Nafion Film Research Articles

Woltamperometric determination of copheine on electrode modified by Nafion film and mixed valent iridium oxides in energy beverages

Abstract. It was found that mixed valent iridium oxides electrodeposited on the surface of a glass-carbon electrode exhibit catalytic activity in the oxidation of caffeine. A more pronounced catalytic effect was obtained on the electrode modified with a composite based on a film of perfluorinated sulfonated polymer (Nafion) and mixed valent iridium oxides. A selective voltammetric method for the determination of caffeine was developed. A linear logarithmic dependence of current on caffeine concentration was observed in the range from 1×10–8 to 5×10–3 M. The developed method was used in the determination of caffeine in energy drinks.

Development of Mesoporous Carbon Fibers As Catalyst Supports for PEFC

Introduction Polymer electrolyte fuel cells (PEFCs) have being considered for adaptation to heavy duty vehicles, and the optimization of catalyst layers is essential for further improvement of IV performance. Recently, mesoporous carbon (MC) supports have been used in second-generation MIRAI and have attracted much attention owing to several advantages, such as reducing the direct contact between Pt particles and Nafion ionomer and suppressing Pt particle growth. Our laboratory is currently developing mesoporous carbon fibers (MCF), which are fibers containing mesopores. For the purpose of controlling both nano- and macrostructures, MCF sheet electrodes were investigated. In this study, the effect of structures of MCF sheet on IV performance was investigated by developing membrane electrode assemblies (MEAs) with MCF sheet electrodes. Experimental MCF sheet was synthesized by an electrospinning method. The precursor solution was prepared by mixing and stirring Pluronic F127, phloroglucinol dehydrate, formaldehyde, and trimethyl orthoacetate in acidic water/ethanol, followed by addition of polyvinyl alcohol (PVA) according to our previous study1. Fiber sheet was prepared by electrospinning the precursor solution and by heating in the air to complete polymerization of precursors. Then, the sheet was cut into 2 cm x 2 cm pieces. Those pieces were sandwiched between two pieces of quartz plate and heat treated stepwise under a nitrogen atmosphere in order to finally obtain MCF sheet electrodes. Material characterization of MCF sheet electrodes was done by nitrogen adsorption measurements and SEM observations. For applying the cathode of MEAs, MCF sheet electrodes were first cut into a 1 cm x 1 cm piece. Pt was deposited by using Pt(acac)2 as a precursor, and then the Pt loading process was repeated until the required amount of Pt was loaded. Then, Nafion was introduced by spraying Nafion solution.To fabricate a MEA, first, 0.3 mgPt/cm2 of 46.3% Pt/KB (TEC10E50E) was spray printed on Nafion 212 membrane within the area of 1 cm x 1 cm as the anode side. On the cathode side of the Nafion membrane, 0.03 mgPt/cm2, 1/10 of the amount used in the anode, was spray printed as a contact layer. Here, the contact layer was used to suppress the contact resistance between the Nafion film and the MCF sheet. The Pt/MCF sheet was then placed on the cathode side and hot pressed together with the GDL to complete our cathode. Resulting MEA was evaluated electrochemically. Results and Discussion MCF sheet electrodes with different pore diameters were prepared by varying the amounts of ethanol, pure water, and PVA in the precursor solution and named as A and B. In comparison to MCF sheet A, MCF sheet B was made under slightly lower concentration of precursors. An SEM image of MCF sheet B is shown in Figure 1 showing the fiber structure. For the characterization of pore structures, nitrogen sorption measurements were performed. MCF sheet B showed a shift toward smaller pore size distribution and a decrease in pore volume as compared to MCF sheet A.MEAs were fabricated using prepared Pt/MCF sheet electrodes as cathodes, and their IV performance was evaluated. In the low current density region, IV performance was improved when MCF sheet B was used. This result suggests that structures of MCF sheet influence on IV performance.

Molecularly Imprinted Nanoparticle‐Based polymer (Acrylamide‐N‐Vinyl imidazol)/Nafion Film Modified Screen‐Printed Electrode System for Rapid Determination of Hemoglobin

In medical diagnostics, variations in hemoglobin levels can reveal a variety of prevalent health conditions. Abnormal hemoglobin is known to be connected with diseases like anemia, diabetes, hematemesis, hematuria, and hemoglobinuria. Consequently, there is a significant demand for advanced detection technologies and precise methodologies to accurately track and assess hemoglobin levels. This study demonstrates the potential of a novel molecularly imprinted nanoparticle‐based sensor system to rapidly analyze hemoglobin levels without the need for a laboratory environment. Hemoglobin imprinted‐poly(acrylamide‐ <i>co</i>‐vinyl imidazole) [Hb‐imp‐p(AAm‐ <i>co</i>‐VIM)] nanoparticles with high affinity and selectivity for hemoglobin were synthesized and loaded onto the

Unraveling the Intrinsic Thermal Behavior of Freestanding Ionomer Films Depending on Thickness from Commercial Membrane to Nanofilm.

