work establishes nanoconfinement as a powerful lever for steering interfacial environments and reaction pathways in electrocatalysis.</p>