anion conductivity

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Anion conductivity refers to the ability of anions, negatively charged ions, to move through a medium, typically in electrolytes or ionic conductors. It is a critical parameter in understanding ionic transport mechanisms, influencing the performance of batteries, fuel cells, and other electrochemical devices.

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Key research themes

1. How do polymer morphology and microstructural orientation influence anion conductivity in anion exchange membranes (AEMs)?

This theme investigates the relationship between polymer microstructure, molecular orientation, and anion transport efficiency in AEMs. Understanding how mechanical deformation and nanoscale morphology affect OH⁻ conductivity is critical for optimizing membrane performance in fuel cells and electrolyzers, targeting improvements in ionic pathways, water management, and dimensional stability.

Microstructural orientation of anion exchange membrane through mechanical stretching for improved ion transport

by Xianguo Li

2024

Key finding: This study combined molecular dynamics simulation with experiments to demonstrate that mechanical stretching induces polymer chain orientation and elongation of water clusters in quaternized poly(2,6-dimethyl-1,4-phenylene... Read more

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Preparation and Identification of Optimal Synthesis Conditions for a Novel Alkaline Anion-Exchange Membrane

by Angel Irabien

2024, Polymers

Key finding: Developed novel CS:PVA polymer blend AEMs doped with copper nanoparticles incorporated into layered porous titanosilicate, stannosilicate, and various zeolites showed that both synthesis method and filler morphology... Read more

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2. What are the intrinsic and extrinsic factors controlling ion conductivity mechanisms in various electrolyte systems, focusing on polymeric, ceramic, and liquid electrolytes?

This theme covers fundamental conduction mechanisms in different electrolyte classes—conducting polymers, ceramic Na-ion conductors, ionic liquids, and glyme-based electrolytes—addressing the interplay of ion solvation, structural defects, dopant effects, and phonon scattering. It sheds light on how molecular structure, doping, and electrolyte composition influence ionic mobility, activation energies, and overall conductivity, informing electrolyte design for batteries and fuel cells.

Intrinsic conductivity of conducting polymers

by Steven Kivelson

2015

Key finding: Demonstrated that in conducting polymers such as heavily doped polyacetylene, charged dopant ions are spatially separated from quasi-1D conduction paths, suppressing resistive back scattering and avoiding 1D localization due... Read more

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Electrical conductivity of melter type slags

by Sharif Jahanshahi

2023

Key finding: Showed that electrical conductivity of multi-component molten slags depends strongly on iron oxide content, slag basicity, and oxidation state. Iron oxide additions increase both ionic and electronic conduction, with... Read more

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Electric Dipoles and Ionic Conductivity in a Na+Glass Electrolyte

by Jorge Ferreira

2024, Journal of The Electrochemical Society

Key finding: Reported that electric dipoles (A2O and OA⁻) in Na-glass electrolytes condense into ferroelectric clusters below approximately 110°C, leading to alignment under applied fields that significantly enhance Na⁺ ionic conductivity... Read more

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The Nature of Ion Conduction in Methylammonium Lead Iodide: A Multimethod Approach

by Tae-Youl Yang

2024, Angewandte Chemie

Key finding: Using comprehensive experimental methods including NMR and tracer diffusion, established that iodine ions, specifically iodine vacancies, dominate long-range ionic conduction in MAPbI3 perovskite, while Pb²⁺ and... Read more

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3. How do ceramic structure and composition affect Na-ion conductivity and thermal transport in solid electrolytes?

This theme focuses on the transport phenomena in ceramic Na-ion conductors with NASICON structures and related materials, emphasizing the influence of compositional tuning, site occupancy, and lattice dynamics on ionic conductivity and thermal conductivity. Balancing enhanced ion mobility against thermal management is crucial for developing efficient solid-state electrolytes.

