Near-Unity Nitrate to Ammonia conversion via reactant enrichment at the solid-liquid interface.

Electroreduction of nitrate (NO₃^‒) to ammonia (NH₃) is a promising approach for addressing energy challenges. However, the activity is limited by NO₃^‒ mass transfer, particularly at reduction potential, where an abundance of electrons on the cathode surface repels NO₃^‒ from the inner Helmholtz plane (IHP). This constraint becomes pronounced as NO₃^‒ concentration decreases, impeding practical applications in the conversion of NO₃^‒-to-NH₃. Herein, we propose a generic strategy of catalyst bandstructure engineering for the enrichment of negatively charged ions through solid-liquid (S-L) junction-mediated charge rearrangement within IHP. Specifically, during NO₃^‒ reduction, the formation of S-L junction induces hole transfer from Ag-doped MoS₂ (Ag-MoS₂) to electrode/electrolyte interface, triggering abundant positive charges on the IHP to attract NO₃^‒. Thus, Ag-MoS₂ exhibits a ~ 28.6-fold NO₃^‒ concentration in the IHP than the counterpart without junction, and achieves near-100% NH₃ Faradaic efficiency with an NH₃ yield rate of ~20 mg h^‒1 cm^‒2 under ultralow NO₃^‒ concentrations.