The proton conductivity and mechanical properties of Nafion®/ ZrP nanocomposite membrane

Influence of Graphene Oxide on Mechanical and Morphological Properties of Nafion® Membranes

This study explored the influence of graphene oxide (GO) on morphological and mechanical properties of Nafion® 115 membranes with the objective of enhancing the mechanical properties of the most widely employed membrane in Proton Exchange Membrane Water Electrolyzers (PEMWE) applications. The membrane surface was modified by ultrasonically spraying a GO solution and different annealing temperatures were tested. Scanning Electron Microscopy (SEM) cross-sectional images revealed that annealing the composite membranes was sufficient to favor an interaction between the graphene oxide and the surface of the Nafion® membranes. The GO covering only 35% of the membrane surface increased the composite's wettability from hydrophobic (105.2°) to a highly hydrophilic angle (84.4°) while slightly reducing membrane swelling. Tensile tests depicted an increase in both the strain levels and tensile loads before breaking. The samples with GO presented remarkable mechanical properties when the annealing time and temperature increased; while the Nafion® control samples failed at elongations of 95% and 98%, their counterparts with GO on the surface achieved elongations of 248% and 191% when annealed at 80 °C and 110 °C respectively, demonstrating that the presence of GO mechanically stabilizes the membranes under tension. In exchange, the presence of GO altered the smoothness of the membrane surface going from an average 1.4 nm before the printing to values ranging from 8.4 to 10.2 nm depending on the annealing conditions which could affect the quality of the subsequent catalyst layer printing. Overall, the polymer's electrical insulation was unaffected, making the Nafion®-GO blend a more robust material than those traditionally used.

Measurement of Water Uptake and States in Nafion Membranes Using Humidity-Controlled Terahertz Time-Domain Spectroscopy

Perfluorinated sulfonic acid ionomers are well known for their unique water uptake properties and chemical/mechanical stability. Understanding their performance-stability trade-offs is key to realizing membranes with optimal properties. Terahertz time-domain spectroscopy has been demonstrated to resolve water states inside industrially relevant membranes, producing qualitatively agreeable results to conventional gravimetric analysis and prior demonstrations. Using the proposed humidity-controlled terahertz time-domain spectroscopy, here we quantify this detailed water information inside commercially available Nafion membranes at various humidities for direct comparison against literature values from dynamic vapor sorption, differential scanning calorimetry, and Fourier transform infrared spectroscopy on selected samples. Using this technique therefore opens up opportunities for rapid future parameter space investigation for membrane optimization.

Antimicrobial coatings based on amine-terminated graphene oxide and Nafion with remarkable thermal resistance

We present a novel type of layer-by-layer (LbL) waterborne coating based on Nafion and amine-terminated graphene oxide (GO-NH2) that inhibits the growth of Escherichia coli and Staphylococcus aureus by more than 99% and this performance is not compromised upon extensive thermal annealing at 200 °C. Quartz crystal microbalance (QCM) sensorgrams allow the real time monitoring of the build-up of the LbL assemblies, a process that relies on the strong electrostatic interactions between Nafion (pH = 2.7, ζ = -54.8 mV) and GO-NH2 (pH = 2, ζ = 26.7 mV). Atomic force microscopy (AFM), contact angle and zeta potential measurements were used to characterise the multilayer assemblies. We demonstrate here that Nafion/GO-NH2 advanced coatings can offer drug-free and long-lasting solutions to microbial colonization and can withstand dry heat sterilization, without any decline in their performance.

Fabrication of pore-filling cation-exchange membrane from waste polystyrene and Spunbond Meltblown Spunbond (SMS) non-woven polypropylene fabric as the substrate

Commercial ion-exchange membranes are typically thick, possessing limited mechanical strength, and have relatively high fabrication costs. In this study, we utilize a three-layer polypropylene fabric known as Spunbond Meltblown Spunbond (SMS) as the substrate. This choice ensures that the resulting membrane exhibits high strength and low thickness. SMS substrates with various area densities, including 14.5, 15, 17, 20, 25, and 30 g/m2, were coated with different concentrations of waste polystyrene solution (ranging from 5 × 104 to 9 × 104 mg/l) before undergoing sulfonation using concentrated sulfuric acid. The physicochemical and mechanical properties of the membrane were characterized and compared with those of commercial Neosepta CMX and Nafion-117 cation-exchange membranes. Remarkably, the fabricated membrane exhibited good performance compared to commercial ones. The cation-exchange capacity (2.76 meq/g) and tensile strength (37.15 MPa) were higher, and the electrical resistance (3.603Ω) and the thickness (130 μm) were lower than the commercial membranes.