Ionic and Thermal Transport in Na-Ion-Conducting Ceramic Electrolytes

by Ijaz Ul Mohsin

2023, International Journal of Thermophysics

Key finding: Measured ionic and thermal transport in Na1+xAlxTi2−x(PO4)3 (NATP) and Na1+xZr2(SiO4)x(PO4)3−x (NaZSiP) NASICON-type ceramics, finding NaZSiP materials display ionic conductivities two orders of magnitude higher than NATP,... Read more

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Thermodynamic calculation of the ionic conductivity of LiPON glasses and solid electrolytes

by Alberto López-Grande

2025, Journal of Materials Chemistry A

Key finding: Presented a thermodynamic model linking phase equilibrium and oxynitride compound formation in the Li2O–P2O5–P3N5 system to predict ionic conductivity in LiPON glassy solid electrolytes. The approach explains conductivity... Read more

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All papers in anion conductivity

Preparation and Identification of Optimal Synthesis Conditions for a Novel Alkaline Anion-Exchange Membrane

by Angel Irabien

2024, Polymers

The physicochemical and mechanical properties of new alkaline anion-exchange membranes (AAEMs) based on chitosan (CS) and poly(vinyl alcohol) (PVA) polymers doped with unsupported copper nanoparticles (NPs) and copper exchanged over... more

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Preparation and Identification of Optimal Synthesis Conditions for a Novel Alkaline Anion-Exchange Membrane

by Clara Casado-coterillo

2023, Polymers

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The critical relation between chemical stability of cations and water in anion exchange membrane fuel cells environment

by Michal Amar

2023, Journal of Power Sources

Water-free ex-situ stability test simulates the environment of AEMFCs in operation. Water/hydroxide has a critical influence on stability of quaternary ammonium groups. MD show shielding effect of water on the hydroxide, reducing its... more

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Preparation and Identification of Optimal Synthesis Conditions for a Novel Alkaline Anion-Exchange Membrane

by Clara Coterillo

2022, Polymers

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Enhanced OH− Conductivity for Fuel Cells with Anion Exchange Membranes, Based on Modified Terpolymer Polyketone and Surface Functionalized Silica

by Narges Ataollahi

2022, Energies

Several modified terpolymer polyketones (MPK) with N-substituted pyrrole moieties in the main chain and quaternized amine in the side group were synthesized for use as anion exchange membranes for fuel cells. The moieties were carried by... more

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Review of ambient CO2 effect on anion exchange membranes fuel cells

by Dario Dekel

2018

Over the past 10 years, there has been a surge of interest in anion exchange membrane fuel cells (AEMFCs) as a potentially lower cost alternative to proton exchange membrane fuel cells (PEMFCs). Recent work has shown that AEMFCs achieved... more

Figure 7. Effect of CO, on fuel cell performance: a) Fuel cell polarization curves for a comparison of ambient air with clean air/pure O,. Data adapted from Refs. [9, 11, 12,71,72]. b) Immediate effect of switching (at t=0) from CO,-free air to ambient air in the cathode of a fuel cell operating at constant current density. The data shown was normalized by the initial power density or voltage. Data adapted from Refs. [11,73]. to Suzuki et al.,"" an AEMFC operated with H, and clean air with an AEM in the OH™ form could have a cell voltage up to

WiHHaM £. WIUSTAIN FeECeIVved MIs FN.U. in chemical engineering from the Illi- nois Institute of Technology in 2006. He then moved to Georgia Tech for his postdoctoral studies. He now runs the Laboratory for Electrocata- lysts and Fuels as a Full Professor at the University of South Carolina. His group focuses on the development of novel catalysts for electrochemi- cal synthesis, acidic and alkaline fuel cells and electrolyzers, lithium-ion and aqueous batteries, and so forth. He has been the recipient of several awards, including the Illinois Institute of Technology Young Alumnus Award, U.S. Department of Energy Early Career Award, and Fulbright Scholar Fellowship.

