Abstract  A palladium hexacyanoferrate (PdHCF) film as an electrocatalytic material was obtained at an aluminum (Al) electrode by a simple electroless dipping method. The modified Al electrode demonstrated a well-behaved redox couple due to the redox reaction of the PdHCF film. The PdHCF film showed an excellent electrocatalytic activity toward the oxidation of hydrazine. The electrocatalytic oxidation of hydrazine was studied by cyclic voltammetry and rotating disk electrode voltammetry techniques. A calibration graph obtained for the hydrazine consisted of two segments (localized at concentration ranges 0.39-10 and 20-75 mM). The rate constant k and transfer coefficient alpha for the catalytic reaction and the diffusion coefficient of hydrazine in the solution D, were found to be 3.11 x 10(3) M(-1) s(-1), 0.52 and 8.03 x 10(-6) cm2 s(-1) respectively. The modified electrode was used to amperometric determination of hydrazine in photographic developer. The interference of ascorbic acid and thiosulfate were investigated and greatly reduced using a thin film of Nafion on the modified electrode. The modified electrode indicated reproducible behavior and a high level of stability during electrochemical experiments, making it particularly suitable for analytical purposes.

Abstract  Due to their strong acidity and water affinity, sulfated zirconia nanoparticles were evaluated as inorganic additives in the formation of composite Nafion-based membranes. Two types of sulfated zirconia were obtained according to the preparation experimental conditions. Sulfated zirconia-doped Nafion membranes were prepared by a casting procedure. The properties of the composite membranes were compared with those of an unfilled Nafion membrane obtained by the same preparation method. The water uptake, measured at room temperature in a wide relative humidity range, was higher for the composite membranes, this confirming the hydrophilic nature of the selected additives. The membrane doped by zirconia particles having the highest sulphate group concentration showed the highest water diffusion coefficient in the whole range of temperature and relative humidity investigated due to the presence of SO(4) (2-) providing extra acid sites for water diffusion. The proton diffusivity calculated from impedance spectroscopy measurements was compared with water self diffusion coefficients measured by NMR Spectroscopy. The difference between proton and water diffusivity became significant only at high humidification levels, highlighting the role of water in the intermolecular proton transfer mechanism. Finally, great improvements were found when using the composite membrane as electrolyte in a fuel cell working at very low relative humidity.

Abstract  A new and simplified approach for making cathodes for microbial fuel cells (MFCs) was developed by using metal mesh current collectors and inexpensive polymer/carbon diffusion layers (DLs). Rather than adding a current collector to a cathode material such as carbon cloth, we constructed the cathode around the metal mesh itself, thereby avoiding the need for the carbon cloth or other supporting material. A base layer of poly(dimethylsiloxane) (PDMS) and carbon black was applied to the air-side of a stainless steel mesh, and Pt on carbon black with Nafion binder was applied to the solution-side as catalyst for oxygen reduction. The PDMS prevented water leakage and functioned as a DL by limiting oxygen transfer through the cathode and improving coulombic efficiency. PDMS is hydrophobic, stable, and less expensive than other DL materials, such as PTFE, that are commonly applied to air cathodes. Multiple PDMS/carbon layers were applied in order to optimize the performance of the cathode. Two PDMS/carbon layers achieved the highest maximum power density of 1610 +/- 56 mW/m(2) (normalized to cathode projected surface area; 47.0 +/- 1.6 W/m(3) based on liquid volume). This power output was comparable to the best result of 1635 +/- 62 mW/m(2) obtained using carbon cloth with three PDMS/carbon layers and a Pt catalyst. The coulombic efficiency of the mesh cathodes reached more than 80%, and was much higher than the maximum of 57% obtained with carbon cloth. These findings demonstrate that cathodes can be constructed around metal mesh materials such as stainless steel, and that an inexpensive coating of PDMS can prevent water leakage and lead to improved coulombic efficiencies.

