Orbital electron delocalization of axial-coordinated modified FeN4 and structurally ordered PtFe intermetallic synergistically for efficient oxygen reduction reaction catalysis

Abstract

Regulating the chemical environment of materials to optimize their electronic structure, leading to the optimal adsorption energies of intermediates, is of paramount importance to improving the performance of electrocatalysts, yet remains an immense challenge. Herein, we design a harmonious axial-coordination Pt_xFe/FeN₄CCl catalyst that integrates a structurally ordered PtFe intermetallic with an orbital electron-delocalization FeN₄CCl support for synergistically efficient oxygen reduction catalysis. The obtained Pt₂Fe/FeN₄CCl with a favorable atomic arrangement and surface composition exhibits enhanced oxygen reduction reaction (ORR) intrinsic activity and durability, achieving a mass activity (MA) and specific activity (SA) of 1.637 A mg_Pt⁻¹ and 2.270 mA cm⁻², respectively. Detailed X-ray absorption fine spectroscopy (XAFS) further confirms the axial-coupling effect of the FeN₄CCl substrate by configuring the Fe–N bond to ∼1.92 Å and the Fe–Cl bond to ∼2.06 Å. Additionally, Fourier transforms of the extended X-ray absorption fine structure (FT-EXAFS) demonstrate relatively prominent peaks at ∼1.5 Å, ascribed to the contribution of the Fe–N/Fe–Cl, further indicating the construction of the FeN₄CCl moiety structure. More importantly, the electron localization function (ELF) and density functional theory (DFT) further determine an orbital electron delocalization effect due to the strong axial traction between the Cl atoms and FeN₄, resulting in electron redistribution and modification of the coordination surroundings, thus optimizing the adsorption free energy of OH_abs intermediates and effectively accelerating the ORR catalytic kinetic process.