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.