Nafion Resin Research Articles

Ion-Selective Membranes Fabricated Using Finely Controlled Swelling of Non-Ionic Fluoropolymer for Redox Flow Batteries

Ion-selective membranes based on non-ionic polymers are promising for redox flow batteries due to their superior chemical stability and low cost. In this work, a poly(vinylidene fluoride) (PVDF) ion-selective membrane is successfully prepared using a solvent-controlled swelling method, where Nafion is used as a channel-forming promoter. The influences of Nafion on the channel formation of the membranes are studied. The results indicate that the addition of Nafion resin can greatly promote the formation of ion-conducting channels in the PVDF matrix. The obtained membranes show well-controlled proton conductivity and proton/vanadium selectivity. A battery test on a vanadium redox flow single cell is successfully performed. The energy efficiency of the cell equipped with the PVDF-based ion-selective membrane reaches 81.7% at a current density of 60 mA cm−2 and possesses excellent cycling stability and suppressed self-discharge after modification with Nafion.

Large Scalable High Ion Conductive and Selective Double Layer Membrane Achieved through Dual Ion Conducting Mechanisms

As the share of sustainable energy sources in the electricity supply rises, large-scale energy storage becomes increasingly important. All vanadium flow batteries, as one of the most promising large-scale energy storage methods, have reached the commercialization stage because of their unique feature of uncoupling power and energy, as well as the advantages of long life, high safety, and low cost. The ion-selective membrane is an essential part of flow batteries, which allows specific ions to pass through to maintain a neutral charge and prevents the crossover of active species to maintain the capacity. However, the high cost and low ion-selectivity of the commercialized ion-selective membranes (i.e., Nafion membranes) hindered the further promotion of the flow batteries. Herein, we developed a large scalable double-layer ion selectivity membrane with a unique bifunctional nanoporous boron nitride (PBN) ion selective layer and a low-cost porous polyetherimide (PEI) ion conductivity and support layer. PBN was synthesized by a large scalable template-free method, which was further decorated with Nafion resin. The nano-sized and tortuous pores of the PBN can effectively block the crossover of vanadium ions and provide excellent ion selectivity based on the pore size exclusion mechanism. Furthermore, the super-acidic sulfonic acid groups of Nafion decorated on the nanoporous structure of PBN provide high-speed proton transfer channels that increase proton conductivity through both Grotthuss and vehicle mechanisms. The low-cost porous PEI ion conductivity and support layer was prepared by the phase separation method. The well-aligned asymmetric finger-like porous structure of the PEI membrane provides excellent ion conductivity. The addition of a hydrophilic polymer additive, polyvinylpyrrolidone, further increased its ion conductivity. The PBN–PEI double layer membrane, prepared by a simple spray coating method, demonstrated an excellent ion selectivity (1.49×108 mS cm−3 min), which is almost 15 times higher than that of the pristine PEI membrane (6.71×106 mS cm−3 min) while maintaining high ion conductivity (64 mS cm−1). The PBN–PEI membrane achieved superior performance (97% of coulombic efficiency, 94% of voltage efficiency, and 91% of energy efficiency at 40 mA cm−2) than the Nafion 115 membrane in the all-vanadium flow battery with higher discharge capacity at all current densities and high stability with a lower capacity fading rate (0.17% per cycle vs. 0.74% per cycle at 100 mA cm−2). The PBN–PEI membrane also demonstrated a stable operation in the all-vanadium flow battery at a current density of 100 mA cm−2 over 700 cycles. The work presented the remarkable performance of the ultra-thin PBN bifunctional layer in terms of ion conductivity and selectivity; the combination with the low-cost high ion-conductive porous PEI membrane and a simple fabrication process demonstrated a great potential for commercialization of the PBN-PEI double-layer membrane.

High Ion Conductive and Selective Membrane Achieved through Dual Ion Conducting Mechanisms.