Abstract  Electrochemical sensors have great potential for environmental monitoring of toxic metal ions in waters due to their portability; field-deployability and excellent detection limits. However, electrochemical sensors employing mercury-free approaches typically suffer from binding competition for metal ions and fouling by organic substances and surfactants in natural waters, making sample pretreatments such as wet ashing necessary. In this work, we have developed mercury-free sensors by coating a composite of thiol self-assembled monolayers on mesoporous supports (SH-SAMMS (TM)) and Nafion on glassy-carbon electrodes. With the combined benefit of SH-SAMMS (TM) as an outstanding metal preconcentrator and Nafion as an antifouling binder, the sensors could detect 0.5 ppb of Pb and 2.5 ppb of Cd in river water, Hanford groundwater, and seawater with a minimal amount of preconcentration time (few minutes) and without any sample pretreatment. The sensor could also detect 2.5 ppb of Cd, Pb, and Cu simultaneously. The electrodes have long service times and excellent single and inter-electrode reproducibility (5% R.S.D. after 8 consecutive measurements). Unlike SAMMS (TM)-carbon paste electrodes, the SAMMS (TM)-Nafion electrodes were not fouled in samples containing albumin and successfully detected Cd in human urine. Other potentially confounding factors affecting metal detection at SAMMS (TM)-Nafion electrodes were studied, including pH effect, transport resistance of metal ions, and detection interference. With the ability to reliably detect low metal concentration ranges without sample pretreatment and fouling, SAMMS (TM)-Nafion composite sensors have the potential to become the next-generation metal analyzers for environmental and bio-monitoring of toxic metals. (c) 2008 Elsevier B.V. All rights reserved.

Abstract  Graphene nanosheets, dispersed in Nafion (Nafion-G) solution, were used in combination with in situ plated bismuth film electrode for fabricating the enhanced electrochemical sensing platform to determine the lead (Pb2+) and cadmium (Cd2+) by differential pulse anodic stripping voltammetry (DPASV). The electrochemical properties of the composite film modified glassy carbon electrode were investigated. It is found that the prepared Nafion-G composite film not only exhibited improved sensitivity for the metal ion detections, but also alleviated the interferences due to the synergistic effect of graphene nanosheets and Nafion. The linear calibration curves ranged from 0.5 mu g L-1 to 50 mu g L-1 for Pb2+ and 1.5 mu g L-1 to 30 mu g L-1 for Cd2+. respectively. The detection limits (S/N = 3) were estimated to be around 0.02 mu g L-1 for Pb2+ and Cd2+. The practical application of the proposed method was verified in the water sample determination. (C) 2009 Elsevier B.V. All rights reserved.

Abstract  In this study, we examined the influence of the dispersion solvent in three dipropylene-glycol/water (DPG/water) mixtures, with DPG contents of 0, 50, and 100 wt%, on ionomer morphology and distribution, using dynamic light scattering (DLS) and molecular-dynamics (MD) simulation techniques. The DLS results reveal that Nafion-ionomer aggregation increases with decreasing DPG content of the solvent. Increasing the proportion of water in the solvent also led to a gradual decrease in the radius of gyration (Rg) of the Nafion ionomer due to its strong backbone hydrophobicity. Correspondingly, MD simulations predict Nafion-ionomer solvation energies of -147 ± 9 kcal/mol in water, -216 ± 21 kcal/mol in the DPG/water mixture, and -444 ± 9 kcal/mol in DPG. These results suggest that higher water contents in mixed DPG/water solvents result in increased Nafion-ionomer aggregation and the subsequent deterioration of its uniform dispersion in the solvent. Moreover, radial distribution functions (RDFs) reveal that the (-CF2CF2-) backbones of the Nafion ionomer are primarily enclosed by DPG molecules, whereas the sulfonate groups (SO3-) of its side chains mostly interact with water molecules.

Abstract  All presently used batteries contain reactive, corrosive or toxic components and require strong cases, usually made of steel. As a battery is miniaturized, the required case dominates its size. Hence, the smallest manufactured batteries are about 50 mm3 in size, much larger then the integrated circuits or sensors of functional analytical packages, as exemplified by implantable glucose sensors for diabetes management. The status of the miniaturization of the power sources of such implantable packages is reviewed. Three microcells, consisting only of potentially harmless subcutaneously implantable anodes and cathodes, are considered. Because their electrolyte would be the subcutaneous interstitial fluid, the cells do not have a case. One potentially implantable cell has a miniature Nafion-coated Zn anode and a biocompatible hydrogel-shielded Ag/AgCl cathode. The core innovation on which the cell is based is the growth of a hopeite-phase Zn2+ conducting solid electrolyte film on the discharging anode. The film blocks the transport of O2 to the Zn, preventing its corrosion, while allowing the necessary transport of Zn2+. The second cell, with the same anode, would have a bioinert hydrogel-shielded wired bilirubin oxidase-coated carbon cathode, on which O2 dissolved in the subcutaneous fluid would be electroreduced to water. In the third cell, the glucose of the subcutaneous interstitial would be electrooxidized to gluconolactone at an implanted wired glucose anode, similar to that tested now for continuous glucose monitoring in diabetic people, and O2 in the subcutaneous fluid would be electroreduced to water on its wired bilirubin oxidase cathode.

