Anion Exchange Membrane Research Articles

Modulating the Electronic Structure of Cobalt-Vanadium Bimetal Catalysts for High-Stable Anion Exchange Membrane Water Electrolyzer.

Modulating the electronic structure of catalysts to effectively couple the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for developing high-efficiency anion exchange membrane water electrolyzer (AEMWE). Herein, a coral-like nanoarray composed of nanosheets through the synergistic layering effect of cobalt and the 1D guiding of vanadium is synthesized, which promotes extensive contact between the active sites and electrolyte. The HER and OER activities can be enhanced by modulating the electronic structure through nitridation and phosphorization, respectively, enhancing the strength of metal-H bond to optimize hydrogen adsorption and facilitating the proton transfer to improve the transformation of oxygen-containing intermediates. Resultantly, the AEMWE achieves a current density of 500 mA cm-2 at 1.76 V for 1000 h in 1.0 M KOH at 70°C. The energy consumption is 4.21 kWh Nm-3 with the producing hydrogen cost of $0.93 per kg H2. Operando synchrotron radiation and Bode phase angle analyses reveal that during the high-energy consumed OER, the dissolution of vanadium species transforms distorted Co-O octahedral into regular octahedral structures, accompanied by a shortening of the Co-Co bond length. This structural evolution facilitates the formation of oxygen intermediates, thus accelerating the reaction kinetics.

Hydrogen Bonding Dominated Anion-Exchange Membranes Based on Flexible and Rigid Backbones

Hydrogen Bonding Dominated Anion-Exchange Membranes Based on Flexible and Rigid Backbones

Strong electronic metal-support interaction of Ni4Mo/N-SrMoO4 promotes alkaline hydrogen electrocatalysis

Ni4Mo electrocatalyst stands out as the promising candidate for hydrogen evolution/oxidation reaction (HER/HOR), yet the intensive hydrogen adsorption leads to sluggish kinetics, decreasing hydrogen catalysis efficiency. Herein, the structure of Ni4Mo nanoparticles anchored on wafer-biscuit-like N-SrMoO4 nanorods (Ni4Mo/N-SrMoO4) is developed to accelerate reaction kinetics by modulating electronic structure. The designed N-SrMoO4 support enables strong electronic metal-support interaction with Ni4Mo, resulting in a downward shift of d-band center and achieving thermally neutral hydrogen adsorption. Ni4Mo/N-SrMoO4 exhibits HER performance with an ultralow overpotential of 15 mV at 10 mA cm−2, superior to Pt/C (η10=18 mV). The outstanding exchange current density of 10.2 mA cm−2 for HOR is three times higher than that of Pt/C (3.5 mA cm−2). Ni4Mo/N-SrMoO4 is further assembled in anion exchange membrane water electrolyzer (AEMWE), resulting in a current density of 100 mA cm−2 at voltage of 1.71 V and the excellent stability of 300 hours. Theoretical calculations and in-situ spectroscopy indicate that the introduction of Sr in N-SrMoO4 effectively enhances electronic metal-support interaction, facilitates the enrichment of adsorbed hydroxyl (OHads) on active sites and weakens hydrogen adsorption on Ni4Mo, thereby accelerating reaction kinetics of hydrogen electrocatalysis.

Electrochemical Oxidative Upgrading of Alkali-Sensitive Furfural and 5-Hydroxymethylfurfural in an Anion-Exchange Membrane Electrolyzer with High-Concentration Products

Electrochemical Oxidative Upgrading of Alkali-Sensitive Furfural and 5-Hydroxymethylfurfural in an Anion-Exchange Membrane Electrolyzer with High-Concentration Products

Impact of functionalized titanium oxide on anion exchange membranes derived from chemically modified PET bottles

The accessibility of newly affordable materials has drawn significant attention to the anion exchange membrane (AEM) technology. However, developing a high-performance AEM with excellent hydroxide conductivity and long-term durability is still challenging. The present work aims to improve the overall properties of AEMs synthesized by chemical modification of Polyethylene terephthalate (PET) bottles as the starting material. The modified PET structure was confirmed using IR, NMR, and HPLC-ESIMS analyses. AEMs were developed by incorporating quaternary ammonium (QA) functional groups into the modified PET structure, necessary for transporting anionic species (OH−). In addition, TiO2 nanoparticles grafted with silane coupling agents containing amine functional groups were synthesized via the sol-gel method and embedded in the polymer matrix. Then, the prepared nanocomposite membranes were thoroughly characterized, and the results displayed an overall improvement in the membrane's physicochemical properties. The composite membrane with 3wt% content of nanoparticle (NC3 %/M-PETm) showed remarkable conductivity, reaching 126 mS/cm at 80 °C, doubling the value of pristine membranes (64 mS/cm) while also displaying alkaline stability, retaining up to 92.2 % of conductivity after 20 days in harsh 2 M KOH at 80 °C. These results proved the suitability of these membranes for electrochemical energy applications. This innovative approach offers potential cost savings in preparing the new membranes while aligning with sustainable and circular economy principles.

