Showing papers on "Nafion published in 2020"

An Interface-Bridged Organic-Inorganic Layer that Suppresses Dendrite Formation and Side Reactions for Ultra-Long-Life Aqueous Zinc Metal Anodes.

Abstract: Aqueous zinc (Zn) batteries (AZBs) are widely considered as a promising candidate for next-generation energy storage owing to their excellent safety features. However, the application of a Zn anode is hindered by severe dendrite formation and side reactions. Herein, an interfacial bridged organic-inorganic hybrid protection layer (Nafion-Zn-X) is developed by complexing inorganic Zn-X zeolite nanoparticles with Nafion, which shifts ion transport from channel transport in Nafion to a hopping mechanism in the organic-inorganic interface. This unique organic-inorganic structure is found to effectively suppress dendrite growth and side reactions of the Zn anode. Consequently, the Zn@Nafion-Zn-X composite anode delivers high coulombic efficiency (ca. 97 %), deep Zn plating/stripping (10 mAh cm-2 ), and long cycle life (over 10 000 cycles). By tackling the intrinsic chemical/electrochemical issues, the proposed strategy provides a versatile remedy for the limited cycle life of the Zn anode.

Post-synthetic modification of porous materials: superprotonic conductivities and membrane applications in fuel cells

Abstract: Proton exchange membrane fuel cells (PEMFCs) have attracted considerable attention and applications in the field of transportation because they achieve eco-friendly electricity generation with water as the only by-product. As the preferred solid electrolyte in PEMFCs, Nafion possesses various desirable attributes and high proton conductivity, but its prohibitive cost and practical limitations in operation are problematic. Recently, several types of porous platforms, including metal–organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic polymers (POPs), and hydrogen-bonded organic frameworks (HOFs) have been deployed to develop conducting systems. Post-synthetic modification for porous platforms is a flagship smart methodology in membrane electrolyte fabrication for fuel cells that concurrently combines original and other desirable features that are complementary to each other and induce enhanced conductivity. Additionally, the introduction of proton conductive mixed matrix membranes, which has recently received considerable attention as a practical method to fabricate membranes, has inspired recent research trends. This review discusses post-synthetic modification-based proton conductors and their membranes in terms of design strategies, conduction mechanisms, and diverse diagnostic modalities for future electrolyte materials in fuel cell technology.

Ceria Stabilized by Titanium Carbide as a Sustainable Filler in the Nafion Matrix Improves the Mechanical Integrity, Electrochemical Durability, and Hydrogen Impermeability of Proton-Exchange Membrane Fuel Cells: Effects of the Filler Content

Abstract: Cerium oxide-anchored titanium carbide (CeO2-TiC) is realized as a potential inorganic filler when modifying the Nafion matrix of a proton-exchange membrane fuel cell (PEMFC). A hydrothermal strategy was employed to synthesize CeO2-TiC of high crystallinity as a filler to mitigate the problematic properties of a proton-exchange membrane (PEM). CeO2-TiC with a weight ratio of 0.5, 1, 1.5, or 2% was incorporated into a Nafion matrix to form a hybrid by adopting a solution-casting procedure. Reinforcement owing to the presence of TiC provides increased tensile strength to PEM, and the addition of CeO2 improves the durability of PEM by scavenging free radicals. The microstructural, thermomechanical, physiochemical, and electrochemical properties of PEM, including contact angle, water sorption, water uptake, and proton conductivity, were extensively studied. Random dispersion of CeO2-TiC in the Nafion matrix improves the thermal stability, tensile strength, and water uptake while retaining proton conductivity, as compared with those of pristine Nafion. As a result, optimized Nafion/CeO2-TiC (1 wt %) achieved undiminished PEMFC performance compared to that of pristine Nafion while operating the device at 60 °C and 100% relative humidity. In addition, Nafion/CeO2-TiC (1 wt %) experienced the degradation of merely 0.6 mV h-1 during 200 h operation under identical conditions. Compared to that of Nafion/CeO2-TiC (1 wt %), pristine Nafion and Nafion-212 displayed accelerated and comparable degradation (for pristine Nafion, 1.3 mV h-1; for Nafion-212, 0.4 mV h-1). PEMFC power output, hydrogen permeability, and morphology of samples were examined after the durability test; the results indicate that Nafion/CeO2-TiC (1 wt %) is extremely stable. Since various Nafion hybrids have been reported as highly durable PEMs, this study is expected to open up new perspectives to expanding their applications, especially in sustainable PEMFC technology.

