An Atomic-Scale View at γ’-Fe4N as Hydrogen Barrier Material

Abstract

Hydrogen, while a promising sustainable energy carrier, presents challenges such as the embrittlement of materials due to its ability to penetrate and weaken their crystal structures. Here γ’-Fe4N nitride layers, formed on iron through a cost-effective gas nitriding, are investigated as an effective hydrogen permeation barrier. The relatively short process carried out at 570 °C consisted of pre-nitriding in an atmosphere with higher nitriding potential, followed by treatment in a nitriding potential of 0.0016 Pa−1/2 to obtain a pure γ’ layer. A combination of screening methods, including atom probe tomography, density functional theory calculations, and hydrogen permeation analysis, revealed that the nitride layer reduces hydrogen diffusion (steady-state hydrogen flux 3.21 x 10−8 mol/m2·s) by a factor of 20 compared to pure iron, at room temperature. This reduction is achieved by creating energetically unfavorable states due to stronger hydrogen-binding at the surface and high energy barriers for diffusion. The findings demonstrate the potential of γ’-Fe4N as a cost-efficient and easy-to-process solution to protect metallic materials exposed to hydrogen at low temperatures, with great advantages for large-scale applications.