Proton exchange membrane fuel cells (PEMFCs) for automotive applications are required to achieve mechanical reliability at various temperatures ranging from subfreezing to 80 °C. The thermal behavior of the electrode should be considered at the initial design stage to design a robust automotive fuel cell electrode. Recently, a behavior different from that of the bulk state has been reported for ionomers with a few nanometers of thickness. Therefore, the intrinsic thermal behavior of ionomer films with thicknesses from micrometers to nanometers is quantitatively investigated in this study. By introducing the fabrication of a pseudo-freestanding Nafion thin film and in-plane thermal strain measurement method on the water surface, the thermal expansion of the freestanding Nafion thin film was successfully measured with minimizing substrate constraints. Thermal strain measurement and X-ray scattering studies revealed that the weakening of intermolecular interaction within the hydrophobic and hydrophilic domains in the Nafion thin film caused thermal expansion, and well-structured hydrophobic domains could suppress thermal expansion. The thermal expansion behavior with different heat treatments provides evidence of the thin-film-to-bulk transition of the fully hydrated Nafion film. Intrinsic thermal behavior without substrate interactions can facilitate an understanding of the thermal behavior of electrodes and provide insight into designing a robust PEMFC in temperature-varying environments.

Enhanced electromechanical performance of Nafion actuator doped by poly(ethylene glycol)‐grafted graphene oxide

AbstractCurrent ionic polymer–metal composite (IPMC) actuators have severe actuation drawbacks (i.e. low force output and poor stability), hampering their applications. To address these issues, poly(ethylene glycol)‐grafted graphene oxide (PEG‐GO) is synthesized and incorporated into a Nafion matrix, thus producing a PEG‐GO hybrid Nafion film with better physiochemical properties for fabricating a high‐performance, low‐cost IPMC actuator. The modification of PEG to GO not only prevents GO agglomeration and sedimentation, but also avoids loss of PEG in water. Driven by a 0.2 Hz, 2.5 V electric field, the hybrid IPMC actuator exhibits superior electromechanical behaviors, i.e. a swing angle of 110.3°, a blocking force of 6.89 mN and a stable working time of 485 s, respectively increasing by 92%, 209% and 294% when compared to a pure Nafion actuator. © 2024 Society of Chemical Industry.

Effect of pH on the Selectivity of γ‐MnO2 Electrocatalysts towards Oxygen Evolution Reaction in the Presence of Chloride Ions in Alkaline Environment

AbstractIn this manuscript, we explore the effect of pH on the selectivity of a hydrothermally synthesized nanostructured γ‐MnO2 electrocatalyst in the alkaline environment. Selectivity of electrodeposited γ‐MnO2 toward oxygen evolution reaction (OER) in 0.5 M NaCl at pH 12 has been demonstrated by Fujimura et al (Mat. Sci. Eng., A267 (1999) 254–259). Herein, we extend the pH region from pH 8.2 to pH 13 and demonstrate by thin‐film rotating disk electrode (RDE) method that the catalyst is selective toward the OER at current densities up to ca 15 mA/cm2 in the entire range of pH, if buffer is utilized to mitigate the effect of local pH. In synthetic seawater, at pH 8.2, the catalyst is not selective toward the OER. The analysis of the OER Tafel slopes at low current densities (<3 mA/cm2) shows that the slopes were not affected by pH in 0.5 M NaCl solutions, which suggests the same OER mechanism. At the same time, reaction rate decreased with decrease in pH. Nafion ionomer in the catalyst layer may adversely affect the catalyst's performance at pH ≤12 by limiting diffusion of OH− ions through the Nafion film. Catalyst layers need to be carefully designed to avoid negative effects of Nafion.

