Engineering Spin States of Isolated Copper Species in a Metal–Organic Framework Improves Urea Electrosynthesis

Abstract

The catalytic activities are generally believed to be relevant to the electronic states of their active center, but understanding this relationship is usually difficult. Here, we design two types of catalysts for electrocatalytic urea via a coordination strategy in a metal–organic frameworks: CuIII-HHTP and CuII-HHTP. CuIII-HHTP exhibits an improved urea production rate of 7.78 mmol h−1 g−1 and an enhanced Faradaic efficiency of 23.09% at − 0.6 V vs. reversible hydrogen electrode, in sharp contrast to CuII-HHTP. Isolated CuIII species with S = 0 spin ground state are demonstrated as the active center in CuIII-HHTP, different from CuII with S = 1/2 in CuII-HHTP. We further demonstrate that isolated CuIII with an empty $${d}_{{{\text{x}}^{2}\text{-y}}^{2}}^{0}$$ d x 2 -y 2 0 orbital in CuIII-HHTP experiences a single-electron migration path with a lower energy barrier in the C–N coupling process, while CuII with a single-spin state ($${d}_{{{\text{x}}^{2}\text{-y}}^{2}}^{1}$$ d x 2 -y 2 1 ) in CuII-HHTP undergoes a two-electron migration pathway.

Review on strategies for improving the added value and expanding the scope of CO2 electroreduction products

“…Since then, researchers have increasingly focused on the design of highly efficient catalysts to enhance the electrocatalytic co-reduction of CO 2 and N 2 for urea synthesis under ambient conditions. 290 These efforts have explored various catalysts materials, including metal atoms (such as Cu III -HHTP, 291 Cu phthalocyanine, 292 Co-MOF, 293 PdCu, 294 TiCo, 295 and ZnMn 296 diatomic catalyst), nanoclusters (Sb x Bi 1− x O y 297 ), metal alloys (CuBi alloy 298 ), metallic nano-heterojunctions (such as Bi-BiVO 4 299 and BiFeO 3 /BiVO 4 300 ), metal composites with frustrated Lewis pairs 258 and transition metal phosphides. 301…”

“…Metal atom catalysts have attracted widespread attention from researchers due to their maximum atomic utilization and adjustable coordination environments. Recently, researchers have utilized Cu 291,292 and Co 293 single atoms for the electrocatalytic co-reduction of CO 2 and N 2 to produce urea. The interaction between metal single atoms and carbon supports leads to a change in the spin state of the metal single atoms, which may facilitate the reduction of energy barriers in C–N coupling reactions.…”

“…The interaction between metal single atoms and carbon supports leads to a change in the spin state of the metal single atoms, which may facilitate the reduction of energy barriers in C–N coupling reactions. 291,293 In addition, nitrogen species in the carrier structure may provide multiple active sites during the electrocatalytic co-reduction of CO 2 and N 2 for urea synthesis. For instance, Ghorai et al reported the utilization of Cu phthalocyanine nanotubes (Fig.…”

Engineering the spin configuration of electrocatalysts for electrochemical renewable conversions

“…16,143 Based on this principle, the spin catalysis in the perovskites mainly focuses on the doping of A and B in the ABO 3 structures, which affects the filling state of the spin electron orbitals, such as LaCo 0.90 Fe 0.10 O 3 , 144 SrNb 0.1 Co 0.7 Fe 0.2 O 3− δ 145 and (La 0.8 Sr 0.2 ) 1− x Mn 1− x Co x O 3− δ . 146 In addition, the change of spin states caused by doping, 147 ligand structure, 148,149 crystal planes 20 and sizes 21 may generate different spin states (Fig. 7e).…”

Designing bifunctional catalysts for urea electrolysis: progress and perspectives

“…Besides being used as precursors for designing metal-based catalysts, MOFs can be directly used as electrocatalysts owing to their highly porous feature and flexible composition. 196 For example, the nickel terephthalate nanosheets self-assembled 3D aggregates, with rich unsaturated coordination nickel sites, take 1.52 V at 10 mA cm −2 for urea electrolysis. 19 The performance of single metal-based MOFs can be enhanced by introducing a second metal.…”