Anhydrous solid proton conductors based on perfluorosulfonic ionomer with polymeric solvent for polymer electrolyte fuel cell

Novel anhydrous polymeric proton conductors have been prepared from perfluorosulfonic acid ionomer with polymer solvent as supplying proton pathway through the segmental motion of polymer chains for polymer electrolyte fuel cell (PEFC) application. Since the membranes do not contain liquid-state acid or solvent, the membranes may promise more stable performances during the operation of PEFC. The Nafion-based anhydrous proton conductors showed maximum proton conductivity of about 4.0 × 10^?3 S cm^?1 at 130 °C under anhydrous condition. The mechanical properties of the membranes were enhanced by introducing H⁺-doped TiO₂ nanoparticles without the conductivity degradation. In addition, the electrochemical properties of the membrane electrode assembly (MEA) employing the anhydrous membrane as ionomer have been investigated, showing stable open circuit voltages (OCVs) over 0.9 V under non-humidified condition.     

Electrochemical and thermodynamic properties of hexacyanoferrate(II)/(III) redox system on multi-walled carbon nanotubes

Novel films consist of multi-walled carbon nanotubes (MWCNT) were fabricated by means of catalytic chemical vapor deposition (CVD) technique with decomposition of either acetonitrile (ACN) or benzene (BZ) using ferrocene (FeCp₂) as catalyst. The electrochemical and thermodynamic behavior of the ferrocyanide/ferricyanide, [Fe(CN)₆]^3−/4− redox couple on synthesized MWCNT-based films was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques at T = (278.15, 283.15, 293.15, and 303.15) K. The redox couple [Fe(CN)₆]^3−/4− behaves quasi-reversibly on fabricated MWCNT-based films and its reversibility is enhanced upon increasing temperature. Namely, the findings establish that with the rise in temperature the barrier for interfacial electron transfer decreases, leading, consequently, to an enhancement of the kinetics of the charge transfer process. According to thermodynamics the equilibrium of the redox process is shifted towards the formation of [Fe(CN)₆]³⁻ at elevated temperatures.     

A disposable impedance sensor for electrochemical study and monitoring of adhesion and proliferation of K562 leukaemia cells

A polyaniline-modified screen-printed carbon electrode (PANI/SPCE) was prepared by electropolymerization for the construction of a novel disposable cell impedance sensor. The conductive polymer improved greatly the electron transfer of SPCE and was very effective for cell immobilization. The adhesion of cells increased the electron transfer resistance (R_et) of redox probe on the PANI/SPCE surface, producing an impedance sensor for K562 leukaemia cells with a semilogarithm linear range from 10⁴ to 10⁷ cells ml⁻¹ and a limit of detection of 8.32 × 10³ cells ml⁻¹ at 10σ. The proliferation of cells on the conductive polymer increased the R_et, leading to a novel way to monitor the growth process of cells on the PANI/SPCE. The electrochemical monitoring indicated K562 leukaemia cells cultured in vitro on the PANI surface were viable for 60 h, consistent with the analysis from microscopic imaging and MTT assay. This method for monitoring the surface proliferation and detecting the number of viable cells was simple, low-cost and disposable, thus providing a convenient avenue for electrochemical study of cell immobilization, adhesion, proliferation and apoptosis.     

Electrochemical properties of niosomes modified Au electrode and DNA recognition

Non-ionic surfactant vesicles (NSVs), also referred to as niosomes, have been studied as an alternative to conventional liposomes. In this paper, electrochemical inspection of the interaction between Herring sperm DNA and niosomes has been investigated after a simple and novel method for the formation of niosomes on Au electrode. Each step of electrode modification has been confirmed with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The assembly of octadecanethiol (ODT) layer on the electrode surface generates a packed film that introduces a barrier to the interfacial electron transfer (R_et), and the subsequent immobilization of niosomes onto the self-assembled monolayer (SAM) layer results in a further increase of R_et, due to the formed bilayer almost blocked the redox probe to the electrode surface. When Herring sperm DNA was added, the R_et value decreased, indicating that the barrier of the redox probe to the surface was disrupted. The addition of DNA caused the formation of some transmembrane channels for the redox probe across the niosomes. A good linear relationship between R_et value and DNA concentration was found over the 0–0.05 mg mL⁻¹ concentration range.     