Simultaneous efficient production of hydrogen peroxide, urea and H2 by bifunctional Cu-doped TiO2 electrocatalyst from CO2, N2 and water

The production of three separated, high-value chemicals (H2O2, urea and H2) from CO2, N2, and H2O represents a significant challenge. It is a prospective and innovative way to simultaneously produce these chemicals in an anion exchange membrane (AEM) electrolyzer, which couples anodic 2e- water oxidation (2e-WOR) and cathodic CO2, N2 and water reduction reaction (CNWRR), but has not yet been realized. Here, we found that bifunctional CuxTi1-xO2-y catalysts can be employed in the electrochemical production of H2O2, urea and H2 from CO2, N2 and water, and the optimized Cu0.12Ti0.88O2-y catalyst exhibits an excellent productivity of 11.8 μmol cm−2 min−1, 0.3 mg cm-2h−1 and 0.82 mmol cm-2h−1 for H2O2, urea and H2 at 4.0 V (50 mA cm−2) in AEM electrolyzer, respectively. Theoretical calculations reveal that the superior performance of the 2e-WOR and CNWRR is attributed to the Cu doping effect, which not only promotes the coupling of *OH but also optimizes the adsorption energy barriers of COOH* and NNH*. It is worth noting that the AEM electrolyzer assembled by bifunctional Cu0.12Ti0.88O2-y reaches a current density of 50 mA cm−2 with a cell voltage of 4.0 V and exhibits excellent stability of 50-hour continuous operation.

Plasma Induced Atomic-Scale Soldering Enhanced Efficiency and Stability of Electrocatalysts for Ampere-Level Current Density Water Splitting.

Industrial water electrolysis typically operates at high current densities, the efficiency and stability of catalysts are greatly influenced by mass transport processes and adhesion with substrates. The core scientific issues revolve around reducing transport overpotential losses and enhancing catalyst-substrate binding to ensure long-term performance. Herein, vertical Ni-Co-P is synthesized and employed plasma treatment for dual modification of its surface and interface with the substrate. The (N)Ni-Co-P/Ni3N cathode exhibits an ultra-low overpotential of 421 mV at 4000 mA cm-2, and the non-noble metal system only requires a voltage of 1.85 V to reach 1000 mA cm-2. When integrated into an anion exchange membrane (AEM) electrolyzer, it can operate stably for >300 h at 500 mA cm-2. Under natural light, the solar-driven AEM electrolyzer operates at a current density up to 1585 mA cm-2 with a solar-to-hydrogen efficiency (SHT) of 9.08%. Density functional theory (DFT) calculations reveal that plasma modification leads to an "atomic-scale soldering" effect, where the Ni3N strong coupling with the Co increases free charge density, simultaneously enhancing stability and conductivity. This research offers a promising avenue for optimizing ampere-level current density water splitting, paving the way for efficient and sustainable industrial hydrogen production.

Research progress and prospect of anionic exchange membrane electrolyzer and OER electrocatalysts

Research progress and prospect of anionic exchange membrane electrolyzer and OER electrocatalysts

Mathematical modelling and performance analysis of an AEM electrolyzer

In this study, an analytical model including electrochemical reactions and mass transfer in an anion-exchange membrane electrolyzer (AEMEL) has been developed by considering water sorption/desorption in electrodes. The model developed was used to investigate the performance of the AEMEL in terms of efficiency, transport phenomena and operating parameters. The numerical results revealed that the voltage losses in the AEMEL are mainly due to activation losses. The effects of important parameters such as membrane thickness, operating pressure on cell performance, and species transport were also investigated. The results also revealed that the AEMEL performance improves with decreasing membrane thickness, but the membrane thickness should be considered together with hydrogen permeability and differential operating pressure to operate the electrolyzer safely.

