Coupling Thermodynamics and Electrochemistry in Aspen Plus: A Framework for Alkaline Water Electrolysis Systems

The global energy transition has positioned hydrogen as a central energy carrier for the decarbonization of industrial and power systems. As supply chains become increasingly complex in the pursuit of net-zero emissions, the ability to analyze and predict system behavior through simulation becomes essential. Digital representations of energy processes allow researchers to identify inefficiencies and anticipate unintended consequences before implementation. In this context, rigorous process simulation emerges not only as a predictive tool but also as a foundation for designing, optimizing, and validating sustainable hydrogen production routes.

 This study focused on validating the vapor–liquid equilibrium (VLE) description required to simulate an alkaline water electrolysis (AWE) plant with high predictive reliability. The gamma–phi approach was adopted, using the E-NRTL model for the liquid phase and the Redlich–Kwong equation of state for the vapor phase. The methodology employed allows for reproducing the polarization curve, including activation, ohmic, and concentration overpotentials, in accordance with the electrochemical formulations.

 Model predictions were compared with experimental data from HRI and PHOEBUS electrolyzers, and the results showed a maximum deviation of  6%. This agreement demonstrates that the adopted VLE framework offers strong predictive capability for alkaline electrolysis systems, providing a reliable tool for process optimization studies and large-scale green hydrogen system assessments.