Commercial Nafion Membrane Research Articles

The effect of irradiation for Nafion membrane electrode rapid separation of hydrogen-methane by electrochemical hydrogen pumps

Designing an efficient and reliable tritium plant has become a major challenge to developing nuclear fusion, which focuses on efficient and safe hydrogen isotope separation and purification. The electrochemical hydrogen pump (EHP) developed in recent years can be used to separate and compress hydrogen. Herein, we used the commercial Nafion membrane electrode in the EHP, which has excellent H2/CH4 separation performance. When the cell voltage is at 0.8 V, the current density is 2.04 A/cm2, the hydrogen separation rate can reach 14.2 mL/ (min ·cm2), and the hydrogen purity is more than 99.99 %. The damage mechanism of electron beam irradiation on the membrane electrode was revealed. It was found that irradiation caused Nafion’s main chain and branch chain to break, producing hydroxyl and carboxyl functional groups. The degree of chain fracture increased with the radiation dose, perforation and cracks occurred in the proton exchange membrane (PEM). Under the electron beam irradiation dose of 10 kGy, the membrane electrode can still maintain excellent H2/CH4 separation performance, and the hydrogen permeability caused by cracks and perforations is at a very low level. This study reveals the change of macroscopic performance caused by the microscopic mechanism of membrane electrode irradiation damage, provides a promising way to separate hydrogen isotope gases and is expected to promote the development of tritium plants in fusion engineering.

Block Copolymer-Based Membranes for Vanadium Redox Flow Batteries: Synthesis, Characterization, and Performance.

Nonfluorinated polymers have been widely proposed to replace Nafion as raw materials for redox flow battery ion-exchange membranes. Hereby, block copolymers based on polysulfone (PSU) and polyphenylsulfone (PPSU) are synthesized and employed as precursors of membranes for vanadium redox flow batteries. A series of copolymers with varying molar proportions of PSU (75/25, 60/40, 50/50 mol %) were prepared. The 60/40 and 75/25 copolymers exhibit concentrated sulfonic groups predominantly in the PSU unit, favoring the formation of hydrophobic and hydrophilic domains. The 50/50 copolymer presents a balanced degree of sulfonation between the two units, leading to a homogeneous distribution of sulfonic groups. An ex situ study of these materials comprising vanadium ion permeability and chemical and mechanical stability was performed. The best performance is achieved with 50/50 membranes, which exhibited performance comparable to commercial Nafion membranes. These results signify a promising breakthrough in the pursuit of high-performance, sustainable membranes for next-generation VRFBs.

Surface modification of expanded polytetrafluoroethylene to reinforced composite membranes for proton exchange membrane fuel cells

The study reports on the fabrication of reinforced composite membranes via hydrophilic surface modification of highly hydrophobic and porous expanded polytetrafluoroethylene (ePTFE) using argon plasma treatment and silane coupling. These processes create amine end group, functionalized onto ePTFE surface, thus improving hydrophilicity. It enables impregnation of Nafion ionomer dissolved in a polar aprotic solvent as well as water/alcohol mixture solvent. The optimal silane coupling concentration is systematically determined and facilitates uniform grafting of amine-functionalized silane without the pore blockage of ePTFE. The resulting reinforced composite membranes show improved mechanical, chemical, and dimensional stabilities and comparable proton conductivity. However, their membrane ohmic resistance is slightly higher than that of a commercial Nafion membrane (N211), leading to slightly reduced fuel cell performance. Note, the processes of this study prove versatile, accommodating partially fluorinated polymers in aprotic polar solvents with ePTFE, holding its potential for creating alternative reinforced composite.

The effect of the number of sulfonic acids in polysiloxanes as fillers for polymer electrolyte membranes in energy storage applications

