While hydrogen pipelines have attracted increased attention, safety of the pipelines has been a concern in terms of hydrogen embrittlement (HE) occurring upon hydrogen atom (H) generation and permeation in the steels. In this work, thermodynamic analyses regarding H generation and adsorption on pipeline steels by two potential mechanisms, i.e., spontaneous dissociation and dissociative adsorption, were conducted through theoretical calculations based on Gibbs free energy change of the H generation reactions. Moreover, H adsorption free energy and configurations were determined based on density functional theory (DFT) calculations. Effects of H adsorption site, H coverage and hydrostatic stress on H adsorption and absorption were discussed. Spontaneous dissociation of hydrogen gas molecules to generate hydrogen atoms is thermodynamically impossible. Dissociative adsorption is thermodynamically feasible at wide temperature and pressure ranges. Particularly, an increased hydrogen gas partial pressure and elevated temperature favor the dissociative adsorption of hydrogen. Hydrogen atoms generated by dissociative adsorption mechanism can adsorb stably at On-Top (OT) and 2-fold (2F) Cross-Bridge sites of Fe (100), while hydrogen adsorption at 2F site is more stable due to a higher electron density and a stronger electronic hybridization between Fe and H. The influence of H atom coverage on dissociative adsorption occurs at low coverages only, i.e., 0.25–1.00 ML as determined in this work. External stresses make dissociative adsorption more difficult to occur compared with a fully relaxed steel. Both tetrahedral sites (TS) and octahedral sites (OS) can potentially host absorbed H atoms at subsurface of the steel. Absorbed H atoms will be predominantly trapped at TS due to a low energy path and exothermic feature. Diffusion of H atoms from steel surface to the subsurface is more difficult compared with the dissociative adsorption.

虽然氢气管道引起了越来越多的关注，但在钢中产生和渗透氢原子 (H) 时发生的氢脆 (HE) 方面，管道的安全性一直受到关注。在这项工作中，通过基于H 生成反应的吉布斯自由能变化的理论计算，通过两种潜在机制，即自发解离和解离吸附，对管线钢上的H 生成和吸附进行了热力学分析。此外，H 吸附自由能和构型是基于密度泛函理论 (DFT) 计算确定的。讨论了H吸附位点、H覆盖率和静水应力对H吸附和吸收的影响。氢气分子自发分解产生氢原子在热力学上是不可能的。解离吸附在广泛的温度和压力范围内在热力学上是可行的。特别地，增加的氢气分压和升高的温度有利于氢的解离吸附。通过解离吸附机制产生的氢原子可以稳定地吸附在 Fe (100) 的 On-Top (OT) 和 2-fold (2F) Cross-Bridge 位点，而在 2F 位点的氢吸附由于更高的电子密度和Fe 和 H 之间更强的电子杂化。H 原子覆盖率对解离吸附的影响仅发生在低覆盖率下，即本工作中确定的 0.25-1.00 ML。与完全松弛的钢相比，外部应力使解离吸附更难发生。四面体位点 (TS) 和八面体位点 (OS) 都可能在钢的表面下承载吸收的 H 原子。由于低能量路径和放热特征，吸收的 H 原子将主要被困在 TS 处。与解离吸附相比，H 原子从钢表面扩散到次表面更困难。