Conventional ion-selective membranes, that ision-exchange and porous membranes, are unable to perform high conductivity and selectivity simultaneously due to the contradictions between their ion selecting and conducting mechanisms. In this work, a bifunctional ion-selective layer is developed via the combination of nanoporous boron nitride (PBN) and ion exchange groups from Nafion to achieve high ion conductivity through dual ion conducting mechanisms as well as high ion selectivity. A template-free method is adopted to synthesize flake-like PBN, which is further enmeshed with Nafion resin to form the bifunctional layer coated onto a porous polyetherimide membrane. The double-layer membrane exhibits excellent ion selectivity (1.49 × 108 mS cm-3 min), which is 22 times greater than that of the pristine porous polyetherimide membrane, with outstanding ion conductivity (64 mS cm-1 ). In a vanadium flow battery, the double-layer membrane achieves a high Coulombic efficiency of 97% and outstanding energy efficiency of 91% at 40mA cm-2 with a stable cycling performance for over 700 cycles at 100mA cm-2 . PBN with ion exchange groups may therefore offer a potential solution to the limitation between ion selectivity and conductivity in ion-selective membranes.

A Composite Membrane with High Stability and Low Cost Specifically for Iron-Chromium Flow Battery.

The iron–chromium flow battery (ICFB), the earliest flow battery, shows promise for large-scale energy storage due to its low cost and inherent safety. However, there is no specific membrane designed that meets the special requirements of ICFBs. To match the harsh operation parameters of ICFBs, we designed and fabricated a composite membrane with high mechanical, chemical, and thermal stability. In the design, a commercial porous polyethylene membrane is selected as the framework material, offering high mechanical stability and reducing the cost. Meanwhile, the Nafion resin is filled in the pores of a porous membrane, which inhibits the transfer of redox-active ions and creates the proton channels via hydrophobic/hydrophilic phase separation. As a result, the composite membrane exhibits high conductivity, selectivity, and stability, especially with almost no swelling at high operating temperatures. Thus, an ICFB with the prepared membrane exhibits a coulombic efficiency of 93.29% at the current density of 80 mA cm−2 and runs stably for over 300 cycles. This work provides an easy method to fabricate high-performance and low-cost membranes specifically for ICFBs and has the potential to promote the development of ICFBs.

The electrochemical properties of iodine cathode in a novel rechargeable hydrogen ion supercapattery system with molybdenum trioxide as anode

Hydrogen ion battery is a promising energy storage device due to its advantages of non-pollution, excellent rate capability and feasibility at low temperature. Herein, we assemble a novel rechargeable hydrogen ion supercapattery with the iodine-absorbed carbon paper doped with N and P (I2-NP-CP) as the cathode electrode and molybdenum trioxide as the anode electrode. Typically, the I2-NP-CP electrode shows the superior rate capability from 1 A g−1 (174.7 mAh g−1, 483.8 F g−1) to 20 A g−1 (111.1 mAh g−1, 307.7 F g−1), mainly ascribed to the strong interaction between iodine and the NP-CP substrate. Furthermore, electrochemical measurement of the I2-NP-CP@Nafion//MoO3 supercapattery manifests that the electrodes exhibit excellent cycling stability, retaining 124.3 mAh g−1 after 500 cycles at 15 A g−1, accounting for 93.2 % of the initial capacity. Although some IO3− dissolves in the electrolyte due to the weak chemical interaction between IO3− and NP-CP, and cannot be completely reduced to I− during discharge process, it can be improved by modification of electrode with Nafion resin to further better the cycling stability. The excellent electrochemical properties in this study show the possibility for the development of novel rechargeable hydrogen ion supercapattery system.

Dual-porous structured membrane for ion-selection in vanadium flow battery

Porous membranes based on low-cost, chemically robust and non-ionic polymers are found to be promising as ion-selective membranes in redox flow batteries. Herein, we fabricate a dual-porous structured membrane where micro and macro pores are formed in the Nafion/poly(vinylidene fluoride) hybrid matrix. The dual-porous structure of the membranes is constructed by using polyethylene glycol as a pore-forming template. It is revealed that Nafion resin has significant impacts on both pore formation and ion conduction. The proton conductivity of the dual-porous membrane reaches 49.1 mS cm−1, and its vanadium permeation can be notably suppressed. Result of the single cell test indicates that, with the dual-porous structured membrane, coulombic efficiency and energy efficiency of the cells can achieve 96.1% and 83.8%, respectively, at 100 mA cm−2. The characteristics of low cost (approximately 50% of the material cost of Nafion), suppressed vanadium permeation, good chemical stability and competitive electrochemical performance make the dual-porous blend membranes promising candidate for redox flow batteries.

