High Proton Conductivity Research Articles

Covalent triazine frameworks crosslinked microporous polymer membranes with fast and selective ion transport for ultra-stable vanadium redox flow batteries

The vanadium redox flow batteries (VRFBs) are an essential pathway to long-duration energy storage with the merits of power and energy decoupling, long lifetime and safety. However, low coulombic efficiency stemming from vanadium crossover across the membrane together with notable ohmic loss originated from low proton conductivity of the membrane still limits high performance operation of the VRFBs. Herein, we proposed 2,2′-bipyridine-based covalent triazine frameworks (bipCTF) crosslinked sulfonated-poly (4,4′-diphenylether-5,5′-bibenzimidazole) (SOPBI) (bipCTF/SP-100) for use as the membrane in VRFBs, which synergistically prevents vanadium crossover and enhances proton conductivity. By delicately tuning the sulfonation degree and properly incorporate bipCTF, the bipCTF/SP-100 membrane is successfully synthesized based on OPBI polymers, which delivers a reduced area resistance of 0.3 Ω cm2 and a low VO2+ permeability of 19.05 × 10−9 cm2 s−1, affording an excellent trade-off between proton conductivity and ion selectivity. Theoretical calculation further corroborates that the high proton conductivity of bipCTF/SP-100 is attributed to the ionic channels formed by bipCTF, while the superior ion selectivity is assigned to protonated imidazole and pyridine. Benefiting from microporous bipCTF/SP-100 membrane, the VRFB exhibits a high CE of 99.8 % and an excellent EE of 78.3 % at 250 mA cm−2 and meanwhile yields a high capacity retention of 94.8 % after 200 cycles at 200 mA cm−2, which shows enormous potential for high power density operation of the VRFBs.

The chemical crosslinking effect of polybenzimidazole/polyvinyl alcohol blend membranes for proton exchange membrane fuel cells: An experimental study

AbstractIn this survey, the different weight ratios of polybenzimidazole (PBI)/polyvinyl alcohol (PVA) blend polymer membranes were produced using the solution‐casting method. The crosslinking agents of phosphoric acid (PA) and glutaraldehyde (GA) were studied separately to prevent the PVA water solubility in the PBI/PVA blend membrane structure. The GA crosslinking (24 h) successfully prevented membrane solubility, reducing it to below 1%. The chemically crosslinked blend membrane (Cr‐PBI/PVA‐9:1) has the highest proton conductivity result which is 0.209 S cm−1 at 80°C and it has excellent oxidative stability since the membrane only lost 4% of its weight in a Fenton agent after 96 h. The Cr‐PBI/PVA‐9:1 also has higher proton conductivity than the commercial PBI membrane (0.122 S cm−1 at 80°C). The glass transition temperature of the synthesized Cr‐PBI/PVA‐9:1 blend membrane is greater than the synthesized PBI membrane (390°C). The current density and power density measured at 0.6 V for the synthesized Cr‐PBI/PVA‐9:1 membrane were found to be 504 mA cm−2and 251 mW cm−2. This work sheds light on the potential use of PVA in PEMFC applications by mixing PVA with a high‐temperature polymer like PBI and crosslinking the membrane with a prepared GA crosslinking agent.

Molecular-Level Modification of Sulfonated Poly(arylene ether ketone sulfone) with Polyoxovanadate-Ionic Liquid for High-Performance Proton Exchange Membranes.

