Search

In 2014, it was reported that protons can traverse between aqueous phases separated by nominally pristine monolayer graphene and hexagonal boron nitride (h-BN) films (membranes) under ambient conditions. This intrinsic proton conductivity of the one-atom-thick crystals, with proposed through-plane conduction, challenged the notion that graphene is impermeable to atoms, ions, and molecules. More recent evidence points to a defect-facilitated transport mechanism, analogous to transport through conventional ion-selective membranes based on graphene and h-BN. Herein, local ion-flux imaging is performed on chemical vapor deposition (CVD) graphene|Nafion membranes using an "electrochemical ion (proton) pump cell" mode of scanning electrochemical cell microscopy (SECCM). Targeting regions that are free from visible macroscopic defects (

Perfluorosulfonic acid (PFSA) ionomers are ubiquitous as proton-exchange membranes (PEMs) in vanadium redox flow batteries (VRFBs), as they provide high proton conductivity and robust chemical stability. However, traditional PFSA ionomers suffer from high vanadium ion crossover, i.e., low ion selectivity, which reduces the efficiency and lifetime of the battery. Herein, a novel method to fabricate PFSA nanocomposites containing fluorocarbon-decorated silica nanoparticles is presented. These composite ionomers exhibit drastically reduced vanadium ion permeability and an almost two orders of magnitude increase in proton selectivity when compared to the current benchmark commercial ionomer. Small-angle neutron scattering data suggest that the nanostructures of these nanocomposites are drastically different from their pristine counterpart, where the periodic spacing of the hydrophobic domains is significantly reduced, while changes to the ionic structure were seen to be minimal. This work suggests that composite PEMs containing a secondary phase that alters the hydrophobic, nonion-conducting phase of the ionomer may prove to be a fruitful fabrication route to produce ionomer membranes with enhanced performance for use in VRFBs.

Graphene and carbon quantum dots (GQDs and CQDs) are relatively new nanomaterials that have demonstrated impact in multiple different fields thanks to their unique quantum properties and excellent biocompatibility. Biosensing, analyte detection and monitoring wherein a key feature is coupled molecular recognition and signal transduction, is one such field that is being greatly advanced by the use of GQDs and CQDs. In this review, recent progress on the development of biotransducers and biosensors enabled by the creative use of GQDs and CQDs is reviewed, with special emphasis on how these materials specifically interface with biomolecules to improve overall analyte detection. This review also introduces nano-enabled biotransducers and different biosensing configurations and strategies, as well as highlights key properties of GQDs and CQDs that are pertinent to functional biotransducer design. Following relevant introductory material, the literature is surveyed with emphasis on work performed over the last 5 years. General comments and suggestions to advance the direction and potential of the field are included throughout the review. The strategic purpose is to inspire and guide future investigations into biosensor design for quality and safety, as well as serve as a primer for developing GQD- and CQD-based biosensors.

Fifty atomic layer deposition (ALD) cycles of trimethylaluminum and water were applied to single-layer graphene on copper and graphene on Nafion membranes that result in alumina coatings that fully...

In 2014, it was reported that hydrated protons are able to traverse nominally pristine monolayer graphene (and hexagonal boron nitride, h-BN) films under ambient conditions. This “intrinsic proton conductivity” of the one-atom-thick crystals, with proposed through-plane conduction, challenged the notion that graphene is impermeable to atoms, ions and molecules. More recent evidence points to a defect-facilitated transport mechanism, analogous to transport through conventional ion-selective membranes based on graphene and h-BN. To clarify the nature of proton transmission through graphene, local ion-flux imaging is performed herein on graphene|Nafion membranes using a new “electrochemical ion (proton) pump cell” mode of scanning electrochemical cell microscopy (SECCM). Targeting regions of the graphene|Nafion membranes that are free from visible macroscopic defects (e.g., cracks, holes etc.), and assessing hundreds to thousands of different sites across the graphene surfaces in a typical experiment, most of the graphene membrane is impermeable to proton transport, with transmission typically occurring at only ≈20 – 60 localized sites across a ≈0.003 mm2 area of membrane (>5000 measurements, total). When localized proton transport occurs, it can be a highly dynamic process, with new transmission sites “opening” and a small number of sites “closing” under an applied electric field, on the seconds timescale. Applying a simple equivalent circuit model of ion-transport through a cylindrical nanopore, the local transmission sites are estimated to possess dimensions (radii) on the (sub)nanometer-scale, implying that rare atomic defects are responsible for proton conductance through monolayer graphene. Overall, this work reinforces SECCM as a premier tool for the structure−property mapping of microscopically complex (electro)materials, with the new configuration reported herein opening up exciting new possibilities in functional membrane characterization, as well as any other application where reactive ion-flux is a highly localized phenomenon, e.g., for diagnosing failure mechanisms in protective surface coatings.

Anion exchange membranes (AEMs) are becoming increasingly common in electrochemical energy conversion and storage systems around the world (EES). Proton-/cation-exchange membranes (which conduct positive charged ions such as H+ or Na+) have historically been used in many devices such as fuel cells, electrolysers, and redox flow batteries. High capital costs and the use of noble metal catalysts are two of the current major disadvantages of polymer electrolyte membrane (PEM)-based systems. AEMs may be able to overcome the limitations of conventional PEMs. As a result, polymers with anion exchange properties have recently attracted a lot of attention due to their significant benefits in terms of transitioning from a highly acidic to an alkaline environment, high kinetics for oxygen reduction and fuel oxidation in an alkaline environment, and lower cost due to the use of non-precious metals. The aim of this research was to learn more about the development of a new AEM based on poly tetraarylphosphonium ionomers (pTAP), which has high ionic conductivity, alkaline stability, thermal stability, and good mechanical properties, making it a more cost-effective and stable alternative to conventional and commercial AEMs. A simple solution casting method was used to build novel anion exchange composite membranes with controlled thicknesses using the synthesized pTAP with polysulfone (PS). To ensure their suitability for use as an electrolyte in alkaline electrochemical systems, the composite membranes were characterized using FTIR, XRD, water uptake, ionic conductivity, and alkaline stability. At 40 °C, the PS/pTAP 40/60 percent membrane had a maximum ionic conductivity of 4.2 mS/cm. The thermal and mechanical stability of the composite membranes were also examined, with no substantial weight loss observed up to 150 °C. These findings pave the way for these membranes to be used in a wide variety of electrochemical applications.