Fabrication and characterization of a novel Nafion‐PTFE composite hollow fiber membrane

AbstractNafion has been widely used in electrochemistry, but there are only a few reports on its application in other fields, such as, gas separation, even though it exhibits good performance. The primary reason for that is the high cost of Nafion and making a composite membrane with a thin Nafion layer is a potential solution to solve this problem. In this study, a novel Nafion‐PTFE composite hollow fiber membrane, which had a thin (~5 μm) and detect‐free Nafion layer on PTFE surface, without Nafion filling substrate pores was developed, differing from the reported ones in which Nafion resin was required to impregnate into porous PTFE membrane as thorough as possible to ensure the ion conductivity and operation stability. The surface morphology, crystallite, solubility in ethanol/water mixture, and water uptake of membranes were systemically investigated. The gas permeance tests were also conducted. The permeances of different gasses of prepared composite membranes were significantly enhanced compared with the commercial membranes due to the decrease of Nafion thicknesses, while the selectivity remained the same, verifying the detect‐free structure of Nafion layer on PTFE substrate. This study provided a good reference for the preparation and application of low‐cost Nafion composite membranes.

The Fe3+ role in decreasing the activity of Nafion-bonded IrO2 catalyst for proton exchange membrane water electrolyser

Fe3+ is a common ion contaminant for the proton exchange membrane water electrolyser (PEMWE). In this work, three-electrode-system was employed to study the effect of Fe3+ on Nafion-bonded IrO2 catalyst which is conventional anode catalyst for PEMWE. Study results showed that Fe3+ contamination decreased IrO2 catalytic activity significantly only when the following two conditions were both satisfied: 1) Nafion resin exists in working electrode; 2) working electrode potential was over 1.471 V (vs. NHE) which is around the initial voltage of oxygen evolution reaction (OER). Besides, the contaminated working electrode activity was recovered to about 16% by being immersed into 3 M H2SO4 solution, but it was recovered to about 59% by ethanol washing method. These study results revealed that Fe3+ plays a role of catalyst for H2O2 production during OER process, which leads to Nafion resin decomposition. The degradation products covered working electrode surface, and thus decreased effective active sites of IrO2. Nafion degradation was further confirmed by analyzing 1) F− content in anode water and 2) FTIR of contaminated Nafion membrane.

Sensitive voltammetric determination of riboflavin in pharmaceutical and biological samples using FSN-Zonyl-Nafion modified carbon paste electrode

An anti-fouling bipolymeric membrane was used to modify a carbon nanoparticle paste electrode for the determination of riboflavin in real samples. This bipolymeric membrane was constructed from two polymers: perfluorate resin Nafion and fluorosurfactant Zonyl-FSN. Nafion membrane was used as an anti-fouling material and the Zonyl-FSN membrane was used for the enhancement of the electrocatalytic activity towards the electrooxidation of riboflavin. The developed method exhibited a good sensitivity for the determination of riboflavin, in real samples, without any preconcentration step. The fouling effect was controlled by the Nafion membrane that possesses the ability to block the anionic and neutral species to reach on the carbon matrix surface. The proposed FSN/Nafion/CNP electrode was used in a wide concentration range with two linear ranges (1.00×10−10 - 1.00×10−7 mol L−1 and 1.00×10−7 - 1.00×10−4 mol L−1, respectively) and very low limit of detection (3.03×10−11 mol L−1). The analytical applicability of the proposed method was demonstrated by performing quantitative measurements of riboflavin from real samples, such as pharmaceutical samples and urine samples with a RSD value lower that 2.75%.