Hydraulic permeation-induced water concentration gradients in ion exchange membranes

Although substantial literature has detailed transport through swollen membranes, there are still conflicting reports regarding the fundamental physics of hydraulic water transport in such materials, with a long-standing debate centered on the applicability of the pore-flow and solution-diffusion mechanisms. The critical thermodynamic distinction between these models is the presence of a membrane-phase concentration gradient. For pure solvent transport, the pore-flow model presumes that a membrane-phase pressure gradient drives transport in the absence of a concentration gradient. In contrast, the solution-diffusion model proposes that a membrane-phase concentration gradient drives transport and that there is a negligible pressure gradient through the membrane. To address this topic for ion exchange membranes, this study reports measurements of water concentration profiles in pressurized films of Nafion and a commercial membrane based on sulfonated poly (styrene-co-divinylbenzene). Several films were stacked together in a custom-built permeation cell, with the feed side pressurized to between 68.9 and 137.9 bar, and the permeate side held at atmospheric conditions. At steady state, the experiment was stopped, the films were separated, and the water content of each film was measured, revealing a water concentration gradient through the stack thickness that increased with increasing feed pressure. The experimental data were in good agreement with theoretical predictions based on Fick's law and polymer-solvent swelling theories (i.e., Flory-Huggins and Flory-Rehner). These results are consistent with the solution-diffusion model and cannot be explained by a pore-flow mechanism.

High-response humidity sensor based on silicon microbridge with edge-constrained sandwich sensing structure

Silicon microbridge structures have attracted the attention of researchers in humidity sensing area owing to their small size and ease of integration with the integrated circuit (IC). However, the preparation of silicon microbridge humidity sensors with high response are still a challenge. This paper proposed a silicon microbridge humidity sensor based on an edge-constrained sandwich sensing structure, in which a graphene oxide core layer with small area was covered on the surface of the silicon bridge by a larger area of Nafion film. Due to the constraint of the peripheral edge, the swelling deformations of this sandwich structure in the vertical direction were effectively magnified during humidity detection. Hence, the proposed humidity sensor exhibited a higher humidity sensitivity (109.97 µV/%RH) compared to the silicon microbridge sensors with general sandwich sensing structure or monolayer sensing film. Meanwhile, the novel sensor also demonstrated a small humidity hysteresis and good linearity in humidity range of 11.3–97.3%.

Electrochemiluminescence aptasensing method for ultrasensitive determination of lipopolysaccharide based on CRISPR-Cas12a accessory cleavage activity

In this study, an ultrasensitive electrochemiluminescence (ECL) aptasensing method was developed for lipopolysaccharide (LPS) determination based on CRISPR-Cas12a accessory cleavage activity. Tris (2,2'-bipyridine) dichlororuthenium (II) (Ru(bpy)32+) was adsorbed on the surface of a glassy carbon electrode (GCE) coated with a mixture of gold nanoparticles (AuNPs) and Nafion film via electrostatic interaction. The obtained ECL platform (Ru(bpy)32+/AuNP/Nafion/GCE) exhibited strong ECL emission. Thiol-functionalized single-stranded DNA (ssDNA) was modified with a ferrocenyl (Fc) group and autonomously assembled on the ECL platform of Ru(bpy)32+/AuNP/Nafion/GCE via thiol-gold bonding, resulting in the quenching of ECL emission. After hybridization of the LPS aptamer strand (AS) with its partial complementary strand (CS), the formed double-stranded DNA (dsDNA) could activate CRISPR-Cas12a to indiscriminately cleave ssDNA-Fc on the surface of Ru(bpy)32+/AuNP/Nafion/GCE, resulting in recovery of the ECL intensity of Ru(bpy)32+ due to the increasing distance between Fc and the electrode surface. The combination of LPS and AS suppressed the formation of dsDNA, inhibited the activation of CRISPR-Cas12a, and prevented further cleavage of ssDNA-Fc. This mechanism aided in upholding the integrity of ssDNA-Fc on the surface of the electrode and was combined with ECL quenching induced by the target. The ECL intensity decreased linearly as the concentration of LPS increased from 1 to 50,000 pg/mL and followed a logarithmic relationship. This method exhibited a remarkably low detection limit of 0.24 pg/mL, which meets the requirement for low-concentration detection of LPS in the human body. The proposed method demonstrates the capacity of CRISPR-Cas12a to perform non-specific cutting of single-stranded DNA and transform the resultant cutting substances into changes in the ECL signal. By amalgamating this approach with the distinct identification abilities of LPS and its aptamers, a simple, responsive, and discriminatory LPS assay was established that holds immense significance for clinical diagnosis.

Nafion-Immobilized Functionalized MWCNT-based Electrochemical Immunosensor for Aflatoxin B1 Detection.