Proton transfer and regulation across chemical interfaces by small-molecule assemblies

We report on measurements and control of proton gradient across interfaces of water and dichloroethane. Such interfaces are interesting as mimics of biological membranes. We use impedance spectroscopy to quantify interfacial proton gradient and identify proton transfer modes. We quantify proton movement using reciprocal of time constant (τ-1 ) acquired from electrochemical impedance modeling. We show that proton gradient across interfaces of water/dichloroethane and τ-1 correlate with the aqueous phase pH, changing from ca. 1 s-1 at pH 1 to 0.2 s-1 at pH 7. τ-1 changes in the presence of proton shuttling fat-soluble molecules. Dinitrophenol acts as a pH activated proton coupler which is active at around neutral pH and inert at pH <4. However, quinone type cofactors change the interfacial proton transport when activated by redox reactions with ferrocene type molecules, such as decamethyl ferrocence (DMFc). Quinone type cofactors show distinct features in their impedance response assigned to a proton coupled electron transfer (PCET) process, different from the uncoupled proton transfer activity of dinitrophenol. The observed PCET reaction significantly changes τ-1 . We use τ-1 as a proton transport descriptor. In particular, CoQ10 -DMFc shows a τ-1 of 3.5 s-1 at pH 7, indicating how small-molecule assemblies change proton availability.

A highly-selective layer-by-layer membrane modified with polyethylenimine and graphene oxide for vanadium redox flow battery

A selective composite membrane for vanadium redox flow battery (VRFB) was successfully prepared by layer-by-layer (LbL) technique using a perfluorosulfonic sulfonic acid or Nafion 117 (N117). The composite membrane referred as N117-(PEI/GO)n, was obtained by depositing alternating layers of positively charged polyethylenimine (PEI) and negatively charged graphene oxide (GO) as polyelectrolytes. The physicochemical properties and performance of the pristine and composite membranes were investigated. The membrane showed an enhancement in proton conductivity and simultaneously exhibited a notable 90% reduction in vanadium permeability. This, in turn, results in a well-balanced ratio of proton conductivity to vanadium permeability, leading to high selectivity. The highest selectivity of the LbL membranes was found to be 19.2 × 104 S.min/cm3, which is 13 times higher than the N117 membrane (n = 0). This was translated into an improvement in the battery performance, with the n = 1 membrane showing a 4-6% improvement in coulombic efficiency and a 7-15% improvement in voltage efficiency at current densities ranging from 40 to 80 mA/cm2. Furthermore, the membrane displays stable operation over a long-term stability at around 88% at a current density of 40 mA/cm2, making it an attractive option for VRFB applications using the LbL technique. The use of PEI/GO bilayers maintains high proton conductivity and VE of the battery, opening up possibilities for further optimization and improvement of VRFBs.

NanoIEA: A Nanopatterned Interdigitated Electrode Array-Based Impedance Assay for Real-Time Measurement of Aligned Endothelial Cell Barrier Functions

A nanopatterned interdigitated electrode array (nanoIEA)-based impedance assay is developed for quantitative real-time measurement of aligned endothelial cell (EC) barrier functions in vitro. A bioinspired poly(3,4-dihydroxy-L-phenylalanine) (poly (l-DOPA)) coating is applied to improve the human brain EC adhesion onto the Nafion nanopatterned surfaces. It is found that a poly (l-DOPA)-coated Nafion grooved nanopattern makes the human brain ECs orient along the nanopattern direction. Aligned human brain ECs on Nafion nanopatterns exhibit increased expression of genes encoding tight and adherens junction proteins. Aligned human brain ECs also have enhanced impedance and resistance versus unaligned ones. Treatment with a glycogen synthase kinase-3 inhibitor (GSK3i) further increases impedance and resistance, suggesting synergistic effects occur on the cell-cell tightness of in vitro human brain ECs via a combination of anisotropic matrix nanotopography and GSK3i treatment. It is found that this enhanced cell-cell tightness of the combined approach is accompanied by increased expression of claudin protein. These data demonstrate that the proposed nanoIEA assay integrated with poly (l-DOPA)-coated Nafion nanopatterns and interdigitated electrode arrays can make not only biomimetic aligned ECs, but also enable real-time measurement of the enhanced barrier functions of aligned ECs via tighter cell-cell junctions.

