Unlocking Synergistic Electron Redistribution via Dual‐Site Reconstruction in Tandem Nanofibers for Efficient Nitrate Electroreduction to Ammonia

ABSTRACT The electrocatalytic nitrate (NO 3 − ) reduction reaction (NO 3 RR) to ammonia (NH 3 ) is a sustainable alternative to the energy‐intensive Haber–Bosch process; however, its efficiency is hampered by its complex multi‐step kinetics. Herein, a rational electrospinning‐calcination strategy is employed to fabricate dual‐content tandem CuCoO x nanofibers (NFs) featuring an interconnected network composed of CuCoO x hollow cubes for the NO 3 RR. The resultant tandem CuCoO x NFs achieve a remarkable Faradaic efficiency for NH 3 of 98.7 ± 0.4% at −0.4 V versus RHE and a maximum NH 3 yield rate of 109.7 ± 1.1 mg cm −2 h −1 at −1.0 V versus RHE, outperforming a host of benchmark NO 3 RR electrocatalysts. In situ X‐ray absorption spectroscopy reveals dynamic dual‐site reconstruction during NO 3 RR, wherein the initial CuCoO x transforms into a Cu/Co(OH) 2 heterostructure, identified as the true active phase. Combined mechanistic and theoretical studies elucidate that the reconstructed interface induces surface electron redistribution, which optimizes intermediate adsorption and lowers the energy barrier of the rate‐determining step. Furthermore, it facilitates proton supply to Co sites and enables spontaneous hydrogen spillover to adjacent Cu sites, synergistically accelerating the reaction kinetics. The practical potential of this catalyst is further demonstrated in a flow‐cell reactor for NH 3 production and in a high‐performance Zn‐NO 3 − battery.