Diffusion Of Hydroxide Ions Research Articles

Atomistic Modeling of Quaternized Chitosan Head Groups: Insights into Chemical Stability and Ion Transport for Anion Exchange Membrane Applications.

The chemical stability and ion transport properties of quaternized chitosan (QCS)-based anion exchange membranes (AEMs) were explored using Density Functional Theory (DFT) calculations and all-atom molecular dynamics (MD) simulations. DFT calculations of LUMO energies, reaction energies, and activation energies revealed an increasing stability trend among the head groups: propyl trimethyl ammonium chitosan (C) < oxy propyl trimethyl ammonium chitosan (B) < 2-hydroxy propyl trimethyl ammonium chitosan (A) at hydration levels (HLs) of 0 and 3. Subsequently, all-atom MD simulations evaluated the diffusion of hydroxide ions (OH-) through mean square displacement (MSD) versus time curves. The diffusion coefficients of OH- ions for the three types of QCS (A, B, and C) were observed to increase monotonically with HLs ranging from 3 to 15 and temperatures from 298 K to 350 K. Across different HLs and temperatures, the three QCS variants exhibited comparable diffusion coefficients, underlining their effectiveness in vehicular transport of OH- ions.

Revealing Structural Evolution of Nickel Phosphide-Iron Oxide Core-Shell Nanocatalysts in Alkaline Medium for the Oxygen Evolution Reaction.

Metal phosphide-containing materials have emerged as a potential candidate of nonprecious metal-based catalysts for alkaline oxygen evolution reaction (OER). While it is known that metal phosphide undergoes structural evolution, considerable debate persists regarding the effects of dynamics on the surface activation and morphological stability of the catalysts. In this study, we synthesize NiP x -FeO x core-shell nanocatalysts with an amorphous NiP x core designed for enhanced OER activity. Using ex situ X-ray absorption spectroscopy, we elucidate the local structural changes as a function of the cyclic voltammetry cycles. Our studies suggest that the presence of corner-sharing octahedra in the FeO x shell improves structural rigidity through interlayer cross-linking, thereby inhibiting the diffusion of OH-/H2O. Thus, the FeO x shell preserves the amorphous NiP x core from rapid oxidation to Ni3(PO4)2 and Ni(OH)2. On the other hand, the incorporation of Ni from the core into the FeO x shell facilitates absorption of hydroxide ions for OER. As a result, Ni/Fe(OH) x at the surface oxidizes to the active γ-(oxy)hydroxide phase under the applied potentials, promoting OER. This intriguing synergistic behavior holds significance as such a synthetic route involving the FeO x shell can be extended to other systems, enabling manipulation of surface adsorption and diffusion of hydroxide ions. These findings also demonstrate that nanomaterials with core-shell morphologies can be tuned to leverage the strength of each metallic component for improved electrochemical activities.

Ratiometric fiber optic fluorescent pH sensor for hydroxide diffusion measurements in concrete

This article delineates the development of an advanced ratiometric pH optode designed for protracted monitoring of pH dynamics in cementitious materials—a crucial aspect of structural management. The optode features a dual-layer Hydromed™ D4 polymer pellet incorporating a pH-sensitive Naphth-AlkyneOMe fluorescent probe (pKa ≈ 12) and CdSe quantum dots as an internal reference. The polymer matrix, optimized with diamond powder and carbon black, enhances the signal while minimizing light artifacts. Demonstrating a robust response to pH fluctuations, the optode, utilizing ratiometric measurements, enables steadfast monitoring for up to 75 days.The experimental setup includes a Delrin® sample compartment housing a glass slide with the optode connected to an optical fiber via an SMA connector. HydroMed™ D4 films, forming the pH-sensitive layer, are deposited on the glass slide and secured. The optode configuration is fine-tuned to optimize signal intensity by reducing its length. For optode-detector coupling, a 1000 µm core diameter optical fiber links the optode, and a 405 nm LED illuminates the sensing film. The emission signal is collected through the optical fiber, and signals are processed using computer-controlled lock-in amplifiers.In the investigation of hydroxide ion diffusion through a concrete sample, the optode's efficacy was validated, aligning with pH electrode measurements. Addressing long-term stability, a degradation model uncovered leisurely kinetics with commendable stability. Slow degradation kinetics, with a reaction rate coefficient of 1.6 × 10⁻⁷ s⁻¹ and a half-life of 1180 h, exceeded expectations.This pH optode, showcasing an accurate and resilient response to pH variations within the 10 to 12.5 range, stands as a promising tool for monitoring pH dynamics in low-pH cementitious materials. The incorporation of a degradation model underscores fidelity over prolonged durations and offers a blueprint for enduring surveillance of concrete structures.

