Proton Exchange Capacity Research Articles

Influence of ceramic separator’s characteristics on microbial fuel cell performance

This study aimed at evaluating the influence of clay properties on the performance of microbial fuel cell made using ceramic separators. Performance of two clayware microbial fuel cells (CMFCs) made from red soil (CMFC-1) typically rich in aluminum and silica and black soil (CMFC-2) with calcium, iron and magnesium predominant was evaluated. These MFCs were operated under batch mode using synthetic wastewater. Maximum sustainable volumetric power density of 1.49 W m-3 and 1.12 W m-3 was generated in CMFC-1 and CMFC-2, respectively. During polarization, the maximum power densities normalized to anode surface area of 51.65 mW m-2 and 31.20 mW m-2 were obtained for CMFC-1 and CMFC-2, respectively. Exchange current densities at cathodes of CMFC-1 and CMFC-2 are 3.38 and 2.05 times more than that of respective anodes, clearly indicating that the cathodes supported much faster reaction than the anode. Results of laboratory analysis support the presence of more number of exchangeable cations in red soil, representing higher proton exchange capacity of CMFC-1 than CMFC-2. Higher power generation was observed for CMFC-1 with separator made of red soil. Hence, separators made of red soil were more suitable for fabrication of MFC to generate higher power.

New Nanocomposite Hybrid Inorganic–Organic Proton‐Conducting Membranes Based on Functionalized Silica and PTFE

Two types of new nanocomposite proton-exchange membranes, consisting of functionalized and pristine nanoparticles of silica and silicone rubber (SR) embedded in a polytetrafluoroethylene (PTFE) matrix, were prepared. The membrane precursor was obtained from a mechanical rolling process, and the SiO₂ nanoparticles were functionalized by soaking the membranes in a solution of 2-(4-chlorosulfonylphenyl)ethyl trichlorosilane (CSPhEtCS). The membranes exhibit a highly compact morphology and a lack of fibrous PTFE. At 125 °C, the membrane containing the functionalized nanoparticles has an elastic modulus (2.2 MPa) that is higher than that of pristine Nafion (1.28 MPa) and a conductivity of 3.6×10⁻³ S cm⁻¹ despite a low proton-exchange capacity (0.11 meq g⁻¹). The good thermal and mechanical stability and conductivity at T>100 °C make these membranes a promising low-cost material for application in proton-exchange membrane fuel cells operating at temperatures higher than 100 °C.

Layered Titanates Intercalating Organic Guest Spacers for Organic/Inorganic Proton Conductors

Two layered organic/inorganic tetratitanate derivatives containing sulfanilic acid (SA) were synthesized from potassium tetratitanate (K2Ti4O9) or its acid form (H2Ti4O9). Scanning electron microscopy (SEM) observations were performed to investigate the microstructural features of the samples. The thermal stability of the compounds was tested by thermogravimetric analysis (TGA). The effect of the presence of organic guest molecules in the layered tetratitanates was investigated in terms of proton exchange capacity (PEC) and conductivity (σ), to evaluate the use of these compounds as fillers for nanocomposite proton exchange membranes for fuel cell applications.

Inorganic–organic membranes based on Nafion, [(ZrO2)·(HfO2)0.25] and [(SiO2)·(HfO2)0.28]. Part I: Synthesis, thermal stability and performance in a single PEMFC

This work reports the preparation, characterization and test in a single fuel cell of two families of hybrid inorganic-organic proton-conducting membranes, each based on Nafion and a different “core-shell” nanofiller. Nanofillers, based on either a ZrO2 “core” covered with a HfO2 “shell” (ZrHf) or a HfO2 “core” solvated by a “shell” of SiO2 nanoparticles (SiHf), are considered. The two families of membranes are labelled [Nafion/(ZrHf)x] and [Nafion/(SiHf)x], respectively. The morphology of the nanofillers is investigated with high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX) and electron diffraction (ED) measurements. The mass fractions of nanofiller x used for both families are 0.05, 0.10 or 0.15. The proton exchange capacity (PEC) and the water uptake (WU) of the hybrid membranes are determined. The thermal stability is investigated by high-resolution thermogravimetric measurements (TGA). Each membrane is used in the fabrication of a membrane-electrode assembly (MEA) that is tested in single-cell configuration under operating conditions. The polarization curves are determined by varying the activity of the water vapour (aH2O) and the back pressure of the reagent streams. A coherent model is proposed to correlate the water uptake and proton conduction of the hybrid membranes with the microscopic interactions between the Nafion host polymer and the particles of the different “core–shell” nanofillers.