Polyvinyl Alcohol/Nafion®-Zirconia Phosphate Nanocomposite Membranes for Polymer Electrolyte Membrane Fuel Cell Applications: Synthesis and Characterisation

PVA (polyvinyl alcohol)-ZrP (PVA/ZrP) and Nafion®/PVA-ZrP nanocomposite membranes were synthesised using the recasting method with glutaraldehyde (GA) as a crosslinking agent. The resulting nanocomposite membranes were characterised using a variety of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results of SEM revealed well-distributed zirconia phosphate (ZrP) within the membrane matrix, and the SEM images showed a uniform and dense membrane structure. Because ZrP nanoparticles are hydrophilic, the Nafion®/PVA-ZrP nanocomposite membrane had a higher water uptake of 53% at 80 °C and higher 0.19 S/cm proton conductivity at room temperature than the commercial Nafion® 117 membrane, which had only 34% and 0.113 S/cm, respectively. In comparison to commercial Nafion® 117 membranes, PVA-ZrP and Nafion®/PVA-ZrP nanocomposite membranes had a higher thermal stability and mechanical strength and lower methanol crossover due to the hydrophilic effect of PVA crosslinked with GA, which can make strong hydrogen bonds and cause an intense intramolecular interaction.

Superacid Resin-Based Heterogeneous Catalysts for the Selective Acylation of 1,2-Methylenedioxybenzene

In this work, we firstly report on the use of highly active and selective Aquivion superacid resins as heterogeneous catalysts for the acylation of 1,2-methylenedioxybenzene (MDB) with propionic anhydride (AP). The reaction was investigated and optimized using solvent-free conditions to selectively produce 3,4-methylenedioxypropiophenone (MDP1P), a key intermediate for the manufacture of active ingredients used in insecticide formulations with a volume of production of roughly 3000 t/y. Interestingly, Aquivion-based catalysts allows to work in mild reaction conditions (i. e. 80 °C), obtaining MDP1P yields as high as 44 % after only 1 h of reaction (selectivity 83 %). A detailed study of the AP reactivity demonstrated its tendency to promote oligomerization reactions that, as confirmed by ex-situ and in-situ FT-ATR analyses, caused the deactivation of the catalyst forming surficial carbonaceous residues. In this context, a fast oxidation of the resin surface organic residues using a diluted HNO3 (or H2 O2 ) solution was proven to be an efficient method to regenerate the catalyst, which can be reused for several reaction cycles. The results obtained in preliminary scale-up tests were basically unaffected by the reaction volume (up to 800 mL), paving the way for possible future applications of the process.

Suppression of Methanol and Formate Crossover through Sulfanilic-Functionalized Holey Graphene as Proton Exchange Membranes

Proton exchange membranes with high proton conductivity and low crossover of fuel molecules are required to realize advanced fuel-cell technology. The selective transportation of protons, which occurs by blocking the transportation of fuel molecules across a proton exchange membrane, is crucial to suppress crossover while maintaining a high proton conductivity. In this study, a simple yet powerful method is proposed for optimizing the crossover-conductivity relationship by pasting sulfanilic-functionalized holey graphenes onto a Nafion membrane. The results show that the sulfanilic-functionalized holey graphenes supported by the membrane suppresses the crossover by 89% in methanol and 80% in formate compared with that in the self-assembled Nafion membrane; an ≈60% reduction is observed in the proton conductivity. This method exhibits the potential for application in advanced fuel cells that use methanol and formic acid as chemical fuels to achieve high energy efficiency.

