Electrode Separators for the Next-Generation Alkaline Water Electrolyzers

Abstract

Multi-gigawatt-scale hydrogen production by water electrolysis is central in the green transition when it comes to storage of energy and forming the basis for sustainable fuels and materials. Alkaline water electrolysis plays a key role in this context, as the scale of implementation is not limited by the availability of scarce and expensive raw materials. Even though it is a mature technology, the new technological context of the renewable energy system demands more from the systems in terms of higher energy efficiency, enhanced rate capability, as well as dynamic, part-load, and differential pressure operation capability. New electrode separators that can support high currents at small ohmic losses, while effectively suppressing gas crossover, are essential to achieving this. This Focus Review compares the three main development paths that are currently being pursued in the field with the aim to identify the advantages and drawbacks of the different approaches in order to illuminate rational ways forward.

Quaternary Ammonium‐Free Membranes for Water Electrolysis with 1 m KOH

“…Then KOH was removed by immersion in water until the pH remained neutral, and the membranes were again dried at 80°C in the vacuum, giving w dedoped . The weight frac- The total uptake, KOH uptake, water uptake and the concentration of the absorbed KOH solution were calculated according to Equations (5)(6)(7)(8) (8) Dimensional changes during doping were analyzed by measuring the length and thickness of the pristine membranes after washing with water to remove residual solvents and drying at 80 °C (initial dimension 𝑑 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 ) and the KOH doped membrane (d 𝐾𝑂𝐻 𝑑𝑜𝑝𝑒𝑑 ). Swelling values were calculated according to Equation (9).…”

“…The drawback is the low alkaline stability of the membranes, which suffer from attack on the polymer backbone (if aromatic ether groups are present), and degradation of the quaternary ammonium groups, which are essential for the ion-conducting properties of the membranes, by nucleophilic substitution and Hofmann elimination. [6] While the initial ambition for AEMWE was to operate with pure water, operation with, e.g., 1 m KOH has the advantages of lower H 2 crossover (because solubility of H 2 decreases with increasing KOH concentration) [8] and improved electrode performance, because ionomer binders are not needed for hydroxide transport. [9] An alternative technology recently investigated is the use of ion-solvating membranes.…”

Opportunities of Ionomer Development for Anion-Exchange Membrane Water Electrolysis

“…Concurrent with the increase in membrane stability in alkaline media, there has also been a significant increase in membrane conductivity, enabling the commercialization of a wide variety of AEMs such as Fumasep FAA-3 (Fumatech), A201 (Tokuyama), Aemion (Ionomr Innovations), Sustainion (Dioxide Materials), Orion TM1 (Orion Polymer), and PiperION (Versogen). , Advances in membrane technology have also been supported by the increasing development of non-noble metal HER − and OER catalysts, − culminating in the rapid advancement of anion-exchange membrane water electrolysis (AEM-WE), for which excellent reviews are available. ,− The beginning of life performance (BOL) of AEM-WE systems is comparable to that of PEM-WE but at a fraction of the cost of materials. It is estimated that the investment cost for a 1 MW AEM-WE stack is 42% lower than that of a PEM-WE (Figure c)…”

In Situ Reactivating Perovskite Oxide Catalysts in Alkaline Water Electrolyzers: A Generalized Approach Based on Selective Cation Leaching

“…Electrocatalytic water splitting, which involves the production of hydrogen and oxygen at the electrodes, is an effective approach for renewable energy storage and offsetting carbon footprint. − Among various technologies, alkaline water electrolyzers are of particular interest due to their high cost-effectiveness and excellent stability. − Yet, the sluggish oxygen evolution reaction (OER) at the anode often causes high polarization losses, resulting in the low-current-density operation. Conventionally, OER proceeds via the adsorbate evolution mechanism (AEM), − forming several adsorbed oxygen-containing intermediates on the active centers.…”