C─N Coupling Enabled by N─N Bond Breaking for Electrochemical Urea Production

Abstract

Urea electrosynthesis under mild conditions has emerged as a promising alternative strategy to replace the harsh industrial HaberBosch process, which is however limited by sluggish CN coupling and low selectivity. Here, a novel mechanism based on the synergistic effect of NN bond cleavage and CN coupling for highly efficient urea production is proposed. It is found that dual vanadium atoms anchoring onto defective graphene (V2N6) can activate the adsorbed *N2, in which the stable N≡N bond can be gradually weakened until being broken after two protonation steps, with superior thermodynamic and kinetic feasibility. CO molecules can be easily adsorbed on the dissociated *NH, followed by an exothermic CN coupling to form the urea precursor *NHCONH with a low kinetic energy barrier of 0.20 eV. The dual‐atom V2N6 not only exhibits superior intrinsic activity for urea formation, with a limiting potential of −0.26 V, but also can significantly suppress the competitive N2 reduction and hydrogen evolution reactions. This study presents a new avenue for developing novel mechanisms and efficient catalysts for urea electrochemical synthesis.

Electrocatalytic Urea Synthesis via N2 Dimerization and Universal Descriptor

“…DFT + U was adopted to justify the utilization of the PBE functional, where the corresponding U − J values for Ti and V metals are 2.58 and 2.72 eV, respectively. 70 The computational hydrogen electrode (CHE) model proposed by Nørskov et al was utilized to establish a free energy profile to describe the electrocatalytic performance of urea synthesis process. 71,72 The Gibbs reaction free energy change (ΔG) for each elementary step was evaluated from the equation…”

“…Atomic relaxations were carried out with the conjugate-gradient algorithm until the Hellmann–Feynman forces were smaller than 0.01 eV/Å. DFT + U was adopted to justify the utilization of the PBE functional, where the corresponding U – J values for Ti and V metals are 2.58 and 2.72 eV, respectively …”

Electrocatalytic C–N coupling for urea synthesis: a critical review

“…Therefore, the construction of the dual-atom structure plays a crucial role in urea synthesis. 75 Wang and coworkers designed a diatomic catalyst (DAC) with bonded Fe–Ni (B-FeNi-DASC) pairs through pyrolysis of the coordination polymer (Fig. 3i and j).…”

Electrocatalytic synthesis of C–N coupling compounds from CO2 and nitrogenous species

“…As shown in Table 1, recent advancements in this field address these challenges through careful design and synthesis of electrocatalysts. 66,67 Wang and coworkers conducted pioneering research on the electrocatalytic coreduction of CO 2 and N 2 to synthesize urea (Figure 2A). 55 They initially synthesized TiO 2 with oxygen vacancies (OVs), by treating original TiO 2 nanosheets under a reductive atmosphere, at high temperature, followed by coreduction of metal precursors, to fabricate PdCu alloy species on OV-rich TiO 2 (Figure 2B).…”

“…However, the competitive reduction between CO 2 and N 2 presents challenges in enhancing the efficiency of C–N coupling, leading to undesirable urea selectivity. As shown in Table 1, recent advancements in this field address these challenges through careful design and synthesis of electrocatalysts 66,67 . Wang and coworkers conducted pioneering research on the electrocatalytic coreduction of CO 2 and N 2 to synthesize urea (Figure 2A).…”