High C-Selectivity for Urea Synthesis Through O-Philic Adsorption to Form OCO Intermediate on Ti-MOF Based Electrocatalysts

The advent of utilizing nitrate (NO3-) for electrochemical co-reduction with carbon dioxide (CO2) to effectively synthesize high-value-added organic nitrogen compounds has captured the attention of the environmental and energy fields. CN coupling is a key step during the electrochemical co-reduction process. An effective strategy to improve the efficiency of synthesis is to explore the optimal reaction pathway and coupling active species. Herein, a p-type semiconductor nanosphere (Ti-DHTP) is presented for electrochemical co-reduction to synthesize urea by combining CO2 and NO3-. At a low voltage of -0.6 V versus RHE, the electrochemical synthesis of urea exhibits 95.5% C-selectivity and 21.75% Faraday efficiency. Comparative experiments, in situ experiments, and theoretical simulations confirm that a new coupling pathway for the synthesis of urea from *NH2 and *OCO intermediates become a key step in Ti-DHTP-driven CN coupling. Moreover, the more efficient *OCO intermediate inhibits the generation of large amounts of C-bearing by-products. Meanwhile, Ti-DHTP has difficulty hydrogenating to form *COOH during the reduction of CO2 leading to the subsequent inability to produce *CO intermediates. This work reveals a new CN coupling mechanism, which provides a feasible strategy for future research on the electrochemical synthesis of organic nitrogen-bearing compounds.