Development of Reasonably Stable Chitosan Based Proton Exchange Membranes for a Glucose Oxidase Based Enzymatic Biofuel Cell

Chitosan based reasonably stable membranes were prepared as polymeric electrolyte and separator for enzymatic fuel cell applications. Glucose oxidase (GOx) bioanode centered biofuel cell with the developed chitosan membranes performed much better in stability with high current densities than that of the biofuel cell utilizing a 125 μ‐thick perfluorosulfonic acid‐type membrane (i. e. Nafion® 115). Proposed chitosan membrane structural stability was enhanced by employing cellulosic support materials and chemical crosslinking. The effects of pH, buffer type, buffer concentration, temperature on the manufactured chitosan membranes along with the biofuel cell system were investigated. The biofuel cell operation parameters were optimized for the current density and stability aspects and more than 3 mA cm^?2 current density was acquired from the cell at optimum conditions. Operational half‐life of the chitosan membrane was found as higher than the half‐life of the GOx immobilized bioanode. Therefore, this result indicates that chitosan membrane structural stability was not a limiting issue for the biofuel cell lifespan.     

Characterization of natural chitosan membranes from the carapace of the soldier crab Mictyris brevidactylus and its application to immobilize glucose oxidase in amperometric flow-injection biosensing system

This study investigated characteristics of a chitosan membrane from the carapace of the soldier crab Mictyris brevidactylus intended to construct an amperometric biosensor. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used in this study to characterize these chitosan membranes intended for constructing enzymatic biosensors. Chitosan membranes suffering various durations (>10 min) of deacetylation had small charge-transfer resistances (<7.88 kohms) but large double-layer capacitances (>0.55 microF). They were found in EIS where both the solution resistance and Warburg impedance upon electrode interface were almost independent of the durations and degree of deacetylation. The degree of deacetylation and the thickness of chitosan membranes were also determined. Membrane thickness was slightly dependent with the duration but degree of deacetylation was slightly dependent on the duration. Chitosan membranes with various thicknesses suffered various durations of deacetylation, but this did not influence their electrochemical characteristics. The chitinous membrane was covalently immobilized with glucose oxidase (EC 1.3.4.3) and then attached onto the platinum electrode of a homemade amperometric flow cell. Sensor signal was linearly related to glucose concentration (r=0.999 for glucose up to 1.0 mM). The system was sensitive (S/N>5 for 10 microM glucose) and reproducible (CV<1.3% for 50 microM glucose, n=5).     

电化学阻抗谱在质子交换膜燃料电池动态的先导应用

通过分析电化学阻抗（EIS）在质子交换膜燃料电池（PEMFC）动态应用,本文指出制约EIS 工具发展的瓶颈问题. EIS 高频电阻确定电池内阻已成普遍方法,但仅在小电流电池可以应用;低频分析因涉及物质传输仍是难点和重点;EIS 改进型Randles 等效电路分析已初步建立,并深入至物质传输-反应、电池操作/衰减、高温电池研究;EIS 正发展为电堆分析工具、电动汽车控制核心. 然而多学科交叉的暂态EIS 发展,仍是前沿突破难点.     

Pore‐filling electrolyte membranes based on microporous polyethylene matrices activated with plasma and sulfonated hydrogenated styrene butadiene block copolymer. Synthesis,microstructural and electrical characterization

In this research a series of pore‐filling electrolyte membranes were prepared, based on a sulfonated and hydrogenated styrene/butadiene block copolymer (SHSBS) and plasma‐treated microporous polyethylene (PE) membranes. The pore‐filling electrolyte membranes were characterized by means of scanning electronic microscopy (SEM), infrared spectroscopy (FTIR‐ATR), and dynamic mechanical analysis (DMA). In addition, the water uptake and methanol/water uptake capacities of these membranes were determined using several methanol in water solutions, as well as the permeability coefficients, for both water and methanol, using a 2 M methanol in water solution and pure methanol. Finally, electrical behavior was recorded by means of electrochemical impedance spectroscopy (EIS) and the four probe technique (FPT). The SEM images recorded show good coating of the pore‐filling electrolyte membranes on the plasma‐treated PE matrices, and DMA shows the proper relaxations of the two components: PE and SHSBS. Furthermore, the methanol/water absorption capacity was observed to diminish with plasma treatment of the matrix. Methanol permeability of the pore‐filling electrolyte membranes is notably lower than that of the Nafion® membrane, ion conductivity moving in the order of 10⁻² S cm⁻¹. Both of these characteristics qualify the experimental membranes as candidates to be applied as proton exchangers in fuel cells (FCs). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1684–1695, 2008     