Mechanism of Heterogeneous Alkaline Deacetylation of Chitin: A Review.

This review provides an analysis of experimental results on the study of alkaline heterogeneous deacetylation of chitin obtained by the authors and also published in the literature. A detailed analysis of the reaction kinetics was carried out considering the influence of numerous factors: reaction reversibility, crystallinity and porosity of chitin, changes in chitin morphology during washing, alkali concentration, diffusion of hydroxide ions, and hydration of reacting particles. A mechanism for the chitin deacetylation reaction is proposed, taking into account its kinetic features in which the decisive role is assigned to the effects of hydration. It has been shown that the rate of chitin deacetylation increases with a decrease in the degree of hydration of hydroxide ions in a concentrated alkali solution. When the alkali concentration is less than the limit of complete hydration, the reaction practically does not occur. Hypotheses have been put forward to explain the decrease in the rate of the reaction in the second flat portion of the kinetic curve. The first hypothesis is the formation of "free" water, leading to the hydration of chitin molecules and a decrease in the reaction rate. The second hypothesis postulates the formation of a stable amide anion of chitosan, which prevents the nucleophilic attack of the chitin macromolecule by hydroxide ions.

Formulation of polymeric particles with controlled charges by alkaline tempering

The control of surface charge of polymeric microparticles is a major challenge because electrostatic interactions stabilize their aqueous suspensions. In this study, anionic PMMA particles were prepared with 5 wt% of methacrylic acid as a comonomer. This comonomer was expected to give a negative charge to the particles, but none was observed from zeta potential measurements. The evolution of the zeta potential in alkaline medium was investigated to better understand this observation. It was demonstrated that the acid groups were present almost only in the core of the particles and that their deprotonation was possible using an alkaline tempering. Two phenomena occurred simultaneously leading to the charge appearance at the particle surface: i) the diffusion of hydroxide ions into the particles, allowing the migration of the negative charges to the particle surface with an appearance rate per mol of particles of 2.0 10−3m3 mol−1 s−1 (multiplied by the hydroxyl ion concentration), and ii) the hydrolysis of ester groups of methyl methacrylate units characterized by a pseudo first order kinetics with k = 3.0 10−9 m3 mol−1 s−1. By carefully choosing the parameters of the tempering process, hydrolysis is minimized and anionic particles can be prepared with stable and controlled charges coming from the anionic comonomer. Doing so, anionic PMMA-like particles exhibited a stable zeta potential of −11.5 mV.

New Insights into High-Temperature Anion-Exchange Membrane Fuel Cells

Until a few years ago, the operation of anion-exchange membrane (AEM) fuel cells (AEMFCs) at temperatures above 70 oC was a real challenge, mainly due to the temperature limitation of the AEMs. Recently, with the remarkable progress made in the development of stable AEMs, more and more AEMFC tests could be performed at higher cell temperatures, mainly at 70-85 oC. Very recently, very few studies even reported the operation of AEMFCs at 90-95 oC. In the past year, we presented the first results of what we call high-temperature AEMFCs (HT-AEMFCs) tested at cell temperatures above 100 oC. At these temperatures, we could obtain hydroxide conductivities close to 300 mS cm-1, the highest hydroxide conductivity ever measured for an AEM. The first HT-AEMFC results are very encouraging and represent a significant landmark for the research and development of fuel cell technology, opening a wide door for a new field of research - the HT-AEMFCs. At this initial stage, however, there are many open questions and unknowns, mainly regarding the stability of the polymeric materials under these high temperatures. In this talk, this topic will be discussed, and new exciting and surprising insights will be presented.References “A high-temperature anion-exchange membrane fuel cell”; John C. Douglin, John R. Varcoe, and Dario R. Dekel; J. Power Sources Advances 5, 100023, 2020.“Quantifying the critical effect of water diffusivity in anion exchange membranes for fuel cell applications”; Karam Yassin, Igal G. Rasin, Simon Brandon, and Dario R. Dekel; J. Membrane Sci. 608, 118206, 2020.“A High-Temperature Anion-Exchange Membrane Fuel Cell with a Critical Raw Material-free Nitrogen-doped Carbon Cathode”; John C. Douglin, Ramesh K. Singh, Saja Haj, Songlin Li, Jasper Biemolt, Ning Yan, John R. Varcoe, Gadi Rothenberg, and Dario R. Dekel; Chemical Engineering J. Adv. 8, 100153, 2021.“A surprising relation between operating temperature and stability of anion exchange membrane fuel cells”; Karam Yassin, Igal G. Rasin, Sapir Willdorf-Cohen, Charles E. Diesendruck, Simon Brandon, and Dario R. Dekel; J. Power Sources Adv. 11, 100066, 2021.“Magnetic-field-oriented mixed-valence-stabilized ferrocenium anion-exchange membrane”; Xin Liu, Na Xie, Jiandang Xue, Mengyuan Li, Chenyang Zheng, Junfeng Zhang, Yanzhou Qin, Yan Yin, Dario R. Dekel, Michael D. Guiver; Nature Energy, just accepted (https://doi.org/10.1038/s41560-022-00978-y) 2022.“Non-Monotonic Temperature Dependence of Hydroxide Ion Diffusion in Anion Exchange Membranes”; Tamar Zelovich, Leslie Vogt-Maranto, Cataldo Simari, Isabella Nicotera, Michael Hickner, Stephen J. Paddison, Chulsung Bae, Dario R. Dekel, and Mark E. Tuckerman; Chemistry Mater., Chem. Mater. 34, 5, 2133-2145, 2022.

