Understanding the Site-Selective Electrocatalytic Co-Reduction Mechanism for Green Urea Synthesis Using Copper Phthalocyanine Nanotubes

摘要

Green synthesis of urea under ambient conditions by electrochemicalco-reduction of N_2 and CO_2 gases using effective electrocatalyst essentiallypushes the conventional two steps (N_2 + H2_ = NH_3 and NH_3 + CO_2 = CO(NH_2)_2)industrial process at high temperature and high pressure, to the brink. The singlestep electrochemical green urea synthesis process has hit a roadblock due tothe lack of efficient and economically viable electrocatalyst with multiple activesites for dual reduction of N_2 and CO_2 gas molecules to urea. Herein, copperphthalocyanine nanotubes (CuPc NTs) having multiple active sites (such as metalcenter, Pyrrolic-N_3, Pyrrolic-N2, and Pyridinic-N1) as an efficient electrocatalystwhich exhibits urea yield of 143.47 μg h~(–1) mg~(–1)_(cat) and faradaic efficiency of 12.99at –0.6 V versus reversible hydrogen electrode by co-reduction of N_2 and CO_2are reported. Theoretical calculation suggests that Pyridinic-N1 and Cu centersare responsible to form CN bonds for urea by co-reduction of N_2 to NN* andCO_2 to *CO, respectively. This study provides the new mechanistic insight aboutthe successful electro-reduction of dual gases (N_2 and CO_2) in a single moleculeas well as rational design of efficient noble metal-free electrocatalyst for thesynthesis of green urea.