Performance Assessment of a Perfluorosulfonic Acid‐type Membrane (i. e. Nafion™ 115) for an Enzymatic Fuel Cell

A high power enzymatic fuel‐cell was anticipated by using a recently developed glucose oxidase (GOx) immobilized bio‐anode, a conventional platinum?carbon based cathode and a popular high performance 125 μ‐thick perfluorosulfonic acid‐type proton exchange membrane (i. e. Nafion® 115). Unexpected current density decay from 2.13 mA cm^?2 to 0.28 mA cm^?2 was observed within 2 hours. Polarization measurements and AC impedance analysis indicated that loss of performance was linked to the membrane behavior. Ion exchange between buffer solution and membrane was perceived as the main cause for the fast performance loss. Saturation of the membrane with the cation in the buffer solution diminished proton transfer needed for cathode reaction. Charge transfer resistances, obtained from AC impedance data, increased with time substantially due to cation exchange within membrane. Replacement of membrane with the same enzyme electrode and cathode has resulted 100 % current density recovery on the fuel cell performance. It was concluded that a membrane, not affected by the buffer cations, was required for successful enzymatic fuel cell applications.     

Fuel cell performance assessment for closed-loop renewable energy systems

Fuel cells and electrolysis are promising candidates for future energy production from renewable energy sources. Usually, polymer electrolyte fuel cell systems run on hydrogen and air, while the most of electrolysis systems vent out oxygen as unused by-product. Replacing air with pure oxygen, fuel cell electrochemical performance, durability and system efficiency can be significantly increased with a further overall system simplification and increased reliability. This work, which represents the initial step for pure H_2/O_2 polymer electrolyte fuel cell operation in closed-loop systems, focuses on performance validation of a single cell operating with pure H_2/O_2 under different relative humidity(RH) levels, reactants stoichiometry conditions and temperature. As a result of this study, the most convenient and appropriate operative conditions for a polymer electrolyte fuel cell stack integrated in a closed loop system were selected.     

Mechanical endurance of polymer electrolyte membrane and PEM fuel cell durability

The life of proton exchange membrane fuel cells (PEMFC) is currently limited by the mechanical endurance of polymer electrolyte membranes and membrane electrode assemblies (MEAs). In this paper, the authors report recent experimental and modeling work toward understanding the mechanisms of delayed mechanical failures of polymer electrolyte membranes and MEAs under relevant PEMFC operating conditions. Mechanical breach of membranes/MEAs in the form of pinholes and tears has been frequently observed after long‐term or accelerated testing of PEMFC cells/stacks. Catastrophic failure of cell/stack due to rapid gas crossover shortly follows the mechanical breach. Ex situ mechanical characterizations were performed on MEAs after being subjected to the accelerated chemical aging and relative humidity (RH) cycling tests. The results showed significant reduction of MEA ductility manifested as drastically reduced strain‐to‐failure of the chemically aged and RH‐cycled MEAs. Postmortem analysis revealed the formation and growth of mechanical defects such as cracks and crazing in the membranes and MEAs. A finite element model was used to estimate stress/strain states of an edge‐constrained MEA under rapid RH variations. Damage metrics for accelerated testing and life prediction of PEMFCs are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2346–2357, 2006     