Effects of direct current bias voltages on supported bilayer lipid membranes on a glassy carbon electrode

The effects of dc bias voltages on supported bilayer lipid membranes (s-BLMs) on a glassy carbon (GC) electrode have been investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The experiments suggested that an appropriate positive bias voltage facilitated the formation of electrically dense membranes, but if the voltage is enough high, the lacunas on s-BLMs increased, and eventually caused the complete oxidation of the lipid membrane. While negative bias voltages could induce the damage of supported membranes to different extent. The changes of the form and quantity of graphite oxide on the surface of the electrode caused by dc bias voltages and the electroporation and damage of the membrane at high potentials may be responsible for the effects.     

Preparation and characterization of porous conducting poly(dl-lactide) composite membranes

Solid conducting biodegradable composite membranes have shown to enhance nerve regeneration. However, few efforts have been directed toward porous conducting biodegradable composite membranes for the same purpose. In this study, we have fabricated some porous conducting poly(dl-lactide) composite membranes which can be used for the biodegradable nerve conduits. The porous poly(dl-lactide) membranes were first prepared through a phase separation method, and then they were incorporated with polypyrrole to produce porous conducting composite membranes by polymerizing pyrrole monomer in gas phase using FeCl₃ as oxidant. The preparation conditions were optimized to obtain membranes with controlled pore size and porosity. The direct current conductivity of composite membrane was investigated using standard four-point technique. The effects of polymerization time and the concentration of oxidant on the conductivity of the composite membrane were examined. Under optimized polymerization conditions, some composite membranes showed a conductivity close to 10⁻³ S cm⁻¹ with a lower polypyrrole loading between 2 and 3 wt.%. A consecutive degradation in Ringer's solution at 37 °C indicated that the conductivity of composite membrane did not exhibit significant changes until 9 weeks although a noticeable weight loss of the composite membrane could be seen since the end of the second week.     

High performance miniature glucose/O2 fuel cell based on porous silicon anion exchange membrane

Mesoporous silicon membranes are functionalized with ammonium groups and evaluated as high efficient anion exchange membrane in a miniaturized alkaline glucose fuel cell setup. N-Trimethoxysilylpropyl-N,N,N-trimethylammonium chloride is grafted onto the pore walls of porous silicon resulting in the anionic conductivity enhancement. The functionalization process is followed by FTIR spectroscopy where the optimized parameter could be determined. The ionic conductivity is measured using impedance spectroscopy and gives 5.6 mS cm^− 1. These modified mesoporous silicon membranes are integrated in a specially designed miniature alkaline (pH 13) glucose/air fuel cell prototype using a conventional platinum-carbon anode and a cobalt phthalocyanine-carbon nanotube cathode. The enhanced anion conductivity of these membranes leads to peak power densities of 7 ± 0.12 mW cm^− 2 at “air breathing” conditions at room temperature.     

Cyclic voltammetric studies of carbohydrate–protein interactions on gold surface

A simple electrochemical method for the determination of association constants between carbohydrates and carbohydrate-binding proteins using cyclic voltammetry (CV) is described. The binding of concanavalin A (Con A) and cholera toxin (CT) to their specific α-mannose and β-galactose derivatives self-assembled on gold electrodes is electrochemically monitored with a redox probe of K₃Fe(CN)₆/K₄Fe(CN)₆. Upon binding of the proteins to the carbohydrate-modified electrodes, the redox current in CV decreases. The binding-induced change in electrochemical signal is thus used to construct Langmuir adsorption isotherm for the carbohydrate–protein interactions and to obtain the association constants. The association constants of carbohydrate–protein interactions determined by CV ((5.8 ± 1.2) × 10⁷ M^− 1 for mannose–Con A, (2.6 ± 0.5) × 10⁸ M^− 1 for galactose-CT) were in good agreement with those measured with electrochemical impedance spectroscopy and quartz crystal microbalance.     