A series of sulfonic acid-functionalized polysiloxanes (MASFPs) that can be used to reduce the cost and improve the properties of proton exchange membranes (PEMs) by acting as fillers have been synthesized. In this paper, we describe the synthesis of MASFPs with varying numbers of sulfonic acid groups with the aid of mercaptoethanol. An array of analytical techniques were employed to characterize the synthesized MASFPs. The broad peak observed in the X-ray diffraction pattern of MASFPs between 2θ = 15–25° signifies their amorphous characteristics. Analyses by infrared spectroscopy also identify MASFPs that contain stretching vibrations for –SO3H, –CH2, and Si–O– group. The thermogravimetric analysis demonstrates the thermal stability of these MASFPs. The surface morphology analysis of the MASFPs using FESEM and HRTEM revealed the presence of spherical particles that exhibited significant aggregation and distortion. By employing X-ray photoelectron spectroscopy (XPS) to determine the atomic weight percentage of sulfur present in the MASFPs, the number of sulfonic acids contained within was verified. The sulfur content of MASFPs is determined by XPS to be as follows: MASFP-4 > MASFP-3 > MASFP-2 > MASFP-1. The presence of Q4, Q3, T3, and T2 signals, as determined by 29Si MAS NMR analysis, confirms the polysiloxane formation. Preliminary studies of the composite membrane prepared using the MASFPs with perfluorosulfonic acid (PFSA:MASFP in 75:25 ratio) exhibited superior ionic conductivity (0.102 S/cm) and ion-exchange capacity (1.16 meq/g) in comparison to the commercial Nafion membrane. Overall, using a mercaptoethanol-assisted process to synthesize sulfonic acid functionalized polysiloxanes is an excellent way to increase the incorporation of sulfonic acids and it can be applied to the synthesis of various other inorganic nanofillers.

Commercial Nafion Membranes for Harvesting Osmotic Energy from Proton Gradients that Exceed the Commercial Goal of 5.0 W/m2.

Osmotic energy from proton gradients in industrial acidic wastewater can be harvested and converted to electricity through membranes, making it a renewable and sustainable power source. However, the currently designed membranes for harvesting proton gradient energy in acidic wastewater cannot simultaneously achieve excellent chemical/mechanical stability and high power density under a large-scale area and require high cost and complex operations. Here, we demonstrate that commercial Nafion membranes with high chemical/mechanical stability and proton transport selectivity can generate a power density of 5.1 W/m2 for harvesting osmotic energy from proton gradients under a test area of 0.2 mm2, which exceeds the commercial goal of 5.0 W/m2. Even under a test area of 12.5 mm2, a power density of 2.1 W/m2 can be achieved under a strong acid condition. In addition, the heat can greatly promote proton transport, and the power density is increased, i.e., 8.1 W/m2 at 333 K (5.1 W/m2 at 293 K) under a test area of 0.2 mm2. By matching membranes with ion selectivity, our work demonstrates the potential of Nafion membranes for harvesting proton gradient energy in acidic wastewater and provides an approach for large-scale conversion of osmotic energy.

Preparation and Evaluation of Nafion/CeO2 Composite Electrolyte Membranes for Polymer Electrolyte Fuel Cells

Polymer electrolyte fuel cells (PEFCs) are increasingly applied to the vehicles (FCVs) toward the suppression of carbon dioxide emission. The larger FCVs requires the high power density to exceed the presumed temperature limit of 80 ℃, causing some issues of material durability and system performances. In particular, a commercial electrolyte membrane of Nafion occurs the decrease of proton conductivity at the high temperatures under an atmospheric pressure. To overcome this problem, our research group has developed a composite electrolyte membrane consisting of Nafion and Ta-TiO2 nanoparticles with a chain-like network structure. The composite electrolyte membrane improves a proton conductivity in a wide temperature range over 100 ℃ by the effect of hydrophilic surface of the oxide. In this study, the other candidate materials of CeO2, nanoparticles with highly hydrophilic surface rather than that of Ta-TiO2 was selected to try to improve the proton conductivity of the composite electrolyte membranes.The hydrophilic CeO2 nanoparticles with a chain-like network structure were prepared using flame oxide-synthesis method. The hydrophilic CeO2 nanoparticles were dispersed in a dispersion solvent in desired ratio. The dispersion was then added to 20 wt.% Nafion dispersion solution (DE2020 CS, Chemours Co.) neutralized with potassium hydroxide. The resulting dispersion was coated onto a die coater and dried using a hot air. The CeO2/Nafion composite membrane was then treated in high purified water with a sulfuric acid solution. The transmission electron microscopy (TEM) and water adsorption, and four-probe alternating current method was conducted to detect the microstructure, water uptake and proton conductivity of the composite membrane.TEM images confirmed that the CeO2 nanoparticles were highly dispersed in the composite membrane. The proton conductivity of the 3 wt.% CeO2 containing composite membrane was 2.1 times higher than that of commercial Nafion membrane (NRE211, Chemours Co.) at 80 ℃, 20% RH, and was 1.5 times higher than that at 80 ℃, 80% RH (Fig. 1). The proton conductivity of the 3 wt.% CeO2 containing composite membrane was found to be higher than that of the Nafion monolayer in each water uptake (Fig. 2), indicating that the morphology of the membrane might be changed by the adding of CeO2 oxide. Further research will be needed to examine the proton conductivity mechanism of this composite membrane, and fuel cell evaluations using this composite membrane. Figure 1

