Efficient electrosynthesis of urea using CO2 and nitrate over a bifunctional In4SnS8 catalyst

Abstract

Electrochemical C–N coupling is emerging as a promising alternative to the current energy-intensive industrial process used to produce urea, and the rational design of efficient electrocatalysts is essential due to the complexity of the reaction. Herein, we developed a binary metal sulfide nanosheet catalyst, In₄SnS₈, and investigated its catalytic performance in urea electrosynthesis with CO₂ and NO₃⁻ as reactants. It is found that the In₄SnS₈ catalyst shows good activity and stability in the reaction, in which the urea formation rate and the faradaic efficiency (FE) of urea can reach 75 mg (h g_cat)⁻¹ and 19.5%, respectively, at −0.65 V vs. RHE. In comparison, unary sulfides, In₂S₃ and SnS₂, show much poorer performance. By combining electrochemical measurements, FTIR characterization and DFT calculations, we infer that CO₂ and NO₃⁻ are hydrogenated to CO and NH₂ on the Sn and In sites, respectively, which act as the key intermediates for the C–N coupling step to CONH₂. The bifunctionality resulting from the Sn and In sites significantly improves the coupling efficiency of In₄SnS₈ with the most favorable pathway in the energetic diagram. This work may inspire more scientific interest in the study of binary transition metal sulfides for electrochemical reactions requiring multiple catalytic sites.