Hybrid inorganic-organic nanocomposite polymer electrolytes based on Nafion and fluorinated TiO2 for PEMFCs

In this report, three hybrid inorganic-organic proton-conducting membranes based on a novel fluorinated titania labeled TiO2F dispersed in Nafion were prepared. The mass fraction of TiO2F nanofiller ranged between 0.05 and 0.15. The water uptake and the proton exchange capacity of the membranes were determined; the membranes were further characterized by TG, DMA and FT-IR ATR investigations. Finally, the hybrid membranes were used in the fabrication of membrane-electrode assemblies (MEAs), which were tested in operating conditions as a function of the back pressure and of the hydration degree of the reagents streams. It was demonstrated that, with respect to pristine recast Nafion, at 25%RH the MEA fabricated with the membrane including a mass fraction of TiO2F equal to 0.10 yielded a higher maximum power density (0.206 W cm−2 vs. 0.121 W cm−2). Finally, it was proposed a coherent structural model of this family of hybrid membranes accounting for both the properties determined from “ex-situ” characterizations and for the performance obtained from measurements in a single fuel cell in operating conditions.

Comparison of the acid–base reactivity of free-living Pseudomonas putida cells and biofilm

The proton reactivity of a soil bacterium, Pseudomonas putida ATCC12633 was investigated in two physiologically different states: (i) as free-living cells, and (ii) as a 5-day biofilm formed in a sandy column. Acid–base data analysis and modeling based on a three-site non-electrostatic model showed that biofilm has a proton exchange capacity 3.8 times higher than that of free-living cells (13.2 mmol/g protein corresponding to 5.9 ± 1.2 mmol/g dry weight for biofilm and 3.8 mmol g protein; 1.56 ± 0.32 mmol/g dry weight for free cells). The higher proton exchange capacity of the biofilm fragments mainly results from the high content of the ‘neutral’ pK 6.5 sites. This increase was explained through sorption on the biofilm of mineral phosphate residues circulating with the nutrient medium during the 5 days of column biofilm growth. SEM biofilm observations show a dense network of excreted organic materials linking the individual cells and organic residues. On the contrary, free cells are clearly individualized. The differences between the morphology and reactivity of biofilms and free cells strongly indicate that the two substrates have different compositions. In opposition to free cells, acidic conditions lead to non reversible biofilm proton exchange properties that could be explained by biofilm coagulation processes. These results show the importance of the growing conditions of biofilm and especially its development on a solid surface in the determination of biofilm composition and reactivity.

Synthesis and performance evaluation of a polymer mesh supported proton exchange membrane for fuel cell applications

Abstract A novel approach to the design and fabrication of proton exchange membrane (PEM) has been developed whereby a non-structural polymer fabricated with high proton exchange capacity was bound to an inert polymer matrix. The patented fabrication techniques used here allow greater flexibility in PEM design. Results related to proton exchange performance of these novel PEMs are presented here. The proton exchange material described herein is a ter-polymer composed of various ratios of monomers. These materials were bound to an inert ethylene–tetrafluoroethylene (ETFE) copolymer mesh that had been rendered adhesive using patented hydroxylation technique in a two-step water-borne process. The basic characteristics of the new membranes were compared to those of Nafion ® 212. An aqueous two-cell testing unit is utilized by which the rate of protons transferred from one cell through the membrane into the other cell was determined by monitoring the change in pH of the cells. Results indicated that the new membrane could transfer protons approximately 10 times faster per unit area compared to Nafion ® 212 under the test conditions utilized at 80 °C. In addition to improvement in induction time and reduced resistance, the new membrane conducts protons at reduced membrane water content compared to Nafion ® 212.