Unusual buffer action of free-standing nanoscopically confined water

The acid–base properties of nanoscopic water confined in the black soap films (BSFs), which were prepared from aqueous solutions of sodium dodecylsulphate (SDS) with the dye neutral red (NR) as a pH probe, were investigated using a combination of UV–vis and FTIR spectroscopy. For the SDS micellar solutions at pH 1.0–9.5 adjusted with HCl/NaOH solutions and at pH 9.4 with ammonium buffered solution, the aqueous core thicknesses in the corresponding BSFs ranged from 2.7 to 6.2 nm, and the nanoscopically confined water exhibits unusual buffer action resistant not only to acidic/alkaline solutions but also to standard buffer solution. In the heavily water-depleted confined zones, it is most likely that charge pairs in proton-transfer reactions could not be formed effectively and proton transfer was prohibited in the absence of sufficient solvating ability. Theoretical analyzes indicated that the buffer action of the nanoscopic water originated from the confinement effect of two charged surfaces of the BSFs. These results might inspire deeper understanding and further studies of biobuffering, enzyme superactivity, acid-catalyzed reactions, and Nafion fuel cell membranes.     

Synthesis and properties of sulfonated polyimides derived from bis(sulfophenoxy) benzidines

A series of aromatic sulfonated polyimides (SPIs) bearing sulfophenoxy side groups have been successfully synthesized and evaluated as polymer electrolyte membranes for fuel cell applications. The SPIs had high viscosity and gave tough and flexible membranes. The SPI membranes showed anisotropic membrane swelling in water with much larger dimensional change in thickness direction than in plane one. They showed the better proton‐conducting performance even in the lower relative humidity (RH) range than the other SPI membranes, for example, a high proton conductivity of 0.05 S/cm at 50 % RH and 120 °C. They maintained high mechanical strength and conductivity after aging in water at 130 °C for 500 h, showing much better water stability compared with the main‐chain‐type SPI and side‐chain‐type SPI membranes reported so far. In polymer electrolyte fuel cells (PEFCs) operated at 90 °C and 84–30%RH, they showed fairly high cell performances and have high potential for PEFC applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1463–1477, 2009     

Pulsed Deposited Manganese and Vanadium Oxide Film Modified with Carbon Nanotube and Gold Nanoparticle: Chitosan and Ionic Liquid‐based Biosensor

Present study describes the synthesis of mixed oxide films of manganese and vanadium by electrochemical pulsed deposition technique on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNT). The film was further decorated with gold nanoparticles to enhance the reduction signal of dissolved oxygen in pH 5.17 acetate buffer solution. All of the electrochemical synthesized modified electrodes have been characterized with Scanning electron microscopy(SEM), High‐resolution transmission electron microscopy (HRTEM), X‐Ray photoelectron spectroscopy (XPS), X‐Ray diffraction (XRD) techniques. The electrode obtained (AuNPs/MnOx?VOx/CNT/GCE) was utilized as a platform for glucose biosensor where the glucose oxidase enzyme was immobilized on the composite film with the aid of chitosan and an ionic liquid. The electrochemical performance of the biosensor was investigated by cyclic voltammetry and the relative parameters have been optimized by amperometric measurements in pH 5.17 acetate buffer solution. The developed biosensor exhibited a linear range for glucose between 0.1–1.0 mM and the limit of detection was calculated as 0.02 mM.     

On the use of gamma irradiation crosslinked PVA membranes in hydrogen fuel cells

There is growing interest in the use of fuel cells (FC) with hydrogen as the main fuel for stationary, mobile, and transportation applications. In the FC concept membranes play increasingly important roles. Polymer electrolyte membrane fuel cells (PEMFCs) are considered as the most promising fuel cell technology for a wide range of applications due to the stable operation, the high energy generation yield and the simplicity of the system.In this work, we develop different types of membranes based on poly(vinyl alcohol) (PVA). PVA is a water-soluble polymer that is used in practical applications because of its easy preparation, excellent chemical resistance, thermal and mechanical properties. Crosslinking of the PVA was performed by gamma irradiation since radiation chemistry is found to be a very effective method for constructing three-dimensional polymeric networks. The samples prepared in this way were then immersed in the alkaline solution over a certain period of time to turn them into conductive membranes. Ionic conductivity of the PVA hydrogels, was then measured as a function of concentration of KOH solutions and temperature. Cyclic voltammetry of these PVA hydrogel electrolytes was performed to determine the width of the electrochemical stability window.We examined these membranes impregnated with saturated 6 M KOH electrolyte as polymer membrane for fuel cells application. Our experiments showed that PEMFCs with PVA and Nafion^® membranes had similar polarization curves, under same conditions. Furthermore, PVA membranes proved to be stable during the real cell tests. This study offers a possibility for more earnest approach to the use of PVA membranes for fuel cell applications.     