The ubiquitous aflatoxin B1 (AFB1) contamination in foods and other complex matrices has brought great challenges for onsite monitoring. In this study, an ultrasensitive Nafion-immobilized functionalized multiwalled carbon nanotube (MWCNT)-based electrochemical (EC) immunosensor was developed for trace AFB1 detection. The introduced Nafion film could steadily stabilize functionalized MWCNTs with uniform distribution and tiling on the surface of a Au electrode. Functionalized MWCNTs with a large specific surface area, numerous active sites to couple with abundant anti-AFB1 monoclonal antibodies (mAbs), and high conductivity served as the signal amplifier for remarkably enhancing the sensing performance of the immunosensor. In the presence of AFB1, it was specifically captured by mAbs to reduce the amplified current signals, which were recorded by differential pulse voltammetry for the accurate quantitation of AFB1. Because of the synergistic effects of Nafion on the stabilization of functionalized MWCNTs as signal enhancers, the developed EC immunosensor exhibited an extremely high selectivity, excellent sensitivity with a limit of detection as low as 0.021 ng/mL, and a wide dynamic range of 0.05-100 ng/mL, besides fascinating merits of easy construction, low cost, good stability in 7 days, and good reusability. The anti-interference ability of the immunosensor was verified against three other mycotoxins, and the practicability and accuracy were confirmed by measuring AFB1 in fortified malt, lotus seed, and hirudo samples with a satisfactory recovery of 92.08-104.62%. This novel immunosensing platform could be extended to detect more mycotoxins in complex matrices to ensure food safety.

Ultra-thin proton conducting carrier layers for scalable integration of atomically thin 2D materials with proton exchange polymers for next-generation PEMs.

Scalable approaches for synthesis and integration of proton selective atomically thin 2D materials with proton conducting polymers can enable next-generation proton exchange membranes (PEMs) with minimal crossover of reactants or undesired species while maintaining adequately high proton conductance for practical applications. Here, we systematically investigate facile and scalable approaches to interface monolayer graphene synthesized via scalable chemical vapor deposition (CVD) on Cu foil with the most widely used proton exchange polymer Nafion 211 (N211, ∼25 μm thick film) via (i) spin-coating a ∼700 nm thin Nafion carrier layer to transfer graphene (spin + scoop), (ii) casting a Nafion film and cold pressing (cold press), and (iii) hot pressing (hot press) while minimizing micron-scale defects to <0.3% area. Interfacing CVD graphene on Cu with N211 via cold press or hot press and subsequent removal of Cu via etching results in ∼50% lower areal proton conductance compared to membranes fabricated via the spin + scoop method. Notably, the areal proton conductance can be recovered by soaking the hot and cold press membranes in 0.1 M HCl, without significant damage to graphene. We rationalize our finding by the significantly smaller reservoir for cation uptake from Cu etching for the ∼700 nm thin carrier Nafion layer used for spin + scoop transfer compared to the ∼25 μm thick N211 film for hot and cold pressing. Finally, we demonstrate performance in H2 fuel cells with power densities of ∼0.23 W cm-2 and up to ∼41-54% reduction in H2 crossover for the N211|G|N211 sandwich membranes compared to the control N211|N211 indicating potential for our approach in enabling advanced PEMs for fuel cells, redox-flow batteries, isotope separations and beyond.

AgInS2-Embedded Photocatalytic Membrane: Insights into the Excited State and Electron Transfer Dynamics.

Photocatalytic reactions at semiconductor nanocrystal surfaces are useful for synthesizing value-added chemicals using sunlight. Semiconductor nanocrystals dispersed in a rigid framework, such as polymer film, can mitigate issues such as aggregation, product separation, and other challenges that are usually encountered in suspensions or slurries. Using a cation exchange technique, we successfully embedded AgInS2 nanoparticles into a Nafion matrix, termed AgInS2-Nafion. This was achieved through a galvanic exchange between In and Ag in In2S3 present within the Nafion film, enabling an adjustable Ag:In ratio for optimized photophysical properties. As in the case of colloidal suspension, the AgInS2 particles embedded in Nafion exhibit a long absorption tail, a broad emission band with a large Stokes shift, and emission lifetimes extending into the microseconds that are characteristic of donor-acceptor pairs, DAP. Remediation of surface states with the treatment of 3-mercaptopropionic acid resulted in significant enhancement in the emission yield. Charge carrier generation through bandgap excitation as well as activation of DAP states which reside within the bandgap is probed through transient absorption spectroscopy. The photocatalytic activity of AgInS2-Nafion was probed by using thionine as an electron acceptor. The electron transfer rate constant from excited AgInS2 to thionine as observed from transient absorption spectroscopy was determined to be ∼6.3 × 1010 s-1. The design of a photoactive membrane offers new ways to carry out photocatalytic processes with greater selectivity.