A dual bubble layer model for reactant transfer resistance in alkaline water electrolysis

Alkaline water electrolysis (AWE) can only operate efficiently at a relatively low current density of up to 0.6 A cm–2 because bubbles cover the electrode surface at high current densities. Generally, the upper limit of current density in an electrochemical reaction is determined by the mass transfer of the reactant. Here, we propose a dual bubble layer model for the reactant transfer resistance of the oxygen evolution reaction in AWE. Using simple cylindrical nickel electrodes of different diameters, we conducted electrochemical impedance spectroscopy and microscopic observations with a high-speed video camera. The relationship between the polarization curve of the oxygen evolution reaction in AWE and the mass transfer resistance of hydroxide ions was investigated. At current densities above 0.5 A cm‒2, the bubble layer completely covered the electrode surface. This bubble layer consisted of two layers: an inner one formed by numerous primary bubbles generated on the electrode, and an outer one formed by coalesced large bubbles. The outer layer induces an additional solution resistance, Rsb. Changes in Rsb under various conditions were successfully explained by the thickness and void fraction of the bubble layer, conductivity of the solution, and tortuosity through the gap between bubbles. The inner layer resists the diffusion of hydroxide ions, and the resistance to hydroxide ion transfer through it (Rd) was modeled using the Warburg impedance element with a finite-length diffusion boundary. The charge-transfer resistance at the electrode surface (Rct) is roughly inversely proportional to the current density. This result indicates Rct is less sensitive to bubble coverage and almost all electrode surfaces are active in electrochemical reaction. The results showed that Rd increases with current density as much as Rct when the current density exceeds 1.0 A cm‒2. Up to a high current density of 2.5 A cm‒2, the change in polarization curve (ΔE/Δi) could be quantitatively explained by the sum of the bulk solution resistance, Rs0, additional solution resistance Rsb in the gaps between large bubbles, diffusion resistance Rd in the inner bubble layer, and charge-transfer resistance Rct at the electrode surface.

Molecular dynamics study of hydroxide ion diffusion in polymer electrolytes

Understanding the transport of hydroxide ion through polymer films designed to function as alkaline exchange membranes in fuel cells or solid-state alkaline electrolytes in batteries is critical to optimizing these materials for high power performance in these devices. We use molecular dynamics (MD) simulations to interrogate solid polymer electrolytes comprising methylated poly(dimethylaminomethyl styrene) (“pDMAMS+”) bearing hydroxide counterions to counterbalance the positively charged quaternized amino moiety. We elucidate the effects on hydroxide ion diffusivity of ion exchange capacity (IEC, 1.5–5.2 mEq g−1), hydration level (λ = 0–3 water molecules per ion), and co-polymerization with 4-butylstyrene (0–75 mol%), a charge-neutral monomer with similar properties to DMAMS. At 300 K, MD simulations yield a hydroxide ion self-diffusion coefficient in anhydrous pDMAMS+ of ∼ 0.02 μm2 s−1 and a glass-transition temperature (Tg) of ∼ 800 K, values that remain relatively unchanged for films with up to 50% 4-butylstyrene content. Increasing the 4-butylstyrene content to 75% results in a polymer with a lower Tg, ∼500 K, and a corresponding three-fold increase in the hydroxide ion diffusion coefficient to ∼ 0.06 μm2 s−1. As expected, increasing the hydration level increases both hydroxide diffusivity and conductivity across the entire range of compositions. 4-butylstyrene content lowers the available ion content, eventually decreasing overall hydroxide conductivity. MD simulations provide a powerful method to estimate the ion and co-monomer contents that will maximize hydroxide conductivity for a given range of polymer compositions and hydration, greatly reducing the need to synthesize and test the full range of compositions experimentally.

