Nafion Membrane Research Articles

Feather-like Gold Nanostructures Anchored onto 3D Mesoporous Laser-Scribed Graphene: A Highly Sensitive Platform for Enzymeless Glucose Electrochemical Detection in Neutral Media.

The authors present a novel sensing platform for a disposable electrochemical, non-enzymatic glucose sensor strip at physiological pH. The sensing material is based on dendritic gold nanostructures (AuNs) resembling feather branches, which are electrodeposited onto a laser-scribed 3D graphene electrode (LSGE). The LSGEs were fabricated via a one-step laser scribing process on a commercially available polyimide sheet. This study investigates several parameters that influence the morphology of the deposited Au nanostructures and the catalytic activity toward glucose electro-oxidation. The electrocatalytic activity of the AuNs-LSGE was evaluated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and amperometry and was compared to commercially available carbon electrodes prepared under the same electrodeposition conditions. The sensor demonstrated good stability and high selectivity of the amperometric response in the presence of interfering agents, such as ascorbic acid, when a Nafion membrane was applied over the electrode surface. The proposed sensing strategy offers a wide linear detection range, from 0.5 to 20 mM, which covers normal and elevated levels of glucose in the blood, with a detection limit of 0.21 mM. The AuNs-LSGE platform exhibits great potential for use as a disposable glucose sensor strip for point-of-care applications, including self-monitoring and food management. Its non-enzymatic features reduce dependence on enzymes, making it suitable for practical and cost-effective biosensing solutions.

Dimerizing Lawsone into Bis-lawsone to Counter Solubility and Attain Facile Zn2+ Ion Diffusion for Stable Capacity in Aqueous Zinc-Ion Batteries

Given the higher volumetric capacity of Zn (5853 mAh cm−3), aqueous zinc-ion batteries can be considered as alternatives to lithium-ion batteries for energy storage applications. Here we focus on redox-active, non-toxic, and eco-friendly organic materials with quinone moiety, i.e., Lawsone (LS) and its dimer Bis-lawsone (BL), as a cathode material for Zn-ion batteries. The reversibility of LS and BL is confirmed by cyclic voltammetry between 0.3 and 1.6 V in zinc sulfate and zinc triflate electrolytes. The electrochemical performance of BL in the zinc triflate electrolyte is improved by the reduction in the solubility of BL in the electrolyte and improvement in Zn2+ diffusion in the BL matrix. Besides, it is known that Zn electrodes passivate better in zinc triflates, which contributes to improved plating/stripping of Zn. The dimerization strategy counteracts solubility and facilitates the diffusion of Zn2+, resulting in a stable charge–discharge with a specific capacity of 200 mAh g–1. The cell attained 77% of the theoretical capacity at a current density of 100 mA g–1. Zn-BL cells show fast kinetics and reversibility for up to 760 cycles retaining 85% of initial capacity despite the partial solubility of BL in electrolytes. In addition, the Nafion-212 membrane is introduced as a separator instead of a traditional glass fiber separator. The negatively charged backbone of Nafion helps eliminate the crossover problem by coulostatic repulsion with negatively charged BL and LS.

A Critical Review of Electrolytes for Advanced Low- and High-Temperature Polymer Electrolyte Membrane Fuel Cells

In the 21st century, proton exchange membrane fuel cells (PEMFCs) represent a promising source of power generation due to their high efficiency compared with coal combustion engines and eco-friendly design. Proton exchange membranes (PEMs), being the critical component of PEMFCs, determine their overall performance. Perfluorosulfonic acid (PFSA) based Nafion and nonfluorinated-based polybenzimidazole (PBI) membranes are commonly used for low- and high-temperature PEMFCs, respectively. However, these membranes have some drawbacks such as high cost, fuel crossover, and reduction in proton conductivity at high temperatures for commercialization. Here, we report the requirements of functional properties of PEMs for PEMFCs, the proton conduction mechanism, and the challenges which hinder their commercial adaptation. Recent research efforts have been focused on the modifications of PEMs by composite materials to overcome their drawbacks such as stability and proton conductivity. We discuss some current developments in membranes for PEMFCs with special emphasis on hybrid membranes based on Nafion, PBI, and other nonfluorinated proton conducting membranes prepared through the incorporation of different inorganic, organic, and hybrid fillers.