Titania Nanosheets (TNS)/Sulfonated Poly Ether Ether Ketone (SPEEK) Nanocomposite Proton Exchange Membranes for Fuel Cells

Sulfonated polyetheretherketone (SPEEK)-based composite membranes containing various amounts of titania nanosheets (TNS) as inorganic filler have been prepared and investigated for proton exchange membrane applications. The SPEEK degree of sulfonation was DS = 0.58 and the TNS content was in the range 0.95−10.00 wt. %. The two-dimensional titanium oxide sheets, have been prepared as stable colloidal suspensions produced by the action of a quaternary ammonium ion, such as tetrabutylammonium, TBA+. SPEEK/TNS composites have been prepared by casting from DMA (dimethylacetamide). The samples have been characterized in terms of thermal stability (TG/DTA, DSC), proton exchange capacity (P.E.C., by titration), water uptake, proton conductivity (EIS), and structural (XRD) and microstructural (SEM) features. Acid treated composites, at the lowest inorganic additive contents, exhibited improved properties in terms of proton conductivity and water uptake with respect to pure SPEEK. The best performing nanocomposite ...

Pore-filling electrolyte membranes based on plasma-activated microporous PE matrices and sulfonated hydrogenated styrene butadiene block copolymer (SHSBS): Single cell test and impedance spectroscopy in symmetrical mode

In this research the performance of proton exchange membrane fuel cells (PEMFC's) was studied, using pore-filling electrolyte membranes based on plasma-activated microporous polyethylene (PE) matrices coated with sulfonated hydrogenated butadiene–styrene block copolymer (SHSBS). The voltage–current and power density curves were recorded under different experimental temperature and pressure conditions. In addition, an electrochemical study was completed by means of electrochemical impedance spectroscopy (EIS) in the symmetrical mode, adjusting the electrical response obtained to an equivalent circuit, which allows for isolation of the different processes occurring within the system. Two parameters were taken into account in the study: the membrane's proton transport or ion resistance ( R 1) and its charge transfer resistance ( R 2). The results obtained indicate that SHSBS shows a single cell behaviour which is comparable to that of the commercial membrane Nafion®. In contrast, the performance of the PE–SHSBS pore-filling electrolyte membranes was lower than that of Nafion®. Likewise it was found that the different plasma treatments applied to the microporous PE matrix have an effect on the proton exchange capacity of the pore-filling electrolyte membrane. EIS allowed to determine the ion resistance of the proton exchange membrane, and it was demonstrated that the kinetics of the cathodic reaction and the cathode itself are decisive elements in membrane performance and hence prime objectives to be optimized, when the reduction of the overvoltages is at stake, which are currently observed in the polarization curve at low and high power densities.

Synthesis and Characterization of a Composite Membrane for Polymer Electrolyte Fuel Cell

A new proton exchange membrane (PEM) has been fabricated using a novel patented polymer structure modification technology. It has been shown that the new membrane has a higher proton transfer rate and lower resistance as compared to Nafion®. This paper discusses issues related to membrane fabrication and testing procedures. (i) A brief fabrication procedure of PEM is outlined. The fabrication technique used here separates the proton exchange and structural requirements of the PEM allowing greater flexibility in membrane design. The proton exchange material developed herein is a terpolymer composed of various ratios of acrylic acid, styrene, and vinylsulfonic acid. Following a patented polymer structure modification technology, these materials were bound to an ethylene-tetrafluoroethylene copolymer mesh that had been rendered adhesive by hydroxylation in a two-step water-borne process. (ii) A previously developed theoretical model is used to calculate the relative resistance and proton transfer rate. According to the model, a simple second order differential equation describes the entire process and established a relationship between the membrane resistance and the total time taken for a specific amount of protons to pass through it. Finally, (iii) a simple two-cell experimental procedure is developed to calculate the relative membrane resistance and proton transfer capacity. The results show that theoretical predictions are in excellent agreement with the experimental observations. The new membrane could transfer protons approximately 80% faster than Nafion® per unit area under the test conditions utilized. Membrane resistance is also 71% lower compared to Nafion®. These results suggest that there is now a new route of fabricating cost effective proton exchange membranes for fuel cell applications wherein one may focus more on the proton exchange capacity of the membrane allowing the structural properties of the membrane to be considered separately.