Global phosphoric acid fuel cell market report 2019–2023 featuring Bharat Heavy Electricals, Doosan Fuel Cell America, Fuji Electric, & Toshiba Energy Systems & Solutions

In this study, long-range ordered straight holes with definable open pattern and diameter of 100–200 μm were manufactured using a 355 nm Nd:YVO4 ultraviolet laser to sustain Nafion resin for durable proton exchange membranes. Composite proton exchange membrane prepared from the straight-hole polyimide support successfully reduced the dimensional swelling and humidity-induced stress of the proton exchange membrane under variable humidities. The effect of laser fluence and overlap rate on the size precision and quality of the straight holes were investigated. The thermodynamic mechanical capacity of composite proton exchange membrane and the single cell performance were also determined. The experimental results showed that long-range ordered straight holes with high precision and good quality could be achieved by laser trepanning with appropriate scanning speed, high repetition frequency and suitable laser fluence.

Novel reactivation allows effective reuse of Nafion® super-acid nano-catalyst

An alternative clean regeneration method to calcination on special grade resins, i.e. Nafion, is introduced. The reactivation strategy makes use of advanced oxidation processes (Fenton and non-Fenton) to remove the organic deposits generated from sequential catalytic cycles. Hot water treatment was considered as a control case to evaluate the extraction capacity of water itself at the oxidative conditions. Advanced oxidation processes were effective in reactivating the Nafion SAC-13 resin, which also rendered a cleaner and more sustainable reactivation process. Beta zeolite was studied as model fouled system prior to the Nafion SAC-13. Even though zeolites are considered to be thermally stable, this approach can be used when a full preservation of the acid sites is required. As far as resin Nafion SAC-13 is concerned, organic species deposition was found to be responsible of a selective poisoning of the sulfonic groups in Nafion, with a consequent drop in catalytic activity of the octanoic acid esterification with methanol. The Nafion resin was reactivated either with H2O2 or with Fenton chemistry; the resin remained stable under these oxidative conditions, which is the benefit of the presented non­thermal methodologies as compared to calcination. The optimal method showed full recovery of the initial activity and 90% of the final conversion. This methodology seems attractive for a whole-range of organic catalytic reactions, including those related to biomass valorization, that require the use of highly acidic catalysts, such as acidic resins, in liquid phase reactions.

Performance of a MEA using patterned membrane with a directly coated electrode by the bar-coating method in a direct methanol fuel cell

This study increased the surface area of a membrane by forming patterns on the Nafion resin membrane using a stainless steel mesh to enhance the performance of a direct methanol fuel cell (DMFC) because the triple-phase boundary is extended. Nafion resin (F-form (SO3F)) was used which has melt-moldability to form a stable surface pattern and to directly coat the catalyst layer by the bar-coating method. The performance (polarization and power density curves) and the resistance of the membrane-electrode assembly (MEA) were analyzed with a single cell and an impedance analyzer. The surface area of the patterned membranes was increased 1.99, 2.10, and 2.12 times compared to the flat membrane, and the power density also increased 12.9, 18.6, and 24.2% at 0.4 V, respectively. The performance of the MEA with the patterned membrane had a lower concentration polarization than that of the MEA with the flat membrane. The performance of the MEAs with the patterned membranes had a greater impact on the cathode side of the membrane than on the anode side. The results of these experiments offer a solution to the problem of a low performance of MEA, which is one of the disadvantages of DMFCs.

The Role of Carbon on Copper–Carbon Composites for the Electrooxidation of Alcohols in an Alkaline Medium

Copper–carbon composites were prepared following various different synthetic routes and using various carbon precursors (i.e., lignocellulose and graphite oxide), and were used as electrocatalysts for the oxidation of propargyl alcohol (PGA) in an alkaline medium. The electrochemical response of the copper-based catalysts was analyzed in terms of the influence of the metallic species, the carbon matrix incorporated in the composites, and the chemical structure of the ionomers—Nafion and poly (4-vinylpyridine) cross-linked methyl chloride quaternary salt resin (4VP)—used in the fabrication of the electrodes. Data has shown that the incorporation of reduced graphene oxide sheets between the copper metallic particles increased the performance due to the increased conductivity provided by the carbonaceous phase. Catalytic inks with ca. 40 wt.% Nafion and 12 wt.% 4VP as ionomers provided the best electrochemical response and cohesion of the catalysts, minimizing the losses in the electroactivity of the copper species.