Abstract  The authors report on a microneedle-based amperometric nonenzymatic glucose sensor for painless and continuous monitoring of glucose. It consists of 3 × 5 sharp stainless steel microneedles micromachined from a stainless steel substrate. The microneedles are 600 and 100 μm in height and width, respectively. Nafion and platinum black were sequentially coated onto the tip of gold-coated microneedles and used for nonenzymatic (direct) sensing of glucose. Attractive features of the modified microneedle electrode include (a) a low working potential (+0.12 V vs. Ag/AgCl), (b) a linear response in the physiologically relevant range (1-40 mM), (c) a sensitivity as high as 175 μA mM-1 cm-2, (d) a 23 μM detection limit, and (e) a response time of 2 s. The sensor also exhibits good reproducibility and stability. The sensor is selective for glucose even in the presence of 10-fold higher concentrations of ascorbic acid, lactic acid, dopamine, uric acid, and acetaminophen. Graphical abstract Schematic representation of the fabrication sequence for a nonenzymatic electrochemical glucose sensor using Nafion and platinum black coated microneedle electrode array. The sensor is based on measuring the faradaic current at +0.12 V vs. Ag/AgCl by the direct electrochemical oxidation of glucose to gluconic acid on the surface of a Pt black sensing layer.

Abstract  We report a unique fuel cell sensor system for the first time direct detection of unlabeled virus particles based on the formation of antibody-virus complexes within the sensor's membrane nanochannels. This strategy exploits the change in the membrane resistance of the powered system, comprising a Prussian blue nanotubes (PB-nt) membrane cathode and a platinum mesh anode. The method reports an impressive shortest response time of ∼5 min toward the specific virus target, at low concentration values of 3-45 plaque-forming units per milliliter (pfu mL(-1)) with detection limit of 0.04 pfu mL(-1), comparable to state-of-the-art polymerase chain reaction (PCR)-based methods. The sensor can clearly differentiate dengue virus serotype 2 from serotype 3. When filled with Nafion perfluorinated resin, the PB-nt membrane demonstrates powerful utilization as a stand-alone fuel cell based virus sensor, and thus offers the outstanding promise of a sustainable, low-cost, and rapid low-power virus detection tool.

Abstract  Nafion membranes are now the most widely used membranes for long-life vanadium flow batteries (VFBs) because of their extremely high chemical stability. Today, the type of Nafion membrane that should be selected and how to pretreat these Nafion membranes have become critical issues, which directly affects the performance and cost of VFBs. In this work, we chose the Nafion 115 membrane to investigate the effect of the pretreatment process (as received, wet, boiled, and boiled and dried) on the performance of VFBs. The relationship between the nanostructure and transport properties of Nafion 115 membranes is elucidated by wide-angle X-ray diffraction and small-angle X-ray scattering techniques. The self-discharge process, battery efficiencies, electrolyte utilization, and long-term cycling stability of VFBs with differently pretreated Nafion membranes are presented comprehensively. An online monitoring system is used to monitor the electrolyte volume that varies during the long-term charge-discharge test of VFBs. The capacity fading mechanism and electrolyte imbalance of VFBs with these Nafion 115 membranes are also discussed in detail. The optimal pretreatment processes for the benchmark membrane and practical application are synthetically selected.

Abstract  Positive Poles: A new type of electrochemical capacitor with two different aqueous solutions, separated by a Nafion membrane is described. High capacitance values as well as excellent energy/power characteristics are reported and discussed. The neutral character of the applied electrolytes makes this capacitor an environmentally friendly, easy to assemble, and cost-effective device for energy storage.