In this work, a proton-conductive inorganic filler based on polyoxovanadate (NH4)7[MnV13O38] (AMV) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM TFSI) was synthesized for hybridization with sulfonated poly(aryl ether ketone sulfone) (SPAEKS) to address the "trade-off" between high proton conductivity and mechanical strength. The novel inorganic filler AMV-EMIM TFSI (AI) was uniformly dispersed and stable within the polymer matrix due to the enhanced ionic interaction. AI provided additional proton transport sites, leading to an elevated ion exchange capacity (IEC) and improved proton conductivity, even at low swelling ratios. The optimized SPAEKS-50/AI-5 (50 for degree of sulfonation of SPAEKS and 5 for weight percentage of AI filler) membrane exhibited the highest proton conductivity of 0.188 S·cm-1 at 80 °C with an IEC of 2.38 mmol·g-1. The enhancement of intermolecular forces improved the mechanical strength from 35 to 55 MPa and improved the elongation at break from 17 to 45%, indicating excellent mechanical properties. The hybrid membrane also demonstrated reinforced methanol resistance due to the hydrogen bonding network and blocking effect, making it suitable for direct methanol fuel cell (DMFC) applications, which exhibited a power density of 15.1 mW·cm-2 at 80 °C. The possibility of further functionalizing these hybrid membranes to tailor their properties for specific applications presents exciting new avenues for research and development. By modification of the type and distribution of fillers or incorporation of additional functional groups, the membranes could be customized to meet the unique demands of various energy storage and conversion systems, enhancing their performance and broadening their application scope. This work provides new insights into the design of polymer electrolyte membranes through inorganic filler hybridization.

High-Performance Proton Field-Effect Transistor Based on Two-Dimensional Cd Vacancy-Resided Cd0.85PS3Li0.15H0.15.

Ion transport is a critical phenomenon underpinning numerous biological, physical, and chemical systems. Proton transistors leveraging proton transport face significant limitations, such as a low on-off ratio and deficient carrier mobility, which restrict their applicability in biological and other scenarios. This study explores the use of two-dimensional (2D) vacancy-residing transition metal phosphorus trichallcogenide-based membranes as the active layer for proton field-effect transistors. The synthesized Cd0.85PS3Li0.15H0.15 membrane exhibits a well-organized layered structure and high hydrophilicity, with nanometer-sized interlayers containing interconnected water networks. These distinct features facilitate proton conduction, leading to a high proton conductivity value of 0.83 S cm-1 at 98% relative humidity and 90 °C, with an activation energy of 0.26 eV. The Cd0.85PS3Li0.15H0.15-based proton transistor demonstrates tunability via gate voltage, thereby enabling effective modulation of proton flow across source and drain electrodes. The transistor notably showcases superior switching characteristics, with an on/off ratio surpassing 5.51 and a carrier mobility of 8.84 × 10-2 cm2 V-1 s-1. The underlying mechanism for this performance enhancement is attributed to electric-field-induced switching in Cd vacancies. This research boosts the development of highly versatile ionotropic devices by introducing advanced 2D ion-conductive membranes.

Quaternary Ammonium Polybenzimidazole/Polymeric Ionic Liquid Cross-Linked Membranes with High Proton Conductivity and Stability for HT-PEM Applications

Quaternary Ammonium Polybenzimidazole/Polymeric Ionic Liquid Cross-Linked Membranes with High Proton Conductivity and Stability for HT-PEM Applications

Intrinsically Microporous Ion-Pair Membranes for HT-PEMFCs

Fuel cells are electrochemical devices with high energy efficiency expected to be applied economically and eco-friendly across various energy sectors. Low-temperature polymer electrolyte membrane fuel cells (LT-PEMFCs) using Nafion operates at a relatively low operating temperature (60-80°C) and fully hydration condition. HT-PEMFC is operable at high temperatures (140-180°C), but requires anhydrous conditions to avoid loss of doped phosphoric acid (PA). In this presentation, polymer membranes designed through with intrinsic microporosity were synthesized through super acid polycondensation. We demonstrated that high proton conductivity (106.33 mS cm-1 at 180℃) is obtained by forming phosphoric acid filled ion-channels within the interconnected microporous structure. Moreover, ion-pair coordinated PIMs are fabricated by methylation of PIMs to improve PA retention even under humidified conditions. It is suggested that the water tolerance of ion-pair coordinated PIMs is improved and can be operated under various conditions regardless of humidification and operating temperature and exceptional membrane electrode assembly performance and durability achieved even under humidified reformate gas conditions.