Biosorption of Cu(II) from aqueous solution by Fucus serratus: Surface characterization and sorption mechanisms

In this work, the brown alga Fucus serratus ( FS) used as a low cost sorbent has been studied for the biosorption of copper(II) ions in batch reactors. Firstly, the characterization of the surface functional groups was performed with two methods: a qualitatively analysis with the study of FT-IR spectrum and a quantitatively determination with potentiometric titrations. From this latter, a total proton exchange capacity of 3.15 mmol g −1 was extrapolated from the FS previously protonated. This value was similar to the total acidity of 3.56 mmol g −1 deduced from the Gran method. Using the single extrapolation method, three kinds of acidic functional groups with three intrinsic p K a were determined at 3.5, 8.2 and 9.6. The point of zero net proton charge (PZNPC) was found close to pH 6.3. Secondly, the biosorption of copper ions was studied. The equilibrium time was about 350 min and the adsorption equilibrium data were well described by the Langmuir’s equation. The maximum adsorption capacity has been extrapolated to 1.60 mmol g −1. The release of calcium and magnesium ions was also measured in relation to the copper biosorption. Finally, the efficiency of this biosorbent in natural tap water for the removal of copper was also investigated. All these observations indicate that the copper biosorption on FS is mainly based on ion exchange mechanism and this biomass could be then a suitable sorbent for the removal of heavy metals from wastewaters.

Zn(H2O)4][Zn2Sn3Se9(MeNH2)]: a robust open framework chalcogenide with a large nonlinear optical response

[Zn(H2O)4][Zn2Sn3Se9(MeNH2)] has an open polar framework based on supertetrahedral clusters with a unique double connectivity mode and exhibits a strong second harmonic generation response, excellent acid stability and proton exchange capacity.

Appraisal of Mixed Amorphous Manganese Oxide/Titanium Oxide Sorbents for the Removal of Strontium-90 from Solutions, with Special Reference to Savannah River Site and Chernobyl Radioactive Waste Simulants

Hydrous, amorphous manganese oxide/titanium oxide composites (AMTO) obtained via template synthesis using alkali metal ions as templates have been characterized. Their applicability in remediation technologies has been tested, specifically for 90Sr removal from Savannah River Site high-level waste supernatants (SHLW) and Chernobyl 4th Block Shelter water (CSW) simulants. Sorption isotherms were used to establish the efficiency of the templating process, while the proton-exchange capacity of AMTO was determined to show that the solids were really protonated. Use of the 90Sr isotope showed that there was little dependence of the distribution coefficients for AMTO on pH, and at pH < 7, i.e., in neutral and acidic media, AMTO had a much greater affinity for strontium than commercial sorbents. Tests with SHLW and CSW simulants revealed that AMTO is capable of removing more than 99% of 90Sr from such wastes. Hence, it could be useful for solving decontamination problems.

Effects of surfactants on the transport properties of redox species through Nafion ® membranes

Previous research in our group has employed tetraalkylammonium bromides to alter the micellar structure of Nafion ® membranes to affect flux of redox species through the membrane. However, research by Patist et al. has shown that maximum micellar stability occurs when the chain lengths of the both the main micellar component and the surfactant are the same in sodium dodecyl sulfate micelles (SDS). When considering the steric hindrance of large, spherical ammonium salts and the effect of chain length compatibility on micellar stability, it was determined that n-alkyltrimethylammonium and n-alkyltriethylammonium surfactants may be more favorable in altering the pore structure. This research focuses on mixture-casting Nafion ® with ammonium-based surfactants in order to form more stable Nafion ® membranes with larger pore structures and a less acidic environment that will be more biocompatible with entrapping dehydrogenase enzymes within the membrane. n-Alkyltriethylammonium and n-alkyltrimethylammonium surfactants decreased the number of available exchange sites to proton (proton exchange capacity) of the membrane and they altered the transport of redox species through the membrane. Phenyltrimethylammonium bromide treated Nafion ® membranes and triethylhexylammonium bromide treated Nafion ® membranes were found to successfully immobilize dehydrogenase enzymes while maintaining enzyme activity.