The relative rates of transmembrane proton and hydrogen gas transmission are of high importance in most PEM-based electrochemical energy conversion devices. Membrane separators that simultaneously have high rates of proton transmission and low rates of gas transmission are highly desired but this property combination is difficult to achieve because most modifications that could give higher proton transmission rates through a membrane, tend also to give higher gas crossover rates. This presentation will present results indicating that one monolayer of CVD single-layer graphene embedded between two polyelectrolyte membranes can give this desired membrane property combination. Proton transmission occurs through single-layer graphene in a PEM sandwich structure with area-specific resistance values less than 40 mΩ cm2, which is less than the resistance of most PEM membranes. Hydrogen crossover rates in PEM / graphene / PEM sandwich structures were measured by a limiting current method and found to be reduced by more than eight times relative to values in similar membranes without graphene. The lecture will present data on these points and discuss the mechanism(s) by which graphene might provide this desirable set of membrane properties.

Transmission rates for protons and deuterons across single-layer graphene embedded in Nafion | graphene | Nafion sandwich structures are measured as a function of temperature in electrochemical hydrogen pump cells. Rates of ion transmission through graphene are obtained in the form of area-normalized ion-transfer resistances, and are interpreted in terms of ion-exchange current densities and standard heterogeneous ion-transfer rate constants. An encounter pre-equilibrium model for the ion-transfer step is then used to provide rate constants for the fundamental microscopic step of ion (proton or deuteron) transmission across graphene. Application of this rate model to interpret variable-temperature data on proton and deuteron transmission rates provides values for the activation energy and pre-exponential factor for the fundamental ion transmission step across graphene. Activation energies obtained from the Arrhenius plots for proton and deuteron transmission are as follows; for proton, Eact = 48 ± 2 kJ/mole (0.50 ± 0.02 eV) and for deuteron, Eact = 53 ± 5 kJ/mole (0.55 ± 0.05 eV). The difference between these two values of approximately 5 kJ/mole is in good agreement with the expected difference in vibrational zero-point energies for O H and O-D bonds, albeit with some uncertainty given the uncertainties in the activation energy values. Pre-exponential frequency factor values of 8.3 ± 0.4 × 1013 s−1 and is 4.7 ± 0.5 × 1013 s−1 were obtained for proton and deuteron transmission respectively across graphene. These pre-factor values are both quite large, on the order of the values predicted from the Eyring – Polanyi equation with a transmission coefficient near one. The ratio of 1.8 for the rate pre-factors (H/D) is in reasonable agreement with the value of 1.3 for the ratio of bond vibrational frequencies for O H and O-D stretching, respectively. Taken together, these data support a model in which proton and deuteron transmission across graphene are largely adiabatic processes for which the differences in transmission rate at room temperature are due largely to differences in activation energies.

Proton transmission through single-layer CVD graphene in graphene/proton-exchange-membrane (PEM) sandwich structures is found to be more than 100 times faster than for any other cation. Ion transmi...

A simple and convenient small-scale fuel-cell test platform was created from a commercial compression fitting and graphite rod current collectors and used to conduct diagnostic tests on disk-shaped membrane-electrode assemblies (MEAs) fabricated from Nafion membranes and Nafion-impregnated platinum-on-carbon-cloth anodes and cathodes. A key advantage of this test platform is that it requires very little material, perhaps just a few milligrams, to conduct a fuel-cell test on a supported catalyst. Electrochemically-active surface area (ECSA) values for supported platinum on carbon-cloth electrodes were obtained by in-situ (in the fuel cell) and ex-situ (in liquid electrolyte) cyclic voltammetry on similarly-prepared electrodes, and values obtained by these methods were compared with each other to estimate the fraction of platinum catalyst contacted by the Nafion ionomer in the fuel-cell cathode. Polarization curves were acquired under controlled-potential conditions using slow-scan cyclic and sampled-current voltammetry and potential-step amperometry methods with conventional electroanalytical instrumentation. Tests performed using this platform are complementary to rotating disk electrode (RDE) voltammetry tests which also allow for catalyst testing on small amounts of material, albeit in the presence of liquid electrolyte, and are commonly used for initial screening of new fuel-cell catalysts. They are also complementary to conventional fuel-cell testing that is commonly performed on MEAs having active areas more than 100 times larger than that in the present cells.

There is an industrial interest in utilizing large volume manufacturing processes such as printing (e.g. stencil, roll-to-roll) to produce thin-film functional components. These components will require power sources, for example thin-film batteries, and it would be advantageous to be able to produce these powering items in-line with the components. Traditional primary thin-film batteries have limited storage capacities due to mass limitations and unavoidable losses. The current effort demonstrates a zinc/manganese oxide reserve battery that has been produced through combination of stencil and roll-to-roll printing on a polyethylene terephthalate (PET) substrate utilizing fish roe for the ion conducting electrolyte storage and separator. The creation of a reserve battery which can be activated when power is required by the deformation of the battery is an approach to extend battery storage times.

A series of nanostructured catalysts based on cobalt-modified molybdenum carbides, intended as alternative replacement for platinum has been developed for the hydrogen evolution reaction (HER) from brine. The catalysts were synthesized by simple impregnation of the metal salts on carbon support and followed by pyrolysis in CH4 atmosphere. The obtained catalysts show impressive HER activities in both brine and alkaline media. At current density of −7.0 mA cm−2, the overpotential for Co modified Mo/C catalysts was greater than that obtained with a commercial Pt/C catalyst by 63–89 mV and 15–148 mV for brine and alkaline solution, respectively. Our findings for HER in both media are consistent with electrochemical desorption of hydrogen gas following the Volmer-Heyrovsky mechanism as the rate-determining step. The HER activities of the catalysts were correlated to their high mesopore surface areas with active pores, nanocrystallites, and low charge transfer resistances as confirmed by electrochemical impedance spectroscopy.

The preparation and photophysical properties of two heavier main group element analogues of boron-dipyrromethene (BODIPY) chromophores are described. Specifically, we have prepared dipyrrin complexes of dichlorogallate (GADIPY) or phenylphosphenium (PHODIPY) units. Whereas cationic PHODIPY is labile, decomposing to a phosphine over time, GADIPY is readily prepared in good yield as a crystalline solid having moderate air- and water-stability. Crystallographically characterized GADIPY displays intense green photoluminescence (λem = 505 nm, Φem = 0.91 in toluene). These inaugural heavier main group element analogues of BODIPY offer a glimpse into the potential for elaboration to a panoply of chromophores with diverse photophysical properties.