Introducing Platinum Cryoaerogel As a Low Loading Cathode Catalyst in PEM Water Electrolysis

An important cost factor for polymer electrolyte membrane water electrolysers is precious metals as the catalyst layers. Therefore, reducing of the platinum loading on the cathode side and the iridium on the anode is essential to reduce the overall costs of hydrogen production. Cryoaerogels from noble metal nanoparticles are a suitable, yet unexplored material for use as a catalyst in water electrolysis. They combine high porosity and surface area with an excellent catalytic activity at low loadings of noble metal.[1] Recently, we have succeeded in producing a carbon-based gas diffusion electrode (GDE) coated with platinum cryoaerogel as the catalyst. The mechanical connection to the carbon underneath as well as maintaining a high protonic conductivity in contact to the Nafion membrane allowed the application to the water electrolysis cell. The manufacturing includes an oven treatment, whose temperature is particularly decisive for the structure of the cryoaerogel. Figure 1 left shows the polarization curves of the samples pyrolyzed at 300°C, 350°C and 500°C compared to a commercial GDE (platinum loading of 0.5 mg/cm²). All measurements are repeated three times and showed good reproducibility, as indicated by the error bars on the graph. Among the different temperatures, 300°C is the optimum for the pyrolysis process as it showed the lowest voltages. The catalytic performance of the different samples can be correlated to the micro-structure of the cryoaerogel layer represented by the SEM images and the electronic-structure of the platinum as shown by X-ray photoelectron spectroscopy (XPS). Although in figure 1 the performance of the cryoaerogel catalyst layers is not better than the commercial GDE, however, the platinum loading is significantly reduced by 70% (0.15 mg/cm2). Moreover, the reproducibility of the measurements proofs the possibility of using cryoaerogels in the full water electrolysis cell.[1] Müller, D., Zámbó, D., Dorfs, D., Bigall, N. C., Cryoaerogels and Cryohydrogels as Efficient Electrocatalysts. Small 2021, 17, 2007908. https://doi.org/10.1002/smll.202007908 Figure 1

High intrinsic proton conduction in one three-dimensional indium(III)-organic framework built by amino terephthalic acid

It is imperative to carry out more research on the proton conduction in metal-organic frameworks (MOFs) made of main group metals. Inspired by this, we synthesized a 3D indium-based MOF, [In(BDC-NH3)(BDC-NH2)]∙1.5DMF∙1.5H2O (namely In-MOF 1), which is made up of [In(CO2)4] metal nodes and 2-amino terephthalic acid (H2BDC-NH2) organic linkers. Meanwhile, organic ligand functionalization has been proven to be one of the effective techniques to boost the proton conductivity of the corresponding metal-organic frameworks. In light of this, the functionalized MOF was successfully synthesized using In(III) ions and H2BDC-NH2, which not only has excellent water stability but also bear some hydrophilic groups such as –NH2 and carboxylate units, which may act as a pivotal role in improving the proton conductivity (σ). Consequently, the σ of In-MOF 1 was thoroughly examined. As expected, its optimal σ can reach 0.81 × 10−2 S cm−1 under 100 °C and 98 % relative humidity (RH), substantially higher than the In-MOF composed only of terephthalic acid. Finally, we estimated its activation energy (Ea) at 98 % and 68 % RHs using the Arrhenius equation, and the proton transport mechanism was further explored.

Highly Fluorinated Nanospace in Porous Organic Salts with High Water Stability/Capability and Proton Conductivity.