Proton-conducting membranes based on poly(2,5-benzimidazole) (ABPBI) and phosphoric acid prepared by direct acid casting

We report the preparation of phosphoric acid doped poly(2,5-benzimidazole) (ABPBI) membranes for PEMFC by simultaneously doping and casting from a poly(2,5-benzimidazole)/phosphoric acid/methanesulfonic acid (MSA) solution. The evaporation of MSA yields a very homogeneous membrane having a better controlled composition, avoiding the use of solvent-intensive procedures. Membranes have been prepared with contents of up to 3.0H₃PO₄ molecules per ABPBI repeating unit. These membranes achieve a maximum conductivity of 1.5 × 10⁻² S cm⁻¹ at temperatures as high as 180 °C in dry conditions. These ABPBI membranes are more conveniently prepared than those conventionally formed and doped in separate steps while featuring comparable conductivities (ABPBI × 2.7H₃PO₄ prepared by the soaking method showed a conductivity of 2.5 × 10⁻² S cm⁻¹ at 180 °C in dry conditions).     

Amperometric sensor for hydrogen peroxide based on direct electron transfer of spinach ferredoxin on Au electrode

A protein-based electrochemical sensor for hydrogen peroxide (H₂O₂) was developed by an easy and effective film fabrication method where spinach ferredoxin (Fdx) containing [2Fe–2S] metal center was cross linked with 11-mercaptoundecanoic acid (MUA) on a gold (Au) surface. The surface morphology of Fdx molecules on Au electrodes was investigated by atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed to study the electrochemical behavior of adsorbed Fdx on Au. The interfacial properties of the modified electrode were evaluated in the presence of Fe(CN)₆^3?/4? redox couple as a probe. From CV, a pair of well-defined and quasi-reversible redox peaks of Fdx was obtained in 10 mM, pH 7.0 Tris–HCl buffer solution at ?170 and ?120 mV respectively. One electron reduction of the [2Fe-2S]²⁺ cluster occurs at one of the iron atoms to give the reduced [2Fe-2S]⁺. The formal reduction potential of Fdx ca. ?150 mV (vs. Ag/AgCl electrode) at pH 7.0. The electron-transfer rate constant, k_s, for electron transfer between the Au electrode and Fdx was estimated to be 0.12 s^?1. From the electrochemical experiments, it is observed that Fdx/MUA/Au promoted direct electron transfer between Fdx and electrode and it catalyzes the reduction of H₂O₂. The Fdx/MUA/Au electrode displays a linear increase in amperometric current for increasing concentration of H₂O₂.The sensor calibration plot was linear with r² = 0.998 with sensitivity approximately 68.24 μAm M^?1 cm^?2. Further, the effect of nitrite on the developed sensor was examined which does not interfere with the detection of H₂O₂. Finally, the addition of H₂O₂ on MUA/Au electrode was observed which has no effect on amperometric current.     

Rapid formation of well-ordered self-assembled monolayers of dodecanethiol on polycrystalline gold by microwave irradiation

This article reports a rapid method of preparing self-assembled monolayers of dodecanethiol (C₁₂SH-SAMs) on polycrystalline gold by microwave irradiation (MWI, 650 W, duty cycle is 10%). The qualities of C₁₂SH-SAMs were characterized by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that the C₁₂SH-SAMs formed by MWI in 120 s (C₁₂SH-SAMs_MWI,120 s) have low ionic permeability (the differential capacitance C_d values are independent of the scan rate and phase angle at 1 Hz Φ_1 Hz = 89 ± 0.9°), excellent electrochemical blocking ability towards the redox probe (the current i_MWI,120 s obtained from CV is lowest when compared to other SAMs and charge transfer resistance R_ct = (1.15 ± 0.19) × 10⁶ Ω cm²), and high surface coverage (99.996 ± 0.001%).     

Adjustable bidirectional extracellular electron transfer between Comamonas testosteroni biofilms and electrode via distinct electron mediators

Bidirectional extracellular electron transfer of strain Comamonas testosteroni I2 was for the first time investigated with electrochemical active biofilms developed under different conditions. The electrochemical active biofilm developed under microbial fuel cell conditions was capable of anodic electron transfer via attached redox species with standard potential of 0.04 V (vs. SCE). Meanwhile the above redox species lost its catalytic capability when the biofilm was developed under a constant potential (− 0.4 V vs. SCE). Instead, the microbe adjusted its electron transfer strategy to a soluble shuttle (standard potential − 0.20 V vs. SCE) and enabled a cathodic current. Air exposure experiment verified that the soluble shuttle at negative potential had a positive response to the oxygen; meanwhile the anodic electron transfer via the attached species was rarely influenced.     

