Achieving Record-Breaking Urea Synthesis on Crystalline–Amorphous Hybrid via Electrochemical-Chemical Looping

Abstract

Electrocatalytic C–N coupling of nitrate and CO₂ represents a paradigm shift in sustainable urea synthesis. We demonstrate that amorphous CuO_x-coated crystalline Cu nanowires achieve a record-breaking urea yield rate of 0.89 mol h^–1 g^–1 via novel electrochemical-chemical looping. Mechanistic investigations reveal a three-step catalytic cycle: (i) electro-reductive generation of Cu⁰ and oxygen vacancies (O_v); (ii) O_v-mediated nitrate activation via oxygen atom insertion, spontaneously yielding nitrogen-bonded nitrite (*NO₂) while oxidizing Cu⁰ to catalytically active Cu⁺; and (iii) Cu⁺-catalyzing C–N coupling between *NO₂ and CO₂ to form urea. This pathway circumvents conventional rate-limiting nitrate reduction step, reducing the electron transfer requirement from 16e^– to 12e^– for urea synthesis. Notably, direct nitrite utilization fails to generate Cu⁺ or nitrogen-bonded intermediates, instead forming oxygen-bonded species with markedly reduced C–N coupling activity–a finding that overturns conventional understanding. Our work establishes new fundamental principles for efficient urea synthesis and provides insights into catalyst design and green chemistry.