Abstract  Proton conducting polymer composite membranes are of technological interest in many energy devices such as fuel cells and redox flow batteries. In particular, polymer composite membranes, such as SiO(2) incorporated Nafion membranes, are recently reported as highly promising for the use in redox flow batteries. However, there is conflicting reports regarding the performance of this type of Nafion-SiO(2) composite membrane in the redox flow cell. This paper presents results of the analysis of the Nafion-SiO(2) composite membrane used in a vanadium redox flow battery by nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier Transform Infra Red (FTIR) spectroscopy, and ultraviolet-visible spectroscopy. The XPS study reveals the chemical identity and environment of vanadium cations accumulated at the surface. On the other hand, the (19)F and (29)Si NMR measurement explores the nature of the interaction between the silica particles, Nafion side chains and diffused vanadium cations. The (29)Si NMR shows that the silica particles interact via hydrogen bonds with the sulfonic groups of Nafion and the diffused vanadium cations. Based on these spectroscopic studies, the chemical environment of the silica particles inside the Nafion membrane and their interaction with diffusing vanadium cations during flow cell operations are discussed. This study discusses the origin of performance degradation of the Nafion-SiO(2) composite membrane materials in vanadium redox flow batteries.

Abstract  Both cation-exchange membranes and anion-exchange membranes are used as ion conducting membranes in vanadium redox flow batteries (VRFBs). Anion-exchange membranes (AEMs) are applied in vanadium redox flow batteries due to the high blocking property of vanadium ions via the Donnan exclusion effect. In this study, novel anion-exchange blend membranes (AEBMs) were prepared, characterized, and applied in VRFBs. Bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide), poly[(1-(4,4′-diphenylether)-5-oxybenzimidazole)-benzimidazole] (PBI-OO) and sulfonated polyether sulfone polymer were combined to prepare 3-component AEBMs with 1,2,4,5-tetramethylimidazole (TMIm) for quaternization. 3-component AEBMs showed significantly enhanced chemical and mechanical properties compared with those of 2-component AEBMs, resulting in an improved performance in VRFBs. The compositions of the anion-exchange polymers in 3-component AEBMs were systematically varied to optimize the AEBMs for the redox-flow battery application. While the 3-component AEBMs showed comparable efficiencies with Nafion® 212 membranes, they displayed improved vanadium ions cross-over as was confirmed by open circuit voltage tests and capacity fade tests conducted in VRFBs. In addition, one of the synthesized 3-component AEBM had a superior coulombic efficiency and capacity retention in a charging⁻discharging test over 300 cycles at a current density of 40 mA/cm². It can thus be concluded that 3-component AEBMs are promising candidates for long-term operation in VRFBs.

Abstract  A novel paper-based potentiometric sensor with an enhanced response for the detection of glucose in biological fluids is presented. The electrode consists on platinum sputtered on a filter paper and a Nafion membrane to immobilize the enzyme glucose oxidase. The response obtained is proportional to the logarithm of the concentration of glucose, with a sensitivity of -119±8mV·decade-1, a linear range that spans from 10-4M to 10-2.5 M and a limit of detection of 10-4.5 M of glucose. It is shown that Nafion increases the sensitivity of the technique while minimizing interferences. Validation with human serum samples shows an excellent agreement when compared to standard methods. This approach can become an interesting alternative for the development of simple and affordable devices for point of care and home-based diagnostics.

Abstract  This work demonstrates the use of amino functionalized Mg-phyllosilicate clay/Nafion nanocomposite film embedded with Pt nanoparticles (Pt/AC/N) for catalyzing oxygen reduction reaction (ORR) in sulphuric acid medium. Pt/AC/N nanocomposite films were surface characterized using transmission electron microscope. Cyclic and linear scan voltammetry studies were carried out under hydrodynamic conditions taking rotating-ring disc electrode (RRDE) as the working electrode. The effects of clay content, Pt mass loading, electrode rotation rate, and temperature on the ORR kinetics were studied. The Tafel slopes were found to vary between 118 and 126 mV dec(-1) indicating a good ORR kinetics. The exchange current density values calculated after mass transfer correction ranged from 5.8×10(-7) to 2.4×10(-6) A cm(-2). From the RRDE disc currents, Koutecky-Levich plots were constructed and the ORR mechanism was found to follow a four electron path with minimum H(2)O(2) formation of ∼1.6%. The effect of temperature on ORR kinetics was found at 25, 40, and 50°C. The energy of activation calculated to be 7.68 kJ mol(-1) and comparable to the standard Pt/C catalyzed ORR systems.