Electrochemical Study of Schiff Bases by Means of Self‐Assembled Monolayers

In this paper, Schiffbases were investigated using cyclic voltammetry (CV) and impedance electrochemical spectroscopy (EIS) techniques by means of self‐assembled monolayers for the first time, where a 0.1 M KCl solution and the redox couple of Fe(CN)₆^3?/Fe(CN)₆^4?were used as the electrolyte and probing‐pin, respectively. The monolayers formed by the employed Schiff base were proved to be relatively stable, and its electrochemical response in the studied system with different pH values was also de scribed clearly with CV and EIS plots. The results show that the monolayer of Schiff bases could exist in the solution with pH value from 2 to 10. In the EIS measurement in the concentration range from 10^?5 M to 5× 10^?4 M, a nearly linear relation ship between the charge transfer resistance (R_ct) and the logarithm concentration of Cu²+was observed, suggesting that Cu²+ could be titrated with the EIS method quasi‐quantitatively. The phenomenon agreed with the former report very well. Using the self‐assembled monolayers to study Schiff bases with the electrochemical method is the major contribution of our work.     

Novel Composite of Multiwalled Carbon Nanotubes and Gold Nanoparticles Stabilized by Chitosan and Hydrophilic Ionic Liquid for Direct Electron Transfer of Glucose Oxidase

A novel composite was fabricated through dispersing multiwalled carbon nanotubes (MWNTs) in gold nanoparticle (GPs) colloid stabilized by chitosan and ionic liquid (i.e., 1‐butyl‐3‐methylimidazolium tetrafluoroborate, BMIMBF₄). Transmission electron microscopy (TEM) experiment showed that the GPs highly dispersed on the MWNTs probably due to the electrostatic interaction among GPs, MWNTs and the imidazolium cation of BMIMBF₄. X‐ray photoelectron spectroscopy (XPS) indicated that thus‐formed gold nanostructure was mediated by BMIMBF₄. When glucose oxidase (GOD) was immobilized on the composite (MWNTs‐GPs) its ultraviolet‐visible absorption spectrum kept almost unchanged. The immobilized GOD coated glassy carbon electrode (GOD/MWNTs‐GPs/GC) exhibited a pair of well‐defined peaks in 0.10 M pH 7.0 phosphate buffer solution (PBS), with a formal potential of ?0.463 V (vs. SCE). The electrochemical process involved two‐electron transfer. The electron transfer coefficient was ca.0.56 and the electron transfer rate constant was 9.36 s^?1. Furthermore, the immobilized GOD presented good catalytic activity to the oxidation of glucose in air‐saturated PBS. The K_m and I_m values were estimated to be 13.7 μM and 0.619 μA. The GOD/MWNTs‐GPs/GC electrode displayed good stability and reproducibility.     

燃料电池聚合物电解质膜的研究进展

本文根据聚合物电解质膜燃料电池操作温度、使用的电解质和燃料的不同,将其分为高温质子交换膜燃料电池、低温质子换膜燃料电池、直接甲醇燃料电池和阴离子交换膜燃料电池,综述了它们所用电解质膜的最新进展.第一部分简要介绍了这4种燃料电池的优点和不足.第二部分首先介绍了Nafion膜的结构模型,并对平行柱状纳米水通道模型在介观尺度上进行了修正;接着分别对应用于不同燃料电池的改性膜的改性思路作了分析;最后讨论了用于不同燃料电池的新型质子交换膜的研究,同时列举了性能突出的改性膜和新型质子交换膜.第三部分介绍了阴离子交换膜的研究现状.第四部分对未来聚合物电解质膜的研究作了展望.     