Accumulation of Liquid Byproducts in an Electrolyte as a Critical Factor That Compromises Long-Term Functionality of CO2-to-C2H4 Electrolysis

Electrochemical conversion of CO2 using Cu-based gas diffusion electrodes opens the way to green chemical production as an alternative to thermocatalytic processes and a storage solution for intermittent renewable electricity. However, diverse challenges, including short lifetimes, currently inhibit their industrial usage. Among well-studied determinants such as catalyst characteristics and electrode architecture, possible effects of byproduct accumulation in the electrolyte as an operational factor have not been elucidated. This work quantifies the influence of ethanol, n-propanol, and formate accumulation on selectivity, stability, and cell potential in a CO2-to-C2H4 electrolyzer. Alcohols accelerated flooding by degrading the hydrophobic electrode characteristics, undermining selective and stable ethylene formation. Furthermore, high alcohol concentrations triggered the catalyst layer's abrasion and structural disfigurements in the Nafion 117 membrane, leading to high cell potentials. Therefore, continuous removal of alcohols from the electrolyte medium or substantial modifications in the cell components must be considered to ensure long-term performing CO2-to-C2H4 electrolyzers.

Gadolinium doped zinc ferrite nanoarchitecture reinforced with a carbonaceous matrix: a novel hybrid material for next-generation flexible capacitors

Herein, nanostructured Gd-doped ZnFe2O4 (GZFO) has been synthesized via the sol-gel route and its CNT-reinforced nanohybrid was formed via an advanced ultrasonication method. The as-synthesized, hybrid electroactive materials have been supported on aluminum foil (AF) to design a flexible electrode for hybrid capacitor (HC) applications. Nanostructured material synthesis, Gd-doping, and CNT reinforcement approaches have been adopted to develop a rationally designed electrode with a high surface area, boosted electrical conductivity, and enhanced specific capacitance. Electrochemical impedance spectroscopy, galvanostatic charge/discharge, and cyclic voltammetry processes have been used to measure the electrochemical performance of the prepared ferrite material-based working electrodes in a 3M KOH solution. A nanohybrid-based working electrode (GZFO/C@AF) shows superior rate capacitive and electrochemical aptitude (specific capacitance, rate performance, and cyclic activity) than its counterpart working electrodes (ZFO@AF and GZFO@AF). The hybrid working electrode (GZFO/C@AF electrode) shows a high specific capacitance of 887 F g-1 and good retention of 94.5% for 7000 cycles (at 15 Ag-1). The maximum energy density and power density values for the GZFO/C@AF electrode are 40.025 Wh Kg-1 and 279.78 W Kg-1, respectively. Based on the findings of the electrochemical experiments, GZFO/C@AF shows promise as an electrode material for hybrid capacitors that provide energy to wearable electronic devices.

Electrostatically driven unidirectional molecular flux for high performance alkaline flow batteries

To mitigate the mismatch between energy availability and energy demand due to day/night shifts and seasonal variations, intensive efforts have been dedicated to storing renewable energy in various energy storage modules. Redox flow batteries have an upper hand over conventional batteries as energy storage modules due to their capability of decoupling energy and power. However, interfacial events, such as mass transport and electron transfer, play pivotal roles in flow batteries' energy storage and conversion mechanisms. We show that by activating electrostatic forces at the interface, unidirectional molecular flux can be achieved to and from the driving electrode surface, thereby generating a parallel or antiparallel electrostatic current along with a diffusion current. This approach of triggering electrostatic forces in flow batteries enhances their volumetric energy density and amplifies the energy efficiency to values as high as ∼92% without altering the solubility limit of the redox active species.

Approaches to the Modification of Perfluorosulfonic Acid Membranes

Polymer ion-exchange membranes are featured in a variety of modern technologies including separation, concentration and purification of gases and liquids, chemical and electrochemical synthesis, and hydrogen power generation. In addition to transport properties, the strength, elasticity, and chemical stability of such materials are important characteristics for practical applications. Perfluorosulfonic acid (PFSA) membranes are characterized by an optimal combination of these properties. Today, one of the most well-known practical applications of PFSA membranes is the development of fuel cells. Some disadvantages of PFSA membranes, such as low conductivity at low humidity and high temperature limit their application. The approaches to optimization of properties are modification of commercial PFSA membranes and polymers by incorporation of different additive or pretreatment. This review summarizes the approaches to their modification, which will allow the creation of materials with a different set of functional properties, differing in ion transport (first of all proton conductivity) and selectivity, based on commercially available samples. These approaches include the use of different treatment techniques as well as the creation of hybrid materials containing dopant nanoparticles. Modification of the intrapore space of the membrane was shown to be a way of targeting the key functional properties of the membranes.