Nanoarchitectonics of fibrous clays as fillers of improved proton-conducting membranes for fuel-cell applications

This work reports on the development of various nanostructured materials based on the assembly of SiO2, TiO2 and ZnO nanoparticles to sepiolite fibers (Sep) and their incorporation as a filler of Nafion to improve their performance as proton exchange membrane for fuel cells applications. Various nanoarchitectures, SiO2-Sep, TiO2-SiO2-Sep and ZnO@SiO2-Sep, were prepared following a colloidal route based on the controlled hydrolysis of alkoxide precursos (tetramethoxysilane and titanium tetraisopropoxide) in the presence of hexadecyltrimethylammonium-sepiolite. The SiO2 and TiO2 nanoparticles were consolidated after a thermal treatment that also removes the surfactant and assures their assembly to the clay. In the case of the ZnO@SiO2-Sep nanostructured material, previously formed ZnO nanoparticles were assembled to the intermediated produced after the hydrolysis-polycondensation of tetramethoxysilane on the organoclay, followed by a thermal treatment that consolidates the nanoarchitecture. The resulting nanoarchitectures were characterized by XRD, FTIR, SEM, TEM and N2 adsorption-desorption isotherms, confirming the formation of the nanoparticles and their assembly through silanol groups at the external surface of the clay. Nafion-based composite membranes were prepared using as nanofiller the produced SiO2-Sep, TiO2-SiO2-Sep and ZnO@SiO2-Sep nanoarchitectures. Thermal properties, water uptake and proton conductivity of the resulting composite membranes were evaluated in comparison to those of a neat Nafion membrane to ascertain their potential usefulness for applications in PEMFC.

Photoelectrochemical Production of Hydrogen Peroxide with TiO2 and 1,5-Di(thien-2-yl)-9,10-anthraquinone via a Selective Two-Electron Oxygen Reduction Reaction in the Two-Compartment Cell

The industrial process of hydrogen peroxide (H2O2) synthesis proceeds through the hydrogenation of anthraquinone followed by successive oxidation in an organic solvent. This process is a multistep synthesis that is far away from green synthesis. An alternative photoelectrochemical (PEC) H2O2 production method requires only sunlight and water. Herein, we established the direct production of H2O2 by using a two-compartment PEC cell composed of TiO2 nanorods hydrothermally grown on fluorine-doped tin oxide as a photoanode for water oxidation and 1,5-di(thien-2-yl)-9,10-anthraquinone (AQTh) anchored carbon cloth as a cathode for the selective two-electron (2e–) reduction of oxygen. This photoanode and cathode are positioned in an anodic compartment and a cathodic compartment of a two-compartment cell, respectively. The Nafion membrane (N-117) separates these two compartments. This PEC cell continuously produces H2O2 at −0.1 VRHE applied voltage, which reaches 60 μM after 3 h. The density functional theory study is carried out to better understand the H2O2 production mechanism and the role of thiophene substituents on anthraquinone.

Multiscale Architectured Nafion Membrane Derived from Lotus Leaf for Fuel Cell Applications.

Hierarchically patterned proton-exchange membranes (PEMs) have the potential to significantly increase the specific surface area, thus improving the catalyst utilization rate and performance of proton-exchange membrane fuel cells (PEMFCs). In this study, we are inspired by the unique hierarchical structure of the lotus leaf and proposed a simple three-step strategy to prepare a multiscale structured PEM. Using the multilevel structure of the natural lotus leaf as the original template, and after structural imprinting, hot-pressing, and plasma-etching steps, we successfully constructed a multiscale structured PEM with a microscale pillar-like structure and a nanoscale needle-like structure. When applied in a fuel cell, the multiscale structured PEM resulted in a 1.96-fold increase in discharge performance and a significant improvement in mass transfer compared to the membrane electrode assembly (MEA) with a flat PEM. The multiscale structured PEM has the combined advantage of a nanoscale and a microscale structure, benefiting from the markedly reduced thickness, increased surface area, and improved water management inherited from the multiscale structured lotus leaf's superhydrophobic characteristic. Using a lotus leaf as a multilevel structure template avoids the complex and time-consuming preparation process required by commonly used multilevel structure templates. Moreover, the remarkable architecture of biological materials can inspire novel and innovative applications in many fields through nature's wisdom.

Cerium-Based Perovskite Mixed Metal Oxide as the Radical Scavenger for PEM Fuel Cells Operating under Low Humidity Conditions.