Abstract  ZnO nanoparticles (nanoZnO) were decorated on multiwalled carbon nanotubes (MWCNTs) and then the prepared nano-hybrids, nanoZnO-MWCNTs, were immobilized on the surface of a glassy carbon electrode (GCE) to fabricate nanoZnO-MWCNTs modified GCE. The prepared electrode, GCE/nanoZnO-MWCNTs, showed excellent electrocatalytic activity towards luminol electrochemiluminescence (ECL) reaction. The electrode was then further modified with lactate oxidase and Nafion to fabricate a highly sensitive ECL lactate biosensor. Two linear dynamic ranges of 0.01-10 μmol L(-1) and 10-200 μmol L(-1) were obtained for lactate with the correlation coefficient better than 0.9996. The detection limit (S/N=3) was 4 nmol L(-1) lactate. The relative standard deviation for repetitive measurements (n=6) of 10 μmol L(-1) lactate was 1.5%. The fabrication reproducibility for five biosensors prepared and used in different days was 7.4%. The proposed ECL lactate biosensor was used for determination of lactate in human blood plasma samples with satisfactory results.

Abstract  The direct electrochemistry and bioelectrocatalysis of horseradish peroxidase (HRP) in Nafion films at glassy carbon electrode (GCE) was investigated in three [BF(4)](-)-type room-temperature ionic liquids (ILs) to understand the structural effect of imidazolium cations. The three ILs are 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF(4)]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]) and 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF(4)]). A small amount of water in the three ILs is indispensable for maintaining the electrochemical activity of HRP in Nafion films, and the optimum water contents decrease with the increase of alkyl chain length on imidazole ring. Analysis shows that the optimum water contents are primarily determined by the hydrophilicity of ILs used. In contrast to aqueous medium, ILs media facilitate the direct electron transfer of HRP, and the electrochemical parameters obtained in different ILs are obviously related to the nature of ILs. The direct electron transfer between HRP and GCE is a surface-confined quasi-reversible single electron transfer process. The apparent heterogeneous electron transfer rate constant decreases gradually with the increase of alkyl chain length on imidazole ring, but the changing extent is relatively small. The electrocatalytic reduction current of H(2)O(2) at the present electrode decreases obviously with the increase of alkyl chain length, and the mass transfer of H(2)O(2) via diffusion in ILs should be responsible for the change. In addition, the modified electrode has good stability and reproducibility; the ability to tolerate high levels of F(-) has been greatly enhanced due to the use of Nafion film. When an appropriate mediator is included in the sensing layer, a sensitive nonaqueous biosensor could be fabricated.

Abstract  The aim of the present study was to investigate whether a GABAB receptor agonist could modulate ATP-activated neuronal excitability of nociceptive TRG neurons using perforated whole-cell patch-clamp and immunohistochemical techniques. Immunohistochemical analysis revealed that 86% of P2X3 receptor-immunoreactive, small-diameter TRG neurons co-expressed GABAB receptor. Under voltage-clamp conditions (Vh=-60mV), application of ATP activated the inward current in acutely isolated rat TRG neurons in a dose-dependent manner (10-50 μM) and this current could be blocked by pyridoxal-phosphate-6-azophenyl-27,47-disulfonic acid (PPADS) (10 μM), a selective P2 purinoreceptor antagonist. The peak amplitude of ATP-activated currents was significantly inhibited after application of GABAB receptor agonist, baclofen (10-50 μM), in a concentration-dependent and reversible manner. The baclofen-induced inhibition of ATP-activated current was abolished by co-application of 3-amino-2 (4-chlorophenyl)-2hydroxypropysufonic acid) saclofen, a GABAB receptor antagonist (50 μM). Under current-clamp conditions, application of 20 μM ATP significantly depolarized the membrane potential resulting in increased mean action potential frequencies, and these ATP-induced effects were significantly inhibited by baclofen and these effects were antagonized by co-application of saclofen. Together, the results suggested that GABAB receptor activation could inhibit the ATP-induced excitability of small-diameter TRG neurons activated through the P2X3 receptor. Thus, the interaction between P2X3 and GABAB receptors of small-diameter TRG neuronal cell bodies is a potential therapeutic target for the treatment of trigeminal nociception.