Translational Jump-Diffusion of Hydroxide Ion in Anion Exchange Membrane: Deciphering the Nature of Vehicular Diffusion.

Earlier, ab initio and reactive force-field-based molecular dynamics (MD) simulation studies suggested an overwhelming contribution of the vehicular diffusion in the total diffusion of hydroxide ions rather than structural diffusion. But does the vehicular diffusion occur via small-step displacement? This question is important to have an understanding of the real characteristics of vehicular diffusion. To answer this question, we perform a classical molecular dynamics simulation of a system containing a hydroxide ion exchange membrane polymer and hydroxide ion at different hydration levels and temperatures using the same molecular force field (Dubey, V. Chem. Phys. Lett. 2020, 755, 137802), which successfully captured the microscopic structure and dynamics of the system. We use the translational jump-diffusion approach, used previously in supercooled water for understanding the origin of breakdown of the Stokes-Einstein relation, to calculate the jump-diffusion coefficient of hydroxide ion and water in the anion exchange membrane. We have seen a significant role of hydration level and temperature in the mechanism of vehicular diffusion. In overhydrated membrane, both hydroxide ions and water molecules diffuse via both small- and large-step displacement. With decreasing hydration level and temperature, the diffusion is increasingly governed by the jump-diffusion mechanism. The larger contribution of jump-diffusion comes from the stronger caging of the diffusing species by the solvent at lower hydration levels and temperature. These results, therefore, suggest that the hydration level and temperature of the hydroxide ion exchange membrane determine the detailed mechanism of the vehicular diffusion of hydroxide ion, especially whether the diffusion follows hydrodynamics or not.

Non-Monotonic Temperature Dependence of Hydroxide Ion Diffusion in Anion Exchange Membranes

Non-Monotonic Temperature Dependence of Hydroxide Ion Diffusion in Anion Exchange Membranes

High-performance COF-based composite anion exchange membrane sandwiched by GO layers for alkaline H2/O2 fuel cell application

With well-defined structure and high stability, covalent organic framework (COF) inspires the preparation of new ion-conducting materials for anion exchange membrane (AEM) in alkaline fuel cell. In order to reveal the influence of micro-nano structure within COF ordered channels on the hydroxide diffusion, we construct a multi-dimensional composite membrane by combining two-dimensional lamellar COF with one-dimensional polymer chains. The quaternary ammonium-modified COF-LZU1 (QAmCOF-LZU1) is incorporated into quaternized poly (2,6-dimethyl-1,4-phenylene oxide) (QAPPO) to fabricate QAmCOF-LZU1/PPO composite membranes. The rapidly diffusion of hydroxide ions in the first solvent shell formed by the huge amount of quaternary ammonium groups in the ordered COF channels is investigated by molecular dynamics simulations. Afterwards, sulfonated graphene oxide (GO) is coated on both surfaces of the membranes via ionic interactions and π-π interactions to obtain GO@QAmCOF-LZU1/PPO sandwich membranes, which would avoid excessive swelling of membranes and leakage of QA groups. Especially, the GO-sandwiched membrane exhibits strikingly high stabilities and excellent H2/O2 fuel cell performance with a peak power density of 242 mW cm−2 at 60 °C. This study provides an effective strategy to construct ion-conducting COF-based composite membranes for high-performance alkaline fuel cell.