Anhydrous proton conducting polymer electrolytes based on poly(vinylphosphonic acid)-heterocycle composite material

The development of anhydrous proton conducting membrane is important for the operation of polymer electrolyte membrane fuel cell (PEMFC) at intermediate temperature (100–200 °C). In this study, we have investigated the acid–base hybrid materials by mixing of strong phosphonic acid polymer of poly(vinylphosphonic acid) (PVPA) with the high proton-exchange capacity and organic base of heterocycle, such as imidazole (Im), pyrazole (Py), or 1-methylimidazole (MeIm). As a result, PVPA-heterocycle composite material showed the high proton conductivity of approximately 10 −3 S cm −1 at 150 °C under anhydrous condition. In particular, PVPA-89 mol% Im composite material showed the highest proton conductivity of 7×10 −3 S cm −1 at 150 °C under anhydrous condition. Additionally, the fuel cell test of PVPA-89 mol% Im composite material using a dry H 2/O 2 showed the power density of approximately 10 mW cm −2 at 80 °C under anhydrous conditions. These acid–base anhydrous proton conducting materials without the existence of water molecules might be possibly used for a polymer electrolyte membrane at intermediate temperature operations under anhydrous or extremely low humidity conditions.

Effect of mixture casting phosphonium salts with Nafion ® on the proton exchange capacity and mass transport through the membranes

This research examined how the physical properties of Nafion ® are affected by mixture casting Nafion ® with quaternary phosphonium salts. Quaternary phosphonium salts can be mixture cast with commercially available Nafion ® suspension to form membranes with decreased proton exchange capacity and altered mass transport of cations, anions and neutral species through the membrane. Since quaternary phosphonium salts are similar in size and hydrophobicity to quaternary ammonium salts, the mass transport of cations, anions and neutral species through tetraethylphosphonium bromide and tetrabutylphosphonium treated Nafion ® is similar to tetraethylammonium bromide and tetrabutylammonium treated Nafion ®, respectively. Although there is no statistically significant difference between transport through tetrabutylphosphonium bromide treated Nafion ® membranes and tetrabutylammonium bromide treated Nafion ® membranes, there is a detectable difference for the transport of ferricyanide, methyl viologen and tetramethylphenylenediamine through tetraethylphosphonium bromide treated Nafion ® membranes. The difference is consistent with the fact that tetraalkylphosphonium bromides are slightly larger than tetraalkylammonium bromides, so the resulting pore size for a tetraalkylphosphonium bromide treated Nafion ® membrane is larger than the pore size for a tetraalkylammonium bromide treated Nafion ® membrane. The proton exchange capacity of tetraalkylphosphonium bromide treated membranes is larger than tetraalkylammonium bromide treated membranes. This data is expected since phosphonium salts are less hydrophobic than the ammonium salts and will have a lower affinity for the sulfonic acid exchange sites. Overall, this research indicates that quaternary phosphonium bromide salts can be employed to further tailor the physical and chemical properties of Nafion ® membranes.

Anhydrous proton conductive membrane consisting of chitosan

We have investigated a low production cost anhydrous proton conductor consisting of a composite of chitosan, one of the world's discarded materials, and methanediphosphonic acid (MP) having a high proton exchange capacity. This chitosan–200 wt.% MP composite material showed the high proton conductivity of 5 × 10 −3 S cm −1 at 150 °C under anhydrous conditions. Additionally, the proton conducting mechanism of the chitosan–MP composite material was due to proton transfer to the proton defect site without the assistance of diffusible vehicle molecules. The utilization of a biopolymer, such as chitosan, for PEMFC technologies is novel and challenging where biological products are usually considered as waste, non-hazardous, and environmentally benign. Especially, the low production cost of the biopolymer is an attractive feature. Anhydrous proton conducting biopolymer composite membranes may have potential not only for PEMFCs operated under anhydrous conditions, but also for bio-electrochemical devices including an implantable battery, bio-sensors, etc.

