## 3 Results and Discussion
### Thermodynamic Analysis of Hydrogen Dissociative Adsorption on Pipeline Steel Surfaces
#### 3.3.3 Changes in Gibbs Free Energy and Chemical Potential  
As the temperature increases, the value of the Gibbs free energy change \(\Delta G\) shows a decreasing trend, which actually means a reduction in its absolute value. This phenomenon reveals that under conditions of rising temperatures inside steel pipes, the spontaneous dissociation tendency of hydrogen on the steel surface increases. In thermodynamics, when the change in Gibbs free energy \(\Delta G\) for a process is less than zero, the process is considered spontaneous. Therefore, a decrease in the absolute value of \(\Delta G\) actually reflects a trend of increased spontaneity in the hydrogen dissociation process. This point is crucial for understanding and predicting the adsorption behavior of hydrogen in natural gas pipeline systems, especially when considering the potential impact of temperature changes on pipeline safety and hydrogen transport efficiency. At a set pressure of 12 MPa, the variations in the chemical potential and Gibbs free energy of hydrogen adsorption on steel pipe surfaces under different temperatures were investigated. The calculation results are shown in Table 3, and the trend is illustrated in Figure 11. As the temperature rises, the chemical potential \(\mu\)(_T,P_) also increases correspondingly. This phenomenon reveals that, in a constant pressure environment, the increase in temperature leads to an increase in the average energy of atoms or molecules in the system, thereby causing the chemical potential to rise. The increase in chemical potential means that, under higher temperature conditions, gas molecules are more inclined to adsorb onto solid surfaces. This trend is consistent with the decrease in the absolute value of the Gibbs free energy change \(\Delta G\) into the negative range, further confirming that with the increase in temperature, the spontaneity of hydrogen adsorption and dissociation processes on steel surfaces significantly enhances. In summary, at a working pressure of 12 MPa, as the temperature increases, the spontaneous adsorption and dissociation activities of hydrogen on steel surfaces show an enhanced trend. This observation is reflected not only in the increase in the absolute value of the negative \(\Delta G\) but also in the continuous rise of the chemical potential \(\mu\), providing an important theoretical basis for a deeper understanding and optimization of hydrogen transportation and storage in natural gas pipelines. At a set temperature of 25 \({}^{\circ}\)C, the variations in the chemical potential and Gibbs free energy of hydrogen adsorption on steel pipe surfaces under different pressures were \begin{table}
\begin{tabular}{c c c} \hline \hline
**T** (\({}^{\circ}\)**C**) & **\(\Delta\)G (kJ/mol)** & **\(\mu\) (kJ/mol)** \\ \hline \(-\)15 & \(-\)115.444 & 10.275 \\ \(0\) & \(-\)116.041 & 10.872 \\ \(15\) & \(-\)116.638 & 11.469 \\ \(25\) & \(-\)117.036 & 11.867 \\ \(30\) & \(-\)117.235 & 12.066 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical potential (\(\mu\)) and Gibbs free energy (\(\Delta G\)) at various temperatures under a pressure of 12 MPa. investigated. The calculation results are shown in Table 4, and the trend is illustrated in Figure 12. The red curve reflects the trend of Gibbs free energy changes within a pressure range of 2 MPa to 16 MPa, showing that as the pressure increases, the negative value of \(\Delta\)G decreases from about \(-\)113 kJ/mol to \(-\)118 kJ/mol, clearly indicating that the spontaneity of the adsorption process increases with pressure. The blue curve displays how the chemical potential \(\mu\) changes with pressure, and it can be clearly seen that the chemical potential rises gradually from 8 kJ/mol to about 12 kJ/mol, suggesting that as the pressure increases, the tendency of hydrogen molecules to adsorb on the steel surface also gradually strengthens.