Electrochemical recovery of phosphorus from wastewater using tubular stainless-steel cathode for a scalable long-term operation

Phosphorus (P) is an irreplaceable element, playing a vital role in living organisms, yet has limited earth reserves. The possibility of P recovery from wastewaters by electrochemically-induced calcium phosphate precipitation (ECaPP) was demonstrated previously. The current study presents a novel scalable prototype consisting of a column-shaped electrochemical reactor, a tubular stainless-steel cathode, and a Pt coated Ti anode. The adhesion of solids to the cathode, important for product recovery, was shown not to be negatively impacted by electrodes’ vertical placement. The influence of current (density), hydraulic retention time (HRT), and initial phosphate concentration in this prototype were examined under continuous flow operation. The system accomplished the highest P removal rate (1267 mg/day) at 1.5 d HRT and 800 mA in treating undiluted cheese wastewater with 48.5 kWh/kg P. Moreover, the prototype showed high stability and efficiency (> 50%) over 173 days of continuous operation without performing maintenance. After turning off the current (0 mA), the system realized a surprising P removal jump up to 97.3%, revealing the delayed diffusion of hydroxide ions by the deposition layer. The calculation of CAPEX and OPEX of ECaPP in treating 100 m3 cheese wastewater per week indicates that the ECaPP plant can realize net-positive from the 12th year. The recovered solids have relatively high P content (> 9wt%) and insignificant contamination of heavy metals. Overall, the proven suitability of the scalable prototype can pave the way towards the actual adoption of the ECaPP process.

Preparation and characterization of basalt fabrics coated with zirconia obtained by sol-gel method for textile reinforced concrete

The poor alkali resistance of basalt fabric greatly affects the mechanical properties of textile reinforced concrete. In this study, dense zirconia coating obtained by sol-gel method was coated on the basalt fabrics surface as additional sizing to improve the alkali resistance of basalt fabrics. The morphology, wettability and phase composition of the fabric surfaces was characterized by scanning electron microscopy (SEM), static water contact angle (SWCA), X-ray powder diffraction (XRD), fourier transform infrared spectra (FI-IR), X-ray photoelectron spectroscopy (XPS) and Raman. The tensile properties of various basalt fabrics immersed in alkaline solution for different time and the mechanical property of concrete composites were examined by universal material testing machine. Results showed that a protective membrane was formed on the surface of basalt fabrics to prevent the diffusion of hydroxide ions. The final strength retention ratio of BF-c-ZrO2 (Basalt fabric-coated-Zirconia) fabrics could maintain at 89.92% compared with that of pristine basalt fabrics, which reached below 40%. The compressive strength and flexural strength of BF-c-ZrO2 fabrics reinforced concrete increased by 10.15% and 19.0% compared with that of pristine basalt fabrics reinforced concrete. A theoretical model was proposed to predict the ultimate flexural bearing capacity of BF-c-ZrO2 fabric reinforced concrete based on the equivalent stress rectangle theory. The corresponding predicted value compared with experimental result indicated a good coincidence and a reasonable accuracy, which was less than 5% of their discrepancy.

Transient simulation of porous cathodes of zinc-nickel single-flow batteries based on lattice Boltzmann method

The charging of positive electrode of zinc-nickel single-flow battery involves processes of hydroxide ion transport in pores, proton diffusion in matrixes and electrochemical reaction on matrix/solution interfaces. A lattice Boltzmann model is developed to study the dynamics of charging processes of positive electrodes at the pore-scale level by considering complex structures of porous electrodes. The concentration evolutions of hydroxide ions and proton during the charging process are revealed, and effects of charging current density, porosity and thickness of the porous electrode on the dynamic processes are investigated. Simulation results show that the diffusion resistance of proton in the small-size particle is low, which is conducive to a quick charging process. Under the same operation condition, the charging rate is limited by the particle size instead of the particle position in the electrode. Increasing the charging current density can reduce the charging time, but the effect gradually weakens. The high charging current density tends to cause the excessive concentration polarization. A large electrode thickness is not conducive to the diffusion of hydroxide ions, and too small porosity may even hinder the diffusion of hydroxide ions. Both cases cause a large concentration polarization in the porous electrode.

Non-Monotonic Change of Hydroxide Ion Diffusion with Increasing Temperature in Anion Exchange Membranes

The development of reliable, cost-effective polymer architectures for use as anion exchange membranes (AEMs) is an important challenge for emerging electrochemical device technologies. In this work, we present a fully atomistic ab initio molecular dynamics study of carefully designed idealized AEM models using nano-confined structures, in order to obtain a molecular-level understanding of the effect of temperature on hydroxide ion diffusion mechanisms in AEMs. We find that the hydroxide ion diffusion coefficient changes non-monotonically with increasing temperature. While this is consistent for all systems, the specific reasons underlying this behavior depends on the level of hydration. Furthermore, while the diffusion of water molecules and hydroxide ions do not necessarily share the same trends, we find that the water structure, distribution, and mobility have a major impact on the hydroxide ion diffusion at all temperatures. The results presented in this study enable us to define the optimal temperature requirements to achieve high hydroxide conductivity, for each setup of AEM model.

