Anion Exchange Membrane Water Research Articles

Microporous Electrode Binders for Anion Exchange Membrane Water Electrolyzers.

In anion exchange membrane (AEM) water electrolyzers, AEMs separate hydrogen and oxygen, but should efficiently transport hydroxide ions. In the electrodes, catalyst nanoparticles are mechanically bonded to the porous transport layer or membrane by a polymeric binder. Since these binders form a thin layer on the catalyst particles, they should not only transport hydroxide ions and water to the catalyst particles, but should also transport the nascating gases away. In the worst case, if formation of gases is >> than gas transport, a gas pocket between catalyst surface and the binder may form and hinder access to reactants (hydroxide ions, water). In this work, the ion conductive binder SEBS-DABCO is blended with PIM-1, a highly permeable polymer of intrinsic microporosity. With increasing amount of PIM-1 in the blends, the permeability for water (selected to represent small molecules) increases. Simultaneously, swelling and conductivity decrease, due to the increased hydrophobicity. Ex situ data and electrochemical data indicate that blends with 50% PIM-1 have better properties than blends with 25% or 75% PIM-1, and tests in the electrolyzer confirm an improved performance when the SEBS-DABCO binder contains 50% PIM-1.

Thermal Shock Synthesis for Loading Sub-2nm Ru nanoclusters on Titanium Nitride as a Remarkable Electrocatalyst towards Hydrogen Evolution Reaction.

Heterogeneous catalysts embracing metal entities on suitable supports are profound in catalyzing various chemical reactions, and substantial synthetic endeavors in metal-support interaction modulation have been made to enhance catalytic performance. Here, it is reported the loading of sub-2nm Ru nanocrystals (NCs) on titanium nitride support (HTS-Ru-NCs/TiN) via a special Ru-Ti interaction using high temperature shock (HTS) method. Direct dechlorination of the adsorbed RuCl3, ultrafast nucleation process and short coalescence duration at ultrahigh temperatures contribute to the immobilization of Ru NCs on TiN support via producing the Ru-Ti interfacial perimeter. HTS-Ru-NCs/TiN shows remarkable activity towards hydrogen evolution reaction (HER) in alkaline solution, yielding ultralow overpotentials of 16.3 and 86.6mV to achieve 10 and 100mAcm-2, respectively. The alkaline and anion exchange membrane water electrolyzers assembled using HTS-Ru-NCs/TiN yield 1.0Acm-2 at 1.65 and 1.67V, respectively, which validate its applicability in hydrogen production industry. Theoretical simulations reveal the favorable formation of Ru-O and Ti-H bond at the interfacial perimeters between Ru NCs and TiN, which accelerates the prerequisite water dissociation kinetics for the enhanced HER activity. This exemplified work motivates the design of specific interfacial perimeters via the HTS strategy to improve the performance of diverse catalysis. This article is protected by copyright. All rights reserved.

Efficient and durable seawater electrolysis with a V2O3-protected catalyst.

The ocean, a vast hydrogen reservoir, holds potential for sustainable energy and water development. Developing high-performance electrocatalysts for hydrogen production under harsh seawater conditions is challenging. Here, we propose incorporating a protective V2O3 layer to modulate the microcatalytic environment and create in situ dual-active sites consisting of low-loaded Pt and Ni3N. This catalyst demonstrates an ultralow overpotential of 80 mV at 500 mA cm-2, a mass activity 30.86 times higher than Pt-C and maintains at least 500 hours in seawater. Moreover, the assembled anion exchange membrane water electrolyzers (AEMWE) demonstrate superior activity and durability even under demanding industrial conditions. In situ localized pH analysis elucidates the microcatalytic environmental regulation mechanism of the V2O3 layer. Its role as a Lewis acid layer enables the sequestration of excess OH- ions, mitigate Cl- corrosion, and alkaline earth salt precipitation. Our catalyst protection strategy by using V2O3 presents a promising and cost-effective approach for large-scale sustainable green hydrogen production.

