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466 KiB

Open AccessArticle

The Effect of Platinum Electrocatalyst on Membrane Degradation in Polymer Electrolyte Fuel Cells

by Merit Bodner, Bernd Cermenek, Mija Rami and Viktor Hacker

Membranes 2015, 5(4), 888-902; https://doi.org/10.3390/membranes5040888 - 08 Dec 2015

Cited by 18 | Viewed by 6143

Membrane degradation is a severe factor limiting the lifetime of polymer electrolyte fuel cells. Therefore, obtaining a deeper knowledge is fundamental in order to establish fuel cells as competitive product. A segmented single cell was operated under open circuit voltage with alternating relative [...] Read more.

Membrane degradation is a severe factor limiting the lifetime of polymer electrolyte fuel cells. Therefore, obtaining a deeper knowledge is fundamental in order to establish fuel cells as competitive product. A segmented single cell was operated under open circuit voltage with alternating relative humidity. The influence of the catalyst layer on membrane degradation was evaluated by measuring a membrane without electrodes and a membrane-electrode-assembly under identical conditions. After 100 h of accelerated stress testing the proton conductivity of membrane samples near the anode and cathode was investigated by means of ex situ electrochemical impedance spectroscopy. The membrane sample near the cathode inlet exhibited twofold lower membrane resistance and a resulting twofold higher proton conductivity than the membrane sample near the anode inlet. The results from the fluoride ion analysis have shown that the presence of platinum reduces the fluoride emission rate; which supports conclusions drawn from the literature. Full article

(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications 2015)

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497 KiB

Open AccessArticle

Characterization of Polyethylene-Graft-Sulfonated Polyarylsulfone Proton Exchange Membranes for Direct Methanol Fuel Cell Applications

by Hyung Kyu Kim, Gang Zhang, Changwoo Nam and T.C. Mike Chung

Membranes 2015, 5(4), 875-887; https://doi.org/10.3390/membranes5040875 - 04 Dec 2015

Cited by 9 | Viewed by 5569

Abstract

This paper examines polymer film morphology and several important properties of polyethylene-graft-sulfonated polyarylene ether sulfone (PE-g-s-PAES) proton exchange membranes (PEMs) for direct methanol fuel cell applications. Due to the extreme surface energy differences between a semi-crystalline and hydrophobic PE backbone and [...] Read more.

This paper examines polymer film morphology and several important properties of polyethylene-graft-sulfonated polyarylene ether sulfone (PE-g-s-PAES) proton exchange membranes (PEMs) for direct methanol fuel cell applications. Due to the extreme surface energy differences between a semi-crystalline and hydrophobic PE backbone and several amorphous and hydrophilic s-PAES side chains, the PE-g-s-PAES membrane self-assembles into a unique morphology, with many proton conductive s-PAES channels embedded in the stable and tough PE matrix and a thin hydrophobic PE layer spontaneously formed on the membrane surfaces. In the bulk, these membranes show good mechanical properties (tensile strength >30 MPa, Young’s modulus >1400 MPa) and low water swelling (λ < 15) even with high IEC >3 mmol/g in the s-PAES domains. On the surface, the thin hydrophobic and semi-crystalline PE layer shows some unusual barrier (protective) properties. In addition to exhibiting higher through-plane conductivity (up to 160 mS/cm) than in-plane conductivity, the PE surface layer minimizes methanol cross-over from anode to cathode with reduced fuel loss, and stops the HO• and HO₂• radicals, originally formed at the anode, entering into PEM matrix. Evidently, the thin PE surface layer provides a highly desirable protecting layer for PEMs to reduce fuel loss and increase chemical stability. Overall, the newly developed PE-g-s-PAES membranes offer a desirable set of PEM properties, including conductivity, selectivity, mechanical strength, stability, and cost-effectiveness for direct methanol fuel cell applications. Full article

(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications 2015)

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603 KiB

Open AccessArticle

Synthesis and Characterization of Cellulose-Based Hydrogels to Be Used as Gel Electrolytes

by Maria Assunta Navarra, Chiara Dal Bosco, Judith Serra Moreno, Francesco Maria Vitucci, Annalisa Paolone and Stefania Panero

Membranes 2015, 5(4), 810-823; https://doi.org/10.3390/membranes5040810 - 27 Nov 2015

Cited by 66 | Viewed by 9069

Abstract

Cellulose-based hydrogels, obtained by tuned, low-cost synthetic routes, are proposed as convenient gel electrolyte membranes. Hydrogels have been prepared from different types of cellulose by optimized solubilization and crosslinking steps. The obtained gel membranes have been characterized by infrared spectroscopy, scanning electron microscopy, [...] Read more.

