Energy and exergy analysis of hydrogen production by a proton exchange membrane (PEM) electrolyzer plant

Hydrogen production by a proton exchange membrane (PEM) electrolyzer provides a promising way to store and better utilize the renewable energy resources. Presently, theoretical studies on PEM electrolyzer are still limited, impeding its technological development. Detailed thermodynamic analysis is valuable to identify the key losses and to optimise the performance of PEM electrolyzer plant for hydrogen production. In this study, energy and exergy analysis has been conducted to investigate the thermodynamic-electrochemical characteristics of hydrogen production by a PEM electrolyzer plant. One important feature of this model is that detailed electrochemical characteristics of the PEM electrolyzer are fully incorporated into the thermodynamic analysis. Heat production in the PEM cell due to irreversible losses has been investigated and compared with the thermal energy demand of PEM cell. It is found that a PEM electrolyzer normally operates in an exothermic mode as the heat production due to overpotentials exceeds the thermal energy demand. As the electrical energy input dominates the overall energy input, the exergy efficiency is found about the same as the energy efficiency. Parametric analyses have been performed to investigate the effect of important design and operating parameters on the plant energy conversion efficiency. This study has quantified how much the energy efficiency can decreases by increasing the operating temperature, lowering the current density, reducing the electrolyte thickness, and increasing the electrode catalytic activity. The analysis presented in this paper also offers better understanding of the characteristics of PEM electrolyzer plant for hydrogen production. With additional energy analysis of electricity generated from solar cells or wind turbines, the model presented in this paper is ready for complete energy/exergy analysis of advanced renewable electrolytic hydrogen production plants. © 2008 Elsevier Ltd. All rights reserved.