Enhancing the physicochemical properties of nickel cobaltite catalyst for oxygen evolution reaction in anion exchange membrane water electrolyzers

Enhancing the physicochemical properties of nickel cobaltite catalyst for oxygen evolution reaction in anion exchange membrane water electrolyzers

Anisotropic polyphenylene-based anion-exchange membranes with flexible side-chains via click reaction for high-performance water electrolysis

Anion-exchange membrane water electrolysis (AEMWE) represents a promising and cost-effective electrochemical energy conversion system for green hydrogen production owing to its utilization of earth-abundant metals for various cell components (catalysts, porous transport layers, bipolar plates) and the zero-gap design. However, the lack of high-performance anion-exchange membranes (AEMs) has hampered the advancement of AEMWE technology. Here, by using colon coupling and click reactions, the ether-free polyphenylene-based AEMs (QPPBTF-TMA-w) with flexible side-chains containing triazole linkers. The QPPBTF-TMA-w membranes stand out for their lower activation energy for hydroxide conduction which is attributed to the well-structured ion-conducting channels via distinct phase separation facilitated by the triazole linker, which optimizes hydrophilicity and ensures efficient ion transport within the membrane. In addition, the QPPBTF-TMA-w membranes exhibit unique anisotropic swelling and ion-conduction behaviors, such as lower in-plane swelling and higher through-plane conductivity, which are advantageous for practical cell applications. Therefore, despite having a modest ion exchange capacity (IEC) value of 2.0, the QPPBTF-TMA-w membrane delivers high-performance in anion-exchange membrane water electrolysis (AEMWE), achieving 6.4 A/cm2 at 2.0 V at 70 °C using a 1.0 M KOH solution.

Non-precious high entropy alloys and highly alkali-resistant composite membranes based high performance anion exchange membrane water electrolyzers

Cost-effective highly efficient and stable catalysts and alkali-resistant anion exchange membranes (AEMs) are critical for practical applications of anion exchange membrane water electrolyzers (AEMWEs). Here, bifunctional non-precious FeCoNiCuMo high entropy alloys (HEAs), electrochemically deposited on nickel mesh as an anode (FeCoNiCuMo/NM) and on carbon paper as a cathode (FeCoNiCuMo/CP), together with a NiFe layered double hydroxide (LDH) loaded AEM (AEM/LDH), were developed for high performance AEMWEs. The AEMWE thus fabricated delivered an ultrahigh current density of 1777 mA cm−2 at 2 V and exhibited remarkable stability with a less than 0.1% cell voltage increase after a 100-hour operation at 100 mA cm−2 at 50 °C, largely outperforming those of the precious metal based AEMWE, composed of IrO2/NM as the anode and Pt/C/CP as the cathode, 1231 mA cm−2@2 V and 4.57% increase in cell voltages. Composition of the alkali-resistant, hydrophilic, and water electrolysis active NiFe LDH into the AEM improved not only the electrolyte uptake and operational stability, but also the efficiency of the AEMWE, with a 10% boost in current density achieved at 2 V and a reduction in cell voltage increases from 2.94% to 0.0951%. The present development demonstrates the practicality of AEMWEs toward green hydrogen production.

Shock-endurable and reversible evolution between CoOOH and intermediate governed by interfacial strain for fluctuating oxygen evolution

Transition metal oxide usually suffers from reconstruction into metal oxyhydroxide during oxygen evolution reaction (OER), while irreversible evolution between metal oxyhydroxides and intermediate species cannot agilely response to the fluctuating power of renewable energy. Herein, an individual CoMoxO4 phase with a tunable Co/Mo stoichiometry is reconstructed into CoOOH skin as active material for OER. Compressive strain induced by CoMo1.14O4/CoOOH interface, downshifting the d-band center of CoOOH, is an effective strategy to not only accelerate the sluggish kinetics of OER, but also enable inspiring the expeditious evolution and the reversibility between CoOOH and intermediate species. The reversibility is an applicable demand for OER in case of fluctuating potential. Reaction current on CoMo1.14O4 at constant potential is demonstrated by the lower fluctuation of 1.7 %, relative to 13.8 % in CoMoO4 after 12 cycles. Meanwhile, an anion exchange membrane water splitting electrolyzer made of CoMo1.14O4 anode can endure current shock of 50 ∼ 800 mA cm−2 in 0.2 s, which has negligible decay at 800 mA cm−2 after 9 shocks. Designing strategy of interfacial strain modulated by stoichiometry can be universally extended into the other oxide electrocatalysts including NiMoO4 and their derivatives.