Direct electrochemistry of hemoglobin at vertically-aligned self-doping TiO2 nanotubes: A mediator-free and biomolecule-substantive electrochemical interface

The present work is dedicated to making the best of vertically-aligned TiO₂ nanotubes (TNTs) array to serve as a prospectively ideal “vessel” for protein immobilization and biosensor applications. The TNTs fabricated by electrochemical anodizing possess the advantageous of perpendicular alignment and tailored tubular architecture, as well as the good biocompatibility and hydrophilicity. But the electron-transfer resistance of the as-grown (AG-) TNTs is too large for the direct electron transfer and electrochemical biosensing. A simple strategy on controllable electrochemical reduction treatment of TNTs is adopted on it, leading TNTs in situ self-doped with Ti(III), which makes the Ti(III)–TNTs much better conductivity while the tubular and crystal structure of TNTs array still well maintained. Results show that the TNTs can be used as a super vessel for rapid and substantive immobilization of hemoglobin (Hb), with a large surface electroactive Hb coverage (Γ*) of 1.5 × 10^?9 mol cm^?2. The enhanced direct electron transfer of Hb is commendably observed on the Ti(III)–TNTs/Hb biosensor with a couple of well-defined redox peaks compared with the AG-TNTs/Hb. The biosensor further exhibits fast response, high sensitivity and stability for the amperometric biosensing of H₂O₂ with the detection limit of 1.5 × 10^?6 M, and the apparent Michaelis–Menten constant of 1.02 mM.     

Application of thin film composite membranes to the membrane aromatic recovery system

The membrane aromatic recovery system (MARS) is a new membrane technology which recovers aromatic acids and bases. The first industrial installation has been operating at a Degussa site in the UK recovering cresols since 2002. The state of the art MARS technology employs a tubular silicone rubber membrane. However, this places some limitations on the process due to relatively low mass transfer rates and limited chemical resistance.In this paper, flat sheet composite membranes were investigated for application to the MARS process. In particular for recovery of compounds, such as 1,2-benzisothiazolin-3-one (BIT) which show low mass transfer rates through the current membrane. These composite membranes are comprised of a thin nonporous PDMS selective layer coated on a microporous support layer cast from polyacrylonitrile, polyvinylidene fluoride, polyetherimide or polyphenylenesulphone. The membranes have been characterised using SEM and gas permeation. The mass transfer of BIT through the composite membranes with no chemical reaction enhancement was an order of magnitude higher than through tubular silicone rubber membranes (10⁻⁷ m s⁻¹ versus 10⁻⁸ m s⁻¹). With chemical reaction enhancement, the mass transfer increased by another order of magnitude to 1.6 × 10⁻⁶ m s⁻¹ for BIT through a PVDF supported composite membrane. Mass transfer through the composite membrane was described well using analysis based on the resistance in series theory with chemical reaction. However, when a high osmotic pressure was applied across the membrane (molarity ∼ 3 M), significant water transport occurred across the membrane.     

Fingerprint imaging by scanning electrochemical microscopy

An efficient strategy for visualizing human fingerprints on a poly(vinylidene difluoride) membrane (PVDF) by scanning electrochemical microscopy (SECM) has been developed. Compared to a classical ink fingerprint image, here the ink is replaced by an aqueous solution of bovine serum albumin (BSA). After placing the “inked” finger on a PVDF membrane, the latent image is stained by silver nitrate and the fingerprint is imaged electrochemically using potassium hexachloroiridate (III) (K₃IrCl₆) as a redox mediator. SECM images with an area of 5 mm × 3 mm have been recorded with a high-resolution using a 25-μm-diameter Pt disk-shaped microelectrode. Pores in the skin (40–120 μm in diameter) and relative locations of ridges were clearly observed. The factors relevant to the quality of fingerprint images are discussed.     

