Breaking the N₂ Solubility Limit to Achieve Efficient Electrosynthesis of NH₃ over Cr-Based Spinel Oxides

Abstract

Electrochemical synthesis of NH 3 from H 2 O and N 2 , as a sustainable alternative to the Haber−Bosch process, has attracted extensive attention. However, the achievement of effective NH 3 electrosynthesis remains challenging since N 2 features remarkable thermodynamic stability and ultralow solubility in aqueous electrolytes. Here, we prepare new-type Cr-based spinel oxides using coprecipitation and hydrothermal methods. The ternary spinel ZnCr 2−x Fe x O 4 phases are formed by substituting Fe 3+ ions for Cr 3+ ions at octahedral sites of ZnCr 2 O 4 . The introduction of Fe results in lattice expansion, lattice distortion, an increase in oxygen vacancies, and a remarkable change in the electronic structure, which further affect nitrogen chemisorption and activation properties. The asfabricated ZnCr 1.2 Fe 0.8 O 4 spinel has bifunctional active sites of Cr 3+ and Fe 3+ and exhibits large capacity and moderate strength of N 2 chemisorption. To break the N 2 solubility limit in the aqueous electrolytes for electrosynthesis of NH 3 , a novel two-step process of gas-phase N 2 adsorption and electroreduction is successfully developed. The catalyst has excellent catalytic performances with an ammonia formation rate of 29.26 μg h −1 cm −2 , the highest Faradaic efficiency of 18.41%, and long-term stability for 20 h. This study provides a new strategy for developing a highly efficient electrocatalyst for the electrosynthesis of NH 3 .

Solar Self-Driven Electrocatalytic Reduction of N2 Directly to CO2-Free Generation of Ammonia on a Coupled Ce-Mediated Cu/Porous Carbon Electrode

“…The peaks denoted as V 0 (882.5 eV), V 1 (885.5 eV), V 2 (889.1 eV), and V 3 (898.5 eV) can be ascribed to Ce 3d 5/2 orbitals, while the U 0 (901.0 eV), U 1 (903.2 eV), U 2 (907.4 eV), and U 3 (916.8 eV) are associated with Ce 3d 3/2 orbitals . All the mentioned peaks are classified to Ce 4+ except for V 1 and U 1 , which are categorized as Ce 3+ . , As the peaks in O 1s spectra of Cu x Ce y -PC (Figure e), the binding energies of ∼529.6 eV and ∼531.7 eV are assigned to lattice oxygen O L and vacancy oxygen O V , respectively. , The peak area and intensity of O V show a significant increase compared to Cu 0.10 -PC, which indicates that more vacancy oxygen are formed after the introduction of Ce. In addition, the position shifts of O L and O V evidence that the cooperative interaction between Cu and Ce species modifies the electronic structure of Cu x Ce y -PC, which may further accelerate charge transfer and enhance the reactivity.…”

“…46,56 As the peaks in O 1s spectra of Cu x Ce y -PC (Figure 2e), the binding energies of ∼529.6 eV and ∼531.7 eV are assigned to lattice oxygen O L and vacancy oxygen O V , respectively. 26,44 The peak area and intensity of O V show a significant increase compared to Cu 0.10 -PC, which indicates that more vacancy oxygen are formed after the introduction of Ce. In addition, the position shifts of O L and O V evidence that the cooperative interaction between Cu and Ce species modifies the electronic structure of Cu x Ce y -PC, which may further accelerate charge transfer and enhance the reactivity.…”

“…Precious metal catalysts such as Au, Pd, − Ru, , Pt, and their alloys have been extensively reported for the last several years. However, large-scale applications of the aforementioned catalysts are almost impossible for the expensive prices and scarce contents. − Accordingly, scholars have diverted their attention to metal-free or non-noble metal materials. Nonmetallic catalysts are inexpensive, but the ability of electron conduction is usually constrained .…”

Recent advances of metal oxide catalysts for electrochemical NH3 production from nitrogen-containing sources

“…9a). 92–94 Chu's group has explored several naturally inspired bimetallic oxides for eN 2 RR application, including MnMoO 4 , 95 FeVO 4 , 96 FeMoO 4 , 97 LiFeO 2 98 and SnNb 2 O 6 . 99 Among these catalysts, the MnMoO 4 sample yielded the highest NH 3 production rate of 60.3 μg h −1 mg cat −1 at −0.4 V versus RHE and a faradaic efficiency of 14.7% at −0.3 V versus RHE, as tested in an H-cell with 0.5 M LiClO 4 electrolyte (Fig.…”