A Membrane‐Free Neutral pH Formate Fuel Cell Enabled by a Selective Nickel Sulfide Oxygen Reduction Catalyst

Polymer electrolyte membranes employed in contemporary fuel cells severely limit device design and restrict catalyst choice, but are essential for preventing short‐circuiting reactions at unselective anode and cathode catalysts. Herein, we report that nickel sulfide Ni₃S₂ is a highly selective catalyst for the oxygen reduction reaction in the presence of 1.0 m formate. We combine this selective cathode with a carbon‐supported palladium (Pd/C) anode to establish a membrane‐free, room‐temperature formate fuel cell that operates under benign neutral pH conditions. Proof‐of‐concept cells display open circuit voltages of approximately 0.7 V and peak power values greater than 1 mW cm⁻², significantly outperforming the identical device employing an unselective platinum (Pt) cathode. The work establishes the power of selective catalysis to enable versatile membrane‐free fuel cells.     

Alkaline Zn-air and Al-air cells based on novel solid PVA/PAA polymer electrolyte membranes

High ionic conducting solid polymer electrolyte membranes (SPEM) had been successfully prepared from poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA). The solution casting method yielded highly hydrophilic membranes with uniform structure that were suitable for electrochemical applications. The room temperature ionic conductivity of the alkaline PVA/PAA polymer electrolyte membranes was in the range of 0.142–0.301 S cm⁻¹ depending on the composition. The cyclic voltammetry analysis was carried out using Zn|SPEM|Zn and Al|SPEM|Al cells. The analysis results revealed the excellent electrochemical stability of these newly developed alkaline solid PVA/PAA polymer electrolyte membranes. Metal-air fuel cells were also prepared from the alkaline solid PVA/PAA polymer electrolyte membranes. The electrochemical cell performance was evaluated based on Zn-air and Al-air cells at C/10 and C/5 discharge rates. The experimental results exhibited high percent of utilization for metal powders at room temperature. It was up to 90% for Zn-air cell when assembled with PVA:PAA = 10:7.5 polymer electrolyte membrane and discharged at C/10 rate. The power density could be as high as 50 mW cm⁻² at room temperature. However, the cell percent utilization was reduced to 73% with the same composition electrolyte membrane when C/5 discharge rate was tested.     

Preparation of chitosan‐modified silica nanoparticles and their applications in the separation of auxins by capillary electrophoresis

In recent years, nanoparticles have gained more attention when used in separation science. In this study, chitosan‐modified silica nanoparticles were successfully synthesized and characterized by transmission electron microscopy, elemental analysis and zeta potential measurements, etc. When added into the running buffer solution as pseudo‐stationary phase in capillary electrophoresis, the separation of four representative auxins, i.e., indole‐3‐acetic acid, indole butyric acid, 2,4‐dichlorophenoxyacetic acid, 1‐naphthaleneacetic acid, was carried out. Some important factors, such as the nanoparticles concentration, the pH and concentration of the running buffer solution, were also investigated on the separation. Under optimized experimental conditions, all the auxins investigated can be baseline separated within 5 min with higher column performance. The method established can also be used for quantitative analysis. The relative standard deviations obtained for indole‐3‐acetic acid, indole butyric acid, 2,4‐dichlorophenoxyacetic acid, 1‐naphthaleneacetic acid were in the range of 1.6–5.7% for peak area and 0.53–1.60% for migration time. The calibration curves obtained from the peaks areas for auxins were linear in the range of 0.1–80 mg/L with the correlation coefficients of 0.994–0.999. The limit of detection (S/N = 3) was 11–75 μg/L. The developed method was also successfully used for the determination of auxins in fruits and vegetables samples with good recoveries.     