Impact of side chain length on the properties and alkaline fuel cell performance of OEG-grafted poly(terphenyl piperidinium) anion exchange membranes

In designing comb-shaped anion exchange membranes (AEMs), replacing alkyl side chains with ethylene glycol (EG)-based ones significantly enhances membrane properties and boosts AEM fuel cell performance. Although much research has focused on optimizing the placement of EG segments within the polymer matrix, the effect of EG chain length remains less explored. In this work, a series of poly(terphenyl piperidinium) AEMs with N-oligo(ethylene glycol) (OEG) terminal pendants having two to five EG repeating units were prepared by simple post-polymerization quaternization. The membrane properties showed a strong correlation with the length of the OEG side chains, influenced by both chemical composition and phase behavior. Among the OEG-grafted AEMs, PTP-OEG3 with moderate three EG repeating units, exhibited the best properties due to a careful balance between EG and cationic groups, leading to a favorable microphased separation. It achieved high hydroxide conductivity (114 mS cm−1 at 80 °C in water), robust mechanical strength (tensile strength >52 MPa), and good ex situ alkaline stability. As a result, the AEM fuel cells with the property-balanced PTP-OEG3 membrane achieved the highest peak power density of 976 mW cm−2. The in situ stability of these AEMs was also investigated. Evidently, understanding the optimal EG side chain length is an important criterion for designing AEM materials for alkaline fuel cells.

Transport Mechanism of Hydroxide Ions Focused on the Vehicle Mechanism Near the Cation Sites in Anion Exchange Membranes

We investigated the transport factors of hydroxide ions in anion exchange membrane (AEM). We used partially fluorinated quaternized QPAF-4 polymer with trimethylammonium groups as the AEM material and analyzed it using classical molecular dynamics (MD) simulations. Analysis of the dependence of density on water content (λ) suggested that the voids in the QPAF-4 polymer are fully filled with water molecules under high λ conditions (λ = 15), and as the polymer absorbs additional water molecules, it expands, resulting in a decrease in density. Furthermore, radial distribution function analysis and existence ratio analysis of hydroxide ions in the solvation shells of trimethylammonium groups indicated that increasing λ reduces the overlap of the first solvation shells and causes hydroxide ions to migrate from the first to the second solvation shell. This result indicates that these structural factors contribute to the enhanced diffusivity of hydroxide ions under high λ conditions.

Development of a Superior Anion Exchange Membrane with Hyperbranched Polymer for Anion Exchange Membrane Water Electrolysis

The production of hydrogen using membrane-based electrolyzersposes significant advantages and benefits compared to traditionalelectrolysis methods. Among the electrolyzers, anion exchangemembrane water electrolysis (AEMWE) has emerged as one of thepromising technologies owing to its unique advantages. However,the development of efficient AEMs for water electrolysis presentssignificant challenges, particularly in achieving enhanceddimensional stability and conductivity. In this study, ahyperbranched polyesteramide (HPEA) was synthesized andblended with poly(ether sulfone) (PES) to address the challenges.The resulting QPES-HPEA blend membrane exhibited a lowswelling ratio and high water uptake, which are critical formaintaining dimensional stability and enhancing the hydroxide iontransport efficiency of AEM. The enhanced physical properties andoptimized structure of the membrane make it a promising candidatefor next-generation AEMs in water electrolysis systems.

Deciphering Anion Exchange Membrane Water Electrolysis: A Distribution of Relaxation Times Approach

Anion exchange membrane water electrolysis (AEM-WE) is a promising method for hydrogen production, offering advantages over proton exchange membrane water electrolysis (PEM-WE), such as the use of nonprecious metal catalysts and perfluorosulfonic acid free membranes. Despite achieving impressive current densities, challenges in efficiency and stability remain. This study employs electrochemical impedance spectroscopy (EIS), the equivalent circuit model (ECM) and distribution of relaxation times (DRT) analysis to investigate AEM-WE cells. DRT analysis identifies and quantifies five loss mechanisms within the AEM-WE system, including hydrogen and oxygen evolution reactions and ionic transport losses. Long-term experiments reveal catalyst degradation and its impact on performance, providing insights for targeted optimisation. The findings enhance understanding of the electrochemical processes in AEM-WE, offering pathways to improve stability and efficiency.

Weakening O-Intermediates Adsorption Strength Over the Pd Metallene via Lewis-Acidic Site Modulation for Enhanced Oxygen Reduction.

