Boosting Electrochemical Nitrate Reduction Over a Wide Concentration Range through Constructing Bidirectional...

Electrocatalytic nitrate (NO₃^-) reduction reaction (NO₃RR) to ammonia (NH₃) provides a sustainable solution for the nitrogen cycle and a new pathway for green NH₃ synthesis. Nevertheless, the NO₃RR over a wide concentration range remains challenging due to mass transfer resistance at low concentrations and insufficient *H supply at high concentrations. Herein, we designed the three-layer composite catalyst (Co/Cu/NC) by embedding Co@Cu core-shell nanoparticles into N-doped carbon substrates (Co@Cu_x/NC, x = Cu/Co atomic ratio) for NO₃RR. The optimal catalyst Co@Cu_1.0/NC exhibits a remarkable FE_NH3 over a wide potential window with the increase in the NO₃^- concentration from 1 to 2000 mM. Both experimental and theoretical studies have demonstrated that the electron-deficient Cu sites formed by the bidirectional electron transport to Co and NC are favorable for NO₃^- adsorption and conversion to *NO₂. Simultaneously, the electron-rich Co sites efficiently facilitate H₂O dissociation, supplying sufficient *H to the adjacent Cu sites to reduce the *NO₂ intermediate to NH₃. As a result, the catalyst Co@Cu_1.0/NC exhibits excellent NO₃RR performance over a record-wide NO₃^- concentration range covering the textile industry effluents to nuclear waste. The bidirectional electron transport channel provides a novel guideline for the design of NO₃RR electrocatalysts over the full concentration range.