Sulfonated poly(ether ether ketone) as an alternative charged material to poly(vinyl chloride) in the design of ion-selective electrodes

To date, poly(vinyl chloride) (PVC) is the most used polymer in the design of ion selective electrode (ISE) membranes. This paper is focused on the use of sulfonated poly(ether ether ketone) (SPEEK) as an alternative material to PVC for the design of ISEs. SPEEK of the desired degree of sulfonation is synthesized from poly(ether ether ketone) (PEEK). An NH₄⁺-ISE has been chosen as a model electrode to study the efficiency of SPEEK as polymer matrix of the membrane. The material was evaluated in ionophore free ion exchanger membranes as well as in ion-selective electrodes membranes containing nonactine as ionophore. Analytical performance parameters of the prepared electrodes were evaluated. The electrodes show a slope between 50 and 60 mV dec⁻¹ depending on both the calibration medium and the membrane composition. A linear range of response between 10⁻⁴ and 1.0 M and a lifetime of 1-2 months were obtained. The interferences of cations such us Ca²⁺, Na⁺, Li⁺ and K⁺ over the prepared ISEs are studied as well. Although the plasticizer in the SPEEK based membrane matrix is not necessary, its presence improves the sensibility. This makes SPEEK a good potential choice over alternative membrane matrices reported in the literature and a promising platform for the establishment of membrane components.     

PEO/P(VdF-HFP) blend based Li+ ion-conducting composite polymer electrolytes dispersed with dedoped (insulating) polyaniline nanofibers

Composite polymer electrolyte membranes composed of poly(ethylene oxide) (PEO), poly(vinylidene fluoride-hexafluoropropylene) {P(VdF-HFP)} blends, dedoped (insulating) polyaniline (PAni) nanofibers, and LiClO₄ as salt have been synthesized with varying fraction of dedoped PAni nanofibers (from 2 to 10 wt.%). The ionic conductivity of PEO–P(VdF-HFP)–LiClO₄ electrolyte system increases with increase in the fraction of dedoped polyaniline nanofibers. This could be attributed to the incorporation of nanofibers (aspect ratio >50), which may provide high ion conducting path along the interface due to Lewis acid–base interactions between Li⁺ ions and lone pair of electrons of nitrogen atom of polyaniline. However, at higher fraction (>6 wt.%), the nanofibers get phase separated from the polymer matrix and form domain-like structures, which may act as physical barrier to the conduction of Li⁺ ions resulting in decreased ionic conductivity. Electrochemical potential window and interfacial stability of nanofibers dispersed polymer electrolyte membranes are also better than that of nanofibers free membranes.     

Cs+ -selective membrane electrodes based on ethylene glycol-functionalized polymeric microspheres

A new strategy for improving the robustness of membrane-based ion-selective electrodes (ISEs) is introduced based on the incorporation of microsphere-immobilized ionophores into plasticized polymer membranes. As a model system, a Cs⁺-selective electrode was developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) as the ion exchanger. Electrodes were evaluated with respect to Cs⁺ in terms of sensitivity, selectivity, and dynamic response. ISEs containing P-EG and TFPB that were plasticized with 2-nitrophenyl octyl ether (NPOE) yielded a linear range from 10⁻¹ to 10⁻⁵ M Cs⁺, a slope of 55.4 mV/decade, and a lower detection limit (log a_Cs) of −5.3. In addition, these membranes also demonstrated superior selectivity over Li⁺, Na⁺, and alkaline earth metal ion interferents when compared to analogous membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) or membranes containing a lipophilic, mobile ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) as ionophore.     

Cs+ and Ba2+ Selective Transport by a Novel Self-Assembled Isoguanosine Ionophore Through Polymer Inclusion and Bulk Liquid Membranes