Abstract  An ultrasensitive electrochemical aptasensor was successfully fabricated for the detection of adenosine triphosphate (ATP). For the first time, one detection system combined several elements: magnetic aptamer sequences for target recognition and separation, a DNAzyme assisted cyclic signal amplification strategy, layer-by-layer (LBL) quantum dots (QDs) composites for promoting square wave anodic stripping voltammetric (SWASV) analysis and Bi, Nafion (Nf) and three-dimensional ordered macroporous polyaniline-ionic liquid (Bi/Nf/3DOM PANI-IL) film modified glassy carbon electrode (GCE) for monitoring enhanced SWASV signal. The modification of Nf/3DOM PANI-IL on GCE showed that the preconcentration efficiency was improved by the electrostatic absorption of Cd2+ with negative Nf layer with the enhanced analytical sensitivity due to a large active surface area of 3DOM structure. The increased SWASV peak current values of the label (CdS)(4)@SiO2 composites were found to be proportional to the logarithmic value of ATP concentrations in the range of 1 pM-10 nM and 10 nM-1 mu M, with the detection limit as low as 0.5 pM. The proposed aptasensor has shown an excellent performance such as high sensitivity, good selectivity and analytical application in real samples. The results demonstrated that the multiple signal amplified strategy we developed was feasible for clinical ATP assay and would provide a promising model for the detection of other small molecules. (c) 2014 Elsevier B.V. All rights reserved.

Abstract  A colourimetric sensor capable of simultaneously measuring oxidative status (OS) in terms of the hazard produced by reactive oxygen species (ROS) and antioxidant activity (AOA) in regard to ROS-scavenging ability of antioxidant compounds was developed. The coloured cationic semi-quinone derivatives, caused by ROS oxidative degradation of N,N-dimethyl-p-phenylene diamine hydrochloride (DMPD) in pH 5.7 acetate-buffered medium, were formed in solution and immobilized on a perfluorosulfonate-based Nafion membrane. ROS, namely hydroxyl (·OH) and superoxide (O2(·-)) radicals, were produced by Fenton/UV and xanthine/xanthine oxidase methods, respectively. The pink-coloured, (+)-charged chromophore (referred to as DMPD-quinone or DMPDQ), resulting from the reaction between DMPD and ROS, could be completely retained on the solid membrane sensor by electrostatic interaction with the anionic sulfonate groups of Nafion. After equilibration, the Nafion membrane surface was homogeneously coloured enabling an absorbance measurement at 514 nm, while the aqueous phase completely lacked colour. Antioxidants, when present, caused an absorbance decrease on the membrane due to their ROS scavenging action, giving rise to less DMPDQ production. The absorbance decrease on the sensor was linearly dependent on antioxidant concentration over a reasonable concentration range, enabling the simultaneous determination of OS and AOA-against ROS. The proposed antioxidant sensing method was tested in synthetic and real antioxidant mixtures, and validated against standard antioxidant capacity assays (i.e. ABTS and CUPRAC) for a variety of polyphenolic and antioxidant compounds. The dynamic linear ranges of antioxidants with the DMPD sensor in protection against hydroxyl and superoxide radicals generally varied within the micromolar to a few tens of micromolar concentration interval over one order-of-magnitude. Choosing three representative compounds in the high (epigallocatechin gallate), medium (quercetin) and low (p-coumaric acid) molar absorptivity range, the detection limits ranged within the concentration intervals of 0.2-0.9 μM, 0.3-0.8 μM, and 4-14 μM, respectively, depending on the radical scavenged.

Abstract  Composite membranes composed of highly conductive and selective layer-by-layer (LbL) films and electrospun fiber mats were fabricated and characterized for mechanical strength and electrochemical selectivity. The LbL component consists of a proton-conducting, methanol-blocking poly(diallyl dimethyl ammonium chloride)/sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (PDAC/sPPO) thin film. The electrospun fiber component consists of poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) fibers in a nonwoven mat of 60-90% porosity. The bare mats were annealed to improve their mechanical properties, which improvements are shown to be retained in the composite membranes. Spray LbL assembly was used as a means for the rapid formation of proton-conducting films that fill the void space throughout the porous electrospun matrix and create a fuel-blocking layer. Coated mats as thin as 15 μm were fabricated, and viable composite membranes with methanol permeabilities 20 times lower than Nafion and through-plane proton selectivity five and a half times greater than Nafion are demonstrated. The mechanical properties of the spray coated electrospun mats are shown to be superior to the LbL-only system and possess intrinsically greater dimensional stability and lower mechanical hysteresis than Nafion under hydrated conditions. The composite proton exchange membranes fabricated here were tested in an operational direct methanol fuel cell. The results show the potential for higher open circuit voltages (OCV) and comparable cell resistances when compared to fuel cells based on Nafion.

