Optimizing temperature and pressure in PEM electrolyzers: A model-based approach to enhanced efficiency in integrated energy systems

Abstract

Hydrogen stands as a promising energy carrier within the ongoing energy supply transformation, yet its production via electrolyzers remains prohibitively costly. To address this challenge, this paper proposes an advanced equation-oriented process model for a PEM (Polymer-Electrolyte-Membrane) electrolysis system, including the electrolyzer and downstream hydrogen compression, aimed at optimizing the interaction of its operating parameters (i.e., current density, temperature, pressure). Initially, the model is utilized to analyze the isolated performance of the electrolysis system through operational flowsheet optimizations, followed by its integration into a broader energy system for operational planning optimization.

The study reveals several key findings: optimizing operational parameters, rather than using fixed values at the maximum, improves peak system efficiency by approximately 5 %pt. and shifts this peak to lower current densities, thus expanding the range of high-efficiency operation. Each current density has an optimal pair of temperature and pressure, with maximum temperatures only advantageous at loads above 40%, while maximum operating pressure is suboptimal across the entire load range. The analysis indicates that incorporating operating parameter optimization within the operational planning of the electrolysis system reduces energy consumption by 4% and operating costs by 7% in the evaluated energy system.

Additionally, the study distinguishes between optimizing the electrolyzer’s operating parameters for maximizing its own efficiency and for system efficiency (i.e., including hydrogen compression). It demonstrates that maximum system efficiency is achievable only when the electrolyzer considers hydrogen compression in its operation mode, accepting some efficiency losses individually but yielding greater efficiency gains in the context of hydrogen compression.

In summary, the findings of this paper suggest that continuously operating a PEM electrolyzer at maximum temperature and pressure may not be the most efficient approach. Instead, dynamic adjustments based on current density improve operational efficiency, thereby reducing electricity consumption and operating costs. Evaluating the electrolyzer within the broader energy system context – and accepting minor efficiency losses at the electrolyzer level – can yield significant overall benefits and savings. These results underscore the importance of comprehensive, context-aware strategies in advancing cost-effective green hydrogen production.