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

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.