Anion Exchange Membrane Research Articles

Ru Nanoparticles Encapsulated by Defective TiO2 Boost the Hydrogen Oxidation/ Evolution Reaction.

The development of efficient and durable electrocatalysts for the alkaline hydrogen oxidation/evolution reaction is crucial for anion exchange membrane fuel cells/water electrolyzers. However, designing such electrocatalysts poses a challenge due to the need for optimizing various adsorbates. Herein, highly dispersed Ru nanoparticles catalysts is reported encapsulated and supported by defective anatase phase of titanium dioxide (named as Ru NPs/def-TiO2(A)) for boosting hydrogen-cycle electrocatalysis with robust anti-CO-poisoning in alkaline conditions. The Ru NPs/def-TiO2(A) achieves a high-quality activity of 7.65 A mgRu -1, which is 23.2 and 9.5-fold higher than commercial Ru/C and Pt/C in alkaline HOR. Moreover, this catalyst exhibits an outstanding overpotential of 21mV at 10mAcm-2 in alkaline HER. Hydrogen underpotential deposition (Hupd) and CO stripping experiments demonstrate that Ru NPs/def-TiO2(A) has the optimized H*, OH*, and CO* adsorption strength, enabling the Ru NPs/def-TiO2(A) catalyst to display excellent and robust HOR/HER performance under alkaline conditions. Using density functional theory calculations, the enhanced HOR performance mechanism for the Ru NPs/def-TiO2(A) catalyst originates from the TiO2 step face in contact with the Ru nanoparticles, indicating that the kinetics of water formation are considerably more favorable at the Ru NPs/def-TiO2(A) interface.

Doped double spirocyclic cationic POSS for nanocomposite anion exchange membranes with high conductivity and robustness

Organic-inorganic hybridization methods are receiving increasing attention as a method that can improve the performance of anion exchange membranes (AEMs) in a simpler and more effective way. Here, by selecting polyhedral oligomeric silsesquioxane (POSS) with good mechanical and thermal properties as inorganic fillers. Successful introduction of N-spirocyclic cations with bifunctional groups onto POSS yielded MDSU-poss. subsequently, we doped them into qPTP-IC-O-9% membranes as fillers in different ratios to obtain a series of composite membranes. High-density cations introduced by POSS with simultaneous organic-inorganic frameworks effectively inhibit membrane over-swelling. As a result, the membrane is able to achieve high ionic conductivity with the assurance of reasonable dimensional stability. At 80 °C, the 15 % MDSU-poss/qPTP-IC-O membrane achieved the ionic conductivity of 168.6 mS cm−1 at low SR with the peak power density of 431 mW cm−2. In addition, the mechanical properties of the composite membranes were all greatly improved due to the organic cations attached to the POSS with good affinity, contributing to the tensile strength of the 15 % MDSU-poss/qPTP-IC-O membrane of 57.4 MPa. The membrane was finally immersed in 3 M NaOH solution for 1032 h and still maintained 89.3 % of the starting ionic conductivity.

Importing Atomic Rare-Earth Sites to Activate Lattice Oxygen of Spinel Oxides for Electrocatalytic Oxygen Evolution.

Spinel oxides have emerged as highly active catalysts for the oxygen evolution reaction (OER). However, due to covalency competition, the OER process on spinel oxides often follows an arduous adsorbate evolution mechanism (AEM) pathway. Herein, we propose a novel rare-earth sites substitution strategy to tune the lattice oxygen redox of spinel oxides and bypass the AEM scaling relationship limitation. Taking NiCo2O4 as a model, the incorporation of Ce into the octahedral site induces the formation of Ce-O-M (M: Ni, Co) bridge, which triggers charge redistribution in NiCo2O4. The developed Ce-NiCo2O4 exhibits remarkable OER activity with a low overpotential, satisfactory electrochemical stability, and good practicability in anion-exchange membrane water electrolyzer. Theoretical analyses reveal that OER on Ce-NiCo2O4 surface follows a more favorable lattice oxygen mechanism (LOM) pathway and non-concerted proton-electron transfers compared to pure NiCo2O4, as further verified by pH-dependent behavior and in situ Raman analysis.18O-labeled electrochemical mass spectrometry directly demonstrates that oxygen originates from the lattice oxygen of Ce-NiCo2O4 during OER. It is discovered that electron delocalization of Ce 4f states triggers charge redistribution in NiCo2O4 through the Ce-O-M bridge, favoring antibonding state occupation of Ni-O bonding in [Ce-O-Ni] site, thereby activating lattice oxygen redox of NiCo2O4 in OER.