CdPS3 nanosheets-based membrane with high proton conductivity enabled by Cd vacancies.

Abstract: Proton transport in nanochannels under humid conditions is crucial for the application in energy storage and conversion. However, existing materials, including Nafion, suffer from limited conductivity of up to 0.2 siemens per centimeter. We report a class of membranes assembled with two-dimensional transition-metal phosphorus trichalcogenide nanosheets, in which the transition-metal vacancies enable exceptionally high ion conductivity. A Cd0.85PS3Li0.15H0.15 membrane exhibits a proton conduction dominant conductivity of ~0.95 siemens per centimeter at 90° Celsius and 98% relative humidity. This performance mainly originates from the abundant proton donor centers, easy proton desorption, and excellent hydration of the membranes induced by cadmium vacancies. We also observed superhigh lithium ion conductivity in Cd0.85PS3Li0.3 and Mn0.77PS3Li0.46 membranes.

A paper-based inkjet-printed PEDOT:PSS/ZnO sol-gel hydrazine sensor

Abstract: Hydrazine is widely used in industries as a precursor for blowing agents, pharmaceuticals, and pesticides. It is a highly toxic compound; therefore, it is of paramount interest to develop new analytical methods for the detection and control of hydrazine exposure. In this work, we describe the fabrication of an all inkjet-printed paper sensor composed of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) electrode functionalized with zinc oxide (ZnO) and encapsulated in a Nafion matrix for the amperometric determination of low concentrations of hydrazine. The electrochemical properties of the fully inkjet-printed PEDOT:PSS/Nafion and PEDOT:PSS/ZnO/Nafion sensors are compared in the presence and absence of different concentrations of hydrazine. The stability and sensitivity of these electrodes are significantly enhanced after modification with ZnO particles. The layer-by-layer deposition of the materials on the electrode surface is characterized by SEM, XRD, and AFM. The printed sensor exhibits a linear response in the 10–500 μM hydrazine concentration range and a ∼5 μM detection limit (at S/N = 3). The electrochemical sensitivity is 0.14 μA μM−1 cm−2, and the best working voltage is 0.5 V. The developed sensor was applied successfully for the determination of hydrazine content in tap, sea, and mineral water samples validating the accuracy of this sensor.

Review of chitosan-based polymers as proton exchange membranes and roles of chitosan- supported ionic liquids

Abstract: Perfluorosulphonic acid-based membranes such as Nafion are widely used in fuel cell applications. However, these membranes have several drawbacks, including high expense, non-eco-friendliness, and low proton conductivity under anhydrous conditions. Biopolymer-based membranes, such as chitosan (CS), cellulose, and carrageenan, are popular. They have been introduced and are being studied as alternative materials for enhancing fuel cell performance, because they are environmentally friendly and economical. Modifications that will enhance the proton conductivity of biopolymer-based membranes have been performed. Ionic liquids, which are good electrolytes, are studied for their potential to improve the ionic conductivity and thermal stability of fuel cell applications. This review summarizes the development and evolution of CS biopolymer-based membranes and ionic liquids in fuel cell applications over the past decade. It also focuses on the improved performances of fuel cell applications using biopolymer-based membranes and ionic liquids as promising clean energy.

Novel LixSiSy/Nafion as an artificial SEI film to enable dendrite-free Li metal anodes and high stability Li–S batteries