Water in hydrophobic nanospaces shows specific dynamic properties different from bulk water. The investigation of these properties is important in various research fields, including materials science, chemistry, and biology. The elucidation of the correlation between properties of water and hydrophobic nanospaces requires nanospaces covered only with simple hydrophobic group (e.g., fluorine) without impurities such as metals. This work successfully fabricated all-organic diamondoid porous organic salts (d-POSs) with highly fluorinated nanospaces, wherein hydrophobic fluorine atoms are densely exposed on the void surfaces, by combining fluorine substituted triphenylmethylamine (TPMA) derivatives with tetrahedral tetrasulfonic acid. This d-POSs with a highly fluorinated nanospace significantly improved their water stability, retaining their crystal structure even when immersed in water over one week. Moreover, this highly hydrophobic and fluorinated nanospace adsorbs 160 mL(STP)/g of water vapor at Pe/P0=0.90; this is the first hydrophobic nanospace, which water molecules can enter, in an all-organic porous material. Furthermore, this highly fluorinated nanospace exhibits very high proton conductivity (1.34×10-2 S/cm) at 90 °C and 95 % RH. POSs with tailorable nanospaces may significantly advance the elucidation of the properties of specific "water" in pure hydrophobic environments.

Highly Fluorinated Nanospace in Porous Organic Salts with High Water Stability/Capability and Proton Conductivity

AbstractWater in hydrophobic nanospaces shows specific dynamic properties different from bulk water. The investigation of these properties is important in various research fields, including materials science, chemistry, and biology. The elucidation of the correlation between properties of water and hydrophobic nanospaces requires nanospaces covered only with simple hydrophobic group (e.g., fluorine) without impurities such as metals. This work successfully fabricated all‐organic diamondoid porous organic salts (d‐POSs) with highly fluorinated nanospaces, wherein hydrophobic fluorine atoms are densely exposed on the void surfaces, by combining fluorine substituted triphenylmethylamine (TPMA) derivatives with tetrahedral tetrasulfonic acid. This d‐POSs with a highly fluorinated nanospace significantly improved their water stability, retaining their crystal structure even when immersed in water over one week. Moreover, this highly hydrophobic and fluorinated nanospace adsorbs 160 mL(STP)/g of water vapor at Pe/P0=0.90; this is the first hydrophobic nanospace, which water molecules can enter, in an all‐organic porous material. Furthermore, this highly fluorinated nanospace exhibits very high proton conductivity (1.34×10−2 S/cm) at 90 °C and 95 % RH. POSs with tailorable nanospaces may significantly advance the elucidation of the properties of specific “water” in pure hydrophobic environments.

Synergistic Molecular Alignment and Dipole Polarization in Stretched Nafion/Poly(vinylidene fluoride) Blend Membranes for High Proton Conduction in PEMFCs.

The nanostructure of Nafion and poly(vinylidene fluoride) (PVDF) blend membranes is successfully aligned through a mechanical uniaxial stretching method. The phase-separated morphology of Nafion molecules distinctly forms hydrophilic proton channels with increased connectivity, resulting in enhanced proton conductivity. Additionally, the crystalline phase of PVDF molecules undergoes a successful transformation from the α- to β-phase during membrane stretching, demonstrating an alignment of fluorine and hydrogen atoms with a TTTT(trans) structure. The aligned nanostructure of the blend film, combined with the dipole polarization of the β-phase PVDF, synergistically enhances the proton conduction through the membrane for operating proton-exchange membrane fuel cells (PEMFCs). The controlled structures of the blend membranes are thoroughly investigated using atomic force microscopy and small-angle X-ray scattering. Furthermore, the improved in-plane proton conductivity facilitates increased proton conduction at the interface between the membrane and catalyst layer in the membrane-electrode assembly, ultimately enhancing the power generation of PEMFCs.