Figure 1. Schematic representation of electrode reactions and ion and water transport in an A) AEMFC and B) proton-exchange membrane fuel cell (PEMFC). Reprinted with permission from Ref. [14].

Figure 2. The change in alkaline anion content if an OH -form Tokuyama A201 AEM was exposed to air (wet conditions); #: OH”, e: CO,”, a: HCO;. Adapted from Ref. [17] with permission of the Electrochemical Society. Identical carbonation behavior was also found in a model developed by Myles et al.?" They divided the carbonation pro- cess into two regions: hydroxide depletion [corresponding to Equations (1) and (2)], followed by bicarbonate accumulation [corresponding to the backward reaction in Equation (2)], until

Figure 3. Conductivity of AEM (A201, Tokuyama Co.) at 50°C, 95% RH, as a function of the equivalent fraction of carbonate ion species (CO, + HCO, ) to quaternary ammonium base. Adapted from Ref. [10] Copyright 2013, with permission from Elsevier. Figure 3 shows AEM conductivity as a function of the rela- tive fraction of functional groups occupied by CO,” and HCO; , as measured by Suzuki et al." As the fraction of car- bonate and bicarbonate species in the AEM increases, the con- ductivity decreases, which is to be expected from the expres-

Figure 4. Change in OH -form AEM (methylated poly(hexamethyl-p-terphe- nylbenzimidazolium) (HMT-PMBI)) conductivity with time from the beginning of exposure to ambient air containing CO,. Adapted from Ref. [9] with per- mission from The Royal Society of Chemistry.

Figure 5. Conductivity data reported in the literature for AEMs in the three different anion forms. Adapted from Refs. [9, 10,17, 22, 29,37, 38, 40-49].

Figure 6. Effects of CO, concentration in the cathode inlet gas on polariza- tion curves of the AEMFCs at the anode and cathode (the difference in volt- age compared to CO,-free gas is displayed). Adapted from Ref. [60]. The observation of decreasing ORR reaction rate with in- creased carbonation was also observed in reacting environ- ments more similar to those of operating AEMFCs. For exam- ple, Gunasekara et al. studied the effect of carbonation on the ORR at the interface with a membrane, as opposed to the tra- ditional tests in aqueous solutions; a special electrochemical cell was constructed, which consisted of flat-tip microelectro- des pressed against an AEM.°*" Oxygen gas was supplied to the cell through a porous glass filter. Although the exchange current density with a carbonated AEM was slightly lower than that in the case of an AEM with OH” only (carbonate-free), overall, the carbonates had little effect on the intrinsic ORR ki- netics.5*! However, the study also reported a significant de- crease in the O, diffusion coefficient (one order of magnitude lower) with a CO,?--form AEM relative to an AEM in the OH™ form, which greatly affected the electrochemical reaction rate. This small effect of CO, on the intrinsic ORR kinetics was con-

Figure 8. Schematic representation of AEMFC current density on the self-purging process in the AEM. Left: at low current density, OH” is slowly formed in the cathode, but quickly converted into HCO; /CO,”-. Right: at high current density, OH” surpasses the carbonation process and HCO; /CO,?- are released at the anode as CO,. The self-purging mechanism is the process by which HCO; / CO,” can be removed from the AEMFC under high current conditions, which may help to improve cell performance, as demonstrated in several studies.®'*'*'””! The process may be explained as follows: at relatively high current densities, a large amount of OH anions are formed as a result of the high rate of ORR in the cathode [Eq. (7)]. The existing charge, which includes HCO,” and CO,”-, is transported through the AEM to the anode electrode. It is not known whether these ions react directly with H, [Eqs. (10) and (11)] or whether OH” remains the active anion [Eq. (9)] and under hydroxide consumption the equilibrium is shifted in the reverse direction of Equa- tions (1) and (2). As discussed above, anode studies alone sug- gest that it is the latter. In either case, the result is that CO, gas is readily released to the anode and purged from the system. This concept is schematically shown in Figure 8. At in- creased current densities, the rate of OH production in the cathode overcomes the rate of CO, absorption into the mem- brane, and therefore, the overall result is the increase in OH™ concentration at the expense of HCO,~/CO,”- concentration. It

Figure 9. CO, emission from the anode exhaust of an AEMFC operated with ambient air during a stepwise increase in current density. Adapted from Ref. [72] Copyright 2009 with permission from the Electrochemical Society.