Nafion®-Containing Solid Lipid Nanoparticles as a Tool for Anticancer Pt Delivery: Preliminary Studies

Preliminary studies of nanoparticles based on the perfluorosulfonic acid resin Nafion have been carried out with the aim of establishing an ionic connection with the protonable phosphine 1,3,5-triaza-7-phosphaadamantane (PTA), suitable for the coordination of platinum. Nafion-containing nanoparticles (NAF) were produced by homogenization followed by ultrasonication method. After production, NAF were characterized in terms of size, morphology, andin vitrocytotoxicity. The PCS studies showed that theZ-average mean diameter was around 250 nm. Moreover, the polydispersity index showed a monodimensional distribution of nanoparticles. Cryo-TEM analysis showed a uniform and homogenous population of particles, characterized by the presence of both ovoidal and needle-like structures. To evaluate thein vitrocytotoxicity, NAF were tested on human cancer cell lines K562 and A2780. No cytotoxic effect was found on both cell lines. By13P-NMR measures, it is here proved that the strongly acidic sulfonic groups of Nafion-containing nanoparticles (NAF) can act as protonating agents for PTA. The protonation occurs selectively at nitrogen; hence protonated PTA maintains its ability to coordinate platinum via its phosphorus atom.

Activity enhancement of Nafion resin: Vapor-phase carbonylation of dimethoxymethane over Nafion-silica composite

A kind of composite materials consisting of nano-sized Nafion resin homogeneously dispersed in a high-surface silica matrix was prepared by sol–gel method and used as catalysts in the vapor-phase carbonylation reaction of dimethoxymethane for production of methylmethoxy acetate. These composite catalysts showed much higher catalytic activity in comparison with the original pure Nafion resin catalyst. The remarkable improvement of catalytic performance was due to the increased accessibility of acid sites of Nafion resin in the composite catalysts. The contents of Nafion-H resin and silica precursors were found to have a great influence on the structure of the composite, resulting in different catalytic activity during DMM carbonylation reactions. Furthermore, the comparison of the composite catalysts with high-silica H-Y and H-Beta zeolite catalysts demonstrated that the excellent catalytic performance is closely related to the higher acid strength and larger pores of Nafion-silica composite materials.

The influence of Ferric ion contamination on the solid polymer electrolyte water electrolysis performance

Fe3+ is a sort of common metal ion contaminant for the solid polymer electrolyte (SPE) water electrolyser. In this paper, the effect of Fe3+ on the performance of SPE water electrolyser has been investigated by both in-situ and ex-situ characterizations. The electron probe microanalysis and ultraviolet test results showed that Fe3+ could migrate from the anode to the cathode and mostly be reduced to Fe2+ in the cathode rather than occurred underpotential deposition as described in the previous report. The in-situ dynamic contamination test showed that the anode voltage increased sharply as soon as the Fe3+ was fed into the anode, while the cathode voltage kept constant until the contamination time was over 30minutes, indicating the higher tolerance of the cathode than the anode for the Fe3+ contamination. The calculation results based on the electrochemistry impedance spectroscopy test results revealed that the striking increase of the electrolysis voltage was mainly attributed to the ohmic overpotential, which was due to the replacement of H+ by Fe3+ in the Nafion resin. Interestingly, the voltage lagged behind the current for several minutes in the multi-current-step test for the contaminated electrolyser, which phenomenon may be used for judging whether the SPE water electrolyser performance degradation is due to the metal ions contamination. Furthermore, recovery strategy has been developed, and it was found that the contaminated electrolyser could be mostly recovered by 0.5M H2SO4 solution treatment for 13h.