Self-assembly of cis-trans Ta/W mixed-addendum POMs based on hexalacunary [H2P2W12O48]12− building blocks

The synthesis of Ta-substituted polyoxometalates has always been an attractive but challenging goal. Three novel tantalum-containing 12-tungsto-2-phosphates were successfully prepared using the water bath method. The monomer, K11Li[P2W12(TaO2)6O56]·19H2O (1), is composed of {P2W12} and 6 {Ta(O2)} building blocks, similar to [P2W12(NbO2)6O56]12−. Monomer 1 polymerized to form two cis-trans dimers, K13Li6H-cis-[P2W12Ta4(TaO2)2O59]2·61H2O (2) and KNa3Li4H12-trans-[P2W12Ta4(TaO2)2O59]2·37H2O (3). Compounds 1–3 can serve as a structural motif to manufacture additional fascinating molecular clusters, promoting the advancement of POM chemistry. In contrast to [P2W12(NbO2)6O56]12−, compound 1 exhibits exceptional stability, evidenced by ESI-MS, IR, and NMR spectroscopy. In addition, 2 and 3 exhibit high proton conductivity and superior water adsorption properties.

Effect of current density and operating temperature on degradation of protonic ceramic fuel cells containing BaZr0.8Yb0.2O3-δ electrolyte during long-term operation

Barium zirconate doped with 20 mol% Yb (BaZr0.8Yb0.2O3-δ, BZYb20) is one of the most promising candidates for use as an electrolyte material in protonic ceramic fuel cells (PCFCs) due to its high proton conductivity and high chemical stability under CO2-containing fuel conditions. The long-term durabilities of PCFCs prepared using the BZYb20 electrolyte were evaluated as a function of the current density at 500 and 600 °C over a period of 1000 h. At 600 °C, the internal resistance of the cell increased even under open circuit voltage (OCV) condition. Comparing the voltage lowering rates at a current density of 0.172 A cm−2 based on the current density–voltage curves recorded during the durability tests, rates of 3.0, 5.3, and 9.0%/1000 h were achieved at the OCV, 0.047, and 0.172 A cm−2, respectively. A small amount of Ni elements diffused into the electrolyte from the anode to the cathode side, resulting in the formation of cumulus cloud shapes that corresponded to Ni element segregation at the grain boundaries in the electrolyte layer after long-term durability testing at 0.172 A cm−2. At current densities of 0.047–0.048 A cm−2, the voltage lowering rate at 500 °C was higher than that at 600 °C, with values of 6.0 and 2.6%/1000 h being recorded, respectively. This effect may be due to the higher resistance of the cell at 500 °C compared to that at 600 °C.

Highly acid-stable high-temperature proton exchange membrane: Azide-based polymeric ionic liquids for the enhancement of amino-polybenzimidazole

Polybenzimidazole (PBI) is commonly used for high-temperature proton exchange membranes. However, it is undeniably challenging for phosphoric acid (PA)-doped PBI membranes to have both high proton conductivity and excellent long-term stability. In this study, a series of polymer ionic liquid composite PBI membranes were fabricated. These membranes are made using two azide-functional ionic liquids and amino-polybenzimidazole, adjusting the amount of the two ionic liquids. The ionic pairs offered by the ionic liquids positively impact the transportation of protons and the stability of PA through the replacement of anions. It is noteworthy that crosslinked amino-polybenzimidazole membranes containing functional polymeric ionic liquids have proton conductivity of up to 131.7 mS cm−1 at 180 °C, and the PA retention after 240 h at 160 °C under humidity-free conditions is 86.5 %. In addition, the membrane is used in membrane electrodes with hydrogen and oxygen at the anode and cathode, respectively, exhibiting a peak power density of 694.6 mW cm−2 at 160 °C. And the voltage decay rate is 0.28 mV h−1 after long-term test. The findings indicate that membranes made of functional polymeric ionic liquids crosslinked with amino-polybenzimidazoleprovide a new strategy to enhance fuel cell durability.