When the polymer electrolyte membrane fuel cell (PEMFC) is operated under low humidity, the proton conductivity decreases due to membrane dehydration, causing adverse effects on fuel cell performance. Introducing appropriate additives to the membrane and catalyst layer to prevent membrane degradation at low humidity brings significant performance improvements to proton exchange membrane fuel cells. We developed a perovskite-structured multi-metal oxide Ce0.667Zr0.05Ti0.95O3-δ (CZTO) with high radical scavenging properties and good structural stability. The nanostructured ceramic CZTO is introduced into the membrane and cathode catalyst layer to improve the durability of the membrane electrode assembly. The Nafion-CZTO membrane exhibited maximum power densities of 1298 and 519 mW cm-2 at 100 and 20% relative humidity, respectively. The improved performance of Nafion-CZTO membranes over commercial Nafion membranes is due to the high proton conductivity and better radical scavenging properties of the CZTO additive. In addition, the expected positive effects of applying CZTO additives to the catalyst layer are verified by low charge transfer resistance and high electrochemical surface activity of the CZTO catalyst through electrochemical impedance spectroscopy and electrochemical surface area analyses.

Mechanism of monovalent and divalent ion mobility in Nafion membrane: An atomistic simulation study.

Polymer cation exchange membranes (CEMs) are widely used in water treatment processes. The fundamental factors that control the separation and selectivity of cations with different valences in CEMs are not fully understood. In this study, we use atomistic molecular dynamics simulations to investigate the underlying molecular mechanisms that control the mobility of cations with different valences in Nafion membranes. Our results indicate structural differences in binding of monovalent and divalent cations, which gives rise to differences in ion diffusion in Nafion. Monovalent cations are shown to be "territorially" bound, i.e., bound while partially hydrated, to the fixed charge groups whereas divalent cations are shown to be "site" bound, i.e., bound while fully dehydrated, to the charge groups on the polymer. This difference in binding structure gives rise to differences in transport characteristics of cations in Nafion.

Optimizing Sustainable Energy Generation in Ethanol Fuel Cells: An Exploration of Carrageenan with TiO2 Nanoparticles and Ni/CeO2 Composites.

Based on the search for new biodegradable materials that are low cost and easy to synthesize by environmentally friendly methods, we report the use of carrageenan membranes (mixture of κ and λ carrageenans) with different concentrations of titanium dioxide nanoparticles (TiO2 NPs) and Ni/CeO2 (10 wt % Ni) for the fabrication of a novel fuel cell electrode for the oxidation of ethanol. Each membrane was characterized to determine its physicochemical properties using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. Using impedance spectroscopy (IS), a maximum value of 2.08 × 10-4 S/cm in ionic conductivity was found for the carrageenan nanocomposite with a concentration of 5 wt % TiO2 NPs (CR5%). Due to its high conductivity values, the CR5% membrane was mixed with Ni/CeO2 to prepare the working electrode for cyclic voltammetry measurements. Using a solution of 1 M ethanol and 1 M KOH, the oxidation of ethanol over CR5% + Ni/CeO2 resulted in peak current density values at forward and reverse scan voltages of 9.52 and 12.22 mA/cm2, respectively. From our results, the CR5% + Ni/CeO2 membrane proves to be more efficient in the oxidation of ethanol compared with commercially available Nafion membranes containing Ni/CeO2.

Modification of Nafion Membranes by Polycation in the Presence of Lower Alyphatic Alcohols and Salt

Modification of Nafion Membranes by Polycation in the Presence of Lower Alyphatic Alcohols and Salt

Revealing the Surface Species Evolution on Low‐loading Platinum in an Electrochemical Redox Reaction by Operando Ambient‐Pressure X‐ray Photoelectron Spectroscopy

AbstractThe stability and activity of Platinum catalysts under the redox process are the key parameters affecting catalytic performance. Here, we investigated the surface species evolution of low‐loading Pt catalyst deposited on a Nafion membrane through e‐beam deposition during redox reactions by using in situ X‐ray photoelectron spectroscopy (XPS) combined with a static electrochemical cell. Operando ambient‐pressure XPS measurement revealed the oxide species (Ptδ+, Pt2+, and Pt4+) evolution over different potentials in the water layer constructed by an acid solution. The amount of Pt2+ increased with an increment of the anodic potential, whereas Pt4+ suddenly formed when the threshold voltage of the oxygen evolution reaction was crossed. Hysteresis of Pt2+ was revealed as Pt4+ was completely reduced when returning to the open circuit potential. Incorporating depth‐profiling studies enabled us to uncover the mechanism of oxide species evolution between the surface and subsurface of the Pt catalyst during a redox reaction.