Composite Membrane Based on Graphene Oxide Sheets and Nafion for Polymer Electrolyte Membrane Fuel Cells

A composite membrane for fuel cell applications was prepared by incorporating custom-made graphene oxide (GO) in Nafion resin. The GO was used to provide mechanical reinforcement to Nafion. Transmission electron microscopy confirmed the formation of highly crystalline and individually-dispersed graphene oxide sheets. Tensile strength, water uptake, swelling, proton conductivity and electrical conductivity of the composite membranes were measured and compared with pure Nafion. The polarization curves indicated that the fuel cell performance of the 3wt% GO/Nafion composite membrane was similar to that of the pure Nafion membrane, but the composite membrane was superior to Nafion in terms of mechanical properties.

Ultra-thin polytetrafluoroethene/Nafion/silica composite membrane with high performance for vanadium redox flow battery

Ultra-thin and high performance polytetrafluoroethene (PTFE)/Nafion/silica composite membrane has been successfully prepared by solution casting and sol–gel method for all vanadium redox flow battery (VRB). Thickness of ∼25 μm polytetrafluoroethene/Nafion (P/N) membrane is first prepared by impregnating porous PTFE membrane with Nafion solution, and then the P/N membrane is immersed in tetraethoxysilane (TEOS) solution to prepare PTFE/Nafion/silica (P/N/S) composite membranes. The chemical structures of membranes are investigated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR), which prove that the Nafion resin and silica are well impregnated in PTFE membrane. The water uptake, proton conductivity, vanadium permeability and VRB single cell tests of the composite membrane are also investigated in detail. At 80 mA cm−2, coulombic efficiency, voltage efficiency and energy efficiency of the VRB with P/N/S-7 (7 wt.% SiO2 in P/N/S) membrane are 93.9%, 87.2% and 81.9%, respectively. Furthermore, the self-discharge rate of the VRB with P/N/S membrane is much slower than that of the VRB with P/N membrane, which indicates that the membrane has good vanadium block ability. Fifty cycles charge–discharge test proves that the P/N/S membrane is very stable and possesses high chemical stability under the strong acid solutions.

Reinforcement of Nafion into polyacrylonitrile (PAN) to fabricate them into nanofiber mats by electrospinning: characterization of enhanced mechanical and adsorption properties

Electrospinning method was optimized for fabrication of functional and mechanically strong nanofiber mats by reinforcement of Nafion resin into polymer polyacrylonitrile (PAN). Nafion and PAN were blended by the sol–gel method using the solvents N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF). Fabricated membranes were characterized by their geometrical, physicochemical and mechanical properties. The study revealed that, nanofibers of 450–80 nm diameter were fabricated. The Nafion–PAN composite nanofiber exhibited more stability and better mechanical properties due to reinforcement of Nafion into PAN matrices. These composite nanofiber mats exhibited the ultimate tensile strength (UTS) of 376 and 286 kPa as compared to UTS of 157 kPa for neat PAN nanofibers. Nanofiber membranes also possessed adsorption properties showing an adsorption removal affinity for Cr3+ metal ions up to approximately 45%. Electrospun nanofiber mats also exhibited high surface area and can have multifaceted applications.

Poly (vinylidene fluoride-co-hexafluoropropylene)/polybenzimidazole blend nanofiber supported Nafion membranes for direct methanol fuel cells

This article presents preparation of poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-co-HFP) and polybenzimidazole (PBI) blend electrospun nanofiber (PVFP-BI) films from N,N′-dimethyl acetamide (DMAc)/acetone mixture solutions. Using the PVFP-BI nanofiber film (thickness ∼13–15 μm) as a supporting material for impregnating Nafion resin solution, Nafion/PVFP-BI composite membranes (thickness ∼50 μm) are prepared and direct methanol fuel cell (DMFC) tests are performed. Better DMFC performance of the Nafion/PVFP-BI composite membrane than the commercial Nafion-117 (thickness ∼175 μm) and Nafion-212 (thickness ∼50 μm) membranes when blending with 5–10 wt.% of PBI in the PVFP-BI nanofiber support film is demonstrated.