A major challenge in effectively treating infections is to provide timely diagnosis of a bacterial or viral agent. Current cell culture methods require24 h to identify the cause of infection. The Toll-like Receptor (TLR) family of proteins can identify classes of pathogens and has been shown to work well in an impedance-based biosensor, where the protein is attached to an electrode via a self-assembled monolayer (SAM). While the sensitivity of these sensors has been good, they contain a high resistance (1 kΩ) SAM, generating relatively small signals and requiring longer data collection, which is ill-suited to implementation outside of a laboratory. Here, we describe a novel approach to increase the signal magnitude and decrease the measurement time of a TLR-4 biosensor by inserting a redox-active ferrocenyl-terminated alkanethiol into a mixed SAM containing hydroxyl- and carboxyl-terminated alkanethiols. The SAM formation and modification was confirmed via contact angle and X-ray photoelectron spectroscopy measurements, with TLR-4 immobilization demonstrated through a modified immunosorbent assay. It is shown that these TLR-4 biosensors respond selectively to their intended target, Gram-negative bacteria at levels between 1 and 10

Single layer graphene (SLG), with its angstrom-scale thickness and strong Raman scattering cross section, was adapted for measurement of the axial (Z-direction) probe beam profile in confocal Raman microscopy depth-profiling experiments. SLG adsorbed to a glass microscope coverslip (SLG/SiO2) served as a platform for the estimation of axial spatial resolution. Profiles were measured by stepping the confocal probe volume through the SLG/SiO2 interface while measuring Raman scattering from the sample. Using a high numerical aperture (1.4 NA) oil immersion objective, axial profiles were derived from the graphene 2D vibrational mode and fit to a Lorentzian instrument response function (IRF). Subsequently, the Z-direction spatial resolution in depth-profiling studies of polymer interfaces was estimated through convolution of the Lorentzian IRF with a step function representing the ideal junction separating the phases of interest. In the study of a bipolar polymer membrane, confocal Raman depth profiles of the ...

Ionic liquids (IL's) were proposed for use in Li-ion batteries (LIBs), in order to mitigate some of the well-known drawbacks of LiPF6/mixed organic carbonates solutions. However, their large cations seriously decrease lithium transference numbers and block lithium insertion sites at electrode-electrolyte interfaces, leading to poor LIB rate performance. Deep eutectic electrolytes (DEEs) (which share some of the advantages of ILs but possess only one cation, Li+), were then proposed, in order to overcome the difficulties associated with ILs. We report herein on the preparation, thermal properties (melting, crystallization, and glass transition temperatures), transport properties (specific conductivity and viscosity) and thermal stability of binary DEEs based on mixtures of lithium bis(trifluoromethane)sulfonimide or lithium bis(fluoro)sulfonimide salts with an alkyl sulfonamide solvent. Promise for LIB applications is demonstrated by chronoamperometry on Al current collectors, and cycling behavior of negative and positive electrodes. Residual current densities of 12 and 45 nA cm−2 were observed at 5 V vs. Li/Li+ on aluminum, 1.5 and 16 nA cm−2 at 4.5 V vs. Li/Li+, respectively for LiFSI and LiTFSI based DEEs. Capacities of 220, 130, and 175 mAh· g−1 were observed at low (C/13 or C/10) rates, respectively for petroleum coke, LiMn1/3Ni1/3Co1/3O2 (a.k.a. NMC 111) and LiAl0.05Co0.15Ni0.8O2 (a.k.a. NCA).

Phthalocyanines (Pcs) are a class of photosensitizers (PSs) with a strong tendency to aggregate in aqueous solutions, which has a negative influence on their photosensitizing ability for photodynamic therapy. Four new axially disubstituted, non-aggregated silicon phthalocyanines (SiPcs), containing azide or alkyne functional groups have been synthesized and characterized. The method of synthesis is based on the reaction of silicon phthalocyanine dichloride with variable length poly(ethylene glycol) (PEG) chains in the presence of NaH. All synthesized dyes are highly soluble in alcohols, THF, CH2 Cl2, acetone, DMF and other common polar organic solvents, with the PEGylated silicon phthalocyanines (SiPcs) also being soluble in water. Photophysical and electrochemical properties of the dyes have been investigated. The presence of alkyne or azide groups in the phthalocyanine dyes, coupled with their high aqueous solubility, make these compounds useful as building blocks in copper catalyzed Huigsen azide-alkyne cycloaddition reactions (i.e. click chemistry).

The (nitro)([Formula: see text],[Formula: see text]-dimethyl-4-aminopyridine) complex of perfluorinated cobalt(III) phthalocyanine Co(III)F16Pc(Me2Npy)(NO[Formula: see text] catalyzes the electrochemical oxygen reduction reaction (ORR) in pH 4.0, 7.0, and 10.0 buffer and 0.05 M sulfuric acid solution when deposited on a glassy carbon electrode. Cyclic voltammetry (CV), rotating disk electrode voltammetry (RDE), and rotating ring-disk electrode voltammetry (RRDE) have been used to determine the reduction product as hydrogen peroxide although in concentrations too small to observe by qualitative methods such as oxidation of NaI in solution. The dependence of the values of the peak potentials for the reduction on the pH of the solution and the -log[Me2Npy] are consistent with protonation up to pH 7.6 and pyridine ligand loss during the reduction. The addition of nitrite at 0.1 and 1 M to pH 7.0 solutions in contact with films of CoF16Pc on the glassy carbon electrode decreases the ORR current and shifts the peak potential of the ORR from -0.21 V vs. NHE to -0.19 V vs. NHE. The addition of nitrite at 0.1 and 1 M to films of Co(III)F16Pc(Me2Npy)(NO[Formula: see text] on glassy carbon, however, has no effect on either the current or the potential. While the electrochemical evidence for this proposal is not definitive, modeling has been used to examine the center of reduction in the alternative mechanisms by evaluation of the LUMOs of the hypothetical intermediates in both closed and open shell cases. The formation of five-coordinate Co(II)F16Pc(NO) is proposed to occur initially in the reduction mechanism. It is also possible that O2 reduction takes place at the NO ligand center by way of a nitrogen-bound peroxynitrite intermediate. The [Formula: see text] ligand appears to remain bound during the ORR. Direct coordination of O2 to the metal center requiring a six-coordinate species, Co(III)F16Pc(O[Formula: see text](NO[Formula: see text], Co(II)F16Pc(O[Formula: see text](NO) or [Co(II)F16Pc(O[Formula: see text](NO[Formula: see text]][Formula: see text] and has been considered in DFT modeling studies. The instability of the two-electron reduced, protonation species, [Co(I)F16Pc(NO2OH)][Formula: see text] in its loss of peroxynitrous acid suggests that the reduction of O2 may occur by two one-electron reduction steps rather than a two-electron step.

Liquid electrolyte mass transport is a major limitation affecting high-power Li ion batteries. Fast discharging causes Li salt depletion in the current collector region of the cathode which produces overpotential in the electrolyte and consequently a drop of cell voltage to below the cut-off voltage, especially at higher electrode thickness and discharge rate. In this study, through experiment and simulation, we have investigated the effect of electrode thickness, mass loading, discharge rate and tortuosity on electrolyte mass transport and final derived areal capacity and specific energy for electrodes having isotropic (normal tape casting) and anisotropic (freeze tape casting) porous microstructure. The macroporous channels in freeze tape cast electrodes facilitate Li salt transport and reduce the Li salt mass transport limitations even at high electrode thickness and discharge rates, and high electrode tortuosity. Computer simulations show that freeze tape cast electrodes may be fully discharged up to 750 μm thickness at 1 C rate compared to 300 μm for normal tape cast electrodes with the same mass loading. Freeze tape cast electrodes also show stable maximum areal capacity for C rates about double the maximum C rates of their normal tape cast electrode counterparts with the same mass loading.

