Oxidatively stable and highly proton conductive membrane from poly(arylene ether)s containing biphenyl moiety as pendent groups

Novel poly(arylene ether)s with sulfonic acid groups attached onto pendent biphenyl rings were successfully synthesized by the nucleophilic displacement of aromatic dihalides with bisphenols in aprotic solvent in the present of excess potassium carbonate, followed by sulfonation with chlorosulfonic acid. The sulfonation took place only on the pendent biphenyl rings due to the specially designed molecular structure. The sulfonated polymers were very soluble in common organic solvents, such as dimethyl sulfoxide, N,N′-dimethylacetamide, dimethylformamide, and can be readily cast into tough and smooth films. These membranes showed excellent stabilities resistance to both oxidation and hydrolysis, as evidenced by subjecting to both Fenton's reagent test and immersion in boiling water. The proton conductivities (3.2 × 10⁻³ S cm⁻¹) of the as-made membranes were higher than that of Nafion^® 117 (1.9 × 10⁻³ S cm⁻¹) under same conditions. The satisfied properties of these new polymers demonstrated them as promising candidates for proton exchange membrane in PEM fuel cell applications.     

Effects of polyaniline chain structures on proton conduction in a PEM host matrix

This study examined the effects of the conjugated chain structure of polyaniline (PAn) on proton transport in a proton exchange membrane (PEM) containing a small amount of PAn colloidal particles. The PEM host matrix consisted of a hydrophobic three-component polymer blend (TCPB) of poly(4-vinylphenol-co-methylmethacrylate) P(4-VP-MMA), poly(butyl methacrylate) (PBMA), and Paraloid^® B-82 acrylic copolymer resins; in which a hydrophilic network of 2-acrylamido-2-methyl propanesulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol)dimethylacrylate (PEGDMA) was formed upon embedded polymerization. Colloidal PAn particles were added to the PEM matrix during the embedded polymerization of PEM. Two types of PAn colloidal particles with different chain structures and morphologies were synthesized by inverse miniemulsion polymerization and interfacial polymerization. The PAn(1) particles from inverse miniemulsion polymerization were bar-shaped, contained a higher fraction of quinoid diimine units than the scaffold-like PAn(2) particles from interfacial polymerization, and displayed a strong promotional effect on proton conduction. The oxidation state of the PAn particles was also varied by post-synthesis treatments to evaluate the effect of oxidation state on proton conduction. It was found that a mixed oxidation state such as the emeraldine form of PAn had the best enhancement effect. The PAn loading optimal for proton conductivity enhancement of the composite PEM was determined to be about 2 wt% of PAn(1).     

Nano-structured proton exchange membranes molded by polymerizing bi-continuous microemulsion

A unique type of nano-structured proton exchange membrane (PEM) has been fabricated through photo-polymerizing a bicontinuous microemulsion. This microemulsion is constituted by a polymerizable zwitterionic surfimer 3-((11-acryloyloxyundecyl)imidazoyl)propyl sulfonate (AIPS), 3-sulfopropylmethacrylate, potassium salt (SPM), acrylonitrile and water. As the resulting colloidal system maintains quasi-homogeneous state throughout the polymerization course, the inherent bicontinuous microemulsion structure was successfully transferred to the matrix of the polymer membrane. Such membranes are therefore composed of dual phase channels with ca. 1.5–2 nm of the hydrophilic channel breadth. This particular structural trait imparts to the membranes excellent proton conductivities of up to 10⁻¹ S cm⁻¹ as well as low methanol permeability. The DMFC single cell loaded with the demo PEM manifests ca. 20 mW cm⁻² of power output. The attributes of this PEM are elucidated from the bicontinuous structure of microemulsion.     