Flow-Injection Amperometric Determination of Adrenalin, Melatonin, and Cortisol on an Electrode Modified with a Gold–Palladium Binary System and a Nafion Film

Flow-Injection Amperometric Determination of Adrenalin, Melatonin, and Cortisol on an Electrode Modified with a Gold–Palladium Binary System and a Nafion Film

Gold nanowire mesh electrode for electromechanical device

Ionic polymer-metal composite (IPMC) actuators were prepared with Nafion film as the ionic polymer and gold nanowire (Au-NW) mesh film as the metal electrodes by hot-pressing, which shortened preparation time within 1 h. As a reference, IPMC actuator consisting of Nafion film and gold foil (Au-foil) was also prepared. Au-NW mesh film can be an electrode with thinner (about 150 nm) and lower surface resistivity (about 0.5 Ω sq−1) than the conventional electrode prepared by electroless plating. Larger contact area of the Au-NW mesh electrode than the Au-foil electrode resulted in better actuation performance (60% larger peak-to-peak displacement in actuation). It was confirmed that the transformation behavior of Au-NWs differed depending on the external stimuli condition. Namely Au-NWs transformed to Au nanoparticles in the case of the heat stimulus only. Meanwhile, Au-NWs transformed to plates in the case of the heat and pressure stimuli. While higher temperature improved the adhesion of Au-NW mesh electrode to the Nafion surface, it induced the transformation of nanowire to plates. The IPMC actuator that the Au-NW mesh electrodes were hot-pressed at 90 ºC exhibited the highest capacitance and the largest peak-to-peak displacement in actuation. This research expanded the application field of gold nanowires to the electromechanical devices.

Impact of Formulation of Photocurable Precursor Mixtures on the Performance and Dimensional Stability of Hierarchical Cation Exchange Membranes.

This work presents a systematic approach to formulating UV curable ionomer coatings that can be used as ion-exchange membranes when they are applied on porous substrates. Ion-exchange membranes fabricated in this way can be a cost-effective alternative to perfluorosulfonic acid membranes, such as Nafion and similar thin ionomer film membranes. Hierarchically structured coated membranes find applications for energy storage and conversion (organic redox flow batteries and artificial photosynthesis cells) and separation processes (electrodialysis). Designing the ionomer precursor for membrane formulation requires the introduction of compounds with drastically different properties into a liquid mixture. Hansen solubility theory was used to find the solvents to compatibilize main formulation components: acrylic sulfone salt (3-sulfopropyl methacrylate potassium salt) and hexafunctional polyester acrylate cross-linker (Ebecryl 830), otherwise nonmiscible or mutely soluble. Among the identified suitable solvents, acrylic acid and acetic acid allowed for optimal mixing of the components and reaching the highest levels of sulfonic group content, providing the desired ion-exchange capacity. Interestingly, they represented a case of a reactive and nonreactive solvent since acrylic acid was built into the ionomer during the UV curing step. Properties of the two membrane variants were compared. Samples fabricated with acetic acid exhibit improved handleability compared with the case of acrylic acid. Acetic acid yielded a lower area-specific resistance (6.4 ± 0.17 Ohm·cm2) compared to acrylic acid (12.1 ± 0.16 Ohm·cm2 in 0.5 M NaCl). This was achieved without severely suppressing the selectivity of the membrane, which was standing at 93.4 and 96.4% for preparation with acetic and acrylic acid, respectively.

Effect of water droplet growth dynamics on electrode current in fuel-cell catalyst layers

Fuel cells are a promising next-generation energy-conversion technology designed to replace internal combustion engines in transportation applications. However, much work remains to optimize them. Operation at high humidities causes liquid water droplet formation on Pt catalyst particles during oxygen reduction, potentially impeding reactant arrival to the reactive electrode. In this work, four different cases of water droplet growth in fuel-cell catalyst layers are considered: pinned or advancing droplets on a bare Pt surface, advancing droplets on a Nafion film, and water-layer growth in carbon nanopores. Transient drop growth is captured with a combination of mass, species mass, and momentum balances, and the subsequent limiting current is determined via oxygen diffusion and Tafel kinetics. Water droplets are found not to be mass-transfer limiting due to the relatively large liquid-gas area compared to the Pt nanoparticle. Mass-transfer-limited behavior is calculated in carbon nanopores.

