Electrocatalytic nitrogen reduction performance of Fe-doped C3BN2 monolayers constructed via vacancy engineering: Insights from DFT studies

Abstract

In this study, we designed a series of Fe-doped C₃BN₂ electrocatalysts through vacancy engineering, including Fe-Bv, Fe-Nv, Fe-Cv, Fe-Bv-Cv, and Fe-Cv-Nv, to enhance catalytic activity for electrocatalytic nitrogen reduction reaction (NRR) toward ammonia synthesis. Using density functional theory (DFT) simulations, we investigated nitrogen adsorption and Gibbs free energy changes during the key hydrogenation steps, identifying the first hydrogenation step (∗N₂→∗N₂H) as a potential-determining step (PDS). Among the catalysts, Fe anchored at C-vacancy-defected C₃BN₂ (Fe-Cv) exhibited the best nitrogen reduction reaction (NRR) performance with a low Gibbs free energy barrier (ΔG = 0.60 eV) and a low overpotential of 0.44 V, favoring distal and alternating reaction pathways. The superior catalytic activity of Fe-Cv is attributed to strong N₂ chemisorption (ΔG = −1.33 eV) and effective activation of the N ≡N bond via Fe 3d electron back-donation. Additionally, Fe-Cv shows high selectivity for NRR over hydrogen evolution reaction (HER) and excellent thermal stability up to 500 K. These findings suggest that Fe-Cv is a promising catalyst for efficient ammonia synthesis and provide valuable insights into the design of single-atom NRR electrocatalysts.