Electrical circuit modeling of proton exchange membrane electrolyzer: The state-of-the-art, current challenges, and recommendations

The integration of water electrolysis with renewable energy sources (RESs) constitutes a milestone in the transition to neutral and sustainable energy systems. The attractive features of the Proton Exchange Membrane (PEM) electrolyzer such as high purity of hydrogen, operation with high pressure, and high current densities have made it a critical technology to produce green hydrogen from RESs. Accurate models are required for proper design, analysis, and control of the electrolyzer when connected to the grid or renewable energy systems. Amongst the various types of models proposed for modeling the PEM electrolyzer, electrical circuit models are the easiest, most appealing, and straightforward to use for the investigation of electrolyzer operation and control. This paper presents an exhaustive review of the electrical circuit modeling reported in the literature on PEM electrolyzers. The reviewed models are classified analogously to the classifications of physical modeling in terms of voltage components (reversible, ohmic, activation, and concentration voltage drop), model behavior (static/dynamic), and modeling scale (cell/stack). Furthermore, MATLAB simulations of the reviewed models are implemented and the results are compared to pinpoint their similarities and deviations. Moreover, the applications, challenges, benefits, and drawbacks of the electrolyzer's electrical equivalent circuit modeling are discussed and overarching recommendations are set out for further research on the PEM electrolyzer modeling. The paper can be used as a comprehensive reference for choosing the appropriate electrical model of the electrolyzer for beginners as well as for research and industry experts who rely on PEM electrolyzer models in their work.