Mn-doped Sequentially Electrodeposited Co-based Oxygen Evolution Catalyst for Efficient Anion Exchange Membrane Water Electrolysis.

Designing high-performance and durable oxygen evolution reaction (OER) catalysts is important for green hydrogen production through anion exchange membrane water electrolysis (AEMWE). Herein, a series of Mn-doped Co-based OER catalysts supported on FeOxHy (FCMx) are presented to enhance the OER activity. Mn doping effectively reduces the size of the Co oxide particles, thereby augmenting the active surface area. Moreover, Mn doping induces the creation of oxygen vacancies, leading to an efficient structural conversion during the OER, which is confirmed via in situ Raman spectroscopy. Under optimal conditions, the catalyst exhibits an overpotential of 234.4 mV at 10 mA cm-2 and a Tafel slope of 37.2 mV dec-1 under half-cell conditions. The AEMWE single-cell system demonstrates a current density of 1560 mA cm-2 at 1.8 V at 60 °C with a degradation rate of 0.4 mV h-1 for 500 h at 500 mA cm-2. Our development of a robust OER catalyst represents notable progress in the field of nonprecious-metal water electrolysis, marking a step toward cost-effective green hydrogen production.

Synergistic Effects in LaNiO3 Perovskites between Nickel and Iron Heterostructures for Improving Durability in Oxygen Evolution Reaction for AEMWE.

Perovskite materials that aren't stable during the oxygen evolution reaction (OER) are unsuitable for anion-exchange membrane water electrolyzers (AEMWE). But through manipulating their electronic structures, their performance can further increase. Among the first-row transition metals, nickel and iron are widely recognized as prominent electrocatalysts; thus, the researchers are looking into how combining them can improve the OER. Recent research has actively explored the design and study of heterostructures in this field, showcasing the dynamic exploration of innovative catalyst configurations. In this study, a heterostructure is used to manipulate the electronic structure of LaNiO3 (LNO) to improve both OER properties and durability. Through adsorbing iron onto the LNO (LNO@Fe) as γ iron oxyhydroxide (γ-FeOOH), the binding energy of nickel in the LNO exhibited negative shifts, inferring nickel movement toward the metallic state. Consequently, the electrochemical properties of LNO@Fe are further improved. LNO@Fe showed excellent performance (1.98Acm-2, 1m KOH, 50°C at 1.85V) with 84.1% cell efficiency in AEMWE single cells, demonstrating great improvement relative to LNO. The degradation for the 850h durability analysis of LNO@Fe is ≈68mVkh-1, which is ≈58 times less than that of LNO.

Highly efficient anion exchange membrane water electrolyzers via chromium-doped amorphous electrocatalysts

In-depth comprehension and modulation of the electronic structure of the active metal sites is crucial to enhance their intrinsic activity of electrocatalytic oxygen evolution reaction (OER) toward anion exchange membrane water electrolyzers (AEMWEs). Here, we elaborate a series of amorphous metal oxide catalysts (FeCrOx, CoCrOx and NiCrOx) with high performance AEMWEs by high-valent chromium dopant. We discover that the positive effect of the transition from low to high valence of the Co site on the adsorption energy of the intermediate and the lower oxidation barrier is the key factor for its increased activity by synchrotron radiation in-situ techniques. Particularly, the CoCrOx anode catalyst achieves the high current density of 1.5 A cm−2 at 2.1 V and maintains for over 120 h with attenuation less than 4.9 mV h−1 in AEMWE testing. Such exceptional performance demonstrates a promising prospect for industrial application and providing general guidelines for the design of high-efficiency AEMWEs systems.

