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

Abstract

Electrochemical nitrate reduction reaction (NO3RR) is a promising approach to realize ammonia generation and wastewater treatment. However, the transformation from NO3− to NH3 involves multiple proton-coupled electron transfer processes and by-products (NO2−, H2, 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 (NO3− to NO2− and NO2− to NH3) more compatible, avoiding excessive NO2− accumulation and optimizing the whole tandem reaction. Focusing on the initial 2e− process, the inhibited *NO2 desorption on Cu sites in P-Cu gives rise to the more appropriate NO2− released in electrolyte. Subsequently, P-Co(OH)2 exhibits a superior capacity for trapping and transforming the desorbed NO2− during the latter 6e− process due to the thermodynamic advantage and contributions of active hydrogen. In 1 m KOH + 0.1 m NO3−, P-Cu/Co(OH)2 leads to superior NH3 yield rate of 42.63 mg h−1 cm−2 and NH3 Faradaic efficiency of 97.04% at −0.4 V versus the reversible hydrogen electrode. Such a well-matched two-step process achieves remarkable NH3 synthesis performance from the perspective of optimizing the tandem catalytic reaction, offering a novel guideline for the design of NO3RR electrocatalysts.