Enhanced Electroreduction of Acetophenone Using Lipase Stabilization: Improved Conversion to 1‐Phenylethanol

AbstractFew works present effective or viable alternatives to the problem of the electroreduction of acetophenone which usually leads to the pinacol dimer as a primary product in addition to 1‐phenylethanol. Here, various lipases were applied in acetophenone electroreduction. The optimized reaction conditions are tin/lead (63 : 37) combined working electrode coated with Nafion film modified with lipase from Thermomyces lanuginosus, a platinum counter electrode, applied potential of −2.0 V vs. Ag/AgCl (KCl 3.0 mol L−1), acetate buffer (0.1 mol L−1) pH 5.0 in 4 hours, and led to the formation of 87.8 % of 1‐phenylethanol. The same working electrode was used five times over five days, and the conversion remained constant. A voltammetric study indicates an alteration of the electroreduction mechanism in the presence of the cited lipase. Adding lipase from Thermomyces lanuginosus directly in the medium immobilized in a clay mineral or in silica gel (Lipolase 100T) resulted in even higher conversions (93.2–93.9 %). The modified electrode improved the methodology regarding enzyme stability, process reproducibility, and material reusability.

Developing Solution-Processed Distributed Bragg Reflectors for Microcavity Polariton Applications.

Improving the performance of organic optoelectronics has been under vigorous research for decades. Recently, polaritonics has been introduced as a technology that has the potential to improve the optical, electrical, and chemical properties of materials and devices. However, polaritons have been mainly studied in optical microcavities that are made by vacuum deposition processes, which are costly, unavailable to many, and incompatible with printed optoelectronics methods. Efforts toward the fabrication of polariton microcavities with solution-processed techniques have been utterly absent. Herein, we demonstrate for the first time strong light-matter coupling and polariton photoluminescence in an organic microcavity consisting of an aluminum mirror and a distributed Bragg reflector (DBR) made by sequential dip coating of titanium hydroxide/poly(vinyl alcohol) (TiOH/PVA) and Nafion films. To fabricate and develop the solution-processed DBRs and microcavities, we automatized a dip-coating device that allowed us to produce sub-100 nm films consistently over many dip-coating cycles. Owning to the solution-based nature of our DBRs, our results pave the way to the realization of polariton optoelectronic devices beyond physical deposition methods.

The Effect of Direct Electron Beam Patterning on the Water Uptake and Ionic Conductivity of Nafion Thin Films

AbstractThe effect of electron‐beam patterning on the water uptake and ionic conductivity of Nafion films using a combination of X‐ray photoelectron spectroscopy, quartz crystal microbalance studies, neutron reflectometry, and impedance spectroscopy is reported. The aim is to further characterize the nanoscale patterned Nafion structures recently used as a key element in novel ion‐to‐electron transducers by Gluschke et al. To enable this, the electron beam patterning process is developed for large areas, achieving patterning speeds approaching 1 cm2 h−1, and patterned areas as large as 7 cm2 for the neutron reflectometry studies. It is ultimately shown that electron‐beam patterning affects both the water uptake and the ionic conductivity, depending on film thickness. Type‐II adsorption isotherm behavior is seen for all films. For thick films (≈230 nm), a strong reduction in water uptake with electron‐beam patterning is found. In contrast, for thin films (≈30 nm), electron‐beam patterning enhances water uptake. Notably, for either thickness, the reduction in ionic conductivity arising from electron‐beam patterning is kept to less than an order of magnitude. Mechanisms are proposed for the observed behavior based on the known complex morphology of Nafion films to motivate future studies of electron‐beam processed Nafion.

Scanning Ion Conductance Microscopy of Nafion-Modified Nanopores

Single nanopores in silicon nitride membranes are asymmetrically modified with Nafion and investigated with scanning ion conductance microscopy, where Nafion alters local ion concentrations at the nanopore. Effects of applied transmembrane potentials on local ion concentrations are examined, with the Nafion film providing a reservoir of cations in close proximity to the nanopore. Fluidic diodes based on ion concentration polarization are observed in the current-voltage response of the nanopore and in approach curves of SICM nanopipette in the vicinity of the nanopore. Experimental results are supported with finite element method simulations that detail ion depletion and enrichment of the nanopore/Nafion/nanopipette environment.