Embedded hydrophilic nanogranules with radiating proton-conducting channels in a hydrophobic matrix

It is a significant challenge to develop proton exchange membranes (PEMs) possessing both desired proton conductivity and low methanol permeability for the direct methanol fuel cells (DMFC). In this work, a composite PEM was fabricated from a predominantly hydrophobic framework of three-component polymer blend (TCPB) of acrylic polymers and a dispersed proton-conducting hydrophilic copolymer network. The hydrophilic copolymer was designed to contain three co-monomer units of complementary functionalities: 2-acrylamido-2-methyl propanesulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA), and 2-hydroxyl-3-(diethanolamino)propylmethacrylate (DEAPMA). The resultant PEMs were macroscopically homogeneous but contained microscopic heterogeneity in the form of dispersed nanosize AMPS domains with radiating (HEMA-DEAPMA) segments in the TCPB matrix, forming an overall amphiphilic matrix. Formation of such a texture was consequential upon the association of AMPS units and hydrogen bonding between the HEMA and DEAPMA short blocks of the hydrophilic copolymer with TCPB. The polymer blend membranes therefore acquired dual functionalities, i.e., effective proton transport between AMPS granules through interconnecting (HEMA-DEAPMA) segments, resulting in proton conductivity of the order of 10(-2) S/cm, and low water uptake and inhibited methanol passage in the continuous amphiphilic matrix, resulting in methanol permeability of (1.25-8) x 10(-7) cm2/s, which is about 3-8 times smaller than that of Nafion117.     

A novel proton-conductive membrane with reduced methanol permeability prepared from bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO)

A series of proton-conducting membranes were developed for direct methanol fuel cell (DMFC) applications via sulfonation of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) base membranes. Besides the low manufacture cost, the membranes exhibited an excellent control on methanol crossover and swelling, and a sound balance with high proton conductivities. These can be attributed to the inherent properties of membrane structures: (i) benzyl substitution with bromine, which imparted the membrane stronger hydrophobicity, (ii) cross-linking between BPPO chains, which enhances the dimensional stability and renders the membrane a dense texture, (iii) proper content of sulfonic acid groups, which guarantees the proton conductivity. An optimal membrane was obtained after investigating the effects of the bromination degree and sulfonation process on the performances of corresponding membranes, i.e., the membrane possesses the methanol permeability of 2.64 × 10⁻⁸ cm²/s and characteristic factor Φ value of 30 times higher than that of Nafion^® 117. The sulfonation process should be controlled within a proper period of time and in mild sulfonation conditions so as to achieve a proton conductivity higher than 0.07 S/cm for potential applications in DMFC.     

Preparation and characterization of crosslinked PVA/SiO2 hybrid membranes containing sulfonic acid groups for direct methanol fuel cell applications

Organic–inorganic hybrids based on poly(vinyl alcohol) (PVA)/SiO₂ hybrid membranes containing sulfonic acid groups were prepared using the sol–gel process under acidic conditions. The PVA/sulfosuccinic acid (SSA)/silica hybrid membranes were fabricated from different SSA contents. The proton conductivity and methanol permeability of the hybrid membranes were studied with changing SSA content from 5 to 25 wt.%. It was found that the proton conductivity and the methanol permeability were dependent on the SSA content both as a crosslinking agent, and as a donor of the hydrophilic SO₃H group. Up to an SSA content of about 20 wt.%, both of these properties decrease, and above this SSA content, they begin to increase with increasing SSA content. The proton conductivities of the PVA/SSA/silica membranes were in the range of 10⁻³ to 10⁻² S/cm, and the methanol permeabilities ranged between 10⁻⁸ and 10⁻⁷ cm²/s. The presence of silica particles in the organic polymer matrix, which reduce the free water ratio of the membranes, results in hybrids with markedly reduced methanol permeabilities. These characteristics of the PVA/SSA/silica hybrid membranes are desirable for future applications related to direct methanol fuel cells.     