Abstract: Lithium–sulfur batteries are the most promising next-generation power source thanks to their extremely high theoretical capacity. However, the uncontrollable lithium dendrite growth and side reactions between the polysulfides and electrolyte for the Li metal anode result in a short lifespan, rapid capacity decay, low Coulombic efficiency, and safety concerns, impeding their practical development. In this work, a novel dual-layered artificial SEI on the Li metal anode is reported, which consists of organic lithiated Nafion on the top and inorganic LixSiSy on the bottom. The flexible Nafion layer can not only maintain the structural integrity of the SEI, but also hinder the side reactions between soluble polysulfides and the lithium anode, while the rigid inorganic layer is beneficial for diffusion of Li ions within it and suppression of Li dendrite growth. Accordingly, the protected Li electrode can steadily withstand successive Li plating/stripping processes for over 1400 h at a current density of 1 mA cm−2. Li–S batteries with a LixSiSy/Nafion film coated Li anode exhibit better cycling stability (783 mA h g−1 after 300 cycles at 0.5C) and higher rate performance (789 mA h g−1 at 2.0C) than those with a bare Li anode. This work highlights the significance of rational manipulation of the interfacial properties of a working Li metal anode and provides fresh insights into achieving dendrite-free Li deposition behaviors and high-cyclability Li–S batteries.

Electrochemical CO2 reduction to methane with remarkably high Faradaic efficiency in the presence of a proton permeable membrane

Abstract: Nafion is a widely used fluoropolymer that is often mixed with electrocatalysts to facilitate proton transport. In contrast to these Nafion-catalyst composites, this work studies electrodes covered by Nafion overlayers for the CO2 reduction reaction. By varying the thickness, substrates, and voltage, we perform a detailed study of the effect of Nafion overlayers on metal and carbon mesh electrodes for CO2 reduction. Depending on the thickness of the Nafion membrane, CO2 reduction occurs at either the polymer–electrolyte interface or electrode–polymer interface. A Nafion overlayer of 15 μm on a Cu electrode enables an extraordinarily high yield of CH4 production (88% Faradaic efficiency) at a low overpotential (540 mV) via the stabilization of metal-bound CO intermediates. To the best of our knowledge, this yield is the highest for electrocatalytic CO2 reduction to CH4 production at room temperature reported.

A Cost-effective Nafion Composite Membrane as an Effective Vanadium-Ion Barrier for Vanadium Redox Flow Batteries.

Abstract: Ion exchange membranes play a key role in all vanadium redox flow batteries (VRFBs). The mostly available commercial membrane for VRFBs is Nafion. However, its disadvantages, such as high cost and severe vanadium-ion permeation, become obstacles for large-scale energy storage. It is thus crucial to develop an efficient membrane with low permeability of vanadium ions and low cost to promote commercial applications of VRFBs. In this study, graphene oxide (GO) has been employed as an additive to the Nafion 212 matrix and a composite membrane named rN212/GO obtained. The thickness of rN212/GO has been reduced to only 41 μm (compared with 50 μm Nafion 212), which indicates directly lower cost. Meanwhile, rN212/GO shows lower permeability of vanadium ions and area-specific resistance compared to the Nafion 212 membrane due to the abundant oxygen-containing functional groups of GO additives. The VRFB cells with the rN212/GO membrane show higher Coulombic efficiencies and lower capacity decay than those of VRFB cells with the Nafion 212 membrane. Therefore, the cost-effective rN212/GO composite membrane is a promising alternative to suppress migration of vanadium ions across the membrane to set up VRFB cells with better performances.

Composite Polymers Development and Application for Polymer Electrolyte Membrane Technologies—A Review

Abstract: Nafion membranes are still the dominating material used in the polymer electrolyte membrane (PEM) technologies. They are widely used in several applications thanks to their excellent properties: high proton conductivity and high chemical stability in both oxidation and reduction environment. However, they have several technical challenges: reactants permeability, which results in reduced performance, dependence on water content to perform preventing the operation at higher temperatures or low humidity levels, and chemical degradation. This paper reviews novel composite membranes that have been developed for PEM applications, including direct methanol fuel cells (DMFCs), hydrogen PEM fuel cells (PEMFCs), and water electrolysers (PEMWEs), aiming at overcoming the drawbacks of the commercial Nafion membranes. It provides a broad overview of the Nafion-based membranes, with organic and inorganic fillers, and non-fluorinated membranes available in the literature for which various main properties (proton conductivity, crossover, maximum power density, and thermal stability) are reported. The studies on composite membranes demonstrate that they are suitable for PEM applications and can potentially compete with Nafion membranes in terms of performance and lifetime.

Recent Progress in the Development of Aromatic Polymer-Based Proton Exchange Membranes for Fuel Cell Applications.