Figure 10. Modeling results for the effect of operating conditions on AEM ex situ conductivity: a) Model predictions by Grew et al.” for Tokuyama A201 AEM ionic conductivity in equilibrium with gas containing 0 (pure O,; blue line), 1 (green line), and 385 ppm CO, (red line) (Copyright 2011 with permission from the Electrochemical Society). b) Model predictions for AEM conductivity at different hydration levels by Kiss et al.?7) The hydroxide (blue line) and mixed (combined carbonate and bicarbonate; red line) forms are plotted (Copyright 2013 with permission from the Electrochemical Society).

Figure 11. Results of the computational model for profiles of equivalent anion ratios of a) OH~, b) CO,?-, and c) HCO,” across the membrane be- tween the anode (0 um) and cathode (28 um) for different current densities (100, 500, 1000, and 1500 mAcm~”). Reprinted with permission from Ref. [67].

[a] ETFE = ethylene tetrafluoroethylene, PTFE =polytetrafluoroethylene. [b] Anion content in the AEM was measured by ion exchange to Cl” and titratio based on the Warder method. [c] RH = relative humidity. Table 1. Summary of OH -form AEM neutralization to HCO, /CO,*.

[a] ATMPP =aminated trimethyl poly(phenylene), QAPSF = quaternary ammonium polysulfone, PSF = poly(arylene ether sulfone), PSU = polysulfone, TMA trimethylamine, DABCO = 1,4-diazabicyclo[2.2.2]octane, PPO = poly(p-phenylene oxide), PS= polystyrene, BTMA=benzyltrimethylammonium, HB-QPVBC hyperbranched quaternized poly[4-(chloromethyl)styrene]. [b] Exchanged for mixed HCO;-/CO,;” form. [c] Equilibrated with air containing 38% CC [d] Equilibrated with pure O). [e] In water. [f] 95% RH. Table 2. AEM ionic conductivities in different anion forms.

[a] Extracted from polarization curves. [b] At 200 mAcm~. [c] At 100 mAcm~*. [d] At 4 mAcm~®. [e] Volume ratio of 1:2. Table 3. Effect of CO, on AEMFC performance.

Table 4. Summary of computational models for AEM properties.

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A practical method for measuring the true hydroxide conductivity of anion exchange membranes

by Dario Dekel

2018

A B S T R A C T Hydroxide ions in anion exchange membranes (AEMs) are quickly exchanged for larger and less mobile anions (CO₃ 2− and HCO₃ −) when the membrane is exposed to ambient air. Therefore, reported conductivity values of AEMs in... more

Every 10 to 30min, the ionic resistance of the membrane was measured using a standard 4-probe technique [26], and the in-plane anion conductivity was then calculated using the equation: Fig. 2. Changes in AEM conductivity before, during and after applying 100 pA direct current, with a change in the ambient gas after 36 h. Test conditions remained constant at 90% RI and 40°C. As can be seen in Fig. 2, when a current of 100 pA is applied through the membrane, its conductivity starts to increase at an apparently ex- ponential rate. This significant increase in measured anion conductivity is explained by the electrochemical reactions taking place at the elec- trodes. At the positive electrode (cathode), OH” is produced according to:

Fig. 1. Schematic illustration of the experimental setting.

Fig. 3. Schematic illustration of the processes taking place in the AEM while applying the direct current under the conditions of our conductivity test

Fig. 4. Changes in the measured conductivity of the AEM while applying current and changing the ambient gas: first, N2 containing 400 ppm CO,, then pure N>

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