Self‐Encapsulated Ni Nanoparticles on Delignified Wood Carbon for Efficient Urea‐Assisted Hydrogen Production

AbstractDeveloping efficient, low‐cost electrocatalysts for industrial‐level hydrogen production remains a significant challenge. Here lattice‐distorted Ni nanoparticles (NPs) encapsulated within a nitrogen‐doped carbon shell on delignified wood carbon (Ni‐NC@DWC) are constructed through a chitosan‐induced assembly and the pyrolysis process. Experimental and theoretical results indicate that the lattice distortion due to strong metal‐support interactions, boosts electron transfer and reaction intermediate adsorption/desorption, enhancing both the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). Interestingly, the active center Ni3+‐O is dynamically cyclically generated during the UOR. When utilized as a self‐standing electrode in an alkaline electrolyte, the Ni‐NC@DWC exhibits low potentials of 24 mV and 1.244 V at 100 mA cm−2 for HER and UOR, respectively. Moreover, the Ni‐NC@DWC achieves an ultrasmall cell voltage of 1.13 V at 100 mA cm−2 for urea‐assisted water splitting and can operate stably over 1000 h. Furthermore, when it is self‐assembled as an anion exchange membrane (AEM) electrolyzer, it requires only 1.62 V at 2000 mA cm−2 for industrial urea‐assisted water splitting and operates stably for 150 h without degradation, confirming that it is highly attractive for economical, sustainable, and scalable hydrogen production.

Improved Electrode Performance Using Fine‐Tuned Poly(arylene piperidinium) Ionomers In Anion Exchange Membrane Fuel Cells

AbstractIonomers based on poly(arylene piperidinium)s with varying ion exchange capacities are evaluated in different combinations of anode and cathode electrodes in anion exchange membrane fuel cells. The operational conditions are chosen with an asymmetrical regime including a dry anode with 50% relative humidity at the inlet, and full humidification at the cathode. Polarization and impedance measurements are carried out in potentiostatic steps within 0.3–0.9 V and distribution of relaxation times analysis is utilized to deconvolute resistance contributions. The results show that the best cell performance is achieved with both electrodes utilizing an ionomer with the highest ion exchange capacity (IEC) of 2.79 meq g−1. Cells built exclusively from this ionomer achieved a peak power density of 1.01 W cm−2. Deconvolution of the resistance contributions revealed the impact of water content on the effective charge transfer resistance in both electrodes and a diffusion resistance associated with the movement of water from anode to cathode side. The higher conductivity and water uptake of the high IEC ionomer resulted in a reduction of both resistance contributions, leading to the highest performance under the conditions evaluated. These findings provide important insights into how to tailor the electrode layers for optimum fuel cell output.

Electrocatalytic Hydrogenation of Pyridines and Other Nitrogen-Containing Aromatic Compounds.

The production of cyclic amines, which are vital to the pharmaceutical industry, relies on energy-intensive thermochemical hydrogenation. Herein, we demonstrate the electrocatalytic hydrogenation of nitrogen-containing aromatic compounds, specifically pyridine, at ambient temperature and pressure via a membrane electrode assembly with an anion-exchange membrane. We synthesized piperidine using a carbon-supported rhodium catalyst, achieving a current density of 25 mA cm-2 and a current efficiency of 99% under a circular flow until 5 F mol-1. Quantitative conversion of pyridine into piperidine with 98% yield was observed after passing 9 F mol-1, corresponding to 65% of current efficiency. The reduction of Rh oxides on the catalyst surface was crucial for catalysis. The Rh(0) surface interacts moderately with piperidine, decreasing the energy required for the rate-determining desorption step. The proposed process is applicable to other nitrogen-containing aromatic compounds and could be efficiently scaled up. This method presents clear advantages over traditional high-temperature and high-pressure thermochemical catalytic processes.