Cost estimation and performance evaluation of 3D printed membranes for vanadium redox flow batteries

AbstractThe membrane is a central component in the commercialization of vanadium redox flow batteries (VRFB), with Nafion being the preferred material for those membranes. Nafion suffers however from high vanadium crossover and high cost, thus limiting its wider commercial application in VRFB. To address this, studies have focused on sulfonated polyether ether ketone (SPEEK) as an alternative material. This work presents an economic study on the production costs of 3D printed SPEEK (3D‐SPEEK) membranes for VRFB, with multiple production scenarios evaluated. This analysis relies on the performances of 3D‐SPEEK membranes prepared in our laboratory, which have shown higher Coulombic efficiency and lower vanadium ions diffusion than Nafion membranes. Results from the economic analysis revealed that the cost of the 3D‐SPEEK membrane varies from 567.77 to 79.35 €/m2 depending on the production scheme and scale used. Production costs lower than commercial Nafion membranes are achieved when a large production scheme is used. Further analysis shows that 3D‐SPEEK membranes might even be cheaper than conventional SPEEK membranes if their printing time is reduced.

Degradation analysis of polymer electrolyte membrane water electrolyzer with different membrane thicknesses

A constant current density of 3.0 A/cm2 was applied to PEMWE assembled with three commercial Nafion membranes (NR212, N115, and N117) for 144 h to investigate the influence of membrane thickness on the cell durability. The results show that N115-cell exhibits an improvement in performance after 144 h by the decrease of ohmic resistance caused by the topology adaptation. The cells with NR212 and N117 showed voltage increases, and the most significant degradation could be observed in the NR212-cell. The highest exposing potential of N117-cell accelerated the passivation of the porous transport layer (PTL) and the catalyst dissolution, consequently increasing ohmic losses and kinetic losses. The remarkable performance losses of the NR212 originated from severe ohmic degradation. This phenomenon was attributed to the pinhole formation on the membrane and the resulting decrease in the electrical conductivity of the iridium catalyst layer due to the reduction of iridium oxide catalyst.

Click chemistry‐based azide‐substituted polysulfone/alkynyl‐substituted sulfonated polyvinyl alcohol/nafion blend membranes for direct methanol fuel cells

AbstractAt present, commercial Nafion membrane is not suitable for proton exchange membrane used in direct methanol fuel cell (DMFC) due to the severe methanol permeation phenomenon. This work reported the preparation and characterization of azide‐substituted polysulfone (PSU‐N3) and alkynyl‐substituted sulfonated polyvinyl alcohol (SAPVA) crosslinked in the matrix of Nafion membrane base on click chemistry applied in DMFC. The compatibility between PSU‐N3 and SAPVA is promoted due to the formation of crosslinked network structure. Key properties, including dimensional stability, oxidative stability, mechanical behavior, methanol permeability and proton conductivity, are compared with those of the recast Nafion membrane. The prepared blend membranes exhibit lower methanol permeability due to the crosslinked network and well‐dispersed microphase structure of PSU‐PVA in the Nafion matrix. The proton selectivity of the Nafion‐PSU‐PVA‐3 membrane is 9.16 × 104 S s/cm3, much higher than that of the recast Nafion membrane (2.82 × 104 S s/cm3). In DMFC single cell tests, the maximum power density of the Nafion‐PSU‐PVA‐3 membrane is 4.6 mW/cm2, about 58.6% higher than that of the recast Nafion membrane. All the results indicate that the prepared blend membranes have the potential to be applied in DMFC.

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.

Ion-Selective Microporous Polymer Membranes with Hydrogen-Bond and Salt-Bridge Networks for Aqueous Organic Redox Flow Batteries.

