<p lang="en-US">&nbsp;&nbsp;Hydrogen production through electrolysis is an important research topic since the use of hydrogen as a fuel has the potential to significantly reduce gaseous emissions in near future. It is expected then that the environmental and economic benefits that the use of hydrogen will bring to the world will be significant as well. Hydrogen can be produced in different ways including electrolysis. The electrolytic splitting of water into hydrogen and oxygen can be carried out using for instance electricity generated from renewable energy sources such as solar radiation. Electrolysis processes occurring in electrolyzer cells are complex phenomena and a clear and accurate mathematical representation of the referred processes is important in order to understand its functioning and the parameters affecting it. In this work a comprehensive mathematical model capable of properly describing the performance of alkaline electrolyzer cells, in terms of efficiency and hydrogen production rate, is proposed. The mathematical model is based on several physical concepts such as energy losses due to electron and ion transfer, entropy increase, electrolyte flow rate, and electrolyzer physical structure and construction material. The proposed mathematical model has been fine-tuned based on experimental data available in the open literature. Notice that fine-tuning processes are required in order to ensure accurate predictions related to cell voltage, hydrogen production, and overall efficiency. Fine-tuning is required here because, for instance, the difference in cell voltage for the same current density is basically due to over-voltages, which are current, temperature, and pressure-dependent. In particular, the cell reversible voltage decreases as temperature increases, whereas it increases when pressure do so. Even though these changes are not so big they need to be incorporated into a physics-based mathematical model. The same is true for the electrolyte flow rate.</p><p lang="en-US">In the past, many authors have studied and developed mathematical models for electrolyzers key parameters such as cell voltage, Faraday’s efficiency (or current efficiency as it is also referred to), and cell overall efficiency. After doing an extensive literature review, it has been decided to initially study in detail three well-known models, the ones by Ulleberg (2003), Ernesto et al. (2017), and Maximilian et al. (2016). The outcomes from such models have been next employed to develop the physical principles-based mathematical model proposed in this work. When studying the referred previous models, some inconsistencies in the predicted values and the associated comparisons with the experimental data carried out were detected, which are most probably due to typing errors or misreported data by the original authors. A commercial software was used to develop various self-written scripts that were next employed to check and verify existing models. Whenever it was necessary handwritten calculations were carried out to verify script calculations and spot the potential errors. Finally, results obtained using the proposed physics-based mathematical model were compared to others reported in the literature, and conclusions were made. Based on the carried out work, it is concluded that developing a mathematical model based on physical principles is crucial in the comprehension of electrolysis processes and how to utilize them in the simplest and most reliable way.</p>

A Mathematical Model to Predict Alkaline Electrolyzer Performance Based on Basic Physical Principles and Previous Models Reported in Literature

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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