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

Electroreduction of nitrate (NO) to ammonia (NH) is a promising approach for addressing energy challenges. However, the activity is limited by NO mass transfer, particularly at reduction potential, where an abundance of electrons on the cathode surface repels NO from the inner Helmholtz plane (IHP). This constraint becomes pronounced as NO concentration decreases, impeding practical applications in the conversion of NO-to-NH. 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 NO reduction, the formation of S-L junction induces hole transfer from Ag-doped MoS (Ag-MoS) to electrode/electrolyte interface, triggering abundant positive charges on the IHP to attract NO. Thus, Ag-MoS exhibits a ~ 28.6-fold NO concentration in the IHP than the counterpart without junction, and achieves near-100% NH Faradaic efficiency with an NH yield rate of ~20 mg h cm under ultralow NO concentrations.