In situ synchrotron radiation unveils tandem electrocatalytic mechanism in nitrate-to-ammonia conversion enhanced by electron delocalization between cobalt oxide and copper

Cu-based electrocatalysts are cost-effective and highly selective for electrochemical nitrate-to-ammonia reduction (NO₃RR) but suffer from limited active hydrogen (H^*) supplying, competing hydrogen evolution, and ill-defined active sites. Here, we demonstrate that CoO facilitates water dissociation to generate and capture H^*, which migrates to neighboring Cu sites and both enhances NO₃RR performance and suppresses hydrogen evolution on the CoO/Cu heterostructure by electron delocalization. In situ synchrotron radiation analyses reveal that metallic Cu strongly adsorb and electronically activate NO₃⁻, CoO dissociate water to supply H^*, and dynamic modulation of metal valence states and coordination environments synergistically enhances activity and stability by sustaining electron delocalization induced by electron transfer from Cu to CoO. Complementary in situ and ex situ spectroscopies delineate a stepwise reduction pathway (NO₃^* → NO₃^* → NO^* → NOH^* → NHOH^* → NH^* → NH₂^* → NH₃^*), while the built-in electric field generated by the electron delocalization can accelerate the overall kinetics. At −0.4 V versus RHE, the catalyst attains a 95% NH₃ Faradaic efficiency and a yield rate of 14,321 μg h⁻¹ cm⁻². In a flow cell, it sustains 200 mA cm⁻² for over 220 h. Fertilizer trials using recovered NH₄Cl markedly improve lettuce yield and survival, confirming the practical viability of this electrocatalytic strategy.