Characterizing Reversible and Irreversible Degradation Effects of PEM Water Electrolyzer Stacks

Abstract

Polymer electrolyte membrane water electrolyzers (PEMEL) have been identified as a key component in a decarbonized large-scale energy system, as they can produce high-purity hydrogen from renewable electricity sources for the chemical industry or energy storage. However, the long-term durability and performance of PEM electrolyzers remain a major challenge, with degradation being a critical factor that limits their lifespan and efficiency. Recent studies have focused on developing accelerated stress test (AST) protocols for PEM electrolyzers to better understand the conditions and mechanisms that lead to degradation.1, 2 Especially the reversible rise in cell potential, which in the literature is often regarded as apparent or reversible degradation, must be further investigated to find mitigation strategies for operation.3, 4 We present our research on the development of two testing protocols (static, dynamic) characterizing reversible and irreversible degradation effects for PEMEL stacks in different operation modes. Our aim is to gain a better understanding of the variance of these phenomena in general and the recovery of reversible effects across PEMEL stacks. The measurements are carried out on a commercialized Greenlight E400 test bench equipped with a 7kW 8 cell PEMEL stack (Hydrogen Innovation GmbH). The potential of all cells will be monitored during testing. The measurements include repeated electrochemical characterization protocols measuring i/E-curves, HFR and impedance spectroscopy (EIS) of the PEMEL stack and if possible, every single cell. These protocols include the introduction of low potential regeneration phases before every characterization during the test protocol to distinguish between reversible effects and the irreversible cell degradation. This was seen to be effective for potential recovery by Suermann et al. 2019 for single PEMEL cells.4 The results consist of a description of the two testing procedures and the used equipment. Due to the duration of each test protocol (3000 h) only results of the static test protocol can be presented.The contribution of the presented research is threefold. Firstly, we break down the degradation across a whole stack. Giving valuable insights regarding the distribution of cell efficiency and degradation effects. Secondly, the presented test protocols characterize and account for the reversible rise in cell/stack potential. Thirdly, the characterization of the recovery time of the cell potential across the stack will have implications for the operation of stacks to mitigate or recover these performance losses. We address both static and dynamic operation modes aiming to simulate the application of PEMEL stacks for a constant production of hydrogen used in downstream processes and the volatile operation due to a direct coupling with renewable energy sources.This publication is to be seen as presentation of first results in our ongoing research to find test protocols for short stack systems to develop operation strategies, which can be applied to large scale electrolyzer systems. Furthermore, we try to deepen the understanding of the reversible cell potential rise as well as standardize the general testing of PEMEL stacks.This work is funded by the Federal Ministry of Education and Research (BMBF) in the project “hyBit” under the grant 03SF0687E. The authors declare that the opinions expressed in this submission are their own and are based on a thorough review of existing scientific literature. Sources 1. G. Tsotridis and A. Pilenga, EU harmonized protocols for testing of low temperature water electrolysis, Publications Office of the European Union, Luxembourg (2021). 2. A. Voronova, H.-J. Kim, J. H. Jang, H.-Y. Park and B. Seo, International Journal of Energy Research, 46 (2022) 11867. 3. C. Rakousky, U. Reimer, K. Wippermann, S. Kuhri, M. Carmo, W. Lueke and D. Stolten, Journal of Power Sources, 342 (2017) 38. 4. M. Suermann, B. Bensmann and R. Hanke-Rauschenbach, Journal of The Electrochemical Society, 166 (2019) F645-F652.