Short-time potentiostatic assisted borate to induce the generation of ultrathin NiFe LDH active phase for industrial-level water oxidation

Self-supported NiFe-based oxygen evolution reaction (OER) catalysts with high activity and durability are essential for the industrialization of green hydrogen. Herein, Boron-interfered NiFe LDH nanosheets (B2-NiFe-(a-10)) with abundant wrinkle structure are prepared by introducing nonmetallic sources into the surface reconstruction of layered double hydroxide (NiFe LDH) through a novel short-time potential constant activation strategy. It enhances interactions with the electrolyte, decreases Arrhenius activation energy (Ea), accelerates efficient charge transfer and O2 escape rate. The as-reconstructed B2-NiFe-(a-10) exhibits outstanding alkaline OER activity with an ultralow overpotential of 290 mV at 100 mA cm−2 and excellent durability (100 h). Additionally, density functional theory calculations further reveal that the interaction optimizes the adsorption of oxygenated intermediates (*OH→*O), induces the center of the d-band toward the Fermi energy level, and lowers the dissociation barrier of H2O. Moreover, the anion-exchange membrane water electrolyzer (AEMWE) achieves a current density of 1 A cm−2 at 1.97 V.

A Review of Membrane Electrode Assemblies for the Anion Exchange Membrane Water Electrolyser: Perspective on Activity and Stability

A Review of Membrane Electrode Assemblies for the Anion Exchange Membrane Water Electrolyser: Perspective on Activity and Stability

Practical operating flexibility of a bifunctional freestanding membrane for efficient anion exchange membrane water electrolysis across all current ranges

AbstractThis study explores a symmetric configuration approach in anion exchange membrane (AEM) water electrolysis, focusing on overcoming adaptability challenges in dynamic conditions. Here, a rapid and mild synthesis technique for fabricating fibrous membrane‐type catalyst electrodes is developed. Our method leverages the contrasting oxidation states between the sulfur‐doped NiFe(OH)2 shell and the metallic Ni core, as revealed by electron energy loss spectroscopy. Theoretical evaluations confirm that the S–NiFe(OH)2 active sites optimize free energy for alkaline water electrolysis intermediates. This technique bypasses traditional energy‐intensive processes, achieving superior bifunctional activity beyond current benchmarks. The symmetric AEM water electrolyzer demonstrates a current density of 2 A cm−2 at 1.78 V at 60°C in 1 M KOH electrolyte and also sustains ampere‐scale water electrolysis below 2.0 V for 140 h even in ambient conditions. These results highlight the system's operational flexibility and structural stability, marking a significant advancement in AEM water electrolysis technology.

In Situ Electrochemical Rapid Induction of Highly Active γ-NiOOH Species for Industrial Anion Exchange Membrane Water Electrolyzer.

Limited by the strong oxidation environment and sluggish reconstruction process in oxygen evolution reaction (OER), designing rapid self-reconstruction with high activity and stability electrocatalysts is crucial to promoting anion exchange membrane (AEM) water electrolyzer. Herein, trace Fe/S-modified Ni oxyhydroxide (Fe/S-NiOOH/NF) nanowires are constructed via a simple in situ electrochemical oxidation strategy based on precipitation-dissolution equilibrium. In situ characterization techniques reveal that the successful introduction of Fe and S leads to lattice disorder and boosts favorable hydroxyl capture, accelerating the formation of highly active γ-NiOOH. The Density Functional Theory (DFT) calculations have also verified that the incorporation of Fe and S optimizes the electrons redistribution and the d-band center, decreasing the energy barrier of the rate-determining step (*O→*OOH). Benefited from the unique electronic structure and intermediate adsorption, the Fe/S-NiOOH/NF catalyst only requires the overpotential of 345 mV to reach the industrial current density of 1000mAcm-2 for 120 h. Meanwhile, assembled AEM water electrolyzer (Fe/S-NiOOH//Pt/C-60°C) can deliver 1000mAcm-2 at a cell voltage of 2.24V, operating at the average energy efficiency of 71% for 100 h. In summary, this work presents a rapid self-reconstruction strategy for high-performance AEM electrocatalysts for future hydrogen economy.