Redox flow batteries (RFBs) have great potential for long-duration grid-scale energy storage. Ion-conducting membranes are a crucial component in RFBs, allowing charge-carrying ions to transport while preventing the cross-mixing of redox couples. Commercial Nafion membranes are widely used in RFBs, but their unsatisfactory ionic and molecular selectivity, as well as high costs, limit the performance and the widespread deployment of this technology. To extend the longevity and reduce the cost of RFB systems, inexpensive ion-selective membranes that concurrently deliver low ionic resistance and high selectivity toward redox-active species are highly desired. Here, high-performance RFB membranes are fabricated from blends of carboxylate- and amidoxime-functionalized polymers of intrinsic microporosity, which exploit the beneficial properties of both polymers. The enthalpy-driven formation of cohesive interchain interactions, including hydrogen bonds and salt bridges, facilitates the microscopic miscibility of the blends, while ionizable functional groups within the sub-nanometer pores allow optimization of membrane ion-transport functions. The resulting microporous membranes demonstrate fast cation conduction with low crossover of redox-active molecular species, enabling improved power ratings and reduced capacity fade in aqueous RFBs using anthraquinone and ferrocyanide as redox couples.

Lamellar membrane with orderly aligned glycine molecules for efficient proton conduction

Proton conduction is essential for proton exchange membrane (PEM) in hydrogen fuel cell. However, the proton conductivity of most PEMs is limited by the inferior continuity of transport channels and random arrangement of transfer carriers. Here, charged vermiculite lamellar membrane with orderly aligned glycine molecules in the interlayer channel is fabricated. We demonstrate that sulfonic acid-grafted channel induces and interacts with the end amino groups of glycine molecules, forming ordered acid-base pairs along the wall. Meantime, the carboxyl groups at the other end are located in the middle of channel, forming continuous hydrogen bond networks. Such molecule arrangement creates long-range hoping highways for proton conduction. The Vr-SO3H@Gly membrane (∼8 μm in thickness) with 10.2 wt% glycine obtains horizontal conductivity of 378.5 mS cm−1 at 90 °C and 100% RH, 2.2 times of that of commercial Nafion membrane. Moreover, the molecule arrangement is stable helped by the strong channel-glycine and glycine-glycine interactions, rendering excellent conduction stability. These then bring high hydrogen fuel cell performances with maximum current density and power density of 604 mA cm−2 and 184 mW cm−2, respectively, which are superior to Nafion and most reported 2D lamellar PEMs. This study should provide insights in developing advanced lamellar membranes for application in proton conduction field.

Sustainable Plant-Based Biopolymer Membranes for PEM Fuel Cells

Carboxycellulose nanofibers (CNFs) promise to be a sustainable and inexpensive alternative material for polymer electrolyte membranes compared to the expensive commercial Nafion membrane. However, its practical applications have been limited by its relatively low performance and reduced mechanical properties under typical operating conditions. In this study, carboxycellulose nanofibers were derived from wood pulp by TEMPO oxidation of the hydroxyl group present on the C6 position of the cellulose chain. Then, citric acid cross-linked CNF membranes were prepared by a solvent casting method to enhance performance. Results from FT-IR spectroscopy, 13C NMR spectroscopy, and XRD reveal a chemical cross-link between the citric acid and CNF, and the optimal fuel cell performance was obtained by cross-linking 70 mL of 0.20 wt % CNF suspension with 300 µL of 1.0 M citric acid solution. The membrane electrode assemblies (MEAs), operated in an oxygen atmosphere, exhibited the maximum power density of 27.7 mW cm-2 and the maximum current density of 111.8 mA cm-2 at 80 °C and 100% relative humidity (RH) for the citric acid cross-linked CNF membrane with 0.1 mg cm-2 Pt loading on the anode and cathode, which is approximately 30 times and 22 times better, respectively, than the uncross-linked CNF film. A minimum activation energy of 0.27 eV is achieved with the best-performing citric acid cross-linked CNF membrane, and a proton conductivity of 9.4 mS cm-1 is obtained at 80 °C. The surface morphology of carboxycellulose nanofibers and corresponding membranes were characterized by FIB/SEM, SEM/EDX, TEM, and AFM techniques. The effect of citric acid on the mechanical properties of the membrane was assessed by tensile strength DMA.

Reinforced Nafion Membrane with Ultrathin MWCNTs/Ceria Layers for Durable Proton-Exchange Membrane Fuel Cells.

