MXene potassium titanate nanowire/sulfonated polyether ether ketone (SPEEK) hybrid composite proton exchange membrane for photocatalytic water splitting

A cross-linked sulfonated polyether ether ketone (C-SPEEK) was incorporated with MXene/potassium titanate nanowire (MKT-NW) as a filler and applied as a proton exchange membrane for photocatalytic water splitting. The prepared hybrid composite PEM had proton conductivity of 0.0097 S cm⁻¹ at room temperature with an ion exchange capacity of 1.88 meq g⁻¹. The hybrid composite proton exchange membrane is a reactive membrane which was able to generate hydrogen gas under UV light irradiation. The efficiency of hydrogen gas production was 0.185066 μmol within 5 h for 12% wt of MKT-NW loading. The results indicated that the MKT-NW/C-SPEEK membrane is a promising candidate for ion exchange with hydrogen gas evolution in photocatalytic water splitting and could be applied as a renewable source of energy to use in various fields of applications.

A cross-linked sulfonated polyether ether ketone (C-SPEEK) was incorporated with MXene/potassium titanate nanowire (MKT-NW) as a filler and applied as a proton exchange membrane for photocatalytic water splitting.     

Sulfonated component-incorporated quaternized poly(phthalazinone ether ketone) membranes with improved ion selectivity,stability and water transport resistance in a vanadium redox flow battery

Novel poly(phthalazinone ether ketone)-based amphoteric ion exchange membranes with improved ion selectivity, stability and water transport resistance were prepared for vanadium redox flow battery (VRB) applications. The preparation method ensured the absence of electrostatic interaction. A small amount of sulfonated poly(phthalazinone ether ketone) (SPPEK) with different ion exchange capacity (IEC) values was mixed with brominated poly(phthalazinone ether ketone) (BPPEK) to prepare base membranes with the solution casting method, and they were aminated in trimethylamine to obtain the resulting membranes (Q/S-x, x represents the IEC value of SPPEK). Compared with the AEM counterpart (QBPPEK) prepared from the amination of the BPPEK membrane, Q/S-1.37 showed lower swelling ratio and area resistance (R). The R value of Q/S-1.37 (0.58 Ω cm²) was close to that of Nafion115. The VO²⁺ and V³⁺ permeability values of Q/S-x were 96.7–97.6% and 98.5–99.2% less than those of Nafion115, respectively, demonstrating the excellent ion selectivity of Q/S-x. Compared with Nafion115 and QBPPEK, Q/S-1.37 displayed 90.0% and 92.1% decrease in the static water transport volume and 93.2% and 66.7% decrease in the cycling transport rate, respectively, revealing good water transport resistance. Compared with Nafion115, Q/S-1.37 exhibited an increase of 1.0–5.7% in the coulombic efficiency (CE) and an increase of 2.5–8.7% in the energy efficiency (EE) at 20–200 mA cm⁻². Q/S-x showed better chemical stability in VO₂⁺ solutions than QBPPEK. VRB with Q/S-1.37 could be steadily operated for 400 h without sudden capacity and efficiency drop, while VRB with QBPPEK could hold for only around 250 h. Q/S-1.37 retained higher CE, EE and capacity retention than Nafion115, displaying good long-term stability. Thus, the Q/S-x are promising for use in commercial VRBs.

Novel AIEMs were prepared through successive blending and amination processes, and they exhibited good ion selectivity, stability and water transport resistance.     

Novel sulfonated poly(ether ether ketone)/triphenylamine hybrid membrane for vanadium redox flow battery applications

A novel sulfonated poly(ether ether ketone)/triphenylamine hybrid membrane with various triphenylamine loadings (1%, 2% and 5%) has been successfully fabricated. Optimum triphenylamine loading was confirmed by exploring the physicochemical properties and morphology of different membranes. The hybrid membrane exhibited lower vanadium permeability than pristine SPEEK membranes due to the acid–base interaction between amine groups and sulfonated groups. Introduction of triphenylamine also improved the proton conductivity because the nitrogen atom of triphenylamine can be protonated and contribute to the proton transfer. As the result, the hybrid membrane demonstrated higher ion selectivity compared with SPEEK and Nafion115 membranes. The VRFB single cell with SPEEK/TPAM-1% membrane showed better performance compared to a Nafion115 membrane at the current density of 60 mA cm⁻². The SPEEK/TPAM hybrid membrane has great potential for VRFB application.

