Aspects of dynamics in proton exchange membrane water electrolysis

authored by

Tobias Krenz

supervised by

Richard Hanke-Rauschenbach

Abstract

Green hydrogen, produced from renewable energy sources through water electrolysis, is expected to play a significant role in the decarbonization of society. For its production, Proton Exchange Membrane Water Electrolysis (PEMWE) offers great potential due to its capability for volatile operation, which aligns well with the fluctuating energy provided by renewable sources such as wind and solar. Although PEMWE systems can operate under volatile load profiles, the dynamics of these systems are not yet fully understood. Hence, this work investigates some key phenomena at play in PEMWE stacks and individual cells, excluding long-term degradation. The time constants of the underlying processes range from milliseconds to weeks. A deeper understanding of the underlying processes enables a more efficient utilization, avoidance of harmful operating modes, and better assessment of the system's State of Health (SoH). The fastest dynamics examined in this work pertain to proton transport (time constant τ ≤ 1 ms) within the PEM and the discharge of the double-layer at the catalyst layer (50 ms < τ < 10 s). A better understanding of these processes provides insights into the characteristics of a PEMWE cell. Typically, these characteristics are assessed in a laboratory setting, which permits the use of additional equipment and designated operating schemes. Transferring the techniques used for the characterization to industrial applications presents multiple challenges that could be mitigated by an enhanced understanding of the dynamics at play. Additionally, the dynamics of temperature, as well as its coupling with the cell's polarization behavior, are examined. Concentration dynamics are closely linked to cell design, while temperature dynamics are dominated by the stack's peripheral equipment. Typical time constants for concentration dynamics are τ ≈ 100 ms, and for temperature dynamics, τ ≈ 1 h. An analysis of the coupling of temperature dynamics with the overall performance of a PEMWE stack allows for the detection of potentially harmful operating modes and the development of optimized operating schemes. Finally, an analysis of the changes in catalyst activity is conducted. The anode potential influences the catalyst's activity. This can lead to an increase in activity at relatively low potentials (i.e., during shutdown) with fast dynamics (τ ≈ 5 s), and to slow passivation occurring during operation (τ > 5 d). Understanding this process is crucial for assessing a cell's SoH as well as basic cell characteristics and can be utilized to derive optimized operating schemes. The analyses conducted in this work provide insights into the key dynamics at play and support the further market penetration of PEMWE systems by enhancing the understanding of the systems, facilitating easier assessment of SoH metrics, and suggesting improved operating schemes.

Organisation(s)

Section Electrical Energy Storage Systems

Type

Doctoral thesis

No. of pages

132

Publication date

26.03.2025

Publication status

Published

Sustainable Development Goals

SDG 7 - Affordable and Clean Energy

Electronic version(s)

https://doi.org/10.15488/18786 (Access: Open)