Chitosan-based anion exchange membranes for fuel cell application: Enhanced hydration & durability to dry-wet cycling

Herein, a new type of anion exchange membranes (AEMs) based on chitosan (CS) and poly(4-vinylbenzyl chloride) (PVB) polymers is reported. Depending on whether the PVB side chains are mono-cationic (quaternized PVB, QPVB) or di-cationic (di-quaternized PVB, DQPVB), the AEMs are denoted as QPVB@CS and DQPVB@CS, respectively. Due to the lateral aggregation of chitosan chains assisted by hydrogen bonds, the in-plane expansion is limited (1.4–11.5 % at 80 °C), resulting in excellent mechanical properties of AEMs (dry tensile strength of 55.2–81.0 MPa). And after 10 dry-wet cycles, the AEMs maintain their appearance and show improved mechanical properties. Due to high through-plane swelling degree, AEMs effectively retaining water (water uptake of 272.5–501.5 % at 80 °C) in the AEMs. DQPVB@CS AEMs, with their higher ion content, exhibit superior ionic conductivity (74.2–116.5 mS cm−1 at 80 °C) compared to QPVB@CS (27.7–44.3 mS cm−1 at 80 °C) and achieve a peak power density of 729.6 mW cm−2 in an anion exchange membrane fuel cell (AEMFC), versus 128.1 mW cm−2 for QPVB@CS-2. To the best of our knowledge, the AEMs developed in this study represent the first example of AEMs prepared from chitosan gel membranes, achieving anisotropic swelling degree, high water uptake, and excellent dry-wet cycling resistance without the need for additional chemical cross-linking.

P-functionalization of Ni Fe − Electrocatalysts from Prussian blue analogue for enhanced anode in anion exchange membrane water electrolysers

Efficient hydrogen generation from water-splitting is widely acknowledged as a priority route to promote the hydrogen economy. Anion exchange membrane water electrolyzers (AEMWE) offer multiple advantages in improving performance and minimizing the cost limitations of current electrolysis technologies. However, the persistence of issues related to the limited electrocatalytic activity of such materials and their poor stability under operating conditions makes developing highly active, stable, platinum-group-metal-free electrocatalysts for oxygen evolution reaction (OER) necessary.We report the development of Prussian blue analogues (PBA)-derived NiFe-based electrocatalysts through a mild aqueous phase precipitation method, followed by thermal stabilization and phosphorus doping. The formation of the NiFe-PBA-precursor with a framework nanocubic Ni(II)[Fe(III)(CN)6]2/3 structure was confirmed by X-ray diffraction, scanning electron microscopy, and inductively coupled plasma analysis. The NiFe-PBA-precursor was subjected to thermal stabilization and phosphorus doping to provide the material with enhanced OER catalytic activity and stability. The existence of OER active sites based on NiFe and NiFeP has been revealed by transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical characterization in a three-electrode cell configuration in a 1 M KOH electrolyte. NiFe-PBA and NiFeP-PBA were assembled at the anode side of an AEMWE, resulting in an excellent electrochemical performance both in terms of current density at 2.0 V using 1 M KOH (1.21 A cm−2) and durability, outperforming the benchmark catalyst.

Anion Exchange Membrane Water Electrolysis at 10 A ⋅ cm-2 Over 800 Hours.

Anion exchange membrane water electrolyzer (AEMWE) is a potentially cost-effective technology for green hydrogen production. Although the normal current densities of AEMWEs are below 3 A ⋅ cm-2, operating them at higher current densities represents an efficient, but little-explored approach to decrease the total cost of hydrogen production. We show here that a benchmark AEMWE has an operational lifetime of only seconds at an ultrahigh current density of 10 A ⋅ cm-2. By using a more conductive and robust AEM, and judicious choices of ionomers, catalyst, and porous transport layer, we have developed AEMWEs that stably operate at 10 A ⋅ cm-2 with extended lifetimes. The optimized AEMWE has an operational lifetime of more than 800 hours, a 5-order magnetite improvement over the current benchmark. The cell voltage is only 2.3 V at 10 A ⋅ cm-2, comparable to those of the state-of-the-art devices operating at current densities lower than 3 A ⋅ cm-2. This work demonstrates the potential of ultrahigh current density AEMWEs.