Static and dynamic properties investigation of modified polyethersulfone membrane for direct methanol fuel cell applications

The present study's main focus is understanding the impact of modification, especially through phosphoric acid and acetic acid, on polyethersulfone (PES) membranes for direct methanol fuel cell application, as sulfonation is the preferred modification method. The cross-linking introduces the sulfonate, phosphonate, and carboxylate group in the polymer matrix, while the membrane's semi-crystalline nature and homogeneous surface are confirmed through instrumental analysis. The high ion exchange capacity and water retention capacity of the phosphoric acid cross-linked PES membrane (PPES-2) reveal its potentiality. The impact of different hydration levels and temperatures on proton conductivity indicates that based on the operating conditions, the cross-linked membrane can be used, such as at high temperatures and 50 % hydration level, the PPES-2 membrane shows high proton conductivity as well as has low methanol crossover due to the presence of hydroxyl group. At the same time, the acetic acid-treated PES (CPES-2) membrane shows high proton conductivity at 50 % hydration level and low temperature. The same is confirmed through molecular dynamic simulation by understanding their dynamic and static properties. The PPES-2 membrane shows maximum power density (0.34 Wcm−2). In conclusion, the study indicates that PES modification can be done through phosphorylation and carboxylation, apart from sulfonation.

High proton conduction in zirconium silicate/lignin/ionic liquids based- membranes for high temperature PEM fuel cells

In this work, novel Nafion-free membranes composed of zirconium silicate, lignin, and ionic liquids supported on polytetrafluoroethylene have been synthesized for high-temperature applications. Incorporating lignin into zirconium silicate at room temperature has significantly increased the zirconium silicate’s proton conductivity by two orders of magnitude, from 10−4 to 10−2 S/cm. Furthermore, the addition of ionic liquids caused more enhancement in proton conductivity. Two ionic liquids were studied in this work, 1-Ethyl-3-methylimidazolium bis (trifluoromethyl sulfonyl) imide and 1-Hexyl-3-methylimidazolium tricyanomethanide). The incorporation of 1-Hexyl-3-methylimidazolium tricyanomethanide demonstrated the highest proton conduction at room temperature, reaching 0.106 S/cm with an ion exchange capacity of 1.67 meq/g. This most conductive membrane has also demonstrated a slight decrease in proton conductivity (10−3 S/cm) at 150°C showing a high anhydrous conductivity. The membranes’ conductivity was shown to be stable over time as well. The water uptake and swelling ratio results showed improved water retention and dimensional stability. Additional characterization techniques demonstrated positive effect of lignin and ionic liquids inclusion into zirconium silicate on morphology and mechanical properties. Overall, the reported membranes appear to be suitable for high-temperature proton exchange membrane fuel cell applications.

Incorporation of polydopamine functionalized as double‐sided adhesive to connect phosphotungstic acid in Friedel‐Crafts cross‐linked SPEEK sulfonated poly(ether eether ketone) as proton exchange membranes

AbstractUsing highly sulfonated poly(ether ether ketone) (SPEEK) as the base material, the structure and properties of poly(ether ether ketone) (PEEK) membranes are optimized by precisely controlling the doping of phosphotungstic acid (HPW), dopamine (DA), and various amounts of carbon nanomaterials. Compared with conventional PEEK membranes, this optimized membrane exhibits higher proton conductivity, lower water absorption swelling rate, and excellent thermal stability. Highly SPEEK is soluble in water, thus fails to be used in fuel cell applications. Herein, we conduct Friedel‐Crafts method to obtain cross‐linked highly sulfonated membrane with controlled water uptake and swelling while still maintaining high proton conductivity. The polymer is then doped with phosphotungstic acid (HPW) to acquire enhanced performance. To control HPW leakage, polydopamine (PDA) acting as double‐sided adhesive is incorporated within the membrane. By distributing 1 wt.% PDA, the HPW leakage is reduced almost three times. The composite C‐SPEEK/HPWx/PDAy membranes have exhibited excellent overall performance. Specifically, the best proton conductivity result of C‐SPEEK/HPW50 has reached 0.271 S/cm. Moreover, it has presented superb performance in H2/O2 single cell test recorded as power density of 886.13 mW/cm2 while current density is 1614.20 mA/cm2 at 60°C.

Semiconductor Heterostructure (SrFe0.3TiO3-ZnO) Electrolyte with High Proton Conductivity for Low-Temperature Ceramic Electrochemical Cells.