Graphene and related two-dimensional (2D) materials are being intensively studied for use in membrane separators. The ultrathin nature of 2D materials combined with the opportunities they afford for intentional creation of nanometer-sized pores having controllable size and chemical character could allow for membrane separations with high flux and also high selectivity. Proton transport through graphene is especially interesting because it may occur through the intact pristine graphene rather than through defects / pores. Other cations, for example lithium or sodium, may pass through graphene but that transport is through to occur through defects / pores. This presentation will focus on selective cation transport through graphene layers that are embedded between Nafion membranes. Ion transmission through graphene is measured using a four-electrode cell in which two Luggin capillaries sense the potential difference that develops across the membrane in response to an ion current that is driven by a pair of platinum wire drive electrodes. Proton transmission in this cell configuration occurs more than 100 times faster than transport of any other ion. This difference is thought to reflect the different mechanisms by which protons and other cations pass though graphene. The lecture will discuss defect characterization in CVD graphene films, and will consider the role of defects, which are in fact nanopores, in allowing for selective transport of ions through graphene.

Recent reports from several laboratories indicate that proton transmission through graphene and other 2D materials in contact with proton-conducting electrolytes can occur rapidly with a much lower activation energy than expected from a wide range of computational studies on the proton / graphene interaction energy, and a much higher selectivity relative to transmission of other ions than would be expected based only on ion size. It would be desirable to be able to control transport through the graphene, and many approaches have been tried to rationally control transport rates through graphene via chemical treatments applied to the graphene. One such approach involves use of atomic layer deposition (ALD), in which single layers of inorganic materials, often oxides, are coated in a self-limiting way onto a surface by a series of pulsed reaction steps delivered in series. A common ALD implementation involves coatings of aluminum oxide, or alumina, created by sequential dosing of a surface with trimethyl aluminum and water vapor. We report here on use of the ALD method to coat single-layer CVD graphene supported on copper foil or on Nafion membranes with layers of alumina. Coatings resulting from 50 ALD cycles are found to be thick enough and homogeneous enough to block photoelectron emission from the underlying substrates (copper or Nafion) when the coatings are analyzed by X-ray photoelectron spectroscopy. Electrochemical hydrogen pump experiments were then performed to assess the degree to which ALD treatment of the graphene on Nafion, delivered prior to preparing Nafion | graphene | Nafion sandwich membranes, could change the rate of proton transmission through the graphene that is embedded within the Nafion. As little as two ALD treatment cycles are sufficient to reduce proton transmission currents through graphene by approximately half relative to graphene that is not treated by ALD. Surprisingly, fifty ALD cycles has almost the same effect as two cycles. This finding indicates that that ALD alumina coating is a relatively good proton conductor which is thought to reflect the action of transport pathways on the hydrated surface of the porous ALD alumina layer. The insensitivity of proton transmission to the number of ALD cycles applied suggests that the function of the ALD is to change the transport rates at interfaces, perhaps by creating a new ALD alumina / Nafion interface that protons must traverse in order to pass through the membrane.

Confocal Raman microscopy is being adapted to probe interfaces within bipolar membranes and ionomer-graphene composites of interest for use in fuel cell and related electrochemical devices [1-2]. Although versatile and adaptable to in-situ measurements, confocal Raman microscopy depth-profiling has pitfalls when applied to bulk membranes. Optical aberration and sensitivity to light scattering from sample regions outside the probe beam focus limit depth resolution. With these constraints in mind, initial studies focused on detecting single layer graphene (SLG) as a barrier between two Nafion membranes (Nafion 211, 25 µm thickness). These graphene-sandwich membranes have shown high selectivity for proton transport across electrochemical cells [2]. Using a microscope equipped with oil-immersion optics to provide refractive index matching, the graphene layer was easily detected in confocal Raman microscopy depth-profiles. Spectra were sensitive to defects and stress within the buried graphene layer. Building on the ability to probe membrane-supported SLG, SLG adsorbed to a glass microscope coverslip (SLG/SiO2) was adapted as a platform for confocal aperture alignment and probe volume characterization [1]. Using SLG/SiO2to estimate the limiting axial spatial resolution, the junction separating the AEM/CEM (anion exchange membrane / cation exchange membrane) phases of bipolar polymer membrane (Fumasep FBM) was probed and shown to be consistent with roughness at the boundary on the order of a few micrometers (~3 µm). Continuing efforts are aimed at developing 2-dimensional (x-, y-direction) Raman spatial maps of buried polymer membrane interfaces and model AEM/CEM interfaces for high spatial resolution (< 10 nm) neutron reflectometry depth profiling. 1. Korzeniewski, C.; Kitt, J.P.; Bukola, S.; Creager, S.E.; Minteer, S.D.; Harris, J.M. ”Single layer graphene for estimation of axial spatial resolution in confocal Raman microscopy depth profiling” Anal. Chem.2019, 91, 1049 (DOI:10.1021/acs.analchem.8b04390). 2. Bukola, S.; Liang, Y.; Korzeniewski, C.; Harris, J.M.; Creager, S.E. “Selective proton / deuteron transport through Nafion | graphene | Nafion sandwich structures at very high current density” J. Am. Chem. Soc. 2018, 140, 1743. (DOI: 10.1021/jacs.7b10853)

Our research group has recently demonstrated the ability to probe within composite membranes formed by sandwiching single layer graphene (SLG) between two Nafion layers (Nafion 211, 25 µm thickness). These graphene-sandwich membranes have shown high selectivity for proton transport across electrochemical cells [1,2]. Using a microscope equipped with an oil-immersion objective, the graphene layer is readily detected in confocal Raman microscopy depth-profiles (z-direction profiles) of the composite membranes. Spectra are sensitive to defects and stress within the buried graphene layer. This presentation will discuss the use of confocal Raman microscopy for structural characterization and spatial profiling in the development of composite polymer electrolyte membranes that contain a graphene layer as a barrier to ion transport. In a second application area, infrared spectroscopy is being adapted to investigate properties of Nafion ionomer particles in dilute dispersions and during transformation to gel and solid phases through the use of time-resolved attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Since the properties of dispersing fluids can affect the mechanical strength of solution-cast Nafion thin films [3], it is of interest to gain insights into ionomer properties in the dispersion and during phase changes. A well-resolved peak associated with vibrational motions of the Nafion side chain -SO3 -end group is shown to be sensitive to gel-phase development. The persistence of hydration water in the vicinity of the -SO3 -group helps maintain a constant local refractive index that limits optical distortion in the band as the ionomer assembles into the phase-separated framework structure of the solid membrane. ATR FTIR measurements predict trends in evaporative water loss from the dispersion and entry into the gel-phase consistent with expectations of gravimetric measurements and earlier studies [3] of Nafion ionomer dispersion properties. 1. Bukola, S., et al. J. Am. Chem. Soc. 2018, 140, 1743. 2. Bukola, S., et al., ACS Appl. Nano Mater. 2019, 2, 964. 3. Kim, Y.S., et al., Macromolecules 2015, 48, 2161.

