Analysis of electrochemical ammonia production properties of cobalt-copper dual-atom catalyst

Abstract

The electrochemical reduction of waste nitrate (NO3-) to produce ammonia (NH3) is a promising eco-friendly technology and an alternative to the energy-intensive Haber-Bosch process. However, achieving high energy efficiency is challenging due to the requirement of high reaction overpotential and limited selectivity. In this study, we demonstrate a Co-Cu Dual-Atom Catalyst (DAC) that exhibits high faradaic efficiency at low overpotential due to the synergistic effect between well-dispersed Co and Cu active sites. The Co-Cu DAC was synthesized using a straightforward ligand-mediated method involving the calcination of a mixture of metal precursors, ligands, and carbon black. The formation of a single-atom structure with Metal-N-C coordination was confirmed by FT-EXAFS, TEM, and XPS analysis. In the overall NO3-→NO2-→NH3 conversion pathway of the Co-Cu DAC, the rate-determining step (RDS) for the Co active sites and Cu active sites were located at NO3-→NO2- and NO2-→NH3, respectively. Electrochemical analysis revealed that the Cu active sites in the Co-Cu DAC preferentially catalyze the reduction of NO3- to NO2-, while the Co active sites preferentially catalyze the reduction of NO2- to NH3. The consequent synergistic effect from sequential favorable reactions at each active site allows the bypassing of the RDS, reducing the overall reaction energy barrier. Consequently, the Co-Cu DAC exhibited excellent electrocatalytic activity, achieving a high NH3 faradaic efficiency of 91.2% at -0.3 V vs. RHE. Furthermore, compared to Co SAC and Cu SAC, which comprised active sites of single metal species, the NH3 yield increased by 2.3 and 5.4 times, respectively, at -0.4 V vs. RHE. The dual-atom strategy presented in this study provides further designs for single-atom catalysts and demonstrates the potential for hetero-structured catalysts.