Modification of the Physical Properties of a Nafion Film Due to Inclusion of n-Dodecyltriethylammonium Cation: Time Effect

This study investigates the effects of modifying commercial Nafion-212 thin films with dodecyltriethylammonium cation (DTA+) on their electrical resistance, elastic modulus, light transmission/reflection and photoluminescence properties. The films were modified through a proton/cation exchange process for immersion periods ranging from 1 to 40 h. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the crystal structure and surface composition of the modified films. The electrical resistance and the different resistive contributions were determined via impedance spectroscopy. Changes in the elastic modulus were evaluated using stress-strain curves. Additionally, optical characterization tests, including light/reflection (250-2000 nm) and photoluminescence spectra, were also performed on both unmodified and DTA⁺-modified Nafion films. The results reveal significant changes in the electrical, mechanical and optical properties of the films, depending on the exchange process time. In particular, the inclusion of the DTA⁺ into the Nafion structure improved the elastic behavior of the films by significantly decreasing the Young modulus. Furthermore, the photoluminescence of the Nafion films was also enhanced. These findings can be used to optimize the exchange process time to achieve specific desired properties.

Role of Defects of Carbon Nanomaterials in the Detection of Ovarian Cancer Cells in Label-Free Electrochemical Immunosensors

Developing label-free immunosensors to detect ovarian cancer (OC) by cancer antigen (CA125) is essential to improving diagnosis and protecting women from life-threatening diseases. Four types of carbon nanomaterials, such as multi-wall carbon nanotubes (MWCNTs), vapor-grown carbon fiber (VGCFs), graphite KS4, and carbon black super P (SP), have been treated with acids to prepare a carbon nanomaterial/gold (Au) nanocomposite. The AuNPs@carbon nanocomposite was electrochemically deposited on a glassy carbon electrode (GCE) to serve as a substrate to fabricate a label-free immunosensor for the detection of CA125. Among the four AuNPs@carbon composite, the AuNPs@MWCNTs-based sensor exhibited a high sensitivity of 0.001 µg/mL for the biomarker CA125 through the square wave voltammetry (SWV) technique. The high conductivity and surface area of MWCNTs supported the immobilization of AuNPs. Moreover, the carboxylic (COO-) functional groups in MWCNT improved to a higher quantity after the acid treatment, which served as an excellent support for the fabrication of electrochemical biosensors. The present method aims to explore an environmentally friendly synthesis of a layer-by-layer (LBL) assembly of AuNPs@carbon nanomaterials electrochemical immunoassay to CA125 in a clinical diagnosis at a low cost and proved feasible for point-of-care diagnosis.

Prospects of Polymeric Nanocomposite Membranes for Water Purification and Scalability and their Health and Environmental Impacts: A Review

Water shortage is a major worldwide issue. Filtration using genuine polymeric membranes demonstrates excellent pollutant separation capabilities; however, polymeric membranes have restricted uses. Nanocomposite membranes, which are produced by integrating nanofillers into polymeric membrane matrices, may increase filtration. Carbon-based nanoparticles and metal/metal oxide nanoparticles have received the greatest attention. We evaluate the antifouling and permeability performance of nanocomposite membranes and their physical and chemical characteristics and compare nanocomposite membranes to bare membranes. Because of the antibacterial characteristics of nanoparticles and the decreased roughness of the membrane, nanocomposite membranes often have greater antifouling properties. They also have better permeability because of the increased porosity and narrower pore size distribution caused by nanofillers. The concentration of nanofillers affects membrane performance, and the appropriate concentration is determined by both the nanoparticles' characteristics and the membrane's composition. Higher nanofiller concentrations than the recommended value result in deficient performance owing to nanoparticle aggregation. Despite substantial studies into nanocomposite membrane manufacturing, most past efforts have been restricted to the laboratory scale, and the long-term membrane durability after nanofiller leakage has not been thoroughly examined.