Investigating percolation and clustering effects on aquivion and nafion membranes at the molecular scale

A rationalized study about perfluoronated sulfonic acids based (PFSA) membranes is reported using molecular dynamics simulations. PFSA membranes are a wide used class of materials in proton exchange membranes as solid-electrolytes. Those materials self-organize upon hydration leading to a segregated hydrated nanostructure governing water dynamics and conduction properties. Two commercial membranes, namely Nafion and Aquivion are simulated. The impact of the chemical nature and hydration state on nanostructure and confined water dynamics are both explored. We find that the local nanostructure, depicted by the size of water domains dw and percolation state, and dynamical properties are both irrespective of the side chain length and spacing of the simulated membranes. A transition between a non-percolated water network to a percolated one is evidenced as water content increases and is strongly correlated with water dynamics properties. We find both structural and dynamics properties to be directly dependent on the water volume fraction φw. This study finally points out that the water volume fraction is a key-parameter governing structure/properties relationships in PFSA membranes.

Copper recovery from printed circuit boards leaching solution with bioelectricity generation using microbial fuel cell

Recovery of valuable metals via leaching printed circuit boards (PCBs) has gained moment recently. This work studied the Microbial fuel cell (MFC) performances for recovery of Cu from a Cu2+ solution by examining key operating parameters. A dual-chamber MFC with 6cm × 6cm × 7cm dimensions was constructed. Both anode and cathode electrodes were made of a carbon cloth sheet. The anodic and cathodic chambers were separated by a Nafion membrane. The highest Cu recovery efficiency was 99.7% after 240h batch mode operation, yielding 102 mW/m2 MFC power density output using 1g/L Cu2+ solution as the catholyte (initial pH 3) and an anolyte containing 1g/L sodium acetate inoculated with a sludge from a wastewater treatment plant's anaerobic pond, with 2cm distance between the electrodes made of polyacrylonitrile polymer. The highest open circuit voltage, current density (based on cross-section cathode area) and power density with an external load of 1 kΩ was 555mV, 347mA/m2 and 193 mW/m2, respectively. Additionally, recovery of Cu in the leachate of PCBs using sulfuric acid leaching after 48h was performed and the highest Cu recovery was 50% in 48h.

VRFBs based on benzotriazole grafted polybenzimidazole / polymeric ionic liquid with high ion selectivity

A series of innovative branching OPBI composite membranes (OPBI-BTZ-PIL) were created based on benzotriazole side chain grafted OPBI (OPBI-BTZ) and double-bond ionic liquids for vanadium redox flow battery applications. The benzotriazole contained three nitrogen sites, which helped enhance the proton conductivity and low area resistance. The cation in the polymeric ionic liquid in the matrix and the vanadium ion produces the Donnan effect, which reduces vanadium permeability. Moreover, the hydrogen bond cross-linking network formed by the polymeric ionic liquid in the membrane further helps proton transport. The vanadium permeability of OPBI-BTZ10-PIL10 is as low as 1.51 × 10−9 cm2 min−1, which is one 40th of the Nafion117 (62.54 × 10−9 cm2 min−1). Its ion selectivity is up to 2.45 × 106 S min cm−3. The OPBI-BTZ10-PIL10 membrane performs well at 60 mA cm−2, with CE of 94.12% and EE of 86.2%, both of which are higher than the Nafion117 membrane.

(Digital Presentation) Synthesis of Proton Exchange Membrane Fuel Cell Catalyst and Optimization of Membrane Electrode Assembly Preparation Parameters

The oxygen reduction catalyst was synthesized by depositing Pt nanoparticles on carbon black using ethylene glycol as a reducing agent. The synthesized catalyst material contained approximately 60 wt% of Pt, and the average Pt crystallite size was under 3 nm. The catalyst had a micro-mesoporous structure with a specific surface area of 320 m2 g−1. Electrochemical characterization was performed in H2/air fuel cell. The catalyst was deposited on the Nafion membrane or gas diffusion layer using an ultrasonic coating system. The thickness of Teflon gaskets as well as hot pressing conditions were optimized. Lowering catalyst loading on the anode did not show a decrease in electrochemical activity up to 0.05 mg cm−2. However, it was found that the cathode catalyst loading can be reduced only up to 0.60 mg cm−2.

Hydration and Mobility of Alkaline Metal Cations in Sulfonic Cation Exchange Membranes.

