The tandem CO₂ reduction reaction (CO₂RR) process/nucleophilic addition reaction can be an efficient and environmentally friendly method for the synthesis of urea. However, the low stability of the CO₂^•– intermediates causes a low yield of urea through the nucleophilic addition reaction. Here, we propose an effective method to improve the yield of nucleophilic addition to synthesize urea on Ni single-atom catalysts (Ni-SACs) by introducing acetonitrile into aqueous electrolytes. A high yield of urea of 1.10 mM·g^–1·h^–1 was achieved on the Ni-SACs at −2.2 V (vs saturated calomel electrode) in acetonitrile/water mixture electrolytes, presenting the best performance for urea synthesis via the nucleophilic addition reaction reported so far. Further studies have shown that the acetonitrile stabilizes the CO₂^•– intermediates on the one hand and on the other hand, it lowers the energy barrier of the nucleophilic addition reaction on Ni-SACs through coordination, thus increasing an overall kinetic rate for urea formation.

中文翻译：

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提高 Ni 单原子催化剂上的尿素合成速率：乙腈电解质在串联 CO2 还原/亲核加成反应中的影响

串联CO ₂还原反应(CO ₂ RR)工艺/亲核加成反应是一种高效且环保的尿素合成方法。然而，CO ₂ ^•–中间体的稳定性较低，导致亲核加成反应的尿素收率较低。在这里，我们提出了一种通过将乙腈引入水性电解质中来提高镍单原子催化剂（Ni-SAC）上亲核加成合成尿素产率的有效方法。在乙腈/水混合电解质中，Ni-SAC 在-2.2 V（相对于饱和甘汞电极）下实现了 1.10 mM·g ^–1 ·h ^–1的高尿素产率，呈现出通过亲核合成尿素的最佳性能。加成反应目前已有报道。进一步的研究表明，乙腈一方面稳定CO ₂ ^•–中间体，另一方面通过配位降低Ni-SACs亲核加成反应的能垒，从而提高尿素形成的整体动力学速率。