Proton Conductivity Of Membranes Research Articles

A [V6B20]-based architecture incorporating two types of organic amine ligands: innovative additives for enhancing the proton conductivity of Nafion membrane

The novel composite material VB-1/Nafion demonstrates a remarkable enhancement in proton conductivity when compared to pure Nafion.

Fabrication of -SO3H-functionalized polyphosphazene-reinforced proton conductive matrix-mixed membranes.

Proton exchange membranes (PEMs) have emerged as very promising membranes for automotive applications because of their notable proton conductivity at low temperatures. These membranes find extensive utilization in fuel cells. Several polymeric materials have been used, but their application is constrained by their expense and intricate synthetic processes. Affordable and efficient synthetic methods for polymeric materials are necessary for the widespread commercial use of PEM technology. The polymeric combination of hexachlorocyclotriphosphazene (HCCP) and 4,4-diamino-2,2-biphenyldisulfonic acid facilitated the synthesis of PP-(PhSO3H)2, a polyphosphazene with built-in -SO3H moieties. Characterization revealed that it was a porous organic polymer with high stability. PP-(PhSO3H)2 exhibited a proton conductivity of up to 8.24 × 10-2 S cm-1 (SD = ±0.031) at 353 K under 98% relative humidity (RH), which was more than two orders of magnitude higher than that of its -SO3H-free analogue, PP-(Ph)2 (2.32 × 10-4 S cm-1) (SD = ±0.019) under identical conditions. Therefore, for application in a PEM fuel cell, PP-(PhSO3H)2-based matrix-mixed membranes (PP-(PhSO3H)2-MMMs) were fabricated by mixing them with polyacrylonitrile (PAN) in various ratios. The proton conductivity could reach up to 6.11 × 10-2 S cm-1 (SD = ±0.0048) at 353 K and 98%RH, when the weight ratio of PP-(PhSO3H)2 : PAN was 3 : 1, the value of which was comparable with those of commercially available electrolytes used in PEM fuel cells. PP-(PhSO3H)2-MMM (3 : 1) had an extended lifetime of reusability. Using phosphazene and bisulfonated multiple-amine modules as precursors, we demonstrated that a porous organic polymer with a highly effective proton-conductive matrix-mixed membrane for PEM fuel cells could be produced readily by an intuitive polymeric reaction.

Graphene oxide-based materials as proton-conducting membranes for electrochemical applications.

The rapid advancements of graphene oxide (GO)-based membranes necessitate the understanding of their properties and application potential. Generally, proton (H+)-conducting membranes, including GO-based ones, are crucial components in various energy-relevant devices, significantly determining the transport process, selectivity, and overall efficiency of these devices. Particularly, GO-based membranes exhibit great potential in electrochemical applications owing to their remarkable conductivity and ease of undergoing further modifications. This review is aimed at highlighting recent functionalization strategies for GO with diverse substrates. It is also aimed at emphasizing how these modifications can enhance the electrochemical performances of GO-based membranes. Notably, key aspects, such as the enhanced H+-transfer kinetics, improved conductivity, functionalities, and optimization, of these membranes for specific applications are discussed. Additionally, the existing challenges and future directions for the field of functionalized GO are addressed to achieve precise control of the functionalities of these membranes as well as advance next-generation electrochemical devices.

Ultra-thin, mechanically durable reinforced sulfonated poly(fluorenyl biphenyl) indole proton exchange membrane for fuel cell

Mechanically durable and highly proton-conductive proton exchange membrane (PEM) is a crucial component for PEM fuel cell (PEMFC). Herein, we report a facile method to fabricate poly(tetrafluoroethylene) (PTFE)-reinforced composite membrane based on sulfonated poly(fluorenyl biphenyl) indole ionomer (PTFE-SPFBI). The resultant reinforced membrane exhibits an ultra-thin and dense structure, leading to a reduced swelling ratio, exceptional mechanical durability (with over 200 % elongation at break), and high chemical stability, primarily attributed to the presence of PTFE support. The ultra-thin nature of the PTFE-SPFBI membrane, coupled with its superior proton conductivity, significantly contributes to its performance in fuel cells, achieving a maximum power density of 778 mW cm−2. Notably, this reinforced membrane exhibits remarkable endurance in open-circuit voltage (OCV) test, demonstrating its ability to sustain operation for more than 500 h at 90 °C and 30 % relative humidity. Overall, our work introduces a straightforward and promising approach for the fabrication of high-performance pore-filling PEMs using hydrocarbon ionomers, emphasizing enhanced durability and proton conductivity.