A commercial digital simulation tool was used to simulate cyclic voltammetry (CV) data for redox mediation electrode reactions involving immobilized redox mediators. The system studied consists of a ferrocene-based redox mediator in an alkanethiolate-based self-assembled monolayer (SAM) on gold, with ferrocyanide in solution acting as electron donor to react with electrogenerated ferrocenium in the monolayer. Simulation parameters include rate constants for ferrocene oxidation/reduction in the monolayer, the mediation cross reaction between ferrocenium in the monolayer and ferrocyanide in solution, and the direct (unmediated) ferrocyanide oxidation/reduction reaction by long-range electron transfer across the monolayer. An excellent agreement between simulation and experiment was obtained using simulation parameters derived from independent experiments. The simulation method enables analysis of an entire voltammogram which can offer advantages over analytical approaches that consider only a portion of the data (e.g., a “foot-of-the-wave” analysis). The availability of a validated simulation tool allows questions about the anticipated reactivity of immobilized redox mediators to be addressed definitively via simulation, rather than by speculation on the effects one might expect to observe on a CV waveshape for a particular parameter change.

Ion current densities near 1 A cm–2 at modest bias voltages (

Advances in catalyst and electrolyte materials for hydrogen fuel cells are driving performance gains and cost reductions that are helping to bring hydrogen fuel-cell technology to market. Research on new materials is always a combination of synthesis and characterization, where characterization must eventually include incorporation of materials into an operating fuel cell. It is at this stage that research on leading-edge new materials often stalls, because conventional fuel-cell tests require relatively large amounts of material, e.g. several grams of a new catalyst and tens to hundreds of grams of ionomer, corresponding to many tens of square centimeters of membrane area, are required to run a comprehensive set of tests as is necessary to assure reproducibility and examine behavioral trends. These amounts of material are often not available in early-stage synthetic work, which means that characterization uses other approximate approaches, e.g. rotating disk electrode (RDE) voltammetry to study catalyst activity, with true fuel-cell testing often being delayed until syntheses may be scaled up. This situation is unfortunate because approximate tests often do not adequately screen materials. It would be desirable to run preliminary fuel-cell tests at an early stage to gain a better idea of materials properties before making decisions regarding which materials to scale up. This contribution will present our recent work building and using a miniature PEM fuel-cell test fixture that uses only very small amounts of material to conduct a true solvent-free fuel-cell test. The cell is fabricated from a conventional compression-style fitting and uses 5/8 inch diameter graphite or metal rods for gas delivery and for making electric contact with the electrodes. Membrane-electrode assemblies (MEAs) are made from 3/4-inch diameter PEM disks, typically cut from Nafion ionomer membrane, onto which carbon-cloth-based electrodes are bonded by hot pressing. Electrode diameters range from 1/8 to 3/8 inch. The presentation will include recent published work demonstrating reproducibility and select MEA characterization data, including in-situ voltammetry to assess electrochemically active surface area (ECSA) of catalysts and polarization curve measurements that are easily obtained using conventional linear sweep voltammetry with a conventional laboratory potentiostat. This situation is in contrast to conventional fuel-cell testing that requires specialized instrumentation with passage of very large currents, e.g. tens of amperes. Very recent work using the cells in hydrogen pump configuration will also be presented. This configuration is particularly useful for measuring resistances to proton transport through ionomers in the direction through the membrane plane, in contrast to most measurements which focus on in-plane resistance, because it is easier to measure. Very recent work on the synthesis and properties of new tetra-aryl-phosphonium (TAP) alkaline ionomers which are expected have high alkaline stability and to be good hydroxide-ion conductors, and on the effect of single graphene layers embedded in Nafion membranes on proton and other ion conduction through the Nafion membranes, will also be presented.

Methacrylate derived monomers functionalized with pendant oxadiazole moieties were synthesized and copolymerized with carbazole containing monomers to form polymers with electron and hole transporting fragments in the same molecule. Substituents on the oxidazole moiety were varied with the purpose of bandgap tuning and performance optimization when employed in single-layer organic light emitting devices (OLED). Quantum mechanical calculations of the HOMO-LUMO levels of the oxidazole derivatives were used to down-select promising candidates for chemical synthesis and testing in single-layer OLEDs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1663–1673

A nonconjugated methacrylate terpolymer containing carbazole moieties (electron donors), 1,3,4-oxadiazole moieties (electron acceptors), and Coumarin-6 in the pendant groups was synthesized via free radical copolymerization of methacrylate monomers containing the respective functional groups. The terpolymer was formed into 57 nm particles through a mini-emulsion route. For a thin 100 nm film of the fused particles sandwiched between an indium-tin oxide (ITO) electrode and an Al electrode, the structure behaved as a nonvolatile flash (rewritable) memory with accessible electronic states that could be written, read, and optically erased. The device exhibited a turn-on voltage of ca. -4.5 VDC and a 10(6) current ratio. A device in the ON high conductance state could be reverted to the OFF state with a short exposure to a 360 nm light source. The development of semiconducting colloidal inks that can be converted into electroactive devices through a continuous processing method is a critical step in the widespread adoption of these 2D manufacturing technologies for printed electronics.

An approach based on vibrational spectral measurements is described for determining the ionizable group content of ion conducting polymer membrane materials. Aimed at supporting the assessment of membrane stability and wear characteristics, performance is evaluated for attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, confocal Raman microscopy, and ATR FT-IR microscopy using perfluorinated ionomer membrane standards. One set of ionomer standards contained a sulfonic acid ionizable group and the other a sulfonyl imide group. The average number of backbone tetrafluoroethylene (TFE) units separating the ionizable-group containing side chains was in the range of 7.2–2.1 (sulfonic acid set) and 10.5–4.6 (sulfonyl imide set). A poly(tetrafluoroethylene) (PTFE) sample was included as a blank, representing the limit of zero ionizable group (and maximum TFE) content. Calibration relationships were derived from area-normalized vibrational spectra. For all three methods, calibration models applied to independent spectral measurements of samples predicted the ratio of backbone TFE groups to ionizable groups in the repeat unit ( m) with a standard error of ≤ ±0.3. The confocal Raman and ATR FT-IR microscopy techniques achieved ideal blank responses and the lowest prediction errors, down to m ± 0.1 at the 90% confidence level. With its relative simplicity, low sample size requirements, and potential for quantitative micron-scale spatial mapping of the ionizable group content within a membrane, the approach has application to advancing materials development, including exploratory synthesis, durability and wear assessment, and in situ studies of membrane process.