Fluoropolymers and Their Nanohybrids As Energy Materials: Application to Fuel Cells and Energy Harvesting

The current review article provides deep insight into the fluoropolymers and their applications in energy technology, especially in the field of energy harvesting and the development of fuel cell electrolyte polymeric membranes. Fluoropolymers have gained wide attention in the field of energy applications due to their versatile properties. The incorporation of nanofillers within the fluoropolymer to develop the nanohybrid results in an enhancement in the properties, like thermal, mechanical, gas permeation, different fuel cross-over phenomena through the membrane, hydrophilic/hydrophobic nature, ion transport, and piezo-electric properties for fabricating energy devices. The properties of nanohybrid materials/membranes are influenced by several factors, such as type of filler, their size, amount of filler, level of dispersion, surface acidity, shape, and formation of networking within the polymer matrix. Fluoropolymer-based nanohybrids have replaced several commercial materials due to their chemical inertness, better efficacy, and durability. The addition of certain electroactive fillers in the polymer matrix enhances the polar phase, which enhances the applicability of the hybrid for fuel cell and energy-harvesting applications. Poly(vinylidene fluoride) is one of the remarkable fluoropolymers in the field of energy applications such as fuel cell and piezoelectric energy harvesting. In the present review, a detailed discussion of the different kinds of nanofillers and their role in energy harvesting and fuel cell electrolyte membranes is projected.

A State-of-Art on the Development of Nafion-Based Membrane for Performance Improvement in Direct Methanol Fuel Cells

Nafion, a perfluorosulfonic acid proton exchange membrane (PEM), has been widely used in direct methanol fuel cells (DMFCs) to serve as a proton carrier, methanol barrier, and separator for the anode and cathode. A significant drawback of Nafion in DMFC applications is the high anode-to-cathode methanol fuel permeability that results in over 40% fuel waste. Therefore, the development of a new membrane with lower permeability while retaining the high proton conductivity and other inherent properties of Nafion is greatly desired. In light of these considerations, this paper discusses the research findings on developing Nafion-based membranes for DMFC. Several aspects of the DMFC membrane are also presented, including functional requirements, transport mechanisms, and preparation strategies. More importantly, the effect of the various modification approaches on the performance of the Nafion membrane is highlighted. These include the incorporation of inorganic fillers, carbon nanomaterials, ionic liquids, polymers, or other techniques. The feasibility of these membranes for DMFC applications is discussed critically in terms of transport phenomena-related characteristics such as proton conductivity and methanol permeability. Moreover, the current challenges and future prospects of Nafion-based membranes for DMFC are presented. This paper will serve as a resource for the DMFC research community, with the goal of improving the cost-effectiveness and performance of DMFC membranes.

Hybrid composite of Nafion with surface-modified electrospun polybenzoxazine (PBz) fibers via ozonation as fillers for proton conducting membranes of fuel cells

Nafion was investigated for its compatibility in the preparation of hybrid composites with electrospun Polybenzoxazine (PBz) surface-modified fibers by evaluating the effects on the surface and structure of the composite. A PBz fiber mat was first crosslinked by thermal treatment after electrospinning to enhance the mechanical integrity of the fibers prior to modification. Further surface modification via free radical ozonation was carried out by potentiating oxygen-based functional groups of hydroxyl radicals (-OH) onto fibers' exposed surfaces. The sequential modifications by crosslinking and ozone treatment were evaluated by analyzing surface properties using XPS, ATR-FTIR and water contact angle which determined the enhanced properties of the fibers that were beneficial to the target functionality. Electron spectroscopy confirmed that fibers' surfaces were changed with the new surface chemistry without altering the chemical structure of PBz. The presence of higher oxygen-based functional groups on fibers' surfaces based on the resulting atomic compositions was correlated with the change in surface wettability by becoming hydrophilic with contact angle ranging from 21.27° to 59.83° compared to hydrophobic pristine PBz fibers. This is due to electrophilic aromatic substitution with hydroxyl groups present on the surfaces of the fibers endowed by ozonation. The resulting surface-modified fiber mat was used for the preparation of composites by varying two process parameters, the amount of Nafion dispersion and its homogenization and curing time, which was evaluated for compatibility and interaction as fillers to form hybrid composites. The analyses of SEM images revealed the effects of shorter homogenization and curing time on composites with rougher and wrinkled surfaces shown on the final hybrid composite's structure while decreasing the amount of Nafion at the same homogenization time but longer curing time showed its influence on improvement of compatibility and surface morphology.