An NMR study of methanol diffusion in polymer electrolyte fuel cell membranes

Methanol diffusion in two polymer electrolyte membranes, Nafion 117 and BPSH 40 (a 40% disulfonated wholly aromatic polyarylene ether sulfone), was measured using a modified pulsed field gradient NMR method. This method allowed for the diffusion coefficient of methanol within the membrane to be determined while immersed in a methanol solution of known concentration. A second set of gradient pulses suppressed the signal from the solvent in solution, thus allowing the methanol within the membrane to be monitored unambiguously. Over a methanol concentration range of 0.5–8 M, methanol diffusion coefficients in Nafion 117 were found to increase from 2.9 × 10⁻⁶ to 4.0 × 10⁻⁶ cm² s⁻¹. For BPSH 40, the diffusion coefficient dropped significantly over the same concentration range, from 7.7 × 10⁻⁶ to 2.5 × 10⁻⁶cm² s⁻¹. The difference in diffusion behavior is largely related to the amount of solvent sorbed by the membranes. Increasing the methanol concentration results in an increase in solvent uptake for Nafion 117, while BPSH 40 actually excludes the solvent at higher concentrations. In contrast, diffusion of methanol measured via permeability measurements (assuming a partition coefficient of 1) was lower (1.3 × 10⁻⁶ and 6.4 × 10⁻⁷ cm² s⁻¹ for Nafion 117 and BPSH 40 respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of methanol in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 μm for Nafion 117 and BPSH 40 respectively) whereas the NMR method observes diffusion over a length of approximately 4–8 μm. Regardless of the measurement technique, BPSH 40 is a greater barrier to methanol permeability at high methanol concentrations.     

Fluorenyl-containing sulfonated poly(aryl ether ether ketone ketone)s (SPFEEKK) for fuel cell applications

A series of fluorenyl-containing sulfonated poly(aryl ether ether ketone ketone)s (SPFEEKK) were synthesized via aromatic nucleophilic substitution polymerization. The sulfonation content (SC) was controlled by the feed ratios of sulfonated and nonsulfonated monomers. Flexible and strong membranes in the sulfonic acid form were obtained from cast membranes in the sodium salt forms by treatment with acid. The thermal properties, water uptake, swelling ratio, water state, oxidative stability, proton conductivity and methanol permeability were investigated. All the polymers had proton conductivities greater than 1 × 10⁻² S/cm at room temperature, and the conductivity values of m-SPFEEKK-80 and p-SPFEEKK-80 were up to 1.86 × 10⁻¹ and 1.78 × 10⁻¹ S/cm at 100 °C. This series of polymers also possessed good dimensional stability in water and low methanol crossover.     

Polymer blend membranes of sulfonated poly(arylene ether ketone) for direct methanol fuel cell

The blend membranes of sulfonated poly(arylene ether ketone) (sPAEK) (IEC = 1.0 mequiv./g)/Nafion^® and the blend membranes of sPAEK (IEC = 1.0 mequiv./g)/sPAEK (IEC = 1.7 mequiv./g) were prepared. sPAEK with low IEC was introduced to reduce the methanol permeability through the membrane. Morphology, water uptake, proton conductivity and methanol permeability of the blend membranes were investigated by SEM, AFM, AC impedance spectroscopy and permeability measuring instrument. The cross-sections of blend membranes showed phase-separated morphologies. The effect of phase-separated morphology on the properties of blend membranes was investigated. The properties like water uptake, proton conductivity, and methanol permeability of sPAEK/Nafion^® blend membranes showed similar values with sPAEK and properties of sPAEK/sPAEK blend membranes showed intermediate values of two polymers due to the difference in morphology of the blend membranes. sPAEK/sPAEK blend membranes showed relatively high proton conductivity and lowered methanol permeability compared to Nafion^®. sPAEK/sPAEK blend membranes could be a competent substitution for Nafion^®.     