A monoprotic [(trifluoromethyl)benzenesulfonyl]imide (SI) superacid electrolyte was used to covalently modify a mesoporous carbon xerogel (CX) support via reaction of the corresponding trifluoromethyl aryl sulfonimide diazonium zwitterion with the carbon surface. Electrolyte attachment was demonstrated by elemental analysis, acid-base titration, and thermogravimetric analysis. The ion-exchange capacity of the fluoroalkyl-aryl-sulfonimide-grafted carbon xerogel (SI-CX) was ∼0.18 mequiv g(-1), as indicated by acid-base titration. Platinum nanoparticles were deposited onto the SI-grafted carbon xerogel samples by the impregnation and reduction method, and these materials were employed to fabricate polyelectrolyte membrane fuel-cell (PEMFC) electrodes by the decal transfer method. The SI-grafted carbon-xerogel-supported platinum (Pt/SI-CX) was characterized by X-ray diffraction and transmission electron microscopy to determine platinum nanoparticle size and distribution, and the findings are compared with CX-supported platinum catalyst without the grafted SI electrolyte (Pt/CX). Platinum nanoparticle sizes are consistently larger on Pt/SI-CX than on Pt/CX. The electrochemically active surface area (ESA) of platinum catalyst on the Pt/SI-CX and Pt/CX samples was measured with ex situ cyclic voltammetry (CV) using both hydrogen adsorption/desorption and carbon monoxide stripping methods and by in situ CV within membrane electrode assemblies (MEAs). The ESA values for Pt/SI-CX are consistently lower than those for Pt/CX. Some possible reasons for the behavior of samples with and without grafted SI layers and implications for the possible use of SI-grafted carbon layers in PEMFC devices are discussed.

Platinum catalysts for electrochemical oxygen reduction were prepared on mesoporous carbon supports, some of which included embedded zirconia nanoparticles, by borohydride reduction of hexachloroplatinic acid in ethylene glycol solution. The resulting materials are approximately 20 percent platinum by weight and consist of platinum particles having diameters in the 2-3 nm range, evenly distributed throughout the support structure. Electrochemical surface areas for platinum were measured by hydrogen adsorption/desorption and carbon monoxide stripping and were found to be lower for platinum on carbon containing zirconia than for carbon without zirconia. This finding is thought to reflect a slightly larger platinum particle size and also a higher degree of particle aggregation for platinum on the carbon support containing zirconia, possibly caused by localized patches of positive charge on zirconia particles under the acidic conditions used to deposit platinum. Zirconia-containing carbon supports that had been treated with platinum were subsequently treated with polymer electrolytes having terminal aryl phosphonate groups that can covalently bind to exposed zirconia sites, thereby producing composite materials having intimately integrated platinum catalysts and polymer electrolytes immobilized within a mesoporous carbon support structure. Electrochemical ORR activity of these materials as thin-film electrodes was assessed using rotating disk electrode voltammetry in aqueous sulfuric acid solutions. Activity for platinum on a mesoporous carbon support without zirconia is comparable to that of benchmark materials, e.g., platinum on Vulcan carbon XC-72, but is diminished on the mesoporous carbon support containing zirconia. Remarkably, the platinum ORR activity is fully recovered and slightly enhanced on zirconia-containing supports following treatment with polymer electrolyte. Possible reasons for the recovery of the platinum ORR activity upon polymer electrolyte treatment, and implications for possible application in polyelectrolyte membrane fuel-cell technology, are discussed.

The influence of low-molecular-weight poly(ethylene glycol) (PEG, Mw ≈ 550 Da) plasticizers on the rheology and ion-transport properties of fluorosulfonimide-based polyether ionic melt (IM) electrolytes has been investigated experimentally and via molecular dynamics (MD) simulations. Addition of PEG plasticizer to samples of IM electrolytes caused a decrease in electrolyte viscosity coupled to an increase in ionic conductivity. MD simulations revealed that addition of plasticizer increased self-diffusion coefficients for both cations and anions with the plasticizer being the fastest diffusing species. Application of a VTF model to fit variable-temperature conductivity and fluidity data shows that plasticization decreases the apparent activation energy (Ea) and pre-exponential factor A for ion transport and also for viscous flow. Increased ionic conductivity with plasticization is thought to reflect a combination of factors including lower viscosity and faster polyether chain segmental dynamics in the electrolyte, coupled with a change in the ion transport mechanism to favor ion solvation and transport by polyethers derived from the plasticizer. Current interrupt experiments with Li/electrolyte/Li cells revealed evidence for salt concentration polarization in electrolytes containing large amounts of plasticizer but not in electrolytes without added plasticizer.

High-rate proton transmission through single-layer graphene has been reported by several research groups but the mechanism by which it occurs is still not clear. Low activation energies for proton transmission have been experimentally obtained but are difficult to reconcile with computational modeling studies that predict high activation energies and low transmission rates for protons passing through pristine single-layer graphene at ambient temperatures. It seems likely that a reaction coordinate with an activated complex structure involving proton passage through graphene is involved, though the structural details of such a complex are still not clear. This lecture will review some of our recent experimental results on proton transmission rates through CVD single-layer graphene at variable temperature, with special attention to a kinetics model whereby experimentally-obtained proton-transfer resistances are interpreted as proton-transfer resistances that are linked to heterogeneous proton—transfer rate constants, in a manner that is formally similar to the Butler-Volmer model used to treat electron-transfer rate data in the low overpotential limit. The heterogeneous proton-transfer rate constants are then interpreted using a pre-equilibrium model for protons approaching graphene, coupled to a first-order rate constant for proton transmission through graphene from the pre-equilibrium complex. This first-order proton-transmission rate constant has fundamental significance and may be interpreted in terms of an activation energy and frequency factor for proton transmission. In applying such an analysis to our proton transmission rate data, we obtain a proton-transmission frequency factor that is within a factor of two of the vibrational frequency of the O-H bond in water, suggesting that O-H bond vibration is involved in the rate-determining step of proton transmission.