The reasonable design and modulation of the electronic properties of Pd metallene are acknowledged as a promising avenue for enhancing the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs), yet they remain a formidable challenge. Herein, a thin-sheet structure of Zr-doped Pd metallene (PdZr metallene) with abundant defects is proposed using a facile wet-chemical approach for efficient and highly durable ORR electrocatalysis. Multiple microstructural analyses uncover that orchestrated electronic and oxophilic regulation of PdZr metallene via Lewis-acidic Zr site modulation could concurrently optimize the electronic configuration of Pd, downshift the d-band center of Pd, and, thus, promote the intrinsic activity. Benefiting from the unique two-dimensional morphology and electronic structure optimization facilitated by the Zr coupling effect, the resultant PdZr metallene demonstrates significantly enhanced ORR electrocatalytic performance in basic solutions, with a high half-wave potential (E1/2) of 0.87 V and commendable stability for 30 000 s, surpassing those of Pd metallene and various advanced Pd-based catalysts reported in the literature. Encouragingly, the PdZr metallene-based AEMFC achieves an increased maximum power density (90.4 mW cm-2) and impressive robustness over 12 h in an alkaline environment, manifesting the practical application of PdZr metallene in AEMFCs. This study showcases the applicability of PdZr metallene via Lewis acid site regulation for fabricating highly active electrocatalysts for high-performance AEMFCs.

Deciphering Anion Exchange Membrane Water Electrolysis: A Distribution of Relaxation Times Approach

Anion exchange membrane water electrolysis (AEM-WE) is a promising method for hydrogen production, offering advantages over proton exchange membrane water electrolysis (PEM-WE), such as the use of nonprecious metal catalysts and perfluorosulfonic acid free membranes. Despite achieving impressive current densities, challenges in efficiency and stability remain. This study employs electrochemical impedance spectroscopy (EIS), the equivalent circuit model (ECM) and distribution of relaxation times (DRT) analysis to investigate AEM-WE cells. DRT analysis identifies and quantifies five loss mechanisms within the AEM-WE system, including hydrogen and oxygen evolution reactions and ionic transport losses. Long-term experiments reveal catalyst degradation and its impact on performance, providing insights for targeted optimisation. The findings enhance understanding of the electrochemical processes in AEM-WE, offering pathways to improve stability and efficiency.

Robust branched Poly(p-terphenyl isatin) anion exchange membranes with enhanced microphase separation structure for fuel cells

Anion exchange membrane fuel cells (AEMFCs) are gradually becoming the focus of sustainable hydrogen energy research due to the advantages of clean by-products, faster oxidation-reduction dynamics and allowing cheap platinum-free base materials. As the key components of AEMFCs, anion exchange membranes (AEMs) are required to have high ionic conductivity and dimensional stability. This study focused on the design and preparation of branched AEMs for AEMFCs. The b-PTIN-x membranes were generated by incorporating 1,3,5-triphenylbenzene (TPB) units into rigid poly(p-terphenyl isatin) (PTI) polymer backbones. This innovative approach aimed to induce microphase separation structures by exploiting TPB with high FFV, as well as to enhance the tensile strength of AEMs with the help of branched structures. SAXS and AFM images revealed that the AEMs achieved enhanced microphase separation structures, resulting in the formation of ion transport channels with dimensions in the range of a few nanometers (3.36–3.70 nm). The branched b-PTIN-11 membranes displayed significant OH− conductivity (153.9 mS cm−1 at 80 °C) while having a low ion exchange capacity (IEC) (1.73 mmol g−1). The b-PTIN-11 membranes displayed improved tensile strength (56.69 MPa) and exceptional dimensional stability, with swelling ratio (SR) of 18.5 % at 80 °C. They also showed great chemical stability with 89.64 % conductivity remaining, lasting for more than 1200 h in 3 M NaOH solution at 80 °C. Ultimately, the b-PTIN-11 membrane underwent testing to evaluate its performance in a fuel cell using H2–O2. It demonstrated a peak power density (PPD) of 566 mW cm−2 when subjected to a current density of 1339 mA cm−2.

Boosting Oxygen Evolution Reaction Performance on NiFe-Based Catalysts Through d-Orbital Hybridization

HighlightsThe NiFeLa catalyst with 3d-5d orbital coupling exhibits remarkable oxygen evolution reaction (OER) activity and stability, enabling an anion-exchange membrane water electrolyzers device to achieve a cell voltage of only 1.58 V at 1 A cm−2 as well as long-term stability over 600 h.The introduction of La disrupts the symmetry of Ni-Fe units and optimize d band center, which affects the d-p orbital hybridization between the metal sites on the surface of the catalyst and oxygen-containing intermediates during the OER process.The 5d-introduced NiFeLa has enhanced adsorption strength of oxygen intermediates, which can reduce the rate-determining step energy barrier and prevent catalyst dissolution.