The interconnection of ionogenic channel structure, cation hydration, water and ionic translational mobility was revealed in Nafion and MSC membranes based on polyethylene and grafted sulfonated polystyrene. A local mobility of Li+, Na+ and Cs+ cations and water molecules was estimated via the 1H, 7Li, 23Na and 133Cs spin relaxation technique. The calculated cation and water molecule self-diffusion coefficients were compared with experimental values measured using pulsed field gradient NMR. It was shown that macroscopic mass transfer is controlled by molecule and ion motion near sulfonate groups. Lithium and sodium cations whose hydrated energy is higher than water hydrogen bond energy move together with water molecules. Cesium cations in possession of low hydrated energy are directly jumping between neighboring sulfonate groups. Cation Li+, Na+ and Cs+ hydration numbers (h) in membranes were calculated from 1H chemical shift water molecule temperature dependences. The values calculated from the Nernst-Einstein equation and the experimental conductivity values were close to each other in Nafion membranes. In MSC membranes, calculated conductivities were one order of magnitude more compared to the experimental ones, which is explained by the heterogeneity of the membrane pore and channel system.

Examination of the performance of degraded Nafion membrane with graphene oxide

The degradation of Nafion membrane easily occurs after a long run of proton exchange membrane fuel cell. Graphene-oxide (GO) is regarded as an ideal material to form composite membrane. In this work, a multistate empirical valence bond (MS-EVB) method and molecular dynamics method are employed to investigate the effect of GO on transport and solvation characteristics of protons in the degraded hydration membrane. The hydrophilic cluster and its connectivity are analyzed. The interaction between GO, Nafion membrane and water molecules is discussed. The influence of GO on the thermal conduction of Nafion membrane is also evaluated. The results demonstrate that with the addition of GO, the water cluster connectivity of Nafion membrane becomes better. The distribution of hydronium ions and membranes in the water is more uniform, which increases the proton conductivity. The larger GO may not interact well with water molecules, but promotes the thermal conductivity of degraded Nafion membrane more obviously.

Nafion: New and Old Insights into Structure and Function.

The work reports a number of results on the dynamics of swelling and inferred nanostructure of the ion-exchange polymer membrane Nafion in different aqueous solutions. The techniques used were photoluminescent and Fourier transform IR (FTIR) spectroscopy. The centers of photoluminescence were identified as the sulfonic groups localized at the ends of the perfluorovinyl ether (Teflon) groups that form the backbone of Nafion. Changes in deuterium content of water induced unexpected results revealed in the process of polymer swelling. In these experiments, deionized (DI) water (deuterium content 157 ppm) and deuterium depleted water (DDW) with deuterium content 3 PPM, were investigated. The strong hydration of sulfonic groups involves a competition between ortho- and para-magnetic forms of a water molecule. Deuterium, as it seems, adsorbs competitively on the sulfonic groups and thus can change the geometry of the sulfate bonds. With photoluminescent spectroscopy experiments, this is reflected in the unwinding of the polymer fibers into the bulk of the adjoining water on swelling. The unwound fibers do not tear off from the polymer substrate. They form a vastly extended "brush" type structure normal to the membrane surface. This may have implications for specificity of ion transport in biology, where the ubiquitous glycocalyx of cells and tissues invariably involves highly sulfated polymers such asheparan and chondroitin sulfate.

Polybenzimidazole Membranes as Nafion Replacement in Aqueous HCl Electrolyzers

We demonstrate the use of para-polybenzimidazole (PBI) membranes as replacements for Nafion membranes in aqueous HCl oxygen-depolarized electrolyzers. Both para-PBI and densified para-PBI membranes reduce the cell voltage needed at 0.5 A cm–2 by ≥100 mV. We examine the effect of HCl(aq) flow rate, back-pressure, electrolyzer temperature, and, for the densified para-PBI membranes, H3PO4 swell time on electrolyzer performance. Increased proton conductivity, measured as reduced area-specific membrane resistance, is identified as the primary mechanism to explain the improved performance of the electrolyzer.

Modification of Nafion Membrane by Polycation in the Presemce of Lower Alyphatic Alcohols and Salt

Significant increase of ion selectivity was observed for Nafion membranes modified by poly(diallyldimethylammonium chloride), PDADMAC, in the presence of lower aliphatic alcohols and NaCl. It was found that addition of the salt into the alcohol-containing modification solutions resulted not only in decrease of diffusional permeability towards vanadyl ions, P, but also in simultaneous two- to threefold growth of proton conductivity, σ, in comparison with the membranes modified in the alcohol-water solutions in the absence of a salt. As a result, ion selectivity of the membranes calculated as σ/P ratio was increased in ∼4 orders of magnitude as compared with pristine Nafion 112 membrane. Conceivable mechanism of the ion selectivity increasing is proposed for the membranes modified by PDADMAC in the presence of lower aliphatic alcohols and NaCl.