Comprehensive Review of Anion Exchange Membrane with Ether and Ether-Free Backbone

Comprehensive Review of Anion Exchange Membrane with Ether and Ether-Free Backbone

Synergistic Effect of Localized Three-Dimensional Polymer Backbone and Self-Assembling Cation for the Construction of Novel Anion Exchange Membrane

Synergistic Effect of Localized Three-Dimensional Polymer Backbone and Self-Assembling Cation for the Construction of Novel Anion Exchange Membrane

Engineering potential electrocatalysts for both AEM Electrolyzers and Redox Flow Batteries: Design of experiments at the different scales

Both water electrolysis and electrochemical energy storage are promising technologies for dealing with the intermittency of green electricity generation. In this work we investigated the possibility of using the same electro-catalyst for hydrogen production by Anion Exchange Membrane Water Electrolysis (AEMWE) and energy storage by Redox Flow Batteries (RFB). A complete experimental campaign was designed to investigate the effects of the catalyst nanostructure and morphology on the electrode performance at different scales. Focus was devoted to the choice of the main factors influencing the catalyst structure, its morphology and electrochemical activity; taking further into account the technique to deposit the catalyst on the Gas Diffusion Layer (GDL) and its integration inside the Membrane Electrode Assembly (MEA). Some results are reported for a spinel-based NiCo2O4 catalyst, chosen as a base nanocomposite to develop more complex materials for both the Oxygen Evolution Reaction (OER) in AEMWE and the positive electrode in Vanadium RFB in the future.

Dissociative electrochemical analysis of materials degradation of an anion exchange membrane electrolyser

For anion exchange membrane (AEM) electrolysers, degradation studies provide valuable insights into how individual components degrade. Often, this presents a formidable challenge as each component significantly contributes to overall degradation. Here, we propose a methodology to individually compare the degradation of key components in AEM electrolysers: hydrogen evolution reaction (HER) catalyst, oxygen evolution reaction (OER) catalyst, and the AEM itself. First, to measure the degradation of catalyst-coated substrates (CCS) commonly used in AEM electrolysers, the AEM was replaced with a diaphragm (Zirfon Agfa UTP 500) permeable to OH− ions and stable in alkaline media. Subsequently, a cell with a stable catalytic layer (Nafion-coated Ni-felt substrates) was assembled to focus on membrane degradation with an AEM Sustainion X37-50 Grade 60. Chronopotentiometry and electrochemical impedance spectroscopy (EIS) revealed that the cell with the AEM experienced a threefold increase in ohmic resistance, attributed to the loss of functional groups. Additionally, an ion exchange capacity (IEC) analysis indicated that Sustainion lost approximately 20% of its ion exchange capacity. In contrast, the cell composed of CCS and Zirfon showed lower degradation. EIS data fitting demonstrated increased kinetic-related resistances while the ohmic resistance remained unchanged. This work presents a practical approach for comparing component degradation in AEM electrolysers.

Conductivity-enhanced Poly(biphenyl piperidine) anion exchange membranes with organic tubes

