Screening Efficient C–N Coupling Catalysts for Electrosynthesis of Acetamide and Output Ammonia through a Cascade Strategy of Electrochemical CO₂ and N₂ Reduction Using Cu-Based Nitrogen–Carbon Nanosheets

Abstract

Due to the limitation of the high-value-added products obtained from electrocatalytic CO 2 reduction within an acid environment, introducing additional elements can expand the diversity of the products obtained during the CO 2 reduction reaction (CO 2 RR) and nitrogen reduction reaction (NRR). Thus, coelectroreduction of CO 2 and N 2 is a new strategy for producing acetamide (CH 3 CONH 2 ) via both C−C and C−N bond coupling using Cu-based nitrogen−carbon nanosheets. CO 2 can reduce to CO, and a key ketene (*C�C�O) can be generated from *CO*CO dimerization; this ketene is postulated as an intermediate in the formation of acetamide. However, most studies focus on promoting the C−C bond formation. Here, we propose that C−N bond coupling can form acetamide through the interaction of *C�C�O with NH 3 . The acetamide is formed via a nucleophilic attack between *NH 3 and the *C�C�O intermediate. The C−N coupling mechanism was successfully applied to expand the variety of nitrogen-containing products obtained from CO 2 and N 2 coreduction. Thus, we successfully screened Cu 2 -based graphite and Cubased C 3 N 4 as catalysts that can produce C 2+ compounds by integrating CO dimerization with acetamide synthesis. In addition, we observed that Cu 2 -based C 2 N and Cu-based C 3 N 4 catalysts are suitable for the NRR. Cu-based C 3 N 4 showed high CO 2 RR and NRR activities with small negative limiting potential (U L ) values of −0.83 and −0.58 V compared to those of other candidates, respectively. The formation of *COHCOH from *COHCO was considered the rate-determining step (RDS) during acetamide electrosynthesis. The limiting potential value of Cu 2 -based C 2 N was only −0.46 V for NH 3 synthesis, and the formation of *NNH was via the RDS via an alternating path. The adsorption energy difference analysis both CO 2 and N 2 compare with the hydrogen evolution reaction (HER), suggesting that Cu 2 -based C 2 N exhibited the highest CO 2 RR and NRR selectivity among the 13 analyzed catalysts. The results of this study provide innovative insights into the design principle of Cu-based nitrogen−carbon electrocatalysts for generating highly efficient C−N coupling products.