In recent years, ceramic cells based on high proton conductivity have attracted much attention and can be employed for hydrogen production and electricity generation, especially at low temperatures. Nevertheless, attaining a high power output and durability is challenging, especially at low operational temperatures. In this regard, we design semiconductor heterostructure SFT-ZnO (SrFe0.3TiO3-ZnO) materials to function as an electrolyte for fuel cell and electrolysis applications. Using this approach, the functional semiconductor heterostructure can deliver a better power output and high ionic and proton conductivity at low operational temperatures. The prepared cell in fuel cell mode has demonstrated excellent performance of 700 mW cm-2 and proton performance of 540 mW cm-2 at the low temperature of 520 °C, suggesting dominant proton conduction. Further, the prepared cell delivers exceptional current densities of 1.18 and 0.38 A cm-2 (at 1.6 and 1.3 V, respectively) at 520 °C in the electrolysis mode. Our electrochemical cell is stable in fuel and electrolysis mode at a low temperature of 500 °C.

New triazinephosphonate dopants for Nafion proton exchange membranes (PEM).

A new paradigm for energy is underway demanding decarbonized energy systems. Some of them rely on emerging electrochemical devices, crucial in hydrogen technologies, including fuel cells, CO2 and water electrolysers, whose applications and performances depend on key components such as their separators/ion-exchange membranes. The most studied and already commercialized Nafion membrane shows great chemical stability, but its water content limits its high proton conduction to a limited range of operating temperatures. Here, we report the synthesis of a new series of triazinephosphonate derivatives and their use as dopants in the preparation of new modified Nafion membranes. The triazinephosphonate derivatives were prepared by substitution of chlorine atoms in cyanuric chloride. Diverse conditions were used to obtain the trisubstituted (4-hydroxyphenyl)triazinephosphonate derivatives and the (4-aminophenyl)triazinephosphonate derivatives, but with these amino counterparts, only the disubstituted compounds were obtained. The new modified Nafion membranes were prepared by casting incorporation of the synthesized 1,3,5-triazinephosphonate (TPs) derivatives. The evaluation of the proton conduction properties of the new membranes and relative humidity (RH) conditions and at 60 °C, showed that they present higher proton conductivities than the prepared Nafion membrane and similar or better proton conductivities than commercial Nafion N115, in the same experimental conditions. The Nafion-doped membrane with compound TP2 with a 1.0 wt % loading showed the highest proton conductivity with 84 mS·cm-1.

Encapsulation of Imidazole into Ce-Modified Mesoporous KIT-6 for High Anhydrous Proton Conductivity.

Imidazole molecules entrapped in porous materials can exhibit high and stable proton conductivity suitable for elevated temperature (>373 K) fuel cell applications. In this study, new anhydrous proton conductors based on imidazole and mesoporous KIT-6 were prepared. To explore the impact of the acidic nature of the porous matrix on proton conduction, a series of KIT-6 materials with varying Si/Al ratios and pure silica materials were synthesized. These materials were additionally modified with cerium atoms to enhance their Brønsted acidity. TPD-NH3 and esterification model reaction confirmed that incorporating aluminum into the silica framework and subsequent modification with cerium atoms generated additional acidic sites. UV-Vis and XPS identified the presence of Ce3+ and Ce4+ in the KIT-6 materials, indicating that high-temperature treatment after cerium introduction may lead to partial cerium incorporation into the framework. EIS studies demonstrated that dispersing imidazole within the KIT-6 matrices resulted in composites showing high proton conductivity over a wide temperature range (300-393 K). The presence of weak acidic centers, particularly Brønsted sites, was found to be beneficial for achieving high conductivity. Cerium-modified composites exhibited conductivity surpassing that of molten imidazole, with the highest conductivity (1.13 × 10-3 S/cm at 393 K) recorded under anhydrous conditions for Ce-KIT-6. Furthermore, all tested composites maintained high stability over multiple heating and cooling cycles.