Controllable C─N Coupling Toward Efficient Urea Electrosynthesis via Spin State Modulation on Fe Catalysts

The co-electrolysis of CO₂ and nitrate (NO₃ ^-) presents a promising and sustainable method for urea synthesis. However, it remains challenging to modulate the intermediates reactivity and C─N coupling at the matchable stages. Here, we propose a strategy to regulate the C─N coupling mode on Fe site via spin state modulation. Both experimental and theoretical calculations revealed that the Cu²⁺-doped Fe₃O₄ promoted C─N coupling at the early stage via the *CO + *NO₂→*CONO₂ pathway, enhancing the catalytic performance significantly. The catalysts could achieve a urea Faradaic efficiency of 47.3% and a yield rate of 635.9 µg h^-1 mg_cat. ^-1 at low overpotential, along with exceptional stability over 30 h, representing one of the highest performances reported to date. Detailed experimental and theoretical analyses demonstrated that Cu doping lowered the e_g electron density of Fe and enhanced *NO₂ adsorption. The adsorbed *NO₂ in turn further decreased Fe spin state through π backdonation, which facilitated CO₂ activation and increased *CO coverage. Moreover, optimizing the *NO₂ coverage also reduced the energy barrier for *CO + *NO₂→*CONO₂, and inhibited *NO₂ protonation, leading to high selectivity toward urea.