5'-(Tert-butyldimethylsilyl)-2',3'-O-isopropylidene isoguanosine(isoG 1) serves as a selective Cs⁺ carrier in liquid membrane transport. IsoG~1 is a lipophilic nucleoside that self-assembles via hydrogen bonds and cation-dipole interactions to form a stable decamer sandwich complex with Cs⁺. Using an acidic receiving phase, Cs⁺ transport through polymer inclusion membranes (PIMs) was observed at concentrations of isoG 1 below 21 mM. When isoG 1 was precomplexed with Cs⁺ to give the (isoG 1)₁₀-Cs⁺decamer, flux was observed above 21 mM carrier. The Cs⁺ flux increased with increasing carrier concentration of the precomplexed (isoG 1)₁₀-Cs⁺ decamer. The Cs⁺ transport selectivity by isoG 1 was investigated in the presence of sodium salt solutions of high concentration. Excellent Cs⁺ flux and selectivity over the other alkali metal cations was observed in PIMs and bulk liquid membranes (BLMs). In the absence of Cs⁺, this ionophore exhibitsgood Ba²⁺ selectivity in BLMs.     

Ion transport numbers in crown-containing polymers

The predominant participation of anions of sorbed electrolytes in electrical charge transfer in polymers was demonstrated based on measurement of the transport numbers of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Tl⁺, and NO₃ ^–ions through homogeneous polymer membranes containing dibenzo-18-crown-6 or dibenzo-24-crown-8. The coordination reaction of the cations with the crown ethers in the polymer phase is the cause of the decrease in the proportion of cations in electrical charge transfer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 310–314, February, 1990.     

High Dielectric Poly(vinylidene fluoride)-Based Polymer Enables Uniform Lithium-Ion Transport in Solid-State Ionogel Electrolytes

Ionic liquids (ILs)-incorporated solid-state polymer electrolytes (iono-SPEs) have high ionic conductivities but show non-uniform Li⁺ transport in different phases. This work greatly promotes Li⁺ transport in polymer phases by employing a poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE), PTC] as the framework of ILs to prepare iono-SPEs. Unlike PVDF, PTC with suitable polarity shows weaker adsorption energy on IL cations, reducing their possibility of occupying Li⁺-hopping sites. The significantly higher dielectric constant of PTC than PVDF facilitates the dissociation of Li-anions clusters. These two factors motivate Li⁺ transport along PTC chains, narrowing the difference in Li⁺ transport among varied phases. The LiFePO₄/PTC iono-SPE/Li cells cycle steadily with capacity retention of 91.5 % after 1000 cycles at 1 C and 25 °C. This work paves a new way to induce uniform Li⁺ flux in iono-SPEs through polarity and dielectric design of polymer matrix.     

Potentiometric sensors for Ag+ based on poly(3-octylthiophene) (POT)

Potentiometric ion sensors were prepared from the conjugated polymer poly(3-octylthiopene) (POT). The influence of additional membrane components, including silver 7,8,9,10,11,12-hexabromocarborane (AgCB₁₁H₆Br₆) and potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (KTpFPB) as lipophilic salts, and [2.2.2]p,p,p-cyclophane as silver ionophore, was studied. The membrane components were dissolved in chloroform and membranes were prepared by solution casting on glassy carbon disk electrodes. For comparison, POT-based potentiometric sensors were also prepared by galvanostatic electrosynthesis of POT from the 3-octylthiophene monomer. All the POT-based ion sensors fabricated by solution casting show Nernstian or slightly sub-Nernstian response to Ag⁺, even those based only on POT without any additional membrane components. The potentiometric response of electrochemically polymerized POT depends on the film thickness and the doping anion incorporated in the conducting polymer during polymerization. It is of particular importance that chemically synthesized undoped POT (without any additives) shows a sensitive and selective potentiometric response to Ag⁺ ions although UV-vis results show that POT remains in its undoped form, i.e., POT is not oxidized by Ag⁺. This indicates that undoped POT can exhibit good sensitivity and selectivity to Ag⁺ also in the absence of metallic silver in the polymer film. In this case, the potentiometric response is related to interactions between Ag⁺ and the conjugated polymer backbone. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, 13–16, 2005     

The effect of ferric ions on the conductivity of various types of polymer cation exchange membranes