Anion exchange membrane fuel cells (AEMFCs) present an economically efficient alternative to proton exchange membrane fuel cells because of the use of non-precious metals. The development of high-performance and durable AEMFCs necessitates the use of highly conductive and robust anion exchange membranes (AEMs). In this study, a novel organic-organic composite AEM was synthesized by preparing poly(arylene piperidinium) polymer through Friedel-Crafts acid condensation and incorporating one-dimensional organic tubes as reinforcing materials. The composite AEM exhibits high conductivity (235 mS cm−1 at 80 °C) due to the chain orientation within the organic tubes and the availability of abundant transport sites. Furthermore, in contrast to the incompatibility of inorganic materials with polymers, the flexible nature of organic tubes enhanced polymer entanglement, significantly boosting the mechanical strength (120 MPa) of the AEM. Crosslinking the polymer backbone with the organic tubes facilitated simultaneous swelling, effectively mitigating interfacial compatibility issues, result in high dimensional stability. The H2–O2 fuel cell employing the developed AEM demonstrated a peak power density of 1018 mW cm−2 at 80 °C. This study provides a comprehensive synthetic strategy for producing stable AEMs with high hydroxide ion conductivity and outstanding mechanical properties tailored for alkaline membrane fuel cell applications.

Synthesis and performance of cross-linked poly(aryl ether nitrile) anion exchange membranes with dense cations and flexible side-chain structures for water electrolysis

Anion exchange membranes (AEMs) are the core components in anion exchange membrane water electrolysis (AEMWE), which play crucial role and affect the performance of AEMWE. In this work, a series of cross-linked poly(aryl ether nitrile) anion exchange membranes (CPAEN-dDQA-x) with dense cations and flexible side-chain structures are synthesized. By introducing multiple modification elements into the polymer structure simultaneously, the ion conductivity, dimensional stability, and alkali resistance stability of the prepared AEMs are effectively improved and balanced. The representative CPAEN-dDQA-0.25 showed water absorption of only 27.6 %, swelling rate of 11.2 %, and conductivity of 115.37 mS/cm at 80°C. The IEC and conductivity retention value of CPAEN-dDQA-0.25 after in 2 M NaOH solution at 80°C for 480 h were up to 86.2 % and 82 %, respectively. Meanwhile, the current density of the water electrolysis cell based on CPAEN-dDQA-0.25 is up to 477.0 mA/cm2 in 1 M KOH and 2.2 V, and its voltage don’t has significant change after 480 h of operation at a constant current density of 500 mA/cm2.

Mussel-inspired co-deposition of catechol-amine and graphene oxide (GO) modified anion exchange membranes (AEMs) for antifouling

Mussel-inspired co-deposition has many applications in surface modification of polymer membranes. Organic fouling of ion exchange membranes is one of the common issues that hinder electrodialysis treatment of industrial wastewater. In this work, anion exchange membranes were surface-modified by the mussel-inspired co-deposition of catechol-amine and graphene oxide (GO) nanosheets. Results showed that co-deposition with catechol (CA) and m-phenylenediamine (MPD) as reactant monomers rapidly generated modifying layer on the AEM surface. And the addition of GO into co-deposition helped improve the homogeneity and reduce polymer particle aggregation. The synergistic effect of catechol-amine and GO nanosheets was beneficial to form uniform modifying layer with improved hydrophilicity and negative charge density of membrane surface. In eletrodialysis experiments with sodium dodecyl benzene sulfonate (SDBS) as model foulants, GO-CA-MPD-3h modified AEM maintained high desalination rate close to that without folants, indicating good modifying antifouling performance. Mussel-inspired co-deposition of catecholamines and functional materials give new insights into membrane modificatin through a feasible and cost-effective method

Enhancing nutrient water recovery: An integrated electrodialysis – Forward osmosis approach for reduced energy consumption and membrane fouling

The concept of combining electrodialysis (ED) and forward osmosis (FO) was previously introduced and proven effective in recovering nutrients and clean water from anaerobic effluents to produce safe liquid fertilizer. In this study, a novel and improved EDFO configuration (iEDFO) was proposed by merging the ED diluate with the FO feed solution and the ED concentrate with the FO draw solution, thus overcoming concentration limitations and fouling challenges inherent in traditional ED processes. Experimental results demonstrated significant improvements in performance, including up to 54 % and 43 % reductions in operation time and 21 % and 25 % energy savings for synthetic and real liquid digestate, respectively. These enhancements were attributed to altered ionic composition within the ED process, leading to higher, more stable current density and reduced ion back diffusion. Unlike conventional ED-only systems, the iEDFO configuration enabled continuous operation without requiring larger membrane areas or variable operational conditions. Additionally, the iEDFO configuration benefited from (1) reduced membrane fouling, and (2) decreased transport of organic contaminants across the anion exchange membranes (AEMs) into the ED concentrate product. Overall, the iEDFO system provides significant advantages in efficiency, energy savings, and operational stability, making it a highly effective and sustainable solution for resource recovery from liquid waste.