Enabling high-temperature application of Nafion membrane via imitating ionic clusters in proton conduction channels

Nafion membranes, representative of perfluorosulfonic acid (PFSA) proton exchange membranes are not effective in dehydrated state and high-temperature condition (>100 oC). The traditional hybrid modification would lower the mechanical strength of the membrane due to the large-scale phase separation. In this work, a hyperbranched polyamide (HBM) featuring high sulfonate concentration and nanoparticle morphology is synthesized and non-destructively filled into Nafion matrix to imitate the “ionic cluster” to accelerate the proton conduction at elevated temperature. During the non-destructively membrane modification, the Nafion PFSA membrane is swelled in the solution and the main chain structure is expanded, the HBM macromolecules is simultaneously filled into the membrane together with the solvent. After the removal of solvent, HBM end-capped with –COOH forms strong hydrogen bonds with the sulfonate groups in Nafion matrix. As a result, proton conductivity of the composite membrane can reach 0.047 S/cm, which is 1.9 times higher than that of the pristine Nafion membrane, at 110 oC and 60% RH. Given the excellent overall stability, fuel cell performance of the HBM-modified Nafion membrane is studied and a 30% increase in power density is observed, suggesting a viable strategy to expand the operation temperature of PFSA-based fuel cells.

Negative impact of poly(acrylic acid) on proton conductivity of electrospun catalyst layers

The electrospun catalyst layers (E-spun CLs) have attracted great attention recently owing to their decent performance and durability compared to conventional coated CL fabricated by scrape coating. However, proton transport in E-spun CLs is poorly understood, hindering further performance improvements. We unravel herein that the high molecular weight (MW) polymer used to form nanofibers, usually Poly(acrylic acid) (PAA), is a key factor affecting the proton conductivity. Nuclear magnetic resonance (NMR) unravels strong interaction between the ionomer and PAA. The proton conductivity of ionomer membranes with varying PAA content under different ionomer volume fractions and relative humidity (RH) was quantitatively assessed using the four-probe electrochemical impedance spectroscopy (EIS). E-spun CL exhibited lower proton conductivity than coated CL or pseudo catalyst layer (PCL) at the same ionomer volume fraction due to the detrimental effects of PAA. The proton transport tortuosity of E-spun CL increased with RH, likely attributed to the significant swelling ratio of PAA. The proton transport tortuosity of E-spun CL displayed less sensitivity to the ionomer volume fraction, which can be attributed to the homogeneous distribution of the ionomer within the nanofibers. Our work implies that the key to enhancing proton conductivity of E-spun CLs is to remove PAA completely, or to replace PAA with alternatives that would not impair proton transport.

Development of Hydrophilic Oxide/Polymer Composite Membranes for Polymer Electrolyte Fuel Cells Operating at Wide Temperature Range