Surface complex characteristics of synthetic maghemite and hematite in aqueous suspensions

The acid–base properties of the maghemite ( γ-Fe 2O 3)/water and hematite ( α-Fe 2O 3)/water interfaces have been studied by means of high precision potentiometric titrations and the experimental results are evaluated as surface complexation reactions. Synthetic maghemite and hematite were prepared and characterized using a combination of SEM, FT-IR and XRD. The specific surface area of the minerals was determined by the BET method. The titrations were performed at 25.0 ± 0.2 ° C within the range 2.8 < pH < 8.5 , NaNO 3 ionic medium giving total ionic strengths of 0.10 and 0.50 mol dm −3 in both systems. Experimental data were evaluated using the constant capacitance model. The total proton exchange capacities of the solids were determined by saturation of the surfaces with excess acid. The number of protonated surface sites per nm 2 was found to be 0.81 ± 0.05 and 1.03 ± 0.04 for maghemite, at I = 0.10 and 0.50 mol dm −3, respectively. The IEP for maghemite was determined from the ζ-potential using a Zetasizer 4 instrument.

Vertical distribution and characteristics of soil humic substances affecting radionuclide distribution

The humic substances extracted from different soil depths are separated into humic (HA) and fulvic (FA) acids, and characterized for their chemical composition, proton exchange capacity, spectroscopic characteristics and binding properties to the europium ion. The chemical and spectroscopic results show that FA compared to HA has a relatively high O/C ratio, high acidic functional group contents and low aromatic contents. The synchronous fluorescence spectroscopic results show that the stability constant ( K) of the soil humic substances with Eu(III) ion tends to increase as the soil depth becomes deeper, and HA has a slightly stronger binding ability than FA. The measured total site concentrations ( C L) reveal that Eu(III) ion is loaded onto HA by 62–77% of the total acid sites, but FA is only ∼50% covered by Eu(III) ion. Information could be useful in understanding the migration of radionuclides in soil layer.

Extraction studies of aurocyanide using Macronet adsorbents: physico-chemical characterization

Ion exchange technology is situated during the last decade as an alternative to activated carbon in goldcyanide recovery process. The search for suitable resins to Au(CN) 2 − recovery from alkaline cyanide solutions has prompted the synthesis of new resins incorporating new functionalities or modifying the polymer network properties that solve many of the existing problems. A new type of ion-exchange resins (Macronet Hypersol MN100 and MN300) incorporating mixtures of tertiary and quaternary groups, linked onto a styrene-divinylbenzene macroporous hyper-reticulated network are evaluated in this work. The total N content is 0.85 mmol/g for MN-100 and 1.14 mmol/g for MN-300 and the proton exchange capacity is 0.45 mmol/g for MN100 and 0.91 mmol/g for MN-300. Accurate titration curves were used to determine p K a values of the tertiary amine groups (p K H(a)=6.2±0.2 and 6.9 ± 0.2 for MN100 and MN300, respectively). The Hypersol Macronet resins (MN100 and MN300) extract Au(CN) 2 via two different modes of metal extraction based on the tertiary amine groups of the resin and in the small portion of the quaternary ammonium groups present in the resins. The extraction isotherms of Au(CN) 2 − show loadings of 16 mg Au/g and >40 mg Au/g for MN100 and MN300, respectively. Efficient stripping of Au(CN) 2 − from the resin was achieved by using ethanol/water or acetone/water solutions of sodium hydroxide and sodium cyanide. Metal extraction from cyanide solutions, including Brazilian mine leach solution, showed considerable preference for gold and silver in comparison to base metals (copper, iron and nickel).