Two-dimensional BCN matrix inlaid with single-atom-Cu driven electrochemical nitrate reduction reaction to achieve sustainable industrial-grade production of ammonia

Electrochemical methods have been proven to effectively eliminate nitrates in sewage and convert them into high value-added ammonia products. Here, after annealing treatment of metal boron cluster organic polymers formed by the combination of 1,10-phenanthroline, Cu²⁺ and closo-[B₁₂H₁₂]^2-, a Cu single-atom doped BCN (B-doped CN) with a diamond-shaped nanosheet structure was obtained. In the electrochemical reduction reaction of nitrate, BCN-Cu exhibits excellent catalytic activity, specifically: 1) the ammonia yield rate reached as high as 498.85 μg h⁻¹ cm⁻², 1047.14 μg h⁻¹ cm⁻², 1900.07 μg h⁻¹ cm⁻² and 3358.74 μg h⁻¹ cm⁻² at -0.3 V, -0.4 V, -0.5 V and -0.6 V vs reversible hydrogen electrode, respectively, and Faradaic efficiency is 95.90%, 97.28%, 98.23% and 97.37%; 2) after repeated use of BCN-Cu 10 times or continuous operation for 16 h, the activity against electrochemical reduction reaction of nitrate anions is almost unchanged. The ¹⁵NO₃⁻ isotopic labeling experiment proved that the detected NH₃ comes from the reduction of NO₃⁻ on BCN-Cu. Control experiments show that the presence of Cu determines whether BCN-Cu has the possibility of catalyzing electrochemical reduction reactions of nitrate, and the presence of the B element enhances the catalytic activity of BCN-Cu. Density functional calculations indicate that in the water phase the process of reducing NO₃⁻ to NH₃ on Cu⁰ is an exothermic reaction, and that the adsorption process of NO₃⁻ on Cu⁰ is the rate-determining step.