Recently, rejuvenated interest to fuel cells has posed a number of problems regarding the polymer electrolyte membrane properties and their behaviour in different electrolyte solutions. This work was dedicated to study the conductivity of H⁺-, Fe³⁺- and mixed H⁺/Fe³⁺-forms of cation exchange membranes Neosepta CMS, Nafion 112, 115 and 117 and Selemion HSF under conditions similar to these in the Fe³⁺/Fe²⁺–H₂/H⁺ fuel cell in the range of current densities 0–90 mA/cm². It was found that the conductivities of these membranes in 1.09 M H₂SO₄ solution decrease in the following order: Selemion HSF › Nafion 117 ≈ Nafion 115 ≈ Neosepta CMS › Nafion 112. Conductivities of perfluorinated membranes were discussed in terms of Hsu and Gierke percolation theory [20]. The Fe³⁺-forms of Nafion membranes studied displayed a monotonous decline in the resistance when current increased, which is a manifestation of gradual conversion of the Fe³⁺-form into H⁺-form of these membranes. Unlike the Nafion membranes, the Fe³⁺-forms of Neosepta CMS and Selemion HSF membranes exhibited a sharp jump of resistance at relatively high current densities (more than 70 mA/cm²) that is most probably a result of concentration polarization.     

Thiol-functionalized silica–mixed matrix membranes for silver capture from aqueous solutions: Experimental results and modeling

The study deals with an aqueous phase application of mixed matrix membranes (MMMs) for silver ion (Ag⁺) capture. Silica particles were functionalized with 3-mercaptopropyltrimethoxy silane (MPTMS) to introduce free thiol (–SH) groups on the surface. The particles were used as the dispersed phase in the polysulfone or cellulose acetate polymer matrix. The membranes were prepared by the phase inversion method to create more open and interconnected porous structures suitable for liquid phase applications. The effects of the silica properties such as particle size, specific surface area, and porous/nonporous morphology on the silver ion capture capacity were studied. It was demonstrated that the membranes are capable of selectively capturing silver from a solution containing significant concentrations of other metal ions like Ca²⁺. The membranes were studied to quantify the dynamic capacity for silver ion capture and its dependence on residence time through the adjustment of transmembrane pressure. The thiol–Ag⁺ interaction was quantified with quartz crystal microbalance in a continuous flow mode experiment and the observations were compared with the membrane results. One-dimensional unsteady state model with overall volumetric mass transfer coefficient was developed and solved to predict the silver concentration in the liquid phase and the solid silica phase along the membrane thickness at varying time. The breakthrough data predicted using the model is comparable with the experimental observations. The study demonstrates successful application of the functionalized silica–mixed matrix membranes for selective aqueous phase Ag⁺ capture with high capacity at low transmembrane pressures. The technique can be easily extended to other applications by altering the functionalized groups on the silica particles.     

Sulfonated polyimides as proton conductor exchange membranes. Physicochemical properties and separation H+/Mz+ by electrodialysis comparison with a perfluorosulfonic membrane

The properties of new sulphonated polyimide membranes (SP) – ion exchange isotherms, electrical conductivity, selectivity and proton–cation electrotransport – are compared with that of perfluorinated Nafion^® membrane. Both membranes when in contact with H⁺/M^z+ aqueous solutions (M^zM+=Na⁺, Cu²⁺, Cr³⁺) present an affinity to cations which increases with their valencies; however the affinity of one of the SP membranes for protons is approximately 10% higher than that of Nafion^®. The proton transport number is also 10% higher for this SP membrane than for Nafion^®. Using SP membranes for electrodialysis of H⁺/Cu²⁺ solutions produces solutions about 10% more concentrated in H⁺ and about 40% less concentrated in Cu²⁺ ions than with Nafion^® membranes in the same conditions. The difference in conductivity may be explained by differences in ionic clustering because of differences in the polymer structure of the two membranes, block copolymer for SP and statistic copolymer for Nafion^®. The difference in properties for the two SP membranes is explained in terms of the chemical structure of the non-sulfonated diamine groups used in the polymer synthesis. These SP membranes seem to be interesting materials for electromembrane processes in acid media.     

