Oxygen Vacancy Regulation Strategy Promotes Electrocatalytic Nitrogen Fixation by Doping Bi into Ce-MOF-Derived CeO₂ Nanorods

Abstract

Although the mature Haber–Bosch process has become the main method for ammonia production, its high energy consumption nature has motivated people to learn about nitrogenases, which can fix N2 in the atmosphere to NH3 under ambient conditions. Here we show that Bi-CeO2 nanorods with oxygen vacancies can effectively fix N2 to NH3 under ambient conditions by an electrocatalytic nitrogen reduction reaction (NRR). Bismuth has a certain electrocatalytic nitrogen reduction effect because of the strong force between the Bi 6p band and the N 2p orbital. The subsequent one-pot solvothermal method ensure the successful doping of Bi into the CeO2 structure, and the catalyst material Bi-CeO2 has sufficient adhesion with the substrate carbon paper, thereby ensuring electrode stability. Meanwhile, the introduction of a Bi atom to CeO2 is an effective strategy to increase the abundance of oxygen vacancies in CeO2 for the rate-determining step and hence better promote NRR activity compared with classic transition-metal catalysts because the electrons trapped by the oxygen vacancies present in the catalyst material can be injected into the counterbond orbitals of N2 adsorbed on the catalyst material, thereby weakening the NN triple bond for later activation and hydrogenation. The catalyst achieves a high R NH3 of 6.29 μg h–1 cm–2 with a Faradaic efficiency (FE) of 8.56% at −0.5 V (vs RHE) in 0.5 M K2SO4 at room temperature. This Article provides a new avenue for the design and development of efficient catalysts for the electrocatalytic NRR.

Single-Atom Fe-N4 on a Carbon Substrate for Nitrogen Reduction Reaction

“…The ammonia content in the electrolyte was collected by the indophenol blue method. 55 One milliliter of electrolyte was collected from the cathode electrolytic cell and mixed with 1 mL of 1 M NaOH solution containing 5% sodium citrate and 5% salicylic acid, 0.1 mL of 1% C 5 FeN 6 Na 2 O•2H 2 O, and 0.5 mL of 0.05 M NaClO. The ammonia concentration was determined by the UV−Vis absorption spectrum at a wavelength of 655 nm.…”

Assembly of Hydrophobic ZIF-8 on CeO2 Nanorods as High-Efficiency Catalyst for Electrocatalytic Nitrogen Reduction Reaction

“…The peaks at 881.78 eV, 888.32 eV and 897.88 eV correspond to the characteristic peak of Ce 4+ 3d 5/2 (in blue), and the peaks at 900.32 eV, 902.58 eV and 916.18 eV correspond to the characteristic peak of Ce 4+ 3d 3/2 (in purple). The peaks at 884.32 eV and 902.58 eV correspond to the characteristic peaks of Ce 3+ 3d 5/2 (in pink) and Ce 3+ 3d 3/2 (in green), respectively [ 7 , 27 , 35 , 36 , 37 ]. In CeO 2 , Ce exists in +3 and +4 valences.…”

“…Cerium oxide (CeO 2 ) rich in oxygen vacancies has been reported to possess intrinsic NRR activity since the flexible conversion between +3 and +4 valence in CeO 2 offers the coordinatively unsaturated sites for electron transfer to the adsorbed N 2 molecule and weakens the nitrogen–nitrogen bond [ 7 , 27 , 28 , 29 ]. The N≡N triple bond can be softened for future activation and hydrogenation by injecting the abundant oxygen vacancy in CeO 2 into the antibonding orbital of N 2 adsorbed on the surface of the catalyst [ 7 , 27 , 28 , 29 ]. Related research provides a basis for the subsequent research and development of CeO 2 -based electrocatalytic NRR catalysts.…”

“…In our previous work, the synthesized CeO 2 with rich oxygen vacancies proved to have intrinsic NRR activity [ 27 ]. In this work, the co-assembled electrocatalytic nitrogen reduction catalyst CeO 2 -ZIF-8 was synthesized by incorporating porous hydrophobic ZIF-8 on CeO 2 nanorods with abundant oxygen vacancies ( Scheme 1 ).…”

Synergy of Bi2O3 and RuO2 Nanocatalysts for Low‐Overpotential and Wide pH‐Window Electrochemical Ammonia Synthesis

“…[26] In recent years, bismuth (Bi), as an earth-abundant main group metal element with regulated pelectron density and weak hydrogen adsorption, has gained more and more attention for use in NRR. [27,28] Bi-based catalysts, including metallic bismuth (Bi 0 ), [29,30] Bi-based oxides, [31,32] and Bibased hybrids, [33,34] have been demonstrated as promising NRR electrocatalysts. Taking Bi 2 O 3 as an example, it has several obvious advantages for use in NRR such as low cost, high chemical stability, easily prepared and relative nontoxicity, but it suffers from limited conductivity and sluggish activation/ adsorption of *H. [31] Fabricating a "multicomponent" hybrid catalyst, in which different components can play crucial parts as the active catalytic centers, electronic transmission parts, the inert HER competitive sites, and the substrate, should hold high potential to enhance the NRR performance of Bi 2 O 3 .…”