No abstract

During the past decades, a significant amount of excellent scientific results has been generated in the field of polymer electrolyte membrane water electrolysis (PEMWE). Compared to current state-of-the-art technologies, PEMWE offers the opportunity to produce green hydrogen with zero carbon emissions. However, the membrane electrode assembly (MEA), whose price is still high for a rather limited lifetime, needs further improvement in terms of performance, cost, and durability. In order to efficiently process novel materials, accelerated stress tests (ASTs) can be implemented to provoke and investigate cell ageing processes and assess failure modes under real-life conditions. In this review, the different accelerated stressors of the main components of the MEA are discussed, and recent publications of ASTs in the study of PEMWE cell durability are summarized. Furthermore, a concise review of the degradation mechanisms for the individual MEA components depicted in recent publications is presented. The different aspects identified in this review serve as a roadmap to further advance the durability of novel stack materials.

Polymer electrolyte membrane water electrolysis (PEMWE) is a leading candidate for the development of a sustainable hydrogen infrastructure. The heart of a PEMWE cell is represented by the membrane electrode assembly (MEA), which consists of a polymer electrolyte membrane (PEM) with catalyst layers (CLs), flow fields, and bipolar plates (BPPs). The weakest component of the system is the PEM, as it is prone to chemical and mechanical degradation. Membrane chemical degradation is associated with the formation of hydrogen peroxide due to the crossover of product gases (H2 and O2). In this paper, membrane failure due to H2 crossover was addressed in a membrane-focused accelerated stress test (AST). Asymmetric H2O and gas supply were applied to a test cell in OCV mode at two temperatures (60 °C and 80 °C). Electrochemical characterization at the beginning and at the end of testing revealed a 1.6-fold higher increase in the high-frequency resistance (HFR) at 80 °C. The hydrogen crossover was measured with a micro-GC, and the fluoride emission rate (FER) was monitored during the ASTs. A direct correlation between the FER and H2 crossover was identified, and accelerated membrane degradation at higher temperatures was detected.

A new method for measuring membrane degradation in polymer electrolyte fuel cells (PEFCs) is proposed. The method is based on the detection of fluoride ions in effluent water from the cathode- and anode outlet of the PEFC using photometry (PM). The fluoride emission rate (FER) is an indicator of the membrane’s state of health (SoH) and can be used to measure the chemical membrane degradation. Commercial catalyst-coated membranes (CCMs) have been tested at 80 °C and 90 °C at 30% relative humidity (RH) to investigate the reliability of the developed method for fuel cell effluent samples. To verify the measurement, a mean-difference plot was created by measuring the same data with a fluorine selective electrode. The average difference was at ±0.13 nmol h−1 cm−2, which indicates good agreement between the two methods. These new findings imply that PM is a promising method for quick and simple assessment of membrane degradation in PEM technology.

Reducing the high interfacial resistance across the cubic Li7La3Zr2O12 (LLZO) | poly(ethylene oxide) (PEO) interface in LLZO:PEO membranes is one of the key challenges to realize future solid-state lithium batteries.1,2 Recently, several groups presented various approaches to enhance the ionic charge transport across the interface.3,4 As an example, Gupta and Sakamoto showed that heat treatment to remove surface impurities and that an increase in the Li-salt concentration in PEO to match the chemical potential between LLZO and PEO lead to significantly lower interfacial resistance.3 Herein, we present an alternative but complimentary approach to improve the interfacial kinetics by an advance surface modification strategy. For this purpose, we activated the surface terminated oxygen of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particles by plasma etching and functionalized the activated oxygen by immersing the LLZTO particles in a (3-glycidyloxypropyl)trimethoxysilane solution to form covalently bonded self-assembled monolayers (SAMs). The SAMs are terminated by an epoxy group that react with the hydroxyl group of the PEO’s according to a ring-opening reaction. This reaction may lead to an ordered arrangement of covalently bonded PEO segments around the LLZO particles enabling the Li ions to easily cross the LLZTO | PEO interface. Indeed, we managed to lower the interfacial resistance by more than four orders of magnitude. Finally, with our approach we realized an area specific resistance of 500 Ω cm2 at 20 °C; to our knowledge, this value is the lowest one reported so far. Reference s : [1] J. Schwenzel, K. Kun, F. Langer in: R. Murugan, W. Weppner (Eds.), Solid Electrolytes, Springer, Swizerland, 2019, pp. 281–304. [2] X. Judez, G.G. Eshetu, C. Li, L.M. Rodriguez-Martinez, H. Zhang, M. Armand, Joule 2 (2018) 2208–2224. [3] A. Gupta, J. Sakamoto, Electrochem. Soc. Interface 28 (2019) 63–69. [4] Z. Huang, W. Pang, P. Liang, Z. Jin, N. Grundish, Y. Li, C.A. Wang, C.A., J. Mater. Chem. A, 7 (2019) 16425–16436.