Studies on polypyrrole modified nafion membrane for vanadium redox flow battery

In order to prevent the vanadium crossover and preferential water transfer in all-vanadium redox flow battery (VRFB), three methods – electrolyte soaking, oxidation polymerisation and Electrodeposition, were used to modify Nafion 117 membranes using pyrrole. The surface of the modified membranes was uniform and even, and the membranes were characterised in terms of morphology, membrane area resistance, vanadium permeability and water transfer property. The properties of all the modified membranes were improved greatly. The membranes modified by Electrodeposition showed a best combination of the membrane resistance, vanadium permeability and water transfer property, the experimental results showed that the V(IV) ion permeability of polypyrrole modified Nafion membranes by Electrodeposition at the conditions of 0.025 mA cm⁻² and 0 ^°C for 60 min reduced more than 5 times from 2.87 × 10⁻⁶ cm² min⁻¹ to 5.0 × 10⁻⁷cm² min⁻¹, and the water transfer property decreased more than 3 times from 0.72 ml/72 h cm² to 0.22 ml/72 h cm². All above properties made the modified Nafion membranes more applicative in the VRFB system. This paper also reported other methods for Nafion membrane modification and the influences of the deposition conditions on the properties of the membrane selectivity and water transfer.     

‘‘Soggy sand＇＇ polymer composite nanofber membrane electrolytes for lithium ion batteries

A kind of octanol-modifded silica nanoparticle was fabricated and employed as a framework to form‘‘soggy sand’’electrolyte along with 1-butyl-3-methylimidazolium tetrafluoroborate.‘‘Soggy sand’’and poly（vinylidene fluoride-hexafluoropropylene）composite electrolyte membranes were electrospun for the frst time.The properties of this membrane electrolyte have been evaluated by the mechanical test and electrochemical test.The Young’s modulus increased by 275%from 6.8 MPa to 25.5 MPa and the electrical conductivity increased to 7.6 10à5S/cm at 290.15 K when compared to pristine P（VdF-HFP）membrane electrolyte.The conductivity is 3.1 10à4S/cm at 323.15 K.     

Bioelectrocatalytic oxidation of glucose by hexose oxidase directly wired to graphite

Glucose-oxidizing enzymes are widely used in electrochemical biosensors and biofuel cells; in most applications glucose oxidase, an enzyme with non-covalently bound FAD and low capability of direct electronic communications with electrodes, is used. Here, we show that another glucose-oxidizing enzyme with a covalently bound FAD center, hexose oxidase (HOX), adsorbed on graphite, exhibits a pronounced non-catalytic voltammetric response from its FAD, at − 307 mV vs. Ag/AgCl, pH 7, characterized by the heterogeneous electron transfer (ET) rate constant of 29.2 ± 4.5 s^− 1. Direct bioelectrocatalytic oxidation of glucose by HOX proceeded, although, with a 350 mV overpotential relative to FAD signals, which may be connected with a limiting step in biocatalysis under conditions of the replacement of the natural redox partner, O₂, by the electrode; mediated bioelectrocatalysis was consistent with the potentials of a soluble redox mediator used. The results allow development of HOX-based electrochemical biosensors for sugar monitoring and biofuel cells exploiting direct ET of HOX, and, not the least, fundamental studies of ET non-complicated by the loss of FAD from the protein matrix.     

Enhancement of electrochemical and catalytic properties of MoS2 through ball-milling

MoS₂ nanosheets of one to few layer thickness present novel electronic and enhanced catalytic properties with respect to the bulk material. Here we show that a simple and highly scalable ball-milling procedure can lead to significant improvements of the electrochemical and catalytic properties of the bulk natural MoS₂. We characterized the material before and after the milling process by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy in order to evaluate morphological and chemical features. We investigated the electrochemical properties by means of voltammetry techniques to monitor the electron transfer with [Fe(CN)₆]^{4 −/3 −} redox probe and the catalytic properties by monitoring the electrochemical hydrogen evolution reaction (HER). A significant overpotential lowering of about 210 mV is obtained for the HER by the ball-milled material when compared to bulk materials. This has a huge potential for the lowering of the energy consumption during hydrogen evolution. Ball-milling offers highly scalable dry method for large scale production of electrocatalyst with enhanced properties.     

Solid polymer electrochemical capacitors using heteropoly acid electrolytes

An electrochemical capacitor utilizing a polyvinyl alcohol (PVA) and H₄SiW₁₂O₄₀ (SiWA) solid polymer electrolyte was developed. The electrolyte was deposited via precursor solution coating followed by thermal pressing and exhibited an ionic conductivity of 0.01 S/cm. The electrolyte has also shown good stability and cycle life. The performance of the solid polymer electrolyte-based capacitor was characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and was compared to a similar capacitor with an aqueous electrolyte.