Toward the wide-spread use of heavy-duty vehicles (HDVs) operated by polymer electrolyte fuel cells (PEFCs) should approach the higher temperature around 120oC besides normal temperature (60-80oC). Commercial perfluorosulfonic acid-based electrolyte (PFSA, e.g. NafionⓇ) shows better proton conductivity with chemical stability in wide temperatures range, though decreases under low back pressure at 100~120 oC. In order to improve the proton conductivity at the higher temperature range, composite membrane of NafionⓇ with a hydrophilic filler of Ta doped TiO2 (Ta-TiO2) was synthesized. The Ta-TiO2 nanoparticles fillers with fused-aggregate network microstructure were synthesized by the flame method, and were crushed by wet mill(Star Burst, :Sugino Machine Limited CO.). The fillers were mixed with NafionⓇsolution (20 wt.%：D2020 Chemours Co.) by use of a rotary ultrasonic dispersing processor (500 rpm, 60 min. PR-1 :Thnky Co.), a planetary ball mill (500 rpm、30 min.：PULVERISETTE 6：FRITSCH Co.), and a defoaming processor (500 rpm、5 min.：HM-400W: Kyouritu Seiki). The dispersion solution was coated in hot air by use of a die coating system (die coater: Taku-Dai Mini-50: Daimon Co., Ltd.), and were hot-pressed (140 ℃ 3 min. TCMD-2.5:TOHO KOGYO co.) to form composite membranes (9 cm×9 cm ×25 µmt).The cross-sectional backscattered electron image BSE) of the composite membrane observed by scanning electron microscope (SEM, acceleration voltage 2 kV, SU9000: Hitachi High-Tech Co.) and transmission electron microscope (TEM, H-9500: Hitachi High-Tech Co.). The proton conductivity of the composite membrane was measured by the AC four-probe method. The current-voltage (IV) polarization curves of Single cells using the prepared composite membrane (membrane thickness: 25 µm) were measured at 80 ℃ 100% RH and 120 ℃ 20% RH, back pressure 50 kPaG.The obtained composite membranes were well flexibility with softness. The BSE images indicated that the high contrast images of Ta-TiO2 parties were uniformly dispersed in composite membrane. The higher magnified of the cross-sectional TEM images also showed that the hydrophilic surface of Ta-TiO2 adhered to the Nafion® without any air pores. The proton conductivity of the composite membrane at 80% RH increased with increasing Ta-TiO2 content and showed maximum value of 0.13 S cm-1at 3 wt%, and then decreased. The maximum proton conductivity was 1.3 times higher than that of Nafion®. The IV performance of the single cell using composite membrane kept same performance to that using Nafion® membrane at 80 oC 100% RH, and then improved at 120 oC 20% RH. The water content at 120 oC 20% RH kept higher value by the effect of hydrophilicity of the Ta-TiO2, which would be one of the reasons to enhance the cell performance at 120 oC 20% RH. Figure 1

Applicability of Phosponated Poly(pentafluorostyrene) Fiber Reinforced Nafion Composite Membranes in Low-Temperature Fuel Cells