Proton conducting membranes based on poly(vinyl chloride) graft copolymer electrolytes

The direct preparation of proton conducting poly(vinyl chloride) (PVC) graft copolymer electrolyte membranes using atom transfer radical polymerization (ATRP) is demonstrated. Here, direct initiation of the secondary chlorines of PVC facilitates grafting of a sulfonated monomer. A series of proton conducting graft copolymer electrolyte membranes, i.e. poly(vinyl chloride)‐g‐poly(styrene sulfonic acid) (PVC‐g‐PSSA) were prepared by ATRP using direct initiation of the secondary chlorines of PVC. The successful syntheses of graft copolymers were confirmed by ¹H‐NMR and FT‐IR spectroscopy. The images of transmission electron microscopy (TEM) presented the well‐defined microphase‐separated structure of the graft copolymer electrolyte membranes. All the properties of ion exchange capacity (IEC), water uptake, and proton conductivity for the membranes continuously increased with increasing PSSA contents. The characterization of the membranes by thermal gravimetric analysis (TGA) also demonstrated their high thermal stability up to 200°C. The membranes were further crosslinked using UV irradiation after converting chlorine atoms to azide groups, as revealed by FT‐IR spectroscopy. After crosslinking, water uptake significantly decreased from 207% to 84% and the tensile strength increased from 45.2 to 71.5 MPa with a marginal change of proton conductivity from 0.093 to 0.083 S cm^?1, which indicates that the crosslinked PVC‐g‐PSSA membranes are promising candidates for proton conducting materials for fuel cell applications. Copyright © 2008 John Wiley & Sons, Ltd.     

Albumin separation with Cibacron Blue carrying macroporous chitosan and chitin affinity membranes

Cibacron Blue F3GA, Procion Red HE-3B and Procion Blue MX-R were immobilized on macroporous chitosan and chitin membranes with concentrations as high as 10–200 μmol/ml membrane. These dyed membranes were chemically and mechanically stable, could be reproducibly prepared, and operated at high flow rates. Human serum albumin (HSA) and bovine serum albumin (BSA) were selected as model proteins, and their adsorption on and desorption from the dyed chitosan membranes investigated. The Cibacron Blue F3GA membranes had a higher protein adsorption capacity, much greater for HSA than BSA, than the other dyed membranes. About 8.4 mg HSA/ml membrane were adsorbed at saturation by Cibacron Blue F3GA–chitosan membranes from a 0.05 M Tris–HCl/0.05 M NaCl, pH 8 solution. The chitin membranes had a lower dye content and hence a lower protein adsorption capacity than the chitosan membranes. The effects of important operation parameters (flow rate, protein concentration and loading) were also investigated. Cibacron Blue F3GA–chitosan membranes were employed for the separation of HSA from human plasma and high purity HSA thus obtained. This suggests that these membranes could be used for large-scale plasma fractionation.     

Design of Interpenetrated Networks of Mesostructured Hybrid Silica and Nonconductive Poly(vinylidene fluoride)–Cohexafluoropropylene (PVdF–HFP) Polymer for Proton Exchange Membrane Fuel Cell Applications

Organic–inorganic hybrid membranes of poly(vinylidene fluoride)–cohexafluoropropylene (PVdF–HFP) and mesostructured silica containing sulfonic acid groups were synthesized by using the sol‐gel process. These hybrid membranes were prepared by in situ co‐condensation of tetraethoxysilane and an organically modified silane (ormosil) by a self‐assembly route using organic surfactants as templates for tuning the architecture of the hybrid organosilica component. In this paper, we describe the elaboration and characterization of hybrid membranes all the way from the precursor solution to the evaluation of the fuel cell performances. These hybrid materials were extensively characterized by using NMR and IR spectroscopy, electron microscopy, or impedance spectroscopy so as to determinate their physicochemical and electrochemical properties. Even though the ion‐exchange capacity (IEC) was quite weak, the first fuel cell tests performed with these hybrid membranes show promising results relative to optimized Nafion 112 thanks to great water management of the silica inside the hydrophobic polymer.