Olefin-Linked Covalent Organic Frameworks with Electronegative Channels as Cationic Highways for Sustainable Lithium Metal Battery Anodes

Despite the enormous interest in Li metal as an ideal anode material, the uncontrollable Li dendrite growth and unstable solid electrolyte interphase have plagued its practical application. These limitations can be attributed to the sluggish and uneven Li⁺ migration towards Li metal surface. Here, we report olefin-linked covalent organic frameworks (COFs) with electronegative channels for facilitating selective Li⁺ transport. The triazine rings and fluorinated groups of the COFs are introduced as electron-rich sites capable of enhancing salt dissociation and guiding uniform Li⁺ flux within the channels, resulting in a high Li⁺ transference number (0.85) and high ionic conductivity (1.78 mS cm⁻¹). The COFs are mixed with a polymeric binder to form mixed matrix membranes. These membranes enable reliable Li plating/stripping cyclability over 700 h in Li/Li symmetric cells and stable capacity retention in Li/LiFePO₄ cells, demonstrating its potential as a viable cationic highway for accelerating Li⁺ conduction.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin Immobilized in a Polymeric Ionic Liquid Film

A polymer film based on polymeric ionic liquid, which was poly(1‐vinyl‐3‐butylimidazolium chloride) (poly(ViBuIm⁺Cl^?)for short), was firstly used as matrix to immobilize hemoglobin (Hb). FTIR and UV‐vis spectra demonstrated that the native structure of Hb was well preserved after entrapped into the polymer film. The Hb immobilized in the poly(ViBuIm⁺Cl^?) film showed a fast direct electron transfer for the Hb‐Fe^III/Fe^II redox couple. Based on the direct electron transfer of the immobilized Hb, polyvinyl alcohol (PVA)/Hb/poly(ViBuIm⁺Cl^?)/GC electrode displayed good sensitivity and wide linear range for the detection of H₂O₂. The linear range of the PVA/Hb/poly(ViBuIm⁺Cl^?)/GC electrode to H₂O₂ is from 3.5 to 224 μM with a limit of detection of 1.17 μM. Such an avenue, which integrated polymeric ionic liquid and redox protein via a simple method, may provide a novel and efficient platform for the fabrication of biosensors, biofuel cells and other bioelectrochemical devices.     

Regulation of Brønsted acid sites in H-MOR for selective methyl methoxyacetate synthesis

As it is well known, Brønsted acid sites in 8-MR of H-MOR (mordenite) are selective for dimethyl ether (DME) carbonylation to methyl acetate, whereas those in 12-MR are more prone to methanol to olefin reaction. Interestingly, we observed that the Brønsted acid sites in 12-MR of H-MOR are highly active for dimethoxymethane (DMM) carbonylation to methyl methoxyacetate (MMAc), whereas those in 8-MR led to the formation of DME. A series of modified H-MOR catalysts with accurate regulation of Brønsted acid sites in 12-MR or 8-MR were successfully synthesized by selective Na⁺ exchange or pyridine (Py) adsorption. Fourier-transform infrared (FT-IR) spectra, NH₃-temperature-programmed desorption, Py-FT-IR, and inductively coupled plasma analyses suggested that Na⁺ first occupied Brønsted acid sites in 8-MR and then replaced those in 12-MR. All Na⁺-exchanged catalysts exhibited significant acceleration on MMAc selectivity, and the ratio of Brønsted acid amount in 12-MR/total had a positive correlation with MMAc selectivity. The MMAc selectivity (78%) of H-MOR-0.15Na was nearly 2.5 times more than that of untreated H-MOR (31%). However, H-MOR-Py showed almost no carbonylation activity (<1% MMAc) and a highest DME selectivity (98%), indicating that Brønsted acid sites in 12-MR were the only active sites for DMM carbonylation, whereas those in 8-MR tended to accelerate DMM disproportionation to DME.     

Cover Feature: Are the Accompanying Cations of Doping Anions Influential in Conducting Organic Polymers? The Case of the Popular PEDOT (Chem. Eur. J. 63/2019)