Preparation of Zirconium Hydrogen Phosphate Coatings on Sandblasted/Acid-Etched Titanium for Enhancing Its Osteoinductivity and Friction/Corrosion Resistance

Background

Sandblasted/acid-etched titanium (SLA-Ti) implants are widely used for dental implant restoration in edentulous patients. However, the poor osteoinductivity and the large amount of Ti particles/ions released due to friction or corrosion will affect its long-term success rate.

Purpose

Various zirconium hydrogen phosphate (ZrP) coatings were prepared on SLA-Ti surface to enhance its friction/corrosion resistance and osteoinduction.

Methods

The mixture of ZrCl₄ and H₃PO₄ was first coated on SLA-Ti and then calcined at 450°C for 5 min to form ZrP coatings. In addition to a series of physiochemical characterization such as morphology, roughness, wettability, and chemical composition, their capability of anti-friction and anti-corrosion were further evaluated by friction-wear test and by potential scanning. The viability and osteogenic differentiation of MC3T3-E1 cells on different substrates were investigated via MTT, mineralization and PCR assays.

Results

The characterization results showed that there were no significant changes in the morphology, roughness and wettability of ZrP-modified samples (SLA-ZrP0.5 and SLA-ZrP0.7) compared with SLA group. The results of electrochemical corrosion displayed that both SLA-ZrP0.5 and SLA-ZrP0.7 (especially the latter) had better corrosion resistance than SLA in normal saline and serum-containing medium. SLA-ZrP0.7 also exhibited the best friction resistance and great potential to enhance the spreading, proliferation and osteogenic differentiation of MC3T3-E1 cells.

Conclusion

We determined that SLA-ZrP0.7 had excellent comprehensive properties including anti-corrosion, anti-friction and osteoinduction, which made it have a promising clinical application in dental implant restoration.

The Effect of Sulfated Zirconia and Zirconium Phosphate Nanocomposite Membranes on Fuel-Cell Efficiency

To investigate the effect of acidic nanoparticles on proton conductivity, permeability, and fuel-cell performance, a commercial Nafion^® 117 membrane was impregnated with zirconium phosphates (ZrP) and sulfated zirconium (S-ZrO₂) nanoparticles. As they are more stable than other solid superacids, sulfated metal oxides have been the subject of intensive research. Meanwhile, hydrophilic, proton-conducting inorganic acids such as zirconium phosphate (ZrP) have been used to modify the Nafion^® membrane due to their hydrophilic nature, proton-conducting material, very low toxicity, low cost, and stability in a hydrogen/oxygen atmosphere. A tensile test, water uptake, methanol crossover, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM) were used to assess the capacity of nanocomposite membranes to function in a fuel cell. The modified Nafion^® membrane had a higher water uptake and a lower water content angle than the commercial Nafion^® 117 membrane, indicating that it has a greater impact on conductivity. Under strain rates of 40, 30, and 20 mm/min, the nanocomposite membranes demonstrated more stable thermal deterioration and higher mechanical strength, which offers tremendous promise for fuel-cell applications. When compared to 0.113 S/cm and 0.013 S/cm, respectively, of commercial Nafion^® 117 and Nafion^® ZrP membranes, the modified Nafion^® membrane with ammonia sulphate acid had the highest proton conductivity of 7.891 S/cm. When tested using a direct single-cell methanol fuel cell, it also had the highest power density of 183 mW cm^-2 which is better than commercial Nafion^® 117 and Nafion^® ZrP membranes.

