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.