High specific energy is always desirable in battery systems, especially for electric vehicles. A key towards improving specific energy for a particular combination of anode and cathode active material is to maximize the mass fraction of active material, which means minimizing the fraction of inactive material such as the separator, the binder, electrode additives for improving electronic conductivity, and the current collector. A seemingly simple strategy for maximizing the mass fraction of active materials is to make the electrodes as thick as possible. However, ion transport in thick electrodes can be particularly problematic since salt diffusion into and through the electrode pore space is slow and can easily limit the battery charge / discharge rate. An ideal microstructure is one that allows for direct line of sight or path for the electrode active material access to the electrolyte, for rapid ion-transport throughout the entire electrode thickness. Therefore, a need exists for electrode fabrication methods that create microstructures that maximize electrolyte transport, as is needed to achieve high-rate charging/discharging in electrodes having high mass loading. Optimal microstructures in electrodes help to achieve the ideal balance of active material and electrolyte mass to give high gravimetric and volumetric energy density. As to design a microstructure with the goal of Li ion salt transport facilitation, we synthesized ordered porous microstructure electrodes using combination of freeze cast and tape cast techniques. This method enjoys the combination of conventional tape casting, a main technique in manufacturing Li ion electrodes in industrial scale, and freeze casting. This study simulate two dimensional ordered porous electrode cross-sections and presents the electrochemical performance results of Mo-doped LTO in a electrochemical cell consist of a lithium metal anode, polymer separator, and liquid ethylene carbonate and ethyl methyl carbonate electrolyte. The electrochemical performance of ordered porous microstructure is investigated by varying electronic conductivity, tortuosity, particle size, electrode thickness, and C rate. We show that these engineered porous electrodes considerably reduces the electrolytes mass transport limitation and electrochemical response of electrode is independent of tortuosity, making it possible to synthesize ultra thick electrode for high energy and power density applications. Simulation results show that 10 micron thickness of wall and pore freeze tape cast Mo-doped LTO with electronic conductivity of 1 S/m, tortuosity as high as 10, electrode thickness of 458 micron and mass loading of 30 mg/cm^2 can deliver full capacity even at 2 C-rate.

This talk will cover a wide range of recent studies involving proton transmission across CVD graphene layers incorporated into proton-exchange-membrane (PEM) sandwich structures. Many low-temperature electrochemical systems including fuel cells and water electrolysis cells involve proton transmission across proton-exchange membranes integrated with electrodes. A key to optimizing such systems is the accomplishment of selective proton transmission at high rates, while simultaneously inhibiting crossover transmission of other molecular species such as water, hydrogen / oxygen, methanol, and other species. Single-layer CVD graphene has been shown to accomplish this. Proton transmission across graphene in Nafion | graphene | Nafion sandwich structures has been shown to occur with an area-normalized resistance of less than 0.05 ohm cm2 at room temperature, with high selectivity relative to other ions. The graphene layer is nearly defect free and should be an excellent barrier to other species besides protons. The talk will include studies of proton transmission rates using hydrogen pump cells, water electrolysis using PEM cells, and related work. Graphene characterization studies using confocal Raman spectroscopy and X-ray photoelectron spectroscopy, and graphene defect characterization using chemical etching of graphene on copper, will also be covered. Effects of the graphene structure (single vs double layer) and the nature of the 2D material (graphene vs. hexagonal boron nitride) on proton transmission rates, and the rates for other ions besides proton, will also be discussed.

Proton transmission rates across single-layer CVD graphene embedded in sandwich structures with proton-exchange membranes made from the perfluorosulfonic acid (PFSA) ionomer Nafion were measured and found to occur more than 100 times larger than for any other cation. Measurements were made for protons and a series of other cations including Li+, Na+, K+, Rb+, Cs+ and NH4 + using a four-electrode method in which two platinum electrodes drive ionic current through the membrane and two reference electrodes installed in Luggin capillaries sense the transmembrane potential difference induced by the forced ion flow. Proton transmission rates across graphene were between 150 and 350 times larger than for any of the other cations studied. Characterization studies of graphene on Nafion using confocal Raman microscopy and X-ray photoelectron spectroscopy, and defect counting for graphene on copper by chemical etching through graphene on copper will also be reported. Findings are consistent with transport through physical defect structures for all cations except protons. Proton transmission occurs at very high rates and may involve sites that are more widely distributed and that have much higher proton selectivity than the sites responsible for transmission of other ions. Proton transmission rates across graphene were also measured using electrochemical hydrogen pump cells at variable temperature, which provides an activation energy for proton transmission across graphene. Rate constants for proton transmission are interpreted using a charge-transfer resistance model that allows for interpretation of ionic currents in terms of a rate constant for interfacial proton-transfer. Anrhenius analysis of the rate constants gives values for the activation energy and frequency factor for the interfacial proton-transfer reaction.

Rechargeable batteries are important components of many systems and devices and a high capacity battery that can be rapidly charged remains a top research and development priority. Important performance factors like capacity, energy density, and power density strongly depend on chemical nature and the microstructure of the porous electrodes. Highly tortuous porous electrodes and long lithium ion pathway due to pore blockage by inactive material are detrimental to the energy and power density. Our goal is to investigate the potential of fabricating low tortuosity, controlled porosity Li-ion battery electrodes by taking advantage of the hierarchical ordered porous microstructure, which can be obtained using freeze tape casting technique. For this research, Lithium titanate (Li4Ti5O12) powders with and without molybdenum doping (LTO and MoLTO respectively) were synthesized by a solid-state method and used to fabricate electrodes on Cu foil using a normal tape-cast method and a novel freeze-tape-cast. Modest molybdenum doping produces a significant electronic conductivity increase (e.g. 1 mS cm-1 for MoLTO vs 10-7 mS.cm-1 for LTO) that is thought to reflect a partial Ti4+ reduction to Ti3+ with charge compensation by the Mo6+ dopant, producing a stable mixed-valent Ti4+/3+ state. Freeze-tape-cast electrodes were fabricated by a variant of the normal tape-cast method that includes a rapid freezing step in which the solvent in the Cu-foil-supported slurry is rapidly frozen on a cold finger then subsequently sublimed to create unidirectional columnar macropores in the electrode. The effect of Mo doping, freezing rate, electrode thickness on electrochemical behavior of electrodes were investigated. The resulting freeze tape cast electrodes exhibit high porosity and low tortuosity which enhances electrolyte accessibility throughout the full electrode thickness. Freeze-tape-cast electrodes subjected to galvanostatic charge-discharge testing as cathodes in cells vs. a lithium metal anode exhibit higher specific capacity and lower capacity loss at high discharge rates compared with normal-tape-cast electrodes of the same mass loading, despite the fact that the freeze-tape-cast electrodes are nearly twice as thick as the normal tape cast electrodes. We show that these engineered porous electrodes of MoLTO have improved energy and power density compared with randomly oriented uniform porosity electrodes – feature of the current generation of battery electrodes.

The redox chemistry of the nitro, nitrosyl, and peroxynitro ligands in cobalt porphyrins and phthalocyanines has been shown to be able to catalytically activate dioxygen in its electrochemical reduction. Two compounds have been focus of this study by cyclic voltammetry and density functional theory computational methods: the cationic porphyrin complex (nitro)(pyridyl)cobalt(III)TMpyP-2 immobilized in a Nafion® film with silver nanoparticles, and (nitro)(dimethylaminopyridyl)cobaltperfluoro-phthalocyanine, (NO2)(Me2Npy)CoF16Pc on a glassy carbon electrode. The porphyrin complex shows catalytic ORR activity that is short-lived, but the phthalocyanine complex appears to be a robust catalyst. DFT computational studies were used to evaluate the possible intermediates of the system and to corroborate the observed behavior.

