Enhancing Tandem Electrochemical Nitrate Reduction to Ammonia Through Cu-MOF/Co-MOF@NF Composite Nanoflower

Electrocatalytic nitrate reduction (eNO3RR) has gained widespread application as a green and efficient technique for ammonia synthesis. However, the accumulation of nitrite (NO2–) during the electrochemical reduction process significantly hampers the efficiency of converting nitrate (NO3–) into ammonia (NH3). In this study, a Cu-MOF/Co-MOF@NF composite catalyst was developed on a nickel foam substrate using a hydrothermal method. The catalyst is composed of interconnected Cu-MOF@NF and Co-MOF@NF nanosheets, forming a flower-like nanostructure. X-ray photoelectron spectroscopy (XPS) reveals there is an electronic transfer between copper (Cu) and cobalt (Co) sites at the interface of Cu-MOF/Co-MOF@NF, thereby accelerating both the adsorption and reduction of NO3– at Cu sites and enhancing selective conversion to NH3 at Co sites. At a potential of – 0.5 V vs RHE, the Cu-MOF/Co-MOF@NF exhibits a NO3– conversion to NH3 that surpasses those of the Cu-MOF@NF and Co-MOF@NF by 8.5 and 39.6%, respectively, achieving NH3 selectivity and yield of 93.3% and 318.5 μg·h–1·cm–2. In addition, Cu-MOF/Co-MOF@NF possesses exceptional catalytic activity and durability. Electron Paramagnetic Resonance (EPR) experiments reveal a significant amount of *H generated at the cathode interface. In-situ differential electrochemical mass spectrometry (DEMS) detection shows that the reduction pathway for NO3– over the Cu-MOF/Co-MOF@NF is as follows: *NO3– → *NO2– → *NO → *N → *NH → *NH2 → *NH3.