The novel TPAM hybrid membrane exhibited both lower vanadium permeability and higher proton conductivity than pristine SPEEK membrane.     

Sulfonated graphene oxide/Nafion composite membranes for high temperature and low humidity proton exchange membrane fuel cells

Iron oxide (Fe₃O₄) nanoparticles anchored over sulfonated graphene oxide (SGO) and Nafion/Fe₃O₄–SGO composites were fabricated and applied as potential proton exchange membranes in proton exchange membrane fuel cells (PEMFCs) operated at high temperature and low humidity. Fe₃O₄ nanoparticles bridge SGO and Nafion through electrostatic interaction/hydrogen bonding and increased the intrinsic thermal and mechanical stabilities of Nafion/Fe₃O₄–SGO composite membranes. Nafion/Fe₃O₄–SGO composite membranes increased the compactness of ionic domains and enhanced the water absorption and proton conductivity while restricting hydrogen permeability across the membranes. The proton conductivity of Nafion/Fe₃O₄–SGO (3 wt%) composite membrane at 120 °C under 20% relative humidity (RH) was 11.62 mS cm⁻¹, which is 4.74 fold higher than that of a pristine recast Nafion membrane. PEMFC containing the Nafion/Fe₃O₄–SGO composite membrane delivered a peak power density of 258.82 mW cm⁻² at a load current density of 640.73 mA cm⁻² while operating at 120 °C under 25% RH and ambient pressure. In contrast, under identical operating conditions, a peak power density of only 144.89 mW cm⁻² was achieved with the pristine recast Nafion membrane at a load current density of 431.36 mA cm⁻². Thus, Nafion/Fe₃O₄–SGO composite membranes can be used to address various critical problems associated with commercial Nafion membranes in PEMFC applications.

Preparation process of Nafion/Fe₃O₄–SGO composite membranes.     

A graphene oxide polymer brush based cross-linked nanocomposite proton exchange membrane for direct methanol fuel cells

Functional polymer brush modified graphene oxide (FPGO) with functional linear polysiloxane brushes was synthesized via surface precipitation polymerization (sol–gel) and chemical modification. Then, FPGO was covalently cross-linked to the sulfonated polysulfone (SPSU) matrix to obtain novel SPSU/FPGO cross-linked nanocomposite membranes. Meanwhile, SPSU/GO composite membranes and a pristine SPSU membrane were fabricated as control groups. Reduced agglomeration of the inorganic filler and better interfacial interaction, which are benefit to increase diffusion resistance of methanol and to generate continuous channels for fast proton transportation at elevated temperature, were observed in SPSU/FPGO cross-linked membranes. Moreover, the enhanced membrane stability (thermal, oxidative and dimensional stability) and good mechanical performance also guaranteed their proton conducting durability. It is noteworthy that the SPSU/FPGO-1 cross-linked membrane possesses the best comprehensive properties among all the prepared membranes and Nafion®117, it acquires the highest proton conductivity of 0.462 S cm⁻¹ at 90 °C under hydrated conditions together with a low methanol permeability of 1.71 × 10⁻⁶ cm² s⁻¹ at 30 °C. The resulting high membrane selectivity displays the great potential of the SPSU/FPGO cross-linked membrane for DMFCs application.

A novel proton exchange nanocomposite which was cross-linked by functional graphene oxide polymer brushes shows interesting and comprehensive advantages for DMFCs.     

Ladder-type sulfonated poly(arylene perfluoroalkylene)s for high performance proton exchange membrane fuel cells

Sulfonated poly(arylene perfluoroalkylene)s containing a sulfone-bonded ladder structure (SPAF-P-Lad) were synthesized by treating the precursor SPAF-P polymers with oleum as a novel proton exchange membrane for fuel cells. SPAF-P-Lad membranes had excellent solubility in polar organic solvents and high molecular weight (M_n = 145.4–162.9 kDa, M_w = 356.9–399.1 kDa) to provide bendable membranes with ion exchange capacity (IEC) ranging from 1.76 to 2.01 meq. g⁻¹. SPAF-P-Lad membranes possessed higher proton conductivity than that of the precursor SPAF-P membranes because of the stronger water affinity. Compared with SPAF-P membranes (T_g: 72–90 °C, Young''s modulus: 0.08–0.42 GPa; yield stress: 5.7–15.1 MPa), SPAF-P-Lad membranes showed better mechanical stability to humidity and temperature and improved tensile properties (Young''s modulus: 0.51–0.59 GPa; yield stress: 23.9–29.6 MPa). The selected membrane, SPAF-mP-Lad, exhibited improved fuel cell performance, in particular, under low humidity with air; the current density at 0.5 V was 0.56 A cm⁻², while that for SPAF-pP was 0.46 A cm⁻². The SPAF-mP-Lad membrane endured an open circuit voltage hold test for 1000 h with average decay of as small as 70 μV h⁻¹. A series of post-analyses including current–voltage characteristics, molecular structure, molecular weight, and IEC suggested very minor degradation of the membrane under the accelerated testing conditions.