Reducing the fuel crossover of proton exchange membranes (PEMs) is an important measure to improve the fuel efficiency and performance of fuel cells and electrolyzers 1, 2. Additionally, the long-term stability and safety of PEM-based systems increase with a reduction in the gas crossover 1, 3, 4. A possible approach for reducing the gas crossover of a PEM is the implementation of fiber meshes to form a composite membrane 5. Furthermore, fiber-reinforced composite membranes can also increase the mechanical properties of PEMs and therefore enable the utilization of thinner membranes without sacrificing the mechanical integrity of the membrane or causing safety risks 6.In this work, we demonstrate the successful fabrication of electrospun fibers of a partially phosophonated, conductive polymer (phosponated poly(pentafluorostyrene); PWN70) and its non-phosphonated and, therefore, non-conductive equivalent (poly(pentafluorostyrene); PPFSt). Two different loadings of both fiber meshes were successfully infiltrated with Nafion, analyzed mechanically and electrochemically, and compared to a non-reinforced Nafion reference. We show that the mechanical properties of both fiber-reinforced composite membranes are superior to the reference membrane. The electrochemical analysis of the membrane electrode assemblies (MEAs) shows a reduction in performance with the incorporation of the non-conductive PPFSt fibers. An increase in the high-frequency resistance (HFR) of the MEAs containing the non-conductive PPFSt fibers explains the reduced performance and scales with fiber loading. In contrast, the MEAs with the proton conductive PWN70 fiber reinforcement maintained the same HFR and performance as the reference, independently of the fiber loading. Additionally, hydrogen crossover measurements revealed a significantly reduced hydrogen crossover of the MEAs composed of the conductive PWN70 fiber-reinforced membranes (between 30 and 40 % less than the reference). We hypothesize that PWN70 shows a decreased diffusivity for hydrogen compared to Nafion, and therefore, the fibers in the Nafion matrix increase the tortuosity of the membrane for fuel crossover.In summary, we developed a fiber-reinforced Nafion membrane with improved mechanical and gas barrier properties while maintaining the membrane's proton conductivity compared to the same membrane without reinforcement.References Q. Tang, B. Li, D. Yang, P. Ming, C. Zhang and Y. Wang, Int. J. Hydrog. Energy, 46(42), 22040–22061 (2021).M. Schalenbach, M. Carmo, D. L. Fritz, J. Mergel and D. Stolten, Int. J. Hydrog. Energy, 38(35), 14921–14933 (2013).B. Wu, M. Zhao, W. Shi, W. Liu, J. Liu, D. Xing, Y. Yao, Z. Hou, P. Ming, J. Gu and Z. Zou, Int. J. Hydrog. Energy, 39(26), 14381–14390 (2014).C. Klose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach and S. Thiele, J. Electrochem. Soc., 165(16), F1271-F1277 (2018).J. Choi, K. M. Lee, R. Wycisk, P. N. Pintauro and P. T. Mather, Macromolecules, 41(13), 4569–4572 (2008).J. B. Ballengee and P. N. Pintauro, Macromolecules, 44(18), 7307–7314 (2011).

Non-destructively incorporating ceria in Nafion membrane as hydroxyl radical scavenging agent for long-term PEMFC application

Aiming at enhancing the long-term operation of proton exchange membrane fuel cell (PEMFC), Nafion as a typical example of perfluorosulfonic acid proton exchange membrane is non-destructively modified by sulfonated ceria (CeO2-DS) nanoparticles via a swelling-filling strategy. CeO2-DS nanoparticles in Nafion matrix can not only act as radical scavenging agent to improve the durability of Nafion, but also assist the re-construction of the efficient proton conduction channel in the composite Nafion membrane. Both oxidative stability and proton conductivity of the Nafion membrane are therefore remarkably improved with the great mechanical and thermal stability of Nafion maintained. PEMFC equipped with the modified Nafion membrane therefore outperforms that with the pristine Nafion membrane in terms of both power output and durability. Specifically, the maximum power density of the PEMFC equipped with modified Nafion after Fenton accelerated degradation test was significantly improved by ca. 25 % compared with that of the pristine Nafion membrane. This work hence provides a facile way to improve the durability of the PEMFC for practical applications.

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

Casting Electrodes on PEEK Reinforced Sulfonated Polyphenylsulfone Membrane

Researchers are exploring the potential of proton exchange membranes made from hydrocarbon polymers that do not contain fluorine. These polymers possess desirable properties that could make them more environmentally friendly and cost-effective compared to current perfluorinated sulfonic acids (PFSA). Hydrocarbon polymers have a unique structure that maintains high proton conductivity while reducing gas crossover, thus presenting a promising alternative to PFSA membranes [1]. Previous studies have demonstrated the potential of hydrocarbon membranes in electrolyzers using sulfonated polyphenylene sulfone (sPPS) [2]. However, sPPS has a high ion exchange capacity (2.17 – 3.57 meq/g), leading to excessive water uptake that causes the membrane to swelling and impedes upscaling, such as casting anodes directly onto the membrane. To overcome this issue, a woven, open-mesh PEEK substrate was incorporated into the membrane. The reinforced membrane exhibited a significant reduction in water uptake of up to 53% at room temperature and 43% at 60°C compared to the initial membrane. This improvement made it possible to cast the anode directly onto the membrane, resulting in a homogeneous surface (Fig. 1 left). In addition, preliminary electrolysis tests showed promising performance with low membrane resistance of 69 mΩcm² for a 74 µm thick membrane (Fig. 1 right). Literature: [1] Miyake, J.; Taki, R.; Mochizuki, T.; Shimizu, R.; Akiyama, R.; Uchida, M.; Miyatake, K. Design of flexible polyphenylene proton-conducting membrane for next-generation fuel cells. Sci. Adv. 2017, 3(10), eaao0476. DOI: 10.1126/sciadv.aao0476[2] Klose, C.; Saatkamp, T.; Münchinger, A.; Bohn, L.; Titvinidze, G.; Breitwieser, M.; Kreuer, K.; Vierrath, S. All‐Hydrocarbon MEA for PEM Water Electrolysis Combining Low Hydrogen Crossover and High Efficiency. Adv. Energy Mater. 2020, 10 (14), 1903995. DOI: 10.1002/aenm.201903995 Figure 1