Recovery and fractionation of volatile fatty acids from fermented solutions by electrodialysis: electrochemical characterization of anion-exchange membranes

Electrodialysis can be used to recover charged precursors, such as volatile fatty acids (VFAs), of the biopolymers polyhydroxyalkanoates (PHAs). In general, all VFAs are recovered in a receiver solution, despite their advantageous partial fractionation. Herein, the separation of acetic, propionic, butyric, and valeric acids by electrodialysis was evaluated using three anion-exchange membranes (namely, Ralex AMH-PES, Fumasep FAS-PET-130 and PC200D) applying cell voltages from 0V to 2.88V. The mass transfer mechanisms were evaluated by linear sweep voltammetry and chronopotentiometry. Fumasep showed a slightly greater VFAs fractionation capacity than Ralex, while it was much greater for PC200D due to the presence of tertiary amines in its fixed functional groups. Overall, increasing the operating voltage and/or time reduced the degree of VFAs fractionation with all membranes. The higher percent extraction values and greater VFAs fractionation degrees obtained with the PC200D membrane could enhance PHAs storage efficiency.

Selenate oxyanion-intercalated NiFeOOH for stable water oxidation via lattice oxygen oxidation mechanism

Transition metal-based compounds can serve as pre-catalysts to obtain genuine oxygen evolution reaction (OER) electrocatalysts in the form of oxyhydroxides through electrochemical activation. However, the role and existence form of leached oxygen anions are still controversial. Herein, we selected iron selenite-wrapped hydrated nickel molybdate (denoted as NiMoO/FeSeO) as a pre-catalyst to study the oxyanion effect. It is surprising to find that SeO42− exists in the catalyst in the form of intercalation, which is different from previous studies that suggest that anions are doped with residual elements after electrochemical activation, or adsorbed on the catalyst surface. The experiment and theoretical calculations show that the existence of SeO42− intercalation effectively adjusts the electronic structure of NiFeOOH, promotes intramolecular electron transfer and O–O release, and thus lowers the reaction energy barrier. As expected, the synthesized NiFeOOH-SeO only needs 202 and 285 mV to attain 100 and 1000 mA cm−2 in 1 M KOH. Further, the anion exchange membrane water electrolyzer (AEMWE) consisting of NiFeOOH-SeO anode and Pt/C cathode can reach 1 A cm−2 at 1.70 V and no significant attenuation within 300 h. Our findings provide insights into the mechanism, by which the intercalated oxyanions enhance the OER performance of NiFeOOH, thereby facilitating large-scale hydrogen production through AEMWE.

Electrochemical activation of Pt electrode for efficient and stable anion exchange membrane ammonia electrolyzer

Replacing the oxygen evolution reaction in water electrolysis with ammonia oxidation reaction enables low voltage hydrogen production. Pt is a promising catalyst for the ammonia oxidation reaction due to its superior dehydrogenation and low affinity for *N, but Nads poisoning deactivates the Pt surface. This study proposes a method to improve ammonia oxidation performance and stability through electrochemical activation, introducing cathodic corrosion and recovery conditions. The half-cell results showed a peak current density of 74.2 mA cm−2 and retention ratio of 17 %. Adjusting the lower and upper cell voltage in a membrane electrode assembly based single cell optimized surface cleaning and inhibits further poisoning by O/OHads above 0.75 Vcell. Furthermore, incorporation of recovery conditions can enhance the stability of poisoned electrode compared to that in chronoamperometry test. The results of pulsed ammonia electrolysis tests incorporating recovery conditions suggested a novel approach to practical hydrogen production by stabilizing catalysts with a 83 % Faradaic efficiency at 0.1 A cm−2