###### Abstract  
This study employs first principles calculations and thermodynamic analyses to investigate the dissociative adsorption of hydrogen on the Fe(110) surface. The results show that the adsorption energies of hydrogen at different sites on the iron surface are \(-1.98\) eV (top site), \(-2.63\) eV (bridge site), and \(-2.98\) eV (hollow site), with the hollow site being the most stable adsorption position. Thermodynamic analysis further reveals that under operational conditions of \(25\)\({}^{\circ}\)C and \(12\) MPa, the Gibbs free energy change (\(\Delta\)G) for hydrogen dissociation is \(-1.53\) eV, indicating that the process is spontaneous under pipeline conditions. Moreover, as temperature and pressure increase, the spontaneity of the adsorption process improves, thus enhancing hydrogen transport efficiency in pipelines. These findings provide a theoretical basis for optimizing hydrogen transport technology in natural gas pipelines and offer scientific support for mitigating hydrogen embrittlement, improving pipeline material performance, and developing future hydrogen transportation strategies and safety measures. hydrogen-blended natural gas pipelines; dissociative adsorption; spontaneous dissociation; charge density; Gibbs free energy +
Footnote †: journal: Applied sciences  
Article  
[PERSON], [PERSON], [PERSON], [PERSON], [PERSON], X. Dissociative Adsorption of Hydrogen in Hydrogen-Blended Natural Gas Pipelines: A First Principles and Thermodynamic Analysis. _Appl. Sci._**2025**, 15, 7342. [[https://doi.org/10.3390/appl5137342](https://doi.org/10.3390/appl5137342)]([https://doi.org/10.3390/appl5137342](https://doi.org/10.3390/appl5137342))
and the aging of natural gas pipeline networks. These challenges pose substantial barriers to achieving safe and efficient hydrogen transportation [5; 6]. Hydrogen embrittlement, which predominantly impacts high-strength steel materials, is governed by mechanisms such as hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) [7; 8]. These mechanisms critically influence hydrogen's interaction with metals and consequently affect the mechanical properties of these materials [9; 10]. When using existing natural gas pipelines to transport hydrogen-natural gas mixtures, there are two main types of hydrogen embrittlement that may occur [11]. The first type involves the hydrogen source produced by the electrochemical cathodic reaction (commonly referred to as cathodic hydrogen), which mainly occurs on metal surfaces undergoing cathodic protection or experiencing electrochemical corrosion [12; 13]. These hydrogen atoms may either recombine into hydrogen molecules and be released from the surface or penetrate into the metal, causing hydrogen-induced cracking (HIC) [14; 15]. Cracks may form under external stress or even in the absence of stress, and they extend as hydrogen accumulates at the crack tips, eventually leading to the failure of the metal parts [16]. The second type is called gaseous hydrogen embrittlement, which does not involve liquid electrolytes but occurs due to the direct contact and chemical reaction of hydrogen gas with metals [17; 18]. Hydrogen molecules first dissociate into hydrogen atoms on the metal surface, a crucial step for the formation of gaseous hydrogen embrittlement [19; 20]. The dissociated hydrogen atoms can stably adsorb on the steel surface and penetrate into the metal through surface diffusion or direct penetration, accumulating in the interstitial spaces of the steel lattice, causing lattice distortion and increasing internal stresses, ultimately leading to hydrogen embrittlement [21; 22]. For gaseous hydrogen embrittlement, the process of dissociative adsorption of hydrogen represents the core step in its formation. Not only do these hydrogen molecules undergo chemical reactions on the metal surface, but they also affect the overall mechanical properties of the material, particularly in the context of pipeline operating conditions [23].