Sulfone-bonded ladder-type sulfonated poly(arylene perfluoroalkylene)s (SPAF-P-Lad) were synthesized by an easy method to achieve high thermo-mechanical stability, proton conductivity, fuel cell performance and remarkable in situ durability.     

Novel cross-linked poly(vinyl alcohol)-based electrolyte membranes for fuel cell applications

Herein, a new series of polymer electrolyte membranes was prepared by chemically cross-linked poly(vinyl alcohol) (PVA) and sulfonated poly(ether sulfone) (SPES). A typical polymerization reaction was conducted using three different monomers i.e. bisphenol A, phenolphthalein, and 4,4′-dichlorodiphenyl sulfone. The SPES polymer was obtained by the post-sulfonation technique using chlorosulfonic acid as a sulfonating agent. The resultant SPES polymer at different concentrations was blended with cross-linked poly(vinyl alcohol). Structural analysis of the samples was conducted by FTIR, SEM, and XRD. Among the prepared PEM materials, PVA–SPES-20 blend membranes exhibited higher ion-exchange capacity and % water uptake values than those of the other membranes. In addition, the PVA–SPES-20 membrane exhibits the proton conductivity of 0.0367 S cm⁻¹ at 30 °C, whereas pristine PVA shows the proton conductivity of 0.0259 S cm⁻¹. The overall experimental results revealed that the PVA–SPES blend membranes are promising candidates for fuel cell applications.

A series of cross-linked poly(vinyl alcohol)-sulfonated poly(ether sulfone) blend membranes were prepared. The studies of physico-chemical properties revealed that the reported membranes are promising candidate for PEMFC applications.     

Synthesis and characterization of a novel crosslinkable side-chain sulfonated poly(arylene ether sulfone) copolymer proton exchange membranes

A series of novel crosslinkable side-chain sulfonated poly(arylene ether sulfone) copolymers (S-SPAES(x/y)) was prepared from 4,4′-biphenol, 4,4′-difluorodiphenyl sulfone, and a new difluoro aromatic monomer 1-(2,6-difluorophenyl)-2-(3,5-dimethoxyphenyl)-1,2-ethanedione (DFDMED) via co-polycondensation, demethylation, and further nucleophilic substitution of 1,4-butane sultone. Meanwhile, quinoxaline-based crosslinked copolymers (CS-SPAES(x/y)) were obtained via cyclo-condensation between S-SPAES(x/y) and 3,3′-diaminobenzidine. Both the crosslinkable and crosslinked copolymer membranes exhibit good mechanical properties and high anisotropic membrane swelling. Crosslinkable S-SPAES(1/2) with an ion exchange capacity (IEC) of 2.01 mequiv. g⁻¹ displays a relatively high proton conductivity of 180 mS cm⁻¹ and acceptable single-cell performance, which is attributed to its good microphase separation resulting from the side-chain sulfonated copolymer structures. Compared with S-SPAES(1/1) (IEC of 1.68 mequiv. g⁻¹), crosslinked CS-SPAES(1/2) with a comparable IEC exhibits a larger conductivity of 157 mS cm⁻¹, and significantly higher oxidative stability and lower membrane swelling, suggesting a distinct performance improvement due to the quinoxaline-based crosslinking.

A series of novel crosslinkable and crosslinked side-chain SPAES has been prepared. The S-SPAES(1/2) has high proton conductivity and acceptable single-cell performance.     

A confinement of N-heterocyclic molecules in a metal–organic framework for enhancing significant proton conductivity

A series of N-heterocyclic⊂VNU-23 materials have been prepared via the impregnation procedure of N-heterocyclic molecules into VNU-23. Their structural characterizations, PXRD, FT-IR, Raman, TGA, ¹H-NMR, SEM-EDX, and EA, confirmed that N-heterocyclic molecules presented within the pores of parent VNU-23, leading to a remarkable enhancement in proton conductivity. Accordingly, the