Novel chitosan-ionic liquid immobilized membranes for PEM fuel cells operating above the boiling point of water

Novel chitosan (CS) composite membranes modified with ionic liquids (ILs), namely, 1-Hexyl-3- methylimidazolium tricyanomethanide ([HMIM][TCM]), Diethylmethylammonium methanesulfonate ([DEMA][OMs]), were synthesized to be used as a polymer electrolyte membrane (PEM) in for PEM fuel cells. The ionic conductivities of the prepared membrane samples were evaluated using electrochemical impedance spectroscopy (EIS). The CS is one of the attractive choices of green and sustainable membrane materials in PEMs because of its chemical tunability and cost-effectiveness. The membranes were prepared by solution casting followed by a solvent evaporating procedure. The low proton conductivity of pristine CS biopolymer was enhanced by the incorporation of ILs in the membrane framework. Tensile testing confirmed the excellent membrane mechanical integrity. A significant enhancement in the membranes’ characteristics was observed upon the introduction of [DEMA][OMs] into its matrix. The experimental results showed enhanced proton conductivities of the prepared membranes along with enhanced flexibility. The proton conductivity of pristine CS membrane was increased from 8.4 × 10−4 to 1.25 × 10−2 S/cm and 1.1 × 10−2 S/cm when a 30 wt% [HMIM][TCM] and 100 wt% [DEMA][OMs] were added, respectively. Synergistic effects of amine and imidazolium-based ILs on the electrical, structural, water uptake, and thermal properties of CS-based biopolymer solid electrolyte membranes are reported for the first time in this work. The aforementioned characterization results demonstrate the potential of using these membranes in PEM fuel cells operating above the boiling point of water and at a lower cost. This work showed that there should be an optimization amount of the ILs content in the membrane to maintain its mechanical integrity.

Grafting of Polymer Brushes on MOF Surface to Achieve Proton-Conducting Membranes

Grafting of Polymer Brushes on MOF Surface to Achieve Proton-Conducting Membranes

Impact of deposited Pt particles on water channel connectivity and proton conductivity in proton exchange membranes: A molecular dynamics study

Deposition of platinum ions in the proton exchange membrane significantly affects the long-term stability and proton transport capacity of the membrane electrode assembly. In this study, the impacts of deposited Pt particles on the intrinsic properties of proton exchange membranes and its mechanisms are investigated using molecular dynamics simulation method. The effect of differently sized Pt particles on water channel connectivity and proton conductivity in proton exchange membranes under dry, normal, and saturated conditions was detailly discussed. The results reveal that Pt particles reduce water channel connectivity at low hydration level while increasing it at normal and high hydration levels. However, the enhancement mechanism is different. Moreover, proton conductivity was evaluated by examining the diffusion of hydronium ions and hydrogen bond dynamics. We found that the proton conduction performance of the membranes at low hydration levels is significantly reduced by Pt particles. We believe this study can promote the design of more robust and efficient proton exchange membranes.

Self-Healing Sulfonated Poly(ether ether ketone)-Based Polymer Electrolyte Membrane for Direct Methanol Fuel Cells: Effect of Solvent Content.