A high temperature solution processing method was adapted to prepare durable, freestanding, submicrometer thickness films for transmission infrared spectroscopy studies of ionomer membrane. The materials retain structural integrity following cleaning and ion-exchange steps in boiling solutions, similar to a commercial fuel cell membrane. Unlike commercial membrane, which typically has thicknesses of25 μm, the structural properties of the submicrometer thickness materials can be probed in mid-infrared spectral measurements with the use of transmission sampling. Relative to the infrared attenuated total reflection (ATR) technique, transmission measurements can sample ionomer membrane materials more uniformly and suffer less distortion from optical effects. Spectra are reported for thermally processed Nafion and related perfluoroalkyl ionomer materials containing phosphonate and phosphinate moieties substituted for the sulfonate end group on the side chain. Band assignments for complex or unexpected features are aided by density functional theory (DFT) calculations.

A statically non-wetting, electrospun surface of non volatile room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate, (BMIM-PF 6 ), hosted in a solution-processable, semi-fluorinated perfluorocyclobutyl (BP-PFCB) aryl ether polymer was successfully prepared by electrospinning and compared with a surface prepared by spin casting. The surface properties of undoped and BMIM-PF 6 doped systems were analyzed by water contact angle (WCA) and atomic force microscopy (AFM). BMIM-PF 6 doped BP-PFCB surfaces prepared by spin casting showed a WCA of 90° while non-woven electrospun surfaces with the same BMIM-PF 6 concentration showed high degree of hydrophobicity with a WCA greater than 150°. Morphologies of the electrospun surfaces were characterized by scanning electron microscopy (SEM). The surface composition was analyzed by energy-dispersive X-ray spectroscopy (EDXS) and attenuated total reflectance infrared spectroscopy (ATR-IR). Thermal analysis of the electrospun, non-woven surfaces of the doped and the undoped system of BP-PFCB were done by TGA.

Mesoporous nanocomposite materials in which nanoscale zirconia (ZrO(2)) particles are embedded in the carbon skeleton of a templated mesoporous carbon matrix were prepared, and the embedded zirconia sites were used to accomplish chemical functionalization of the interior surfaces of mesopores. These nanocomposite materials offer a unique combination of high porosity (e.g., ∼84% void space), electrical conductivity, and surface tailorability. The ZrO(2)/carbon nanocomposites were characterized by thermogravimetric analysis, nitrogen-adsorption porosimetry, helium pychnometry, powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Comparison was made with templated mesoporous carbon samples prepared without addition of ZrO(2). Treatment of the nanocomposites with phenylphosphonic acid was undertaken and shown to result in robust binding of the phosphonic acid to the surface of ZrO(2) particles. Incorporation of nanoscale ZrO(2) surfaces in the mesoporous composite skeleton offers unique promise as a means for anchoring organophosphonates inside of pores through formation of robust covalent Zr-O-P bonds.

During PEM fuel cell operation, formation of H 2 O 2 and material corrosion occurs, generating trace amounts of metal cations (i.e., Fe 2+ , Pt 2+ ) and subsequently initiating the deterioration of cell components and, in particular, PFSA membranes (e.g., Nafion). However, most previous studies of this have been performed using conditions not relevant to fuel cell environments, and very few investigations have studied the effect of Nafion decomposition on conductivity, one of the most crucial factors governing PEMFC performance. In this study, a quantitative examination of properties and conductivities of degraded Nafion membranes at conditions relevant to fuel cell environments (30–100%RH and 80 °C) was performed. Nafion membranes were pre-ion-exchanged with small amounts of Fe 2+ ions prior to H 2 O 2 exposure. The degradation degree (defined as loss of ion-exchange capacity, weight, and fluoride content), water uptake, and conductivity of H 2 O 2 -exposed membranes were found to strongly depend on Fe content and H 2 O 2 treatment time. SEM cross-sections showed that the degradation initially took place in the center of the membrane, while FTIR analysis revealed that Nafion degradation preferentially proceeds at the sulfonic end group and at the ether linkage located in the pendant side chain and that the H-bond of water is weakened after prolonged H 2 O 2 exposure.

A new room-temperature ionic liquid (RTIL) consisting of the fluorinated anion bis(trifluoromethyl)-phosphinate((CF3)2PO2−) coupled with the 1-butyl-3-methyl-imidazoliuim (BMIM) cation has been synthesized and characterized by physicochemical and electrochemical means including differential scanning calorimetry (DSC), thermogravimetric analysis, viscosity, conductivity and cyclic voltammetry measurements. Properties are compared with those of the known RTIL consisting of BMIM coupled with the bis(trifluoromethyl)-sulfonylimide (TFSI) anion.

It is known that trace amounts of cations have a detrimental effect on the liquid-phase conductivity of perfluorosulfonated membranes at room temperature. However, the conditions used were very different from typical fuel cell conditions. Recent research has shown the impact of conductivity measurement conditions on NH4+ contaminated membranes. In this study, the impact of nonproton-containing cations (Mn+ = Na+, Ca2+, and Fe3+) on Nafion membrane (N-211) conductivity was investigated both in deionized (DI) water at room temperature (∼25 °C) and in the gas phase at 80 °C under conditions similar to in a PEMFC. These conductivities were compared with those of Nafion membranes contaminated with NH4+ ions. Under the same conditions, the conductivity of a metal cationic-contaminated membrane having the same proton composition ( y H + m ) was similar, but slightly lower than that of an NH4+-contaminated membrane. The conductivity in the purely H+-form of N-211 was more than 12 times greater than the Mn+-form form at 25 °C in DI water. At 80 °C, the gas-phase conductivity was 6 times and 125 times greater at 100%RH and 30%RH, respectively. The quantitative results for conductivity and activation energy of contaminated membranes under typical fuel cell conditions are reported here for the first time.

The effects of increasing perfluoroalkyl chain length on the molecular properties of viscosity, diffusivity, and ionic conductivity of a series of acid model compounds analogous to comb-branch perfluorinated ionomers functionalized with phosphonic, phosphinic, and sulfonic protogenic groups are reported. Anhydrous proton transport by a Grotthuss-like hopping mechanism was observed to occur efficiently in phosphorus-based fluoroalkylated model acids but only when there is a relatively low perfluoroalkyl content. The decrease in degree of dissociation of the protogenic groups follows the order phosphonic > phosphinic > sulfonic, and the degree of dissociation and the magnitude of ion-ion correlations are approximately independent of chain length.