Three-Dimensional Porous Cu/Cu₂₊₁O Nanosheet Arrays Promote Electrochemical Nitrate-to-Ammonia Conversion

The efficiency of electrochemical nitrate (NO₃^-) reduction to ammonia (NH₃) still remains a challenge due to the sluggish kinetics of the complex eight-electron reduction process and competitive hydrogen evolution reaction (HER). Herein, we designed new three-dimensional (3D) porous Cu/Cu₂₊₁O nanosheet arrays (Cu/Cu₂₊₁O NSA) by coupling a template-directed method with in situ electroreduction. Thanks to the 3D porous structure and in-plane heterojunctions, Cu/Cu₂₊₁O NSA can provide abundant active sites and a good interfacial effect, obtaining the maximum Faradaic efficiency (FE) of ammonia (88.09%) and high yield rate of 0.2634 mmol h^-1 cm^-2, which is higher than that of CuO nanosheets (77.81% and 0.2188 mmol h^-1 cm^-2) and CuO nanoparticles (34.60% and 0.0692 mmol h^-1 cm^-2). Experimental results and DFT simulations show that the interface effect of Cu/Cu₂₊₁O can decrease the reaction energy barrier of the key step (*NO to *NOH) and can greatly inhibit the competitive hydrogen evolution reaction, thereby achieving excellent electrocatalytic performance for nitrate-to-ammonia conversion.