Cellulose-based hydrogels, obtained by tuned, low-cost synthetic routes, are proposed as convenient gel electrolyte membranes. Hydrogels have been prepared from different types of cellulose by optimized solubilization and crosslinking steps. The obtained gel membranes have been characterized by infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mechanical tests in order to investigate the crosslinking occurrence and modifications of cellulose resulting from the synthetic process, morphology of the hydrogels, their thermal stability, and viscoelastic-extensional properties, respectively. Hydrogels liquid uptake capability and ionic conductivity, derived from absorption of aqueous electrolytic solutions, have been evaluated, to assess the successful applicability of the proposed membranes as gel electrolytes for electrochemical devices. To this purpose, the redox behavior of electroactive species entrapped into the hydrogels has been investigated by cyclic voltammetry tests, revealing very high reversibility and ion diffusivity. Full article

(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications 2015)

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668 KiB

Open AccessArticle

Selectivity of Direct Methanol Fuel Cell Membranes

by Antonino S. Aricò, David Sebastian, Michael Schuster, Bernd Bauer, Claudia D'Urso, Francesco Lufrano and Vincenzo Baglio

Membranes 2015, 5(4), 793-809; https://doi.org/10.3390/membranes5040793 - 24 Nov 2015

Cited by 64 | Viewed by 9016

Abstract

Sulfonic acid-functionalized polymer electrolyte membranes alternative to Nafion^® were developed. These were hydrocarbon systems, such as blend sulfonated polyetheretherketone (s-PEEK), new generation perfluorosulfonic acid (PFSA) systems, and composite zirconium phosphate–PFSA polymers. The membranes varied in terms of composition, equivalent weight, thickness, and [...] Read more.

Sulfonic acid-functionalized polymer electrolyte membranes alternative to Nafion^® were developed. These were hydrocarbon systems, such as blend sulfonated polyetheretherketone (s-PEEK), new generation perfluorosulfonic acid (PFSA) systems, and composite zirconium phosphate–PFSA polymers. The membranes varied in terms of composition, equivalent weight, thickness, and filler and were investigated with regard to their methanol permeation characteristics and proton conductivity for application in direct methanol fuel cells. The behavior of the membrane electrode assemblies (MEA) was investigated in fuel cell with the aim to individuate a correlation between membrane characteristics and their performance in a direct methanol fuel cell (DMFC). The power density of the DMFC at 60 °C increased according to a square root-like function of the membrane selectivity. This was defined as the reciprocal of the product between area specific resistance and crossover. The power density achieved at 60 °C for the most promising s-PEEK-based membrane-electrode assembly (MEA) was higher than the benchmark Nafion^® 115-based MEA (77 mW·cm⁻² vs. 64 mW·cm⁻²). This result was due to a lower methanol crossover (47 mA·cm⁻² equivalent current density for s-PEEK vs. 120 mA·cm⁻² for Nafion^® 115 at 60 °C as recorded at OCV with 2 M methanol) and a suitable area specific resistance (0.15 Ohm cm² for s-PEEK vs. 0.22 Ohm cm² for Nafion^® 115). Full article

(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications 2015)

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1579 KiB

Open AccessArticle

Influence of the Ionic Liquid Type on the Gel Polymer Electrolytes Properties

by Juan P. Tafur, Florencio Santos and Antonio J. Fernández Romero

Membranes 2015, 5(4), 752-771; https://doi.org/10.3390/membranes5040752 - 19 Nov 2015

Cited by 41 | Viewed by 7095

Abstract

Gel Polymer Electrolytes (GPEs) composed by ZnTf₂ salt, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), and different ionic liquids are synthesized using n-methyl-2-pyrrolidone (NMP) as solvent. Three different imidazolium-based ionic liquids containing diverse cations and anions have been explored. Structural and electrical properties of the GPEs [...] Read more.

Gel Polymer Electrolytes (GPEs) composed by ZnTf₂ salt, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), and different ionic liquids are synthesized using n-methyl-2-pyrrolidone (NMP) as solvent. Three different imidazolium-based ionic liquids containing diverse cations and anions have been explored. Structural and electrical properties of the GPEs varying the ZnTf₂ concentration are analyzed by ATR-FTIR, DSC, TG, and cyclic voltammetry. Free salt IL-GPEs present distinct behavior because they are influenced by the different IL cations and anions composition. However, inclusion of ZnTf₂ salt inside the polymers provide GPEs with very similar characteristics, pointing out that ionic transport properties are principally caused by Zn²⁺ and triflate movement. Whatever the IL used, the presence of NMP solvent inside the polymer’s matrix turns out to be a key factor for improving the Zn²⁺ transport inside the GPE due to the interaction between Zn²⁺ cations and carbonyl groups of the NMP. High values of ionic conductivity, low activation energy values, and good voltammetric reversibility obtained regardless of the ionic liquid used enable these GPEs to be applied in Zn batteries. Capacities of 110–120 mAh·g⁻¹ have been obtained for Zn/IL-GPE/MnO₂ batteries discharged at −1 mA·cm⁻². Full article