Optimizing the Dehydrogenation Kinetics of Metal Nitrides for Energy‐Efficient Seawater Hydrogen Production at 2 A cm−2

AbstractSeawater hydrogen production, vital for sustainable energy solutions and freshwater preservation, faces challenges due to seawater complexity and high energy consumption. A strategy to modulate dehydrogenation kinetics of dual‐phase metal nitrides using low‐loaded Pt quantum dots (QDs), achieving stable and energy‐efficient hydrogen generation is introduced. The Pt QDs@Ni3N‐MoN/Ti catalyst displays outstanding bifunctional seawater catalytic performance, enabling efficient hydrogen production and hydrazine degradation in a flow anion exchange membrane water electrolysis (AEMWE) device. Operating at a low voltage of 1.41 V, it achieves 2 A cm−2 for 300 h, circumventing chlorine corrosion and yielding record‐breaking energy equivalent input (2.68 kWh m−3 H2 at 1 A cm−2), a 47.1% reduction compared to traditional methods. Integration with solar and biomass energy facilitates self‐powered hybrid seawater hydrogen production, highlighting its potential applications. This work facilitates energy‐efficient marine resource conversion to green hydrogen and offers viable insights into industrial hazardous pollutant degradation using metal‐nitride electrocatalysts.

Functionalization of PTFE substrates with quaternary ammonium groups – An approach towards anion conducting properties

Hydrogen produced by electrolysis using renewable energy sources offers a zero-emission alternative to fossil-based sources providing high efficiencies in all energy sectors. Anion Exchange Membrane Water Electrolysis (AEM-WE) combines the advantages of the established technologies, alkaline (AEL) and proton exchange membrane (PEM) water electrolysis. However, AEM-WE still requires optimization, especially with regard to the membrane, catalysts and electrode structure. In this contribution we focus on the improvement of PTFE-based binders for AEM-WE membranes, which provide high chemical stability but lack the required ion conductivity. Thus, the functionalization of PTFE towards quaternary ammonium moieties (QAS) was investigated employing two approaches: (i) NH3-plasma treatment and (ii) O2-plasma with subsequent coupling of aminosilanes. Finally, the surface coupled amino groups were converted into QAS via alkylation with iodomethane (CH3-I), introducing ion conductivity. Successful functionalization was proved by X-ray photoelectron spectroscopy (XPS), displaying changes in the surface composition of PTFE surfaces such as the introduction of amino groups at the expense of fluorine, and the increase in surface carbon content upon alkylation. Furthermore, contact angle measurements revealed increased wettability with water due to the introduction of the polar surface functionalities, while zeta potential measurements confirmed the increase of positive surface charges along the modification processes.

Stable Anion Exchange Membrane Bearing Quinuclidinium for High‐performance Water Electrolysis

AbstractAnion exchange membranes (AEMs) are core components in anion exchange membrane water electrolyzers (AEM‐WEs). However, the stability of functional quaternary ammonium cations, especially under high temperatures and harsh alkaline conditions, seriously affects their performance and durability. Herein, we synthesized a 1‐methyl‐3,3‐diphenylquinuclidinium molecular building unit. Density functional theory (DFT) calculations and accelerated aging analysis indicated that the quinine ring structure was exceedingly stable, and the SN2 degradation mechanism dominated. Through acid‐catalyzed Friedel–Crafts polymerization, a series of branched poly(aryl‐quinuclidinium) (PAQ‐x) AEMs with controllable molecular weight and adjustable ion exchange capacity (IEC) were prepared. The stable quinine structure in PAQ‐x was verified and retained in the ex situ alkaline stability. Furthermore, the branched polymer structure reduces the swelling rate and water uptake to achieve a tradeoff between dimensional stability and ionic conductivity, significantly improving the membrane's overall performance. Importantly, PAQ‐5 was used in non‐noble metal‐based AEM‐WE, achieving a high current density of 8 A cm−2 at 2 V and excellent stability over 2446 h in a gradient constant current test. Based on the excellent alkaline stability of this diaryl‐quinuclidinium group, it can be further considered as a multifunctional building unit to create multi‐topological polymers for energy conversion devices used in alkaline environments.

Stable Anion Exchange Membrane Bearing Quinuclidinium for High-performance Water Electrolysis.

