Recent advances in plasma- and photocatalysis-driven nitrogen oxidation have renewed interest in sustainable N2 → NO3− → NH3 pathways. However, electrocatalytic NO3−-to-NH3 is typically confined to narrow potential windows attributed to the performance trade-offs between activity, selectivity, and stability, hindering energy-efficient operation under fluctuating renewable electricity inputs. To overcome these constraints, we report an anodic activation strategy for transition metal oxides in which lattice disruption and surface reorganization generate a highly active, self-sustaining hydroxide interface. Interfacial hydroxyl groups balance the active proton supply with the stepwise reduction of nitrogenous intermediates, thereby accelerating the hydrogenation kinetics of nitrate reduction reaction (NO3RR) while simultaneously suppressing the competing hydrogen evolution reaction (HER). The activated catalyst delivers a faradaic efficiency of 93.79%, an energy efficiency of 35.42% and an NH3 yield rate of 172.31 mg h−1 mgcat−1 at −0.2 V vs. the reversible hydrogen electrode (RHE), outperforming previously reported NO3RR electrocatalysts under comparable conditions. Notably, the exceptional activity and selectivity are maintained over a broad potential window from −0.2 V to −0.6 V vs. RHE, enabling efficient and robust nitrate-to-ammonia conversion under dynamic renewable-power operation.