Realizing Superior Durability of Water Electrolyzer Using Anion Exchange Membrane with an Interstitial Alkyl Chain : From a Single Cell to Large-Sized 1-Cell Stack
Authors: Lim Haeryang , Jeong Jae-Yeop , Choi Sung Mook , Park Taiho 
Published: December 2024

As the growing utilization of renewable energy continues to grow to address energy and environmental challenges, grid-scale electricity storage technologies are becoming more important. As such, hydrogen has attracted interest over the past few years as an energy carrier for sustainable energy systems. Therefore, water electrolysis is a viable method to mass- produce green hydrogen and can be combined with renewable power generation technologies.

The main commercial electrolysis systems currently used to produce hydrogen on a large-scale are alkaline water electrolysis (AWE) and proton exchange membrane water electrolysis (PEMWE). AWE technology has a low hydrogen production rate, typically less than 200 mA cm−2 at a cell voltage of 1.8 V and with an energy efficiency of 75%. Additionally, PEMWE technology suffers from a high unit cost of hydrogen because of the use of platinum group metal (PGM) electrocatalysts and anode plates.Therefore, anion exchange membrane water electrolysis (AEMWE), which can ensure high efficiency and low cost, is considered a promising systems for overcoming the shortcomings of AWE and PEMWE.

However, current AEMWE technology has struggled to be commercialized because of poor cell performance and durability, which are directly affected by the membrane electrode assembly (MEA) components. These consist of anion exchange membranes (AEMs), catalyst layers (CLs), and porous transport layers (PTLs). Among the MEA components, AEMs generally have unsatisfactory ionic conductivity, mechanical properties, and alkaline stability, which are directly related to cell performance and durability. These factors limit the widespread implementation of AEMWE.

The state-of-the-art cell performance of AEMWEs has advanced dramatically over the past few years and is striving to catch up with the state-of-the-art current density of PEMWEs using a supporting electrolyte (i.e., 1 M KOH). However, the long-term durability of AEMWEs is approximately 10 times lower than that of PEMWEs, which typically operate for 40,000 h; therefore the lifetime of the AEM is currently holding back this technology. When considering only the chemical degradation of an AEM in an alkaline environment (the typical AEMWE operating condition), it can last for more than 1 year. Instead, the factors associated with the durability of AEMWEs are closely related to the alkaline stability of the AEMs as well as the interaction of each component layer, including the ionomer-membrane layer, ionomer-catalyst layer, and ionomer-PTL during cell operation.

The contact properties of ionomer-membrane surfaces are largely determined by the number of contact bonds formed by the surface molecular groups across the interface and the entanglement of the surface segments. Therefore, in the present study, we newly designed aryl ether-free PFPBPF-QA AEMs with interstitial alkyl chains in the conducting groups and a polymer backbone.

The rationally designed PFPBPF-4-QA not only demonstrated excellent mechanical properties, high alkaline stability and satisfactory hydroxide conductivity, but also improved the contact properties of the Nafion ionomer to ensure excellent durability of the AEMWE. An AEMWE single cell using PFPBPF-4-QA demonstrated superior durability with a voltage decay rate of 2 mV kh−1 at an industrially relevant current density of 1.0 A cm−2. We also demonstrated the commercial viability of PFPBPF-4-QA by evaluating the durability of a large-sized (63.6 cm2 active area) AEMWE 1-cell stack with an energy conversion efficiency (ECE) of 80.2% and voltage decay rate of 1.5 mV kh−1, which is expected to operate for more than 49,095 h based on an initial efficiency of 95%.