For further commercializing proton-exchange membrane fuel cells, it is crucial to attain long-term durability while achieving high performance. In this study, a strategy for modifying commercial Nafion membranes by introducing ultrathin multiwalled carbon nanotubes (MWCNTs)/CeO2 layers on both sides of the membrane was developed to construct a mechanically and chemically reinforced membrane electrode assembly. The dispersion properties of the MWCNTs were greatly improved through chemical modification with acid treatment, and the mixed solution of MWCNTs/CeO2 was uniformly prepared through a high-energy ball-milling process. By employing a spray-coating technique, the ultrathin MWCNTs/CeO2 layers were introduced onto the membrane surfaces without any agglomeration problem because the solvent rapidly evaporated during the layer-by-layer stacking process. These ultrathin and highly dispersed MWCNTs/CeO2 layers effectively reinforced the mechanical properties and chemical durability of the membrane while minimizing the performance drop despite their non-ion-conducting properties. The characteristics of the MWCNTs/CeO2 layers and the reinforced Nafion membrane were investigated using various in situ and ex situ measurement techniques; in addition, electrochemical measurements for fuel cells were conducted.

Reduction in particle size of vermiculite and production of the low-cost earthen membrane to achieve enhancement in the microbial fuel cell performance

A membrane used in the microbial fuel cell is one of the most crucial components. It sums up to half the cost of the whole assembled MFC. The novel earthen membrane has been prepared in this study using reduced particle size of vermiculite to give a low-cost alternative to the commercial Nafion 117 membrane. The M5 membrane prepared using red soil, montmorillonite and vermiculite (nano-milled for 5 hr) have outperformed all other fabricated membranes. The reduction in particle size of vermiculite in the earthen membrane has shown better proton diffusion and reduced oxygen mass transfer into the anode. The ion exchange capacity of the membrane has also been improved. The MFC (R5) containing the M5 membrane has yielded the highest COD removal efficiency (88.06 ± 0.9%) and the highest coulombic efficiency (19.4 ± 0.67%). The power density achieved by R5 was 995.73 ± 49.3 mW/m3 which is the highest among all the installed microbial fuel cells and is 8.4 folds higher than the control. The study sums up that the M5 membrane can be utilized as a novel and cost-effective alternative to the commercial Nafion membrane.

Cross-Linking of Proton Exchange Membranes with Enhanced Stability and Reduced Fuel Crossover for Direct-Isopropanol Fuel Cells

Isopropanol fuel cells offer a promising way to provide electric energy from a liquid, non-toxic fuel. The secondary alcohol isopropanol is converted into acetone without producing significant amounts of CO2. The oxidation product acetone can be easily hydrogenated back to isopropanol to close the storage cycle, thereby avoiding fugitive molecular hydrogen with its low volumetric energy density at ambient conditions. Until now, electrodes and membranes for Direct Isopropanol Fuel Cells (DIFC) usually rely on various perfluorosulfonic acid derivates, like Nafion. Besides its high cost and unfavorable high fluorine content, the dissolution of Nafion in isopropanol mixtures has prevented the long time operation of DIFCs so far. Ionomer swelling during operation promotes efficiency-reducing crossover of isopropanol and acetone. This study introduces a new click-like covalent cross-linking strategy for fluoroaromatic ion-exchange polymers. Combined with ionic cross-linking of polymer blends, membranes with increased isopropanol stability were manufactured and compared to commercial Nafion membranes. The ionic and covalently cross-linked membrane resists a dissolution stress test up to 84 w-% and reduces the detected isopropanol/acetone crossover up to 75/100 % during fuel cell operation. Consequently, the cross-linking procedure and respective membrane material can be considered a significant step toward the technical implementation of DIFCs.

Sulfonated Chitosan and HKUST‐1 metal organic frameworks based hybrid membranes for direct methanol fuel cell applications

AbstractSulfonated Chitosan and copper‐based metal–organic frameworks (Hong Kong University of Science and Technology (HKUST‐1) or Cu‐BTC or MOF‐199) based hybrid membranes are fabricated using a solution casting method for direct methanol fuel cell (DMFC) applications. The well‐defined cubic structure and sharp crystalline X‐ray diffraction pattern confirms the successful synthesis of HKUST‐1. The SEM cross‐sectional images showed that incorporated HKUST‐1 acts as a pore‐filling agent as well as creating finger‐like hydrophilic channels into the S‐Chitosan matrix. The existence of intermolecular hydrogen bonding between the COOH groups of HKUST‐1 and SO3H groups of S‐Chitosan enhances the membrane performances such as water uptake, ion exchange capacity, proton conductivity, and thermal stability. Specifically hybrid membrane with 0.5 wt% of HKUST‐1 showed the highest proton conductivity of 5.38 × 10−3 and 6.19 × 10−3 S cm−1 at 25 and 80°C respectively. Besides the S‐Chitosan‐0.5 membrane exhibited lower methanol permeability and selectivity than pristine S‐Chitosan and commercial Nafion membranes due to the small ionic size. Besides the pore reduction ability of HKUST‐1 selectively allowed protons and block the methanol permeation in the membrane matrix. Overall results indicate that the S‐Chitosan‐0.5 hybrid membrane is a suitable candidate for DMFC applications.

