MIL-101(Fe) supported Au-Cu nanoalloy for enhanced electrochemical nitrogen fixation in gas–liquid-solid three-phase reactor

Abstract

Low-temperature electrocatalytic nitrogen fixation technology is a green artificial nitrogen fixation technology. Here, we designed and synthesized AuxCuy/MIL-101 series catalysts, i.e., using simple alloy engineering strategy, the synthesized AuCu nanoalloy particles were efficiently loaded onto MIL-101(Fe) by one-step co-reduction. Experiments and calculations show that (Ⅰ) MIL-101(Fe) as support not only enhances the N2 enrichment ability of catalysts, but also facilitates the high dispersion of AuCu nanoparticles. (II) In AuCu nanoalloy, the strong coupling between Au-Cu sites bridges its effective electron transfer, improves the charge structure of Au sites, thereby enhancing the Au 5d-N2 π* interaction, which not only facilitates the adsorption of N2 by catalysts, but also weakens the N≡N triple bond and reduces RDS (N2 → NNH*, 0.38 eV). (III) Au-Cu alloying increases the hydrogen adsorption free energy (0.76 eV), which weakens the competitive adsorption between H+ and N2 by catalysts, and optimizes the charge transfer efficiency of AuxCuy/MIL-101 catalysts. Therefore, the overall NH3 yield and FE of AuxCuy/MIL-101 catalysts are higher than those of MIL-101, Cu/MIL-101 and Au/MIL-101. After optimization, Au1Cu1/MIL-101 with the highest ECSA and suitable Rct has the highest NRR activity (NH3 yield: 161.07 μg h−1 mg-1cat., FE: 58.86 %), which exceeds most Au-based catalysts. Meanwhile, the in-situ FTIR test results further indicate that Au-Cu alloying can accelerate the cleavage of N≡N and the adsorption of N2 by catalysts. This study demonstrates that the gold-copper alloying strategy not only promotes Au 5d feedback to N≡N bond, reduces RDS but also increases ΔGH*, inhibits proton adsorption, ultimately promoting Au1Cu1/MIL-101 catalyst to perform highly efficient NRR performance.