Proton exchange membranes (PEMs) with superior characteristics are needed to advance fuel cell technology. Nafion, the most used PEM in direct methanol fuel cells (DMFCs), has excellent proton conductivity but suffers from high methanol permeability and long-term performance degradation. Thus, this study aimed to create a healable PEM with improved durability and methanol barrier properties by combining sulfonated poly(ether ether ketone) (SPEEK) and poly-vinyl alcohol (PVA). The effect of changing the N,N-dimethylacetamide (DMAc) solvent concentration during membrane casting was investigated. Lower DMAc concentrations improved water absorption and, thus, membrane proton conductivity, but methanol permeability increased correspondingly. For the best trade-off between these two characteristics, the blend membrane with a 10 wt% DMAc solvent (SP10) exhibited the highest selectivity. SP10 also showed a remarkable self-healing capacity by regaining 88% of its pre-damage methanol-blocking efficiency. The ability to self-heal decreased with the increasing solvent concentration because of the increased crosslinking density and structure compactness, which reduced chain mobility. Optimizing the solvent concentration during membrane preparation is therefore an important factor in improving membrane performance in DMFCs. With its exceptional methanol barrier and self-healing characteristics, the pioneering SPEEK/PVA blend membrane may contribute to efficient and durable fuel cell systems.

Advances in boron nitride‐based materials for electrochemical energy storage and conversion

AbstractEnergy storage and conversion (ESC) devices are regarded as predominant technologies to reach zero emission of carbon dioxide, which still face many challenges, such as poor safety, limited cycle life, low efficiency, etc. Hexagonal boron nitride (h‐BN), distinguished by its robust mechanical strength, chemical inertness, exceptional thermal stability, and superior ion conductivity, has appeared to meet some challenges of ESC devices. Typically, h‐BN can act as a perfect modifier to enhance the safety of batteries by improving the mechanical strength and heat dissipation of separators, extend cycle life of Li metal batteries by protecting solid state electrolyte from reducing and increase efficiency of fuel cells by improving the proton conductivity of membranes. Besides, recent progress on doping, surface modification, tailoring quantum dots, heterostructures, and hybridizations with other nanomaterials has made it possible to extensively apply h‐BN to other ESC technologies. This review provides a comprehensive overview of the up‐to‐date synthetic strategies for BN‐based materials and discusses the most recent breakthroughs on their application in electrochemical ESC technologies. Also, the challenges and future development for BN‐based materials in these fields are assessed.

Development of low-cost nafion-lignin composite conductive membranes for application in direct methanol fuel cells

The advantages of the direct methanol fuel cell (DMFC) are its high energy density, simple size with a compact fuel tank and effortless storage and transportation, making it one of the leading fuel cell types. However, the commercialisation of this technology is hampered by a number of issues, including methanol crossover and the high cost of Nafion membranes. In this study, an environmentally friendly composite membrane Nafion-lignosulfonate (LS) with merits of high proton conductivity and low methanol permeability was prepared by simple solution casting. An Electrochemical Impedance Spectroscopy (EIS) approach was used to determine the proton conductivity of the composite membranes at room temperature. A composite membrane with 10 wt% filler (rN/LS10) is found to show the best selectivity of 1.10 × 104 S s cm−3. In addition, this composite membrane shows a proton conductivity of 0.92 mS cm−1 and a permeability to methanol of 8.34 × 10−8 cm2 s−1. A single-cell performance test confirms that rN/LS10 shows a power density of 11.7 mW/cm2, which is a 20.9% improvement over commercial N117 at room temperature. Compared to N117, rN/LS10 shows acceptable durability for a fuel cell operated at 0.3 V for 24 h with a decay rate of 0.51 mA cm−2.h−1. More importantly, by reducing the amount of Nafion polymer used, the cost of the rN/LS composite membrane can be reduced by 8.02% compared to commercially N117 while maintaining stability and performance. On the road to commercialisation, the Nafion-lignosulfonate composite membrane is, therefore, a competitive choice for DMFCs.