Energetics of Technical Integration of 2‐Propanol Fuel Cells: Thermodynamic and Current and Future Technical Feasibility

2‐Propanol/acetone is a promising liquid organic hydrogen carrier system for fuel cell reactions. Herein, six different concepts for a 2‐propanol/acetone fuel cell system are evaluated in MATLAB simulation with respect to their thermodynamic integration and technical feasibility. Four of the concepts use a direct 2‐propanol fuel cell while the other two first release molecular hydrogen from 2‐propanol and subsequently use a hydrogen fuel cell. The presented liquid phase 2‐propanol fuel cell concept is thermodynamically feasible but cannot be realized technically using commercial Nafion membranes, due to membrane dissolution by the 2‐propanol/acetone/water fuel mixture. Gaseous 2‐propanol fuel cells imply a high heating requirement for the evaporation of the fuel. A direct high‐temperature fuel cell using 2‐propanol is thermodynamically feasible because there is less water in the overall system but is not technically feasible because of the esterification of phosphoric acid. A very interesting option is the conversion of gaseous 2‐propanol to pressurized hydrogen in an electrochemical pumping step followed by a hydrogen fuel cell, because here the waste heat of a sufficiently hot hydrogen fuel cell can drive the 2‐propanol evaporation.

Tunable ion transport across graphene through tailoring grain boundaries

Grain boundaries (GBs) are common features in materials and can tune their physical and/or chemical properties. GBs in graphene could degrade electrical or thermal properties and, thus, are widely supposed to be avoided in related applications. However, the potential to utilize GBs in graphene remains to be explored. Here we reveal that, contrary to traditional negative effects, GBs can efficiently tune ion transport properties, but this remains poorly understood. By controlling the GB density in graphene, we achieve precise tuning of proton permeance with a range of 2 orders of magnitude. We study the reactivity of GBs and attain 3–6 times higher permeance of ions for GB-rich samples than for GB-poor samples. We obtain a proton conductivity 3–4 orders of magnitude higher than commercial Nafion membranes with higher selectivity. Our work discloses the crucial roles of GBs to tailor ion transport and shows the potential of designing GBs in 2D material for membrane applications. • Tuning proton permeance by controlling grain boundary in graphene • Grain boundary sites are preferentially etched under mild etching conditions • Ultrafast proton permeance is achieved by preferential etching of grain boundary Grain boundaries exist widely in graphene. To better understand their role in ionic transport, Zhang et al. experimentally study the role and potential of grain boundaries in graphene to tailor ion transport and achieve enhanced proton permeance by preferential etching of grain boundary sites.

Highly Durable Membrane Electrode Assembly with Multiwalled Carbon Nanotubes/CeO2‐Reinforced Nafion Composite Membrane by Spraying Method for Fuel Cell Applications

AbstractFor achieving economically viable polymer electrolyte membrane fuel cells (PEMFCs) in the commercial market, simplifying the fabrication process and manufacturing of robust membrane electrode assembly (MEA) are important. Herein, a single spray‐coating method for developing a robust and free‐standing reinforced Nafion composite membrane and electrodes is reported. By comparing the fabricated membrane's morphology under diverse process conditions including the nozzle‐to‐substrate distance and solution‐loading rates, the optimized spray‐coating for uniformly deposited spray‐based membrane without any defects has been determined. To explain this optimized condition, a simple theoretical model based on the concept of the surface coverage of sprayed droplets is proposed. The fabricated multiwalled carbon nanotubes/CeO2‐reinforced Nafion composite membrane shows excellent mechanical properties with minimal proton‐conducting loss despite using additional fillers of total 4 wt% in the Nafion matrix. By successively depositing the catalyst layer on that membrane using the same spray‐coating device, an MEA with the reinforced spray‐based membrane has been successfully fabricated; moreover, diverse electrochemical measurements and durability tests have been conducted. The MEA with the reinforced membrane shows comparable initial performance and considerably higher performance after the durability test compared to the MEA with commercial Nafion membrane.