(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications 2015)

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687 KiB

Open AccessArticle

Corrosion Protection of Al/Au/ZnO Anode for Hybrid Cell Application

by Gymama Slaughter and Brian Stevens

Membranes 2015, 5(4), 739-751; https://doi.org/10.3390/membranes5040739 - 16 Nov 2015

Cited by 1 | Viewed by 4667

Abstract

Effective protection of power sources from corrosion is critical in the development of abiotic fuel cells, biofuel cells, hybrid cells and biobateries for implantable bioelectronics. Corrosion of these bioelectronic devices result in device inability to generate bioelectricity. In this paper Al/Au/ZnO was considered [...] Read more.

Effective protection of power sources from corrosion is critical in the development of abiotic fuel cells, biofuel cells, hybrid cells and biobateries for implantable bioelectronics. Corrosion of these bioelectronic devices result in device inability to generate bioelectricity. In this paper Al/Au/ZnO was considered as a possible anodic substrate for the development of a hybrid cell. The protective abilities of corrosive resistant aluminum hydroxide and zinc phosphite composite films formed on the surface of Al/Au/ZnO anode in various electrolyte environments were examined by electrochemical methods. The presence of phosphate buffer and physiological saline (NaCl) buffer allows for the formation of aluminum hyrdroxide and zinc phosphite composite films on the surface of the Al/Au/ZnO anode that prevent further corrosion of the anode. The highly protective films formed on the Al/Au/ZnO anode during energy harvesting in a physiological saline environment resulted in 98.5% corrosion protective efficiency, thereby demonstrating that the formation of aluminum hydroxide and zinc phosphite composite films are effective in the prevention of anode corrosion during energy harvesting. A cell assembly consisting of the Al/Au/ZnO anode and platinum cathode resulted in an open circuit voltage of 1.03 V. A maximum power density of 955.3 mW/ cm² in physiological saline buffer at a cell voltage and current density of 345 mV and 2.89 mA/ cm², respectively. Full article

(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications 2015)

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484 KiB

Open AccessArticle

High Temperature Stable Separator for Lithium Batteries Based on SiO₂ and Hydroxypropyl Guar Gum

by Diogo Vieira Carvalho, Nicholas Loeffler, Guk-Tae Kim and Stefano Passerini

Membranes 2015, 5(4), 632-645; https://doi.org/10.3390/membranes5040632 - 23 Oct 2015

Cited by 30 | Viewed by 9196

Abstract

A novel membrane based on silicon dioxide (SiO₂) and hydroxypropyl guar gum (HPG) as binder is presented and tested as a separator for lithium-ion batteries. The separator is made with renewable and low cost materials and an environmentally friendly manufacturing processing [...] Read more.

A novel membrane based on silicon dioxide (SiO₂) and hydroxypropyl guar gum (HPG) as binder is presented and tested as a separator for lithium-ion batteries. The separator is made with renewable and low cost materials and an environmentally friendly manufacturing processing using only water as solvent. The separator offers superior wettability and high electrolyte uptake due to the optimized porosity and the good affinity of SiO₂ and guar gum microstructure towards organic liquid electrolytes. Additionally, the separator shows high thermal stability and no dimensional-shrinkage at high temperatures due to the use of the ceramic filler and the thermally stable natural polymer. The electrochemical tests show the good electrochemical stability of the separator in a wide range of potential, as well as its outstanding cycle performance. Full article

(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications 2015)

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Review

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751 KiB

Open AccessReview

NMR Studies of Solvent-Free Ceramic Composite Polymer Electrolytes—A Brief Review

by Marc B. Berman and Steven G. Greenbaum

Membranes 2015, 5(4), 915-923; https://doi.org/10.3390/membranes5040915 - 14 Dec 2015

Cited by 8 | Viewed by 5437

Abstract

Polyether-based polymer electrolytes containing ceramic inorganic oxide fillers often exhibit improved mechanical and ion transport properties compared to their filler-free counterparts. The nature of local scale interactions that give rise to these enhanced properties is explored by nuclear magnetic resonance measurements. Full article

(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications 2015)

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