Description of Hydroxide Ion Structural Diffusion in a Quaternized SEBS Anion Exchange Membrane Using Ab Initio Molecular Dynamics

The transport via structural diffusion of hydroxide ions through a segment of the functionalized polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (QSEBS) membrane is analyzed at two ...

Effect of ion exchange capacity and water uptake on hydroxide transport in PSU-TMA membranes: A DFT and molecular dynamics study

Anion Exchange Membranes (AEMs) are nowadays used in a very wide range of different applications, from electrodialytic systems for water treatment, to Fuel Cells for energy generation. In many of these cases, the AEM is in contact with water molecules, either in aqueous or gas phase, which can strongly interact with the AEM polymer, thus affecting membrane properties. The role of water in fully swollen AEM and its effect on the diffusion of hydroxide is the focus of this work. Density Functional Theory (DFT) based calculations were merged with Molecular Dynamics (MD) simulations coming to a more accurate description of the ionic exchange capacity effect on the hydroxide ion diffusion in AEM. Hydration of the polysulfone-tetramethylammonium (PSU-TMA), one of the most studied systems in Alkaline anion exchange Membrane Fuel Cells (AMFC), was determined by DFT developing an efficient algorithm. The ab-initio calculations predicted water uptake, at different Ion Exchange Capacity (IEC), resulted in good agreement with the experimental data. The theory-experiment comparison identified a threshold range of 1.2–1.7 meq/g as critical IEC at which over-swelling of functionalized polymer matrix occurs. From this comparison, three IEC values were chosen to perform MD simulations in order to evaluate the hydroxyl diffusion coefficients as a function of the different IEC where the ab-initio water uptake and partial charges, utilized in the force-field, were adopted. Diffusion coefficients in the bulk of the membrane were calculated through the Mean Square Displacement (MSD) over 100 ns MD trajectories, and then compared with the values obtained by the analytical Mackie-Meares's model, finding good agreement between the two computational methodologies. In addition, the computed diffusion coefficients were compared with the experimental conductivity data with a fair agreement. It is worth noting that, thanks to the minimization of adjustable parameters, the present work can be easily adapted to study any type of Ion Exchange Membrane (IEM) and counter-ions diffusion.

Structure and thermal stability of fluorhydroxyapatite and fluorapatite obtained by mechanochemical method

This work shows that mechanochemical synthesis allows the obtaining of hydroxyapatite in which fluorine ions replace hydroxyl ions either partially or completely after 30 ​min of synthesis. The crystal structure of the materials obtained and their thermal stability when heated in the air were studied. It has been shown that the fluorine ions in the hexagonal channel of hydroxyapatite hinders diffusion of hydroxide ions at high temperatures, which leads to increased thermal stability of the apatite.

Hydroxide Ion Diffusion in Anion-Exchange Membranes at Low Hydration: Insights from Ab Initio Molecular Dynamics

Operation of anion-exchange membrane (AEM) fuel cells (AEMFCs) results in gradients in the cell that can lead to low-hydration conditions within the cell. It is therefore important to investigate h...

Ab Initio Molecular Dynamics Study of Hydroxide Diffusion Mechanisms in Nanoconfined Structural Mimics of Anion Exchange Membranes

The development of reliable, cost-effective polymer architectures for use as anion exchange membranes (AEMs) is an important challenge facing emerging electrochemical device technologies. Elucidation of key design principles underlying these electrolytes requires a fundamental understanding of the hydroxide ion transport mechanism in the aqueous region of an AEM. To this end, we have carried out a series of atomistic ab initio molecular dynamics calculations. To mimic the complex AEM nanoconfined environment, we employ graphane bilayers or carbon nanotubes to which selected cationic groups are attached and which are subsequently filled with water and hydroxide ions to achieve target water-to-cation ratios and overall electrical neutrality. The complex structure of water under nanoconfinement differs from the bulk and is controlled by the shape and size of the confining volume. Consequently, the local hydroxide ion diffusion mechanisms in different chemical and geometric environments is also seen to differ...