Abstract: Proton exchange membranes (PEMs) play a pivotal role in fuel cells; conducting protons from the anode to the cathode within the cell’s membrane electrode assembles (MEA) separates the reactant fuels and prevents electrons from passing through. High proton conductivity is the most important characteristic of the PEM, as this contributes to the performance and efficiency of the fuel cell. However, it is also important to take into account the membrane’s durability to ensure that it canmaintain itsperformance under the actual fuel cell’s operating conditions and serve a long lifetime. The current state-of-the-art Nafion membranes are limited due to their high cost, loss of conductivity at elevated temperatures due to dehydration, and fuel crossover. Alternatives to Nafion have become a well-researched topic in recent years. Aromatic-based membranes where the polymer chains are linked together by aromatic rings, alongside varying numbers of ether, ketone, or sulfone functionalities, imide, or benzimidazoles in their structures, are one of the alternatives that show great potential as PEMs due totheir electrochemical, mechanical, and thermal strengths. Membranes based on these polymers, such as poly(aryl ether ketones) (PAEKs) and polyimides (PIs), however, lack a sufficient level of proton conductivity and durability to be practical for use in fuel cells. Therefore, membrane modifications are necessary to overcome their drawbacks. This paper reviews the challenges associated with different types of aromatic-based PEMs, plus the recent approaches that have been adopted to enhance their properties and performance.

Carbonized silk fabric-based flexible organic electrochemical transistors for highly sensitive and selective dopamine detection

Abstract: In this work, Nafion and reduced graphene oxide-wrapped carbonized silk fabric (Nafion/rGO/CSF) were fabricated into a precious metal-free gate electrode for organic electrochemical transistor (OECT) sensors. The hierarchical structure of CSF can effectively increase the conductivity of the electrode and avoid the aggregation of rGO and Nafion, giving the Nafion/rGO/CSF-based OECT sensors excellent detection capability towards dopamine (DA) with an ultralow detection limit of 1 nM, a broad detection range from 1 nM – 30 μM and a high selectivity. Moreover, the outstanding electrochemical sensing behaviors of the Nafion/rGO/CSF-based OECT sensor are retainable under bent states and in artificial urine, which will greatly facilitate its application in flexible electronics. The abovemenitoned results indicate that OECT sensors with carbon-based gate electrodes can also obtain high sensitivity comparable to that of precious metal gate electrodes, which, therefore, provides an unprecedented strategy for manufacturing flexible OECT sensors with high performance and low cost.

Modelling the Proton-Conductive Membrane in Practical Polymer Electrolyte Membrane Fuel Cell (PEMFC) Simulation: A Review

Abstract: Theoretical models used to describe the proton-conductive membrane in polymer electrolyte membrane fuel cells (PEMFCs) are reviewed, within the specific context of practical, physicochemical simulations of PEMFC device-scale performance and macroscopically observable behaviour. Reported models and their parameterisation (especially for Nafion 1100 materials) are compiled into a single source with consistent notation. Detailed attention is given to the Springer-Zawodzinski-Gottesfeld, Weber-Newman, and "binary friction model" methods of coupling proton transport with water uptake and diffusive water transport; alongside, data are compiled for the corresponding parameterisation of proton conductivity, water sorption isotherm, water diffusion coefficient, and electroosmotic drag coefficient. Subsequent sections address the formulation and parameterisation of models incorporating interfacial transport resistances, hydraulic transport of water, swelling and mechanical properties, transient and non-isothermal phenomena, and transport of dilute gases and other contaminants. Lastly, a section is dedicated to the formulation of models predicting the rate of membrane degradation and its influence on PEMFC behaviour.