Conducting organic polymers (COPs) are made of a conjugated polymer backbone supporting a certain degree of oxidation. These positive charges are compensated by the doping anions that are introduced into the polymer synthesis along with their accompanying cations. In this work, the influence of these cations on the stoichiometry and physicochemical properties of the resulting COPs have been investigated, something that has previously been overlooked, but, as here proven, is highly relevant. As the doping anion, metallacarborane [Co(C₂B₉H₁₁)₂]⁻ was chosen, which acts as a thistle. This anion binds to the accompanying cation with a distinct strength. If the binding strength is weak, the doping anion is more prone to compensate the positive charge of the polymer, and the opposite is also true. Thus, the ability of the doping anion to compensate the positive charges of the polymer can be tuned, and this determines the stoichiometry of the polymer. As the polymer, PEDOT was studied, whereas Cs⁺, Na⁺, K⁺, Li⁺, and H⁺ as cations. Notably, with the [Co(C₂B₉H₁₁)₂]⁻ anions, these cations are grouped into two sets, Cs⁺ and H⁺ in one and Na⁺, K⁺, and Li⁺ in the second, according to the stoichiometry of the COPs: 2:1 EDOT/[Co(C₂B₉H₁₁)₂]⁻ for Cs⁺ and H⁺, and 3:1 EDOT/[Co(C₂B₉H₁₁)₂]⁻ for Na⁺, K⁺, and Li⁺. The distinct stoichiometries are manifested in the physicochemical properties of the COPs, namely in the electrochemical response, electronic conductivity, ionic conductivity, and capacitance.     

PVDF/PAN/SiO<Subscript>2</Subscript> polymer electrolyte membrane prepared by combination of phase inversion and chemical reaction method for lithium ion batteries

PVDF/PAN/SiO₂ polymer electrolyte membranes based on non-woven fabrics were prepared via introducing a chemical reaction into Loeb-Sourirajan (L-S) phase inversion process. It was found that physical properties (porosity, electrolyte uptake and ionic conductivity) and electrochemical properties were obviously improved. A favorable membrane structure with fully connective porous and uniform pore size distribution was obtained. The effects of PVDF/PAN weight ratio on the morphology, crystallinity, porosity, and electrochemical performances of membranes were studied. The optimized PVDF/PAN (70/30 w/w) (designated as M_pc30) polymer electrolyte membrane delivered excellent electrolyte uptake of 246.8 % and the highest ionic conductivity of 3.32 × 10^?3 S/cm with electrochemical stability up to 5.0 V (vs. Li/Li⁺). In terms of cell performance, the Li/M_pc30 polymer electrolyte/LiFePO₄ battery exhibited satisfactory electrochemical properties including high discharge capacity of 149 mAh/g at 0.2 C rate and good discharge performance at different current densities. The promising results reported here clearly indicated that PVDF/PAN/SiO₂ polymer electrolyte membranes prepared by the combination of phase inversion and chemical reaction method were promising enough to be applied in power lithium ion batteries.     

Effect of nanoscale CeO<Subscript>2</Subscript> on PVDF-HFP-based nanocomposite porous polymer electrolytes for Li-ion batteries

New poly (vinylidenefluoride-co-hexafluoro propylene) (PVDF-HFP)/CeO₂-based microcomposite porous polymer membranes (MCPPM) and nanocomposite porous polymer membranes (NCPPM) were prepared by phase inversion technique using N-methyl 2-pyrrolidone (NMP) as a solvent and deionized water as a nonsolvent. Phase inversion occurred on the MCPPM/NCPPM when it is treated by deionized water (nonsolvent). Microcomposite porous polymer electrolytes (MCPPE) and nanocomposite porous polymer electrolytes (NCPPE) were obtained from their composite porous polymer membranes when immersed in 1.0 M LiClO₄ in a mixture of ethylene carbonate/dimethyl carbonate (EC/DMC) (v/v = 1:1) electrolyte solution. The structure and porous morphology of both composite porous polymer membranes was examined by scanning electron microscope (SEM) analysis. Thermal behavior of both MCPPM/NCPPM was investigated from DSC analysis. Optimized filler (8 wt% CeO₂) added to the NCPPM increases the porosity (72%) than MCPPM (59%). The results showed that the NCPPE has high electrolyte solution uptake (150%) and maximum ionic conductivity value of 2.47 × 10⁻³ S cm⁻¹ at room temperature. The NCPPE (8 wt% CeO₂) between the lithium metal electrodes were found to have low interfacial resistance (760 Ω cm²) and wide electrochemical stability up to 4.7 V (vs Li/Li⁺) investigated by impedance spectra and linear sweep voltammetry (LSV), respectively. A prototype battery, which consists of NCPPE between the graphite anode and LiCoO₂ cathode, proves good cycling performance at a discharge rate of C/2 for Li-ion polymer batteries.     

