Ordered Membrane Electrode Assembly with Drastically Enhanced Proton and Mass Transport for Proton Exchange Membrane Water Electrolysis

Abstract

In this work, an ordered membrane electrode assembly (MEA) based on a cone Nafion array with gradient Nafion distribution, tightly bonded catalytic layer/proton exchange membrane (CL/PEM) interface, and abundant vertical channels has been engineered by an anodic aluminum oxide template and magnetron sputtering method. Benefiting from a highly efficient CL/PEM interface, plentiful proton transfer highways, and rapid oxygen bubble release, this ordered MEA achieves an ultralow Ir loading of 20.0 μg cm −2 and a high electrochemical active area by 8.7 times compared to traditional MEA with Ir loading of 1.0 mg cm −2 . It yields a mass activity of 168 000 mA mg Ir −1 cm −2 at 2.0 V, which is superior to most reported PEM electrolyzers. Notably, this ordered MEA maintains excellent durability at a current density of 500 mA cm −2 . This work opens a simple, cost-effective, and scalable route to design ordered MEAs for proton exchange membrane water electrolysis.

Anode Engineering for Proton Exchange Membrane Water Electrolyzers

“…To construct a 3D PEM/CL interface, another approach is to directly fabricate PEM with a patterned surface. Tian et al built a layer of ordered cone-like Nafion array on top of commercial Nafion 115 membrane utilizing an anodic aluminum oxide (AAO) template and sputtered Ir of 20 μg cm –2 on top of the cone structure (Figure b) . The dense layer of sputtered Ir on the enlarged PEM surface enabled effective proton transfer and durable PEM/CL interfacial contact (Figure c), yielding extremely high mass activity of 168 A mg Ir –1 cm –2 at 2.0 V that is superior than most of the reported values.…”

“…(d) EIS comparison of MEA with various Nafion array morphology. Reproduced with permission from ref . Copyright 2023 American Chemical Society.…”

Recent advances and perspectives of Ir-based anode catalysts in PEM water electrolysis

“…42–44 Among them, an ideal PEM should have excellent proton conductivity, low expansion ratio, low gas permeability, low cost, and good durability. 45 Currently, the most commonly used commercial PEMs are perfluorosulfonic acid polymer membranes, mainly including Nafion, Aciplex, and Flemion. 42–44 Among them, Nafion series PEMs (such as Nafion 117, 115, and 112, where the numbers representing different equivalent weights and thicknesses) have good chemical and mechanical stability at high current densities and are considered to be the most representative PEMs.…”

Bubble Engineering on Micro-/Nanostructured Electrodes for Water Splitting

“…Electrochemical gas evolution reactions (GERs) are pivotal in energy conversions and chemical industries, such as water electrolysis, chlor-alkali, and hydrazine oxidation reactions. − To increase the efficiency of these processes, tremendous efforts have been devoted to developing catalysts with high intrinsic activity to promote performance, including electronic structures, defect engineering, spatial confinement, and coordination environments; ,− structural manipulation accuracy has also been developed from nanocrystals to clusters and single-atom catalysts. , Also, the metal–organic frameworks (MOFs) and MOF-based composites have recently displayed great potential in electrocatalysis, not only as the intrinsic catalyst but also as the support, owing to their inherent physical/chemical properties and the interaction with reaction substrates/intermediates. − These efforts have greatly improved the sluggish intrinsic kinetics of the aforementioned reactions. In contrast, mass transfer in GERs, which has played key roles apart from the catalyst screening in such typical multiphase systems, was overlooked for a long time, but only got recognized in the last ten years. ,− The gas bubble adhesion on the electrode surface would induce a series of problems, e.g., undesired blockage of electrolyte diffusion, and consequent energy losses. Generally, three high-speed pathways are required for electrons, ions, and gas diffusion.…”