Anion exchange membranes (AEMs) are core components in anion exchange membrane water electrolyzers (AEM-WEs). However, the stability of functional quaternary ammonium cations, especially under high temperatures and harsh alkaline conditions, seriously affects their performance and durability. Herein, we synthesized a 1-methyl-3,3-diphenylquinuclidinium molecular building unit. Density functional theory (DFT) calculations and accelerated aging analysis indicated that the quinine ring structure was exceedingly stable, and the SN2 degradation mechanism dominated. Through acid-catalyzed Friedel-Crafts polymerization, a series of branched poly(aryl-quinuclidinium) (PAQ-x) AEMs with controllable molecular weight and adjustable ion exchange capacity (IEC) were prepared. The stable quinine structure in PAQ-x was verified and retained in the ex situ alkaline stability. Furthermore, the branched polymer structure reduces the swelling rate and water uptake to achieve a tradeoff between dimensional stability and ionic conductivity, significantly improving the membrane's overall performance. Importantly, PAQ-5 was used in non-noble metal-based AEM-WE, achieving a high current density of 8 A cm-2 at 2 V and excellent stability over 2446 h in a gradient constant current test. Based on the excellent alkaline stability of this diaryl-quinuclidinium group, it can be further considered as a multifunctional building unit to create multi-topological polymers for energy conversion devices used in alkaline environments.

Stabilization of Lattice Oxygen Evolution Reactions in Oxophilic Ce-Mediated Bi/BiCeO1.8H Electrocatalysts for Efficient Anion Exchange Membrane Water Electrolyzers.

The lattice oxygen mechanism (LOM) offers an efficient reaction pathway for oxygen evolution reactions (OERs) in energy storage and conversion systems. Owing to the involvement of active lattice oxygen enhancing electrochemical activity, addressing the structural and electrochemical stabilities of LOM materials is crucial. Herein, a heterostructure (Bi/BiCeO1.8H) containing abundant under-coordinated oxygen atoms having oxygen nonbonding states is synthesized by a simple electrochemical deposition method. Given the difference in reduction potentials between Bi and Ce, partially reduced Bi nanoparticles and surrounding under-coordinated oxygen atoms are generated in BiCeO1.8H. It is found that the lattice oxygen can be activated as a reactant of the OER when the valence state of Bi increases to Bi5+, leading to increased metal-oxygen covalency and that the oxophilic Ce3+/4+ redox couple can maintain the Bi nanoparticles and surrounding under-coordinated oxygen atoms by preventing over-oxidation of Bi. The anion exchange membrane water electrolyzer with Bi/BiCeO1.8H exhibits a low cell voltage of 1.79 V even at a high practical current density of 1.0 A cm-2. Furthermore, the cell performance remains significantly stable over 100 h with only a 2.2% increase in the initial cell voltage, demonstrating sustainable lattice oxygen redox.

Perovskite for Electrocatalytic Oxygen Evolution at Elevated Temperatures.

The development of advanced electrolysis technologies such as anion exchange membrane water electrolyzer (AEMWE) is central to the vision of a sustainable energy future. Key to the realization of such AEMWE technology lies in the exploration of low-cost and high-efficient catalysts for facilitating the anodic oxygen evolution reaction (OER). Despite tremendous efforts in the fundamental research, most of today's OER works are conducted under room temperature, which deviates significantly with AEMWE's operating temperature (50-80 °C). To bridge this gap, it is highly desirable to obtain insights into the OER catalytic behavior at elevated temperatures. Herein, using the well-known perovskite catalyst Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as a proof of concept, the effect of temperature on the variation in OER catalytic activity and stability is evaluated. It is found that the BSCF's activity increases with increasing temperature due to enhanced lattice oxygen participation promoting the lattice oxygen-mediated OER process. Further, surface amorphization and cation leaching of BSCF become more pronounced as temperature increases, causing a somewhat attenuated OER stability. These new understandings of the fundamental OER catalysis over perovskite materials at industrial-relevant temperature conditions are expected to have strong implications for the research of OER catalysts to be deployed in practical water electrolyzers.