Enhancing the selectivity of Nafion membrane by incorporating a novel functional skeleton molecule to improve the performance of direct methanol fuel cells

Abstract: Conventional fillers have limitations on the modification of proton exchange membranes because of differences in the sizes and physicochemical properties of matrix molecules. Designing skeleton molecules is a vital way to address the limitations by enabling precise distribution in the matrix and inducing automatic nanoscale aggregation and separation of hydrophilic–hydrophobic phases. In this work, a novel SDF-PAEK polymer was synthesized with a rigid hydrophobic backbone, short high-density trifluoromethyl side chains and long flexible aliphatic pendant side chains as a skeleton molecule for the Nafion membrane. Due to the unique molecular interaction selectivity during the membrane formation process, SDF-PAEK automatically matches the Nafion molecular conformation by self-assembly. Combining an improved solution formulation and membrane-casting method, the degree of composition can therefore rise to 20%, which can effectively reduce the cost. Morphological studies show that there is a certain degree of bicontinuous phase microcrystalline domains, and the proton transport channels are highly concentrated. In contrast to the Nafion membrane, SDF-PAEK@Nafion-15% exhibits better performances with higher selectivity (9.73 × 104 S s cm−3) and single-cell maximum power density (PDmax–139 mW cm−2, at 80 °C), which demonstrates the feasibility of SDF-PAEK as a novel PEM skeleton molecule for fuel cell applications.

Breakthrough Carbon Nanotube–Silicon Heterojunction Solar Cells

Abstract: DOI: 10.1002/aenm.201903261 the properties of the nanotube film,[3] or the silicon surface,[4] as well as in understanding of the underlying operational principles.[5] Although relatively good power conversion efficiency of 17% has previously been reported with this architecture, it came from devices with less than 1 mm2 active areas.[6] Typical efficiencies and active areas reported in recent years have been on the order of 13–16% for ≈9 mm2,[7] but as the active area has increased into the range of 1 cm2 or more, the reported efficiencies have tended more toward 10–12% largely due to resistive power losses in the thin nanotube film.[8] Various nanotube dopants and doping schemes have been introduced, such as nitric acid,[9] metal salts,[5c,7c] and metallocenes,[10] as well as a host of interlayers[11] and antireflection/encapsulant coatings.[6,7,12] Of the dopants that have been reported, only the Cu(I)/Cu(II) redox couple reported by Cui et al.[7b] has demonstrated long term stability (up to one year in ambient). Although random pyramid antireflective texturing is a key process throughout silicon photovoltaics, only two previous reports have used it conjunction with nanotube films.[13] The use of the perfluorinated polymeric acid Nafion has been reported as a stable p-type dopant for carrier selective carbon nanotube films in organic solar cells by Jeon et al. in 2018,[14] and its excellent passivation properties on n-type silicon have been separately detailed by Chen et al.[15] Furthermore, the use of thin polymer films as refractive index matching and/ or interference-based antireflection layers has been reported for the nanotube–silicon architecture.[12,16] However, through the results of new investigations into the use of Nafion in state of the art carbon nanotube–silicon heterojunction solar cells, developed in response to a recent review of advances in the field,[1d] this Communication reports the ability to combine all of these properties within the carbon nanotube–silicon architecture and further compares the performance of devices made using this material to the copper colloid doping method. Using the new doping regime, rationally designed contact finger geometry, combined single-walled/double-walled nanotube film, and an optimized tetramethyl ammonium hydroxide based random pyramid texture etch, record efficiency for the field is achieved over previously unsurpassed active areas. To begin, high quality, moderately doped, n-type Cz silicon wafers (0.1–0.3 Ω cm, SSP, <100>, 380 μm thickness) with a 100 nm thermal oxide were used, then a two-step UV lithography process and Cr/Au evaporation was applied to form the structure shown in Figure 1 (with additional photographs in Figure S1, Supporting Information). In the first lithography The latest advances in carbon nanotube–silicon heterojunction solar cells are combined with a new doping protocol based on the outstanding electron withdrawing properties and excellent silicon surface passivation ability of sulfonated polytetrafluoroethylene (Nafion). Using this new dopant for carbon nanotube–silicon solar cells, advanced substrate design, and an optimized antireflective texture fast etch with organic base, breakthrough performance is obtained from research grade devices with active areas of 1 and 5 cm2, which yield power conversion efficiencies of 17.2 and 15.5%, respectively.

Atomistic MD Study of Nafion Dispersions: Role of Solvent and Counterion in the Aggregate Structure, Ionic Clustering, and Acid Dissociation

Abstract: A theory-based understanding of perfluorosulfonic acid (PFSA) class of ionomer aggregation in different solvents is crucial for transitioning from empirically guided fabrication of high-performance...