Electrosynthesis of Green Urea by co-reduction of N2 and CO2 Using Dual Active Sites of Copper Phthalocyanine Nanotube

Abstract

Green synthesis of urea under ambient conditions by electrochemical co-reduction of N 2 and CO 2 gases using effective electrocatalyst essentially pushes the conventional two steps (N 2 + H 2 = NH 3 & NH 3 + CO 2 = CO (NH 2 ) 2 ) industrial process at high temperature and high pressure, to the brink. The single step electrochemical green urea synthesis process has hit a roadblock due to the lack of efficient and economically viable electrocatalyst with multiple active sites for dual reduction of N 2 and CO 2 gas molecules to urea. Herein, copper phthalocyanine nanotubes (CuPc NTs) having multiple active sites (such as metal center, Pyrrolic-N3, Pyrrolic-N2, and Pyridinic-N1) are reported to exhibit urea yield of 143.47 µg h -1 mg -1 cat and FE of 12.99% at -0.6 V vs RHE by co-reduction of N 2 and CO 2 . Theoretical calculation suggests that Pyridinic-N1 and Cu centers are responsible to form C-N bonds for urea by reduction of N 2 to NN* and CO 2 to *CO respectively. This study not only provides the new mechanistic insight about the successful electro-reduction of dual gases (N 2 and CO 2 ) in a single component, but also helps to select for rational design of the efficient noble metal-free electrocatalyst for the synthesis of green urea.

A Reliable and Precise Protocol for Urea Quantification in Photo/Electrocatalysis

“…creatively synthesized acetamide via electrocatalytic conversion of carbon monoxide and ammonia, [ 4 ] which opened the prelude to the sustainable synthesis of fine chemicals using small molecules (e.g., CO 2 , CO, and N 2 ). Accordingly, the strategies for fixing small molecules into attractive fine chemicals via electrocatalysis have inspired the enthusiastic research on photo/electrocatalytic CN or CC coupling of small molecules to synthesize high‐value‐added chemicals including urea, [ 5,6,9–22 ] methylamine, [ 23 ] glycine, [ 24 ] and n‐propanol. [ 25 ]…”

“…Among the above fine chemicals, urea as a substance that kicked off the artificial synthesis of organic matter has been popularly studied through exhaustive experiments, [ 5,6,9–22,26–39 ] as well as theory, [ 40–42 ] and also endowed with huge expectations. [ 1–3,43–47 ] After a detailed survey ( Figure and Table S1, Supporting Information), the reported works regarding urea photo/electrocatalytic synthesis to date were summarized.…”

“…[4][5][6][7][8] In 2019, Jiao et al creatively synthesized acetamide via electrocatalytic conversion of carbon monoxide and ammonia, [4] which opened the prelude to the sustainable synthesis of fine chemicals using small molecules (e.g., CO 2 , CO, and N 2 ). Accordingly, the strategies for fixing small molecules into attractive fine chemicals via electrocatalysis have inspired the enthusiastic research on photo/electrocatalytic CN or CC coupling of small molecules to synthesize high-value-added chemicals including urea, [5,6,[9][10][11][12][13][14][15][16][17][18][19][20][21][22] methylamine, [23] glycine, [24] and n-propanol. [25] Among the above fine chemicals, urea as a substance that kicked off the artificial synthesis of organic matter has been popularly studied through exhaustive experiments, [5,6,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][26][27][28]…”