Tuning the interfacial reaction environment via pH-dependent and induced ions to understand C–N bonds coupling performance in NO3− integrated CO2 reduction to carbon and nitrogen compounds over dual Cu-based N-doped carbon catalyst

Abstract

Dual atomic catalysts (DAC), particularly copper (Cu₂)-based nitrogen (N) doped graphene, show great potential to effectively convert CO₂ and nitrate (NO₃⁻) into important industrial chemicals such as ethylene, glycol, acetamide, and urea through an efficient catalytical process that involves C–C and C–N coupling. However, the origin of the coupling activity remained unclear, which substantially hinders the rational design of Cu-based catalysts for the N-integrated CO₂ reduction reaction (CO₂RR). To address this challenge, this work performed advanced density functional theory calculations incorporating explicit solvation based on a Cu₂-based N-doped carbon (Cu₂N₆C₁₀) catalyst for CO₂RR. These calculations are aimed to gain insight into the reaction mechanisms for the synthesis of ethylene, acetamide, and urea via coupling in the interfacial reaction micro-environment. Due to the sluggishness of CO₂, the formation of a solvation electric layer by anions (F⁻, Cl⁻, Br⁻, and I⁻) and cations (Na⁺, Mg²⁺, K⁺, and Ca²⁺) leads to electron transfer towards the Cu surface. This process significantly accelerates the reduction of CO₂. These results reveal that *CO intermediates play a pivotal role in N-integrated CO₂RR. Remarkably, the Cu₂-based N-doped carbon catalyst examined in this study has demonstrated the most potential for C–N coupling to date. Our findings reveal that through the process of a condensation reaction between *CO and NH₂OH for urea synthesis, *NO₃⁻ is reduced to *NH₃, and *CO₂ to *CCO at dual Cu atom sites. This dual-site reduction facilitates the synthesis of acetamide through a nucleophilic reaction between NH₃ and the ketene intermediate. Furthermore, we found that the I⁻ and Mg²⁺ ions, influenced by pH, were highly effective for acetamide and ammonia synthesis, except when F⁻ and Ca²⁺ were present. Furthermore, the mechanisms of C–N bond formation were investigated via ab-initio molecular dynamics simulations, and we found that adjusting the micro-environment can change the dominant side reaction, shifting from hydrogen production in acidic conditions to water reduction in alkaline ones. This study introduces a novel approach using ion-H₂O cages to significantly enhance the efficiency of C–N coupling reactions.