Swollen polymeric complex membranes for olefin/paraffin separation

Swollen complex membrane of linear low density polyethylene-graft-poly(acrylic acid)-Ag⁺ (LLDPE-g-AA-Ag⁺) were studied and compared with the corresponding membranes based on silicone rubber (SR) and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), such as SR-g-AA-Ag⁺ and PTMSP-g-AA-Ag⁺. The polymeric matrix was first grafted with acrylic acid (AA) and then incorporated with silver ions (Ag⁺) in glycerol solution for forming the swollen complex membrane. Various metal ions and swollen agents in membranes for isobutene/isobutane separation were presented. The swelling of the complex membrane containing Ag⁺ with glycerol shows a higher olefin/paraffin selectivity than those membranes containing Cu⁺ or Cu²⁺ ions and/or other swelling agents. The gas permeability coefficients and the isobutene/isobutane selectivity of LLDPE-g-AA-Ag⁺ membrane were compared with those of SR-g-AA-Ag⁺ and PTMSP-g-AA-Ag⁺ membranes. The PTMSP-g-AA-Ag⁺ complex membrane was found to reach high gas permeability and high olefin/paraffin selectivity. The effects of solubility and diffusivity in membranes are compared with the corresponding non-Ag membranes. The sorption properties in these complex membranes were also included.     

Evaluation of Polyurethane-Based Membrane Matrices for Optical Ion-Selective Sensors

Abstract

Plasticized thin films of polyurethane (PU) mixed with poly(vinyl chloride)(PVC) or a terpolymer of poly(vinyl chloride)/(vinyl acetate)/(vinyl alcohol) (PVA) are examined as membrane matrices for the preparation of reversible optical ion sensors. Optical sensors for Na⁺, NH₄ ⁺, Cl^? and ClO₄ ^? are prepared by casting thin films of the polymer mixtures (PU/PVC (1:1 wt) and PU/PVA (4:1 wt)) containing appropriate ion carriers and pH chromophores on glass slides. The optical response properties of these membranes is essentially the same as conventional pure PVC membranes reported in the literature. However, significantly enhanced membrane adhesion to glass or silicon wafer surfaces is observed using the polyurethane based matrices, making them more suitable than PVC for use in the development of solid-state optical ion sensing devices.     

Separation and Removal of Metal Ionic Species by Polymer Inclusion Membranes

Competitive alkali metal cation transport across polymer inclusion membranes (PIMs) containing sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid carriers provides excellent selectivity for Na⁺ transport with the total fluxes being strongly influenced by the length of the alkyl chain that is attached geminal to the functional side arm in the lariat ether. Removal of chromium(VI) anions by PIMs from acidic aqueous phases was also investigated. Using tri-n-octylamine (TOA) as the ion carrier, Cr(VI) was removed by a PIM to decrease the source phase metal concentration from 1.0 to 0.010 ppm after 30 hours of transport. Competitive transport of Cr(VI) and Cr(III) ions from acidic source phases through PIMs and supported liquid membranes (SLMs) containing TOA and tri-n-octylphosphine oxide (TOPO) as carriers was evaluated and a very high Cr(VI)/Cr(III) separation ratio of 4800 was achieved with a PIM containing TOA. Competitive transport of Zn(II), Cd(II), and Cr(VI) from acidic aqueous solutions through PIMs containing TOA was investigated. The selectivity order for metal ion transport was: HCrO₄ ^–>CdCl₄ ^2–+CdCl₃ ^–>ZnCl₄ ^2–+ ZnCl₃ ^–. Non-contact atomic force microscopy was used to obtain images of the pores in cellulose triacetate membranes containing a plasticizer.     

Electrochemical studies on ion-selective polymer membrane electrodes

The selectivity and response of neutral carrier based polymer membrane electrodes are investigated via exchange current measurements for systems containing valinomycin, dibenzo-18-crown-6, and plasticizer alone in a polyvinyl chloride matrix. Using a transient galvanostatic step method, apparent exchange current densities of 1.3 X 10^?3 A/cm², 5.4 X 10^?6 A/cm², and 2.2 X 10^?9 A/cm² were obtained with K⁺ as the primary ion for the three types of membranes, respectively. Preliminary results indicate that the exchange current data obtained with this technique are complementary to the potentiometric response observed for the membranes studied.