Abstract  Capillary zone electrophoresis (CE) under conditions of reversed polarity is used in conjunction with electrochemical detection (EC) at carbon fiber microcylinder electrodes for the selective and sensitive determination of uric acid in human blood serum. Comigration of anions with the electroosmotic flow is accomplished with reversed polarity and the buffer additive cetyltrimethylammonium bromide (CTAB) in a 2-(N-morpholino)ethanesulfonic acid (MES) buffer system, giving rise to rapid and sensitive analyses. Optimal buffer conditions (pH 7.0), detection potential (0.80 V vs. Ag/AgCl), and electrokinetic injection are employed to allow for maximal resolution and signal intensity. Amperometric end-column detection with a carbon fiber microcylinder electrode results in lower limits of detection for uric acid of about 25 nM (ca. 140 amol injected) without the need for decoupling. Linear calibration plots using uric acid standards in water and serum are obtained over a linear range from 5.00 x 10(-4) M to 2.50 x 10(-7) M. Uric acid concentrations obtained for human sera using the CE-EC approach described here are shown to compare favorably to the accepted laboratory values.

Abstract  Four polypyridyl redox catalysts Fe(bp)3(2+), Fe(ph)3(2+), Fe(dm)3(2+), and Fe(tm)3(2+) (with bp, ph, dm, and tm representing 2,2'-bipyridine, 1,10-phenanthroline, 4,4'-dimethyl-2,2'-bipyridine, and 3,4,7,8-tetramethyl-1,10-phenanthroline, respectively) are investigated for the electrocatalytic oxidation of three analytes (nitrite, arsenite, and isoniazid). The poly-pyridyl iron complex is exchanged into a Nafion film immobilized on a glassy carbon electrode, which is then immersed in 0.1 M Na2SO4. Cyclic voltammetry is employed for the evaluation of the mechanism and estimation of kinetic parameters. The electrocatalytic behaviour going from low to high substrate concentration is consistent with the Albery-Hillman cases of "LEty" switching to "LEk" (changing from the first order in the substrate to half order in the substrate), denoting a process that occurs in a reaction zone close to the electrode surface with diffusion of charge (from the electrode surface into the film) and of anionic or neutral analyte (from the Nafion-solution interface into the film). The relative hydrophobicity of the iron polypyridyl catalyst within the film is shown to affect both the diffusion of charge/electrons and analyte within the film with Fe(tm)3(2+) providing the mildest catalyst. All three analytes, nitrite, isoniazid, and arsenite, exhibit linear calibration ranges beneficial for analytical applications in the micro-molar to the milli-molar range.

Abstract  We report a suite of coordination-driven self-assembled prisms for heterogeneous electrocatalytic oxygen reduction (ORR) differing in the molecular clips linking two porphyrin faces in a cofacial arrangement. ORR activities and selectivities of monomeric CoTPyP along with cofacial prisms Ox-Co, Oxa-Co, and Benzo-Co were probed using cyclic voltammetry and rotating ring-disk techniques. All species were immobilized as heterogeneous catalysts on glassy carbon electrodes using a Nafion ink method. The selectivities of Ox-Co, Oxa-Co, and Benzo-Co prisms towards H2 O as determined by RRDE were 87, 97, and 75 %, respectively. The current density of the Oxa-Co plateaus at five times that of Pt/C when normalized per Co/Pt. The high synthetic yield (79 %), competitive overpotential (η ≈800 mV) and high selectivity (%H2 O ≈97 %) of the Oxa-Co highlights how self-assembly can be used to address multi-electron multi-proton transformations using polynuclear catalysts.

Abstract  Robust water oxidation catalysts using earth abundant metals are required as part of an overall scheme to convert sunlight into fuels. Here, we report the immobilization of [[Formula: see text]O(5)(terpy)(4)(H(2)O)(2)](ClO(4))(6) (terpy = 2,2';6',2″-terpyridine), [Mn(4)O(6)(tacn)(4)](ClO(4))(4) (tacn = 1,4,7-triazacyclononane), and manganese dioxide nanoparticles in Nafion on fluorine-doped tin oxide conducting glass electrodes. The electrodes are illuminated with white light in the presence of an applied potential and the resulting photocurrent is assigned to the oxidation of solvent water. Photodecomposition of the tetrameric complexes results in a material that is more active for light-driven electrooxidation of water. The reactivity, wavelength dependence, and stability of the compounds in Nafion under illumination are discussed.