Electrodialysis with sacrificial magnesium anode for nutrient recovery from primary municipal wastewater: Effect on membrane fouling behaviours

The fertilizer industry is experiencing tremendous stress due to its dependence on limited natural resources and high energy consumption, thus great attention has been paid for alternative nitrogen and phosphorus resources. This study employed electrodialysis (ED) with sacrificial magnesium anode to recover nitrogen and phosphorus (towards struvite formation) from primary municipal wastewater and examined the effects of various operating conditions on ED membranes' fouling behaviour. The results revealed that (1) lowering the concentrate to feed volume (C/F) ratio would reduce overall ED stack resistance, while at a C/F < 0.5, the magnesium corrosion rate decreased with an increase of pH in the concentrate stream; (2) the cation exchange membranes (CEM) adjacent to the feed chamber were more susceptible to foulant depositions (especially organics) than the anion exchange membrane (AEM); the total foulant density was linearly correlated with the increased electrical resistance; (3) increasing current density led to higher ion transport rate, however also promoted membrane fouling for the wastewater containing more solids; (4) the ammonium and phosphate mass transport rates were enhanced by increasing their concentrations in the feed instead of elevating current density. Higher concentrations of nutrient levels in the feed facilitated reduced scaling on membranes, possibly due to more formation of struvite. This study highlights the feasibility of simultaneously treating primary wastewater and recovering nutrients by combining gravity-driven membrane (GDM) filtration with ED.

Unraveling Lattice Dislocation‐Driven Energy Band Convergence Mechanism to Enhance Electrocatalytic Hydrogen Production in Alkaline Seawater

AbstractHydrogen evolution reaction (HER) from seawater electrolysis still faces challenges of low reactivity and chloride ions poison at the active sites, leading to reduced efficiency and stability of electrocatalysts. This study presents edge dislocation strategy aimed at inducing lattice strain in ferric oxide through Mo doping, consequently regulating the catalyst's band structure. Through in situ characterizations and DFT analysis, it is confirmed that lattice strain effectively modulates the band structure, intensifies the hybridization between Mo(d)‐Fe(d)‐O(p) orbitals, thereby accelerating the charge transfer rate of HER. Furthermore, band structure modulated by lattice strain enhances water adsorption capacity, reduces the adsorption energy of Cl−, and optimizes the hydrogen adsorption‐free energy (ΔGH*) for HER. Benefiting from above, the optimized 2%‐Mo‐Fe2O3 catalyst demonstrates HER activity and stability in alkaline seawater electrolysis comparable to that of commercial Pt/C. Additionally, the assembled electrolytic cell utilizing an anion exchange membrane (AEM) maintains long‐term stability for &gt;100 h at 500 mA cm−2, showcasing a sustained catalytic effect.

One-pot synthesis of FeNi3/FeNiOx nanoparticles for PGM-free anion exchange membrane water electrolysis

Low-temperature anion exchange membrane water electrolysis (AEMWE) is one of the most promising technologies to produce green hydrogen. To date, membrane-electrode assembly (MEA) based on platinum group metal (PGM) electrocatalysts shows higher performance than PGM-free ones. Here, a single and easy synthesis for non-noble metal electrocatalysts (PGM-free) for both hydrogen and oxygen evolution reactions (HER and OER) was developed. Both electrocatalysts consist of FeNi3/FeNiOx nanoparticles obtained through chemical reduction using hydrazine. The electrocatalyst exhibits an overpotential of 210 mV and 234 mV for HER and OER respectively, at a current density of 10 mA cm−2 in 1 M KOH electrolyte, allowing a comparison between mass activity and geometric activity compared to PGM catalysts. In addition to a preliminary electrochemical characterization of the FeNi3/FeNiOx, the electrocatalyst were integrated into a pilot-scale AEMWE at both anode and cathode, which reaches (without iR-correction) 1.72 V and 1.94 V at a current density of 0.4 A cm−2 and 1 A cm−2 respectively at 60 °C. This PGM-free MEA outperforms the one based on Pt/C at cathode and RuO2 at anode with a voltage gap of 284 mV at 1 A cm−2. The aforementioned MEA was tested for 150 h with a discontinuous power profile, in order to get an idea of the possible degradation trends for a future industrial application, the reversible and irreversible voltage losses were calculated resulting in a degradation rate of 886 µV/h. This work demonstrates a simple and scalable synthesis of earth-abundant electrocatalytic materials for high-efficiency AEM water electrolysis.