Boosting Electrochemical Nitrate Reduction Over a Wide Concentration Range through Constructing Bidirectional Electron Transfer Channels

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@Cux/NC, x = Cu/Co atomic ratio) for NO3RR. The optimal catalyst Co@Cu1.0/NC exhibits a remarkable FENH3 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@Cu1.0/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.