Halide diffusion in polyaniline membranes

The feasibility of application of polyaniline (PAni) as electrolyte in polymer–electrolyte–membrane fuel cells (PEMFC) was investigated. PAni was dissolved in N-methyl pyrrolidone (NMP), cast as emeraldine base membranes (EB) and then doped with halide acids. The proton conductivity was measured according to Hittorf. The chloride ion distribution within the membrane was evaluated using energy-dispersive-X-ray analysis (EDX) and the diffusion coefficient was calculated using EDX, impedance spectroscopy and photometric analysis. The specific resistance was determined using conventional four-point measurement. The proton conductivity of HCl_conc.-doped PAni is approximately half that of the reference material Nafion^®117. The diffusion coefficient for the chloride ion within the membrane was determined to be between 1.86 and 3.4 × 10⁻⁸ cm² s⁻¹. Although halide-doped membranes were found to be proton conducting, slow halide removal during fuel cell operation occurred causing a rapid decline in cell performance. It is, therefore, concluded that in order to prepare suitable PAni membranes for fuel cell applications, it will be necessary to dope PAni with acids in such a way that loss of the dopant can not occur. Doping with solid acids or large molecular acids (in order to reduce their diffusivity) may be a solution to the problem.     

Proton conductive membranes of sulfonated poly(ether ketone ketone)

Poly(ether ketone ketone) was sulfonated using fumic sulfuric acid and used for preparation of proton conductive membranes. The sulfonation degree was evaluated by elemental and thermal analysis and the IEC values were determined by titration. The proton conductivity of membranes with sulfonation degrees up to 70% was determined as a function of temperature by impedance spectroscopy. Membranes with sulfonation degree 38–70% were tested in DMFC experiments. Their performance was comparable to Nafion^® with the same pretreatment and clearly better than sulfonated poly(ether ether ketone) membranes with similar functionalization. The methanol crossover was lower than that of Nafion^® in the same conditions.     

Characterization of the novel ETFE-based membrane

Recently developed ETFE-SA membrane (sulphonated poly(ethylene-alt-tetrafluoroethylene)) has proved to be chemically stable in the direct methanol fuel cell (DMFC). According to methanol permeability measurements, the MeOH permeability through the ETFE-SA membrane is less than 2% of the corresponding value of the Nafion^® membranes. The characterization of the ETFE-SA membranes is done with sophisticated microscopy techniques. The electrochemical inhomogeneity of the membranes is investigated with the scanning electrochemical microscopy (SECM) by mapping proton distribution across the membrane surface. The atomic force microscopy (AFM) is used, when the surface morphology and morphology changes originating from swelling are investigated, while with the scanning electron microscopy (SEM), the composition and the structure of the membranes can be clarified in detail. The sulphur profile along the membrane cross-section gives information about the distribution of sulphonic acid groups and it is detected with the SEM combined with a energy dispersive X-ray spectrometer. Surface hydrophobicity is investigated by water contact angle (CA) measurement. Many remarkable structural differences between different samples are observed during the measurements, e.g. the surface roughness of the ETFE-SA membrane is much higher, when compared to the Nafion^® membranes. Altogether, the surface properties of the ETFE-SA and the Nafion^® membranes are found to differ significantly from each other and the properties of ETFE-SA vary also as a function of manufacturing parameters.     

Preparation and characterization of CPPO/BPPO blend membranes for potential application in alkaline direct methanol fuel cell

A series of hydroxyl-conducting anion-exchange membranes were prepared by blending chloroacetylated poly(2,6-dimethyl-1,4-phenylene oxide) (CPPO) with bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO), and their fuel cell-related performances were evaluated. The resulting membranes exhibited high hydroxyl conductivities (0.022–0.032 S cm⁻¹ at 25 °C) and low methanol permeability (1.35 × 10⁻⁷ to 1.46 × 10⁻⁷ cm² s⁻¹). All the blend membranes proved to be miscible or partially miscible under the investigations of scanning electron microscopy (SEM) and differential scanning calorimeters (DSC). By condition optimization, the blend membranes with 30–40 wt% CPPO are recommended for application in direct methanol alkaline fuel cells because they showed low methanol permeability, excellent mechanical properties and comparatively high hydroxyl conductivity.     

