Bi1-CuCo₂O₄ Hollow Carbon Nanofibers Boosts NH₃ Production from Electrocatalytic Nitrate Reduction

Ammonia, as a high-energy-density carrier for hydrogen storage, is in great demand worldwide. Electrocatalytic nitrate reduction reaction (NO₃RR) provides a green NH₃ production process. However, the complex reaction pathways for NO₃RR to NH₃ and the difficulty in controlling intermediate products limit the reduction process. Herein, by incorporating atomic-level bismuth (Bi) into CuCo₂O₄ hollow carbon nanofibers, the catalytic activity of the electrocatalyst for NO₃RR is enhanced. The maximum Faradaic efficiency of Bi_1-CuCo₂O₄ is 95.53%, with an NH₃ yield of 448.74 µmol h⁻¹ cm⁻² at −0.8 V versus RHE. Density Functional Theory calculations show that the presence of Bi lowers the reaction barrier for the hydrogenation step from *NO₂ to *NO₂H, while promoting mass transfer on the release of *NH₃ and the reactivation of surface-active sites. Differential charge density calculations also show that after Bi doping, the charge supplied by the catalyst to NO₃₋ increases from 0.62 to 0.72 e^-, thus reasoned for enhanced NO₃RR activity. The established nitrate-Zn battery shows an energy density of 2.81 mW cm⁻², thus implying the potential application.