Spin State Modulation with Oxygen Vacancy Orientates C/N Intermediates for Urea Electrosynthesis of Ultrahigh Efficiency.

Abstract

The co-electrolysis of CO₂ and NO₃ ^- to synthesize urea has become an effective pathway to alternate the conventional Bosch-Meiser process, while the complexity of C-/N-containing intermediates for C-N coupling results in the urea electrosynthesis of unsatisfactory efficiency. In this work, an electronic spin state modulation maneuver with oxygen vacancies (Ov) is unveiled to effectively meliorate the oriented generation of key intermediates ^*NH₂ and ^*CO for C-N coupling, furnishing urea in ultrahigh yield of 2175.47 µg mg^-1 h^-1 and Faraday efficiency of 70.1%. Mechanistic studies expound that Ov can induce the conversion of the high-spin state Ni²⁺ (t_2g ⁶e_g ²) of Ni@CeO_2-x to the low-spin state Ni³⁺ (t_2g ⁶e_g ¹), which markedly enhances the hybridization degree of the Ni 3d and the N 2p orbitals of ^*NO, facilitating the selective formation of ^*NH₂. Notably, the in situ generated ^*NH₂ intermediates can serve as a localized proton donor to promote the electroreduction of CO₂ on the adjacent site Ce³⁺-O to exclusively afford ^*CO, followed by C-N coupling of each other to efficiently synthesize urea. The strategy of tailored switching of the active site spin state provides a reliable reference to rectify the electronic structure of electrocatalysts for directional CO₂ valorization.