燃料电池用侧链型磺化聚砜质子交换膜的性能

在制备氯甲基化聚砜(CPS)的基础上,以1,2-二羟基苯-3,5-二磺酸钠为试剂,通过亲核取代反应制备一种侧链末端为磺酸基团的侧链型磺化聚砜(PS-BDS),并采用溶液浇注法制备相应的质子交换膜(PEM),研究温度对PEM性能的影响规律。 结果表明,由于亲水基团远离疏水聚合物主链,该PEM能够形成亲水微区远离疏水微区的相分离结构,亲水区域对主链的影响较小,该PEM在高磺化度下仍能保持较好的尺寸稳定性,随着温度的升高,PEM的吸水率(WU)、吸水溶胀率(SW)和质子传导率(PC)升高,其中PS-BDS-4(离子交换容量为1.57 mmol/g)在25和85 ℃时的SW仅为22.1%和55.0%,甲醇的渗透率(DK)仅为10.17×10^-7 cm²/s,低于商业化的Nafion115(16.8×10^-7 cm²/s)和Nafion117(23.8×10^-7 cm²/s),表现出很好的综合性能。     

Simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional ion-selective electrodes in series

An on-line automated system for the simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional calcium-selective and fluoride-selective membrane electrodes as sensors in series is described. Samples (30 μl) are injected into a TISAB II (pH=5.50) carrier solution as an ionic strength adjustment buffer. The sample-buffer zone formed is first channeled to a fluoride-selective membrane electrode and then via the calcium-selective membrane electrode to the reference electrodes. The system is suitable for the simultaneous on-site monitoring of calcium (linear range 10⁻⁵–10⁻² mol l⁻¹ detection limit 1.94×10⁻⁶ mol l⁻¹ recovery 99.22%, RSD<0.5%) and fluoride (linear range 10⁻⁵–10⁻² mol l⁻¹ detection limit 4.83×10⁻⁶ mol l⁻¹ recovery 98.63%, RSD=0.3%) at a sampling rate of 60 samples h⁻¹.     

Flow-injection potentiometric determination of triiodide by plasticized poly(vinyl chloride) membrane electrodes and its application to the determination of chlorine-containing disinfectants

Plasticized poly(vinyl chloride) (PVC) membranes of different compositions were tested for use in the construction of potentiometric flow detectors for triiodide. A membrane with a 2:1 (w/w) 2-nitrophenyl octyl ether to PVC ratio was selected. The influence of thiosulphate in the carrier solution composition and of the flow-injection variables on the determination of triiodide was studied. In the selected conditions, a linear relationship between peak height and log[I₃⁻] was obtained between 5 × 10⁻⁶ and 1 × 10⁻⁴ mol l⁻¹ triiodide. Peak height relative standard deviations for 2 × 10⁻⁵ and 1 × 10⁻⁴ mol l⁻¹ triiodide were ±0.4 and ±1.8%, respectively, and sampling frequency was 80 samples per hour. The method proposed was applied satisfactorily to the iodometric determination of different chlorine-containing disinfectants, among them trichloroisocyanuric acid and dichloroisocyanurate in several types of commercial sample.     

Preparation of a novel fluorescence probe based on covalent immobilization by emulsion polymerization and its application to the determination of metronidazole

A novel method of preparing fluorescence particle probe by emulsion polymerization with covalent immobilization of indicator dye was described. A terminal double bond was attached to 3-amino-9-ethylcarbazole (AEC) via methacryloyl chloride, and the resultant compound was copolymerized with butyl methacrylate. The obtained polymer particles were used as a fluorescence probe, which is almost free of dye leaching, and has higher photostability and lower toxicity in comparison with free AEC. This probe holds great potential for the applications in intracellular measurements. In present study the prepared probe was used for the determination of metronidazole. The results revealed that the probe showed good selectivity and had a linear response to the analyte in the range from 2.0 × 10⁻⁵ to 1.0 × 10⁻³ mol l⁻¹ with a detection limit of 9.0 × 10⁻⁶ mol l⁻¹.     

