Enhancing Compatibility of Two‐Step Tandem Catalytic Nitrate Reduction to Ammonia Over P‐Cu/Co(OH) ₂

Abstract Electrochemical nitrate reduction reaction (NO ₃ RR) is a promising approach to realize ammonia generation and wastewater treatment. However, the transformation from NO ₃ ⁻ to NH ₃ involves multiple proton‐coupled electron transfer processes and by‐products (NO ₂ ⁻ , H ₂ , etc.), making high ammonia selectivity a challenge. Herein, a two‐phase nanoflower P‐Cu/Co(OH) ₂ electrocatalyst consisting of P‐Cu clusters and P‐Co(OH) ₂ nanosheets is designed to match the two‐step tandem process (NO ₃ ⁻ to NO ₂ ⁻ and NO ₂ ⁻ to NH ₃ ) more compatible, avoiding excessive NO ₂ ⁻ accumulation and optimizing the whole tandem reaction. Focusing on the initial 2e ⁻ process, the inhibited ^* NO ₂ desorption on Cu sites in P‐Cu gives rise to the more appropriate NO ₂ ⁻ released in electrolyte. Subsequently, P‐Co(OH) ₂ exhibits a superior capacity for trapping and transforming the desorbed NO ₂ ⁻ during the latter 6e ⁻ process due to the thermodynamic advantage and contributions of active hydrogen. In 1 m KOH + 0.1 m NO ₃ ⁻ , P‐Cu/Co(OH) ₂ leads to superior NH ₃ yield rate of 42.63 mg h ^{− 1} cm ^{− 2} and NH ₃ Faradaic efficiency of 97.04% at −0.4 V versus the reversible hydrogen electrode. Such a well‐matched two‐step process achieves remarkable NH ₃ synthesis performance from the perspective of optimizing the tandem catalytic reaction, offering a novel guideline for the design of NO ₃ RR electrocatalysts.