Organic-Inorganic Novel Green Cation Exchange Membranes for Direct Methanol Fuel Cells

Commercializing direct methanol fuel cells (DMFC) demands cost-effective cation exchange membranes. Herein, a polymeric blend is prepared from low-cost and eco-friendly polymers (i.e., iota carrageenan (IC) and polyvinyl alcohol (PVA)). Zirconium phosphate (ZrPO4) was prepared from the impregnation–calcination method and characterized by energy dispersive X-ray analysis (EDX map), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM), then incorporated as a bonding and doping agent into the polymer blend with different concentrations. The new fabricated membranes were characterized by SEM, FTIR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and XRD. The results revealed that the membranes’ physicochemical properties (oxidative stability, tensile strength) are enhanced with increasing doping addition, and they realized higher results than Nafion 117 because of increasing numbers of hydrogen bonds fabricated between the polymers and zirconium phosphate. Additionally, the methanol permeability was decreased in the membranes with increasing zirconium phosphate content. The optimum membrane with IC/SPVA/ZrPO4-7.5 provided higher selectivity than Nafion 117. Therefore, it can be an effective cation exchange membrane for DMFCs applications.

Potential carbon nanomaterials as additives for state-of-the-art Nafion electrolyte in proton-exchange membrane fuel cells: a concise review

Proton-exchange membrane fuel cells (PEMFCs) have received great attention as a potential alternative energy device for internal combustion engines due to their high conversion efficiency compared to other fuel cells. The main hindrance for the wide commercial adoption of PEMFCs is the high cost, low proton conductivity, and high fuel permeability of the state-of-the-art Nafion membrane. Typically, to improve the Nafion membrane, a wide range of strategies have been developed, in which efforts on the incorporation of carbon nanomaterial (CN)-based fillers are highly imperative. Even though many research endeavors have been achieved in relation to CN-based fillers applicable for Nafion, still their collective summary has rarely been reported. This review aims to outline the mechanisms involved in proton conduction in proton-exchange membranes (PEMs) and the significant requirements of PEMs for PEMFCs. This review also emphasizes the improvements achieved in the proton conductivity, fuel barrier properties, and PEMFC performance of Nafion membranes by incorporating carbon nanotubes, graphene oxide, and fullerene as additives.

Polyoxadiazoles as proton exchange membranes for fuel cell application

The number of researches on the ion exchange membrane has increased considerably in recent years showing interest in fuel cell technology for the automobile and portable applications. The most promising fuel cell technology for low-temperature operation (80 °C < T < 150 °C) uses a polymer membrane separating the anode and cathode compartments in an electrochemical cell. Polyoxadiazoles (PODs) belong to a class of heterocyclic polymers, which possess a number of unique properties, such as thermal, mechanical, and chemical resistance. In the present review, numerous ways of POD synthesis are discussed in relation to their functional properties. In addition, different approaches to the elaboration of POD-based composite membranes are discussed in details in order to reveal the structure/properties relationship.

On the Conductivity of Proton-Exchange Membranes Based on Multiblock Copolymers of Sulfonated Polysulfone and Polyphenylsulfone: An Experimental and Modeling Study

The effect of relative humidity (RH) and degree of sulfonation (DS) on the ionic conductivity and water uptake of proton-exchange membranes based on sulfonated multiblock copolymers composed of polysulfone (PSU) and polyphenylsulfone (PPSU) is examined experimentally and numerically. Three membranes with a different DS and ion-exchange capacity are analyzed. The heterogeneous structure of the membranes shows a random distribution of sulfonated (hydrophilic) and non-sulfonated (hydrophobic) domains, whose proton conductivity is modeled based on percolation theory. The mesoscopic model solves simplified Nernst-Planck and charge conservation equations on a random cubic network. Good agreement is found between the measured ionic conductivity and water uptake and the model predictions. The ionic conductivity increases with RH due to both the growth of the hydrated volume available for conduction and the decrease of the tortuosity of ionic transport pathways. Moreover, the results show that the ionic conductivity increases nonlinearly with DS, experiencing a strong rise when the DS is varied from 0.45 to 0.70, even though the water uptake of the membranes remains nearly the same. In contrast, the increase of the ionic conductivity between DS=0.70 and DS=0.79 is significantly lower, but the water uptake increases sharply. This is explained by the lack of microphase separation of both copolymer blocks when the DS is exceedingly high. Encouragingly, the copolymer membranes demonstrate a similar performance to Nafion under well hydrated conditions, which can be further optimized by a combination of numerical modeling and experimental characterization to develop new-generation membranes with better properties.