Electrokinetic characterization of a microporous non-commercial polysulfone membrane: phenomenological coefficients and transport parameters

Electrical and electrokinetic phenomena (electrical resistance, streaming potential and membrane potential) in a porous polysulfone membrane was studied in the framework of the linear thermodynamics of irreversible processes and the phenomenological coefficients were determined for different concentrations of NaCl and MgCl₂ solutions (10⁻³M<5×10⁻²M). From experimental values, other characteristic membrane parameters such as the concentration of fixed charge in the membrane (=−3×10⁻³M), the ionic transport numbers and permeabilities through the membrane (t(Na⁺)=0.392 and t(Mg⁺²)=0.363; P(Na⁺)=3.5×l0⁻⁸m/sec and P(Mg⁺²)=2.9×10⁻⁸m/sec) were also obtained. Membrane surface-electrolyte solution interface was characterized by zeta potential values. The effect of both salt concentration and pH on zeta potential results was also studied.     

Sulfonated poly(ether ether ketone)/polyaniline composite proton-exchange membrane

Sulfonated poly(ether ether ketone) (PEEK) was prepared by sulfonation of commercial Victrex^@ PEEK and degree of sulfonation was found to be about 44.5% by ¹H NMR. Sulfonated PEEK/polyaniline composite membranes, in order to prevent methanol crossover, were prepared by chemical polymerization of a thin layer of polyaniline (PANI) in the presence of a high oxidant concentration on a single face modification. FTIR and PANI coating density studies confirmed the loading of PANI in sulfonated PEEK membrane matrix. PANI composite membranes with different polymerization time were prepared and subjected to thermogravimetric analysis as well as electrochemical and methanol permeability study to compare with sulfonated PEEK and Nafion 117 membrane. Ion-exchange capacity, water uptake, proton transport numbers and proton conductivities for different PANI composite sulfonated PEEK (SPEEK) membranes were found to be dependent on the coating density of the PANI in the membrane matrix and were slightly lower than that of Nafion 117 membrane. Methanol permeability of these membranes (especially SPEEK/PANI-1.5) was about four times lower than Nafion 117 membrane. Among the all SPEEK membranes synthesized in this study, SPEEK-1.5 appears to be more suitable for direct methanol fuel cell (DMFC) application considering optimum physicochemical and electrochemical properties, thermal stability as well as very low methanol permeability. Above all, the cost-effective and simple fabrication technique involved in the synthesis of such composite membranes makes their applicability quite attractive.     

Microcoated wire sensors for the determination of anticancer drugs cyclophosphamide and ifosphamide in the presence of their degradates

The construction and electrochemical response characteristics of poly (vinyl chloride) and poly (vinyl chloride) carboxylate membrane sensors for the determination of cyclophosphamide and ifosphamide are described. Based on the formation of an ion-pair complex between the drug cation and sodium tetraphenylborate, two poly (vinyl chloride) sensors, namely a cyclophosphamide membrane sensor and ifosphamide membrane sensor were fabricated. They show a linear response for both drugs over the concentration range 10⁻²–10⁻⁴ M with cationic slopes of 56 and 54.6 mV per concentration decade, for sensor 1 and sensor 2, respectively. Based on the interaction between the drug solution and the dissociated COOH groups in the poly (vinyl chloride) carboxylate, sensor 3 was fabricated. It shows a linear response for both drugs over the concentration range 10⁻³–10⁻⁵ M with a cationic slope of 49.7 mV per concentration decade. The direct potentiometric determination of cyclophosphamide and ifosphamide in their pharmaceutical preparations using the proposed sensors gave average recoveries of 101.3±0.6, 100.8±10.7 and 102.0±11.0% for the sensors 1, 2 and 3, respectively, which compares reasonably well with the data obtained using the British Pharmacopoeial method (1993). Sensors 1 and 2 were also used to follow up the stability of the drugs studied in the presence of their degradates. These degradation products have no diverse effect on the responses of sensors 1 and 2.