Effect of solvent-free membranes-forming processes on HT-PEM properties of highly soluble polybenzimidazole

The cost-effective sol-gel process for the preparation of phosphoric acid (PA) doped P-PBI membranes using PPA as both condensation reagent and solvent could avoid the use of hazardous organic solvents. However, optimizing the trade-off effect between mechanical properties and proton conductivity of sol-gel membranes by increasing polymer content is ineffective due to the limited solubility of P-PBI in PPA. Herein, we successfully fabricated a series of sol-gel membranes with tunable properties using a highly soluble polybenzimidazole (N-PBI). In addition, the sol-gel (5 wt%) N-PBI membrane was further specially dried and post-doped with PA to obtain a re-doped sol-gel N-PBI membrane. Therefore, the properties of PA-doped N-PBI membranes fabricated using three different processes-conv, sol-gel, and re-doped sol-gel-were thoroughly characterized. The sol-gel N-PBI membranes demonstrated a dependence of mechanical properties and proton conductivity on polymer content, with a maximum tensile strength of 7.0 MPa at 7 wt% polymer content and a maximum proton conductivity of 205 mS/cm (200 °C) at 2 wt% polymer content. The ADL-controlled re-doped sol-gel N-PBI membrane achieved higher saturated ADL than the sol-gel N-PBI membrane, resulting in higher proton conductivity and fuel cell performance. The sol-gel (2 wt%) N-PBI membrane exhibited an ultra-high H2/O2 peak power density of 1058 mW/cm2 under an optimized operating condition, and the sol-gel (7 wt%) N-PBI membrane achieved stable operation without apparent degradation for over 2000 h at 160 °C with 0.3 A/cm2 current density.

Doped Proton-Conducting Membranes Based on Heat-Resistant Heterochain Polymers

Fuel cells with solid polymer electrolytes are the most popular chemical current sources and versatile sources of energy today. Proton-conducting membranes based on a guanidine-containing polymer of the cationic type on a polybenzimidazole matrix were obtained in this work. The membranes were created by doping film materials with orthophosphoric acid from a polymer-polymer mixture of N-phenyl-substituted polyhexamethylene guanidine (10 %) and polybenzimidazole. In this case, phosphoric acid remains in the membrane due to hydrogen bonds with the functional groups of the polymer and electrostatic interactions resulting from the doping of polyguanidine, which transforms into a polycationic form. As the content of polyguanidine increases in the polymer-polymeric mixture, the proton conductivity of the membrane increases. It was discovered that these membranes possess high thermal stability, with only a 20% mass loss occurring at 350 °C. Additionally, they exhibit high proton conductivity of 0.3·10-1 mS/cm at temperatures of 130°C and higher, as well as satisfactory mechanical properties, with a tensile strength (σр) of 21-27 MPa and elongation at break (εр) of 7–11 %. The value of activation energy (Еа) is also low, at 0.145 eV, which suggests that these membranes have potential for using them in solid polymer electrolyte fuel cells.

Crystallizing Self-Standing Covalent Organic Framework Membranes for Ultrafast Proton Transport in Flow Batteries.

Covalent organic frameworks (COFs) display great potential to be assembled into proton conductive membranes for their uniform and controllable pore structure, yet constructing self-standing COF membrane with high crystallinity to fully exploit their ordered crystalline channels for efficient ionic conduction remains a great challenge. Here, a macromolecular-mediated crystallization strategy is designed to manipulate the crystallization of self-standing COF membrane, where the -SO3 H groups in introduced sulfonated macromolecule chains function as the sites to interact with the precursors of COF and thus offer long-range ordered template for membrane crystallization. The optimized self-standing COF membrane composed of highly-ordered nanopores exhibits high proton conductivity (75 mS cm-1 at 100 % relative humidity and 20 °C) and excellent flow battery performance, outperforming Nafion 212 and reported membranes. Meanwhile, the long-term run of membrane is achieved with the help of the anchoring effect of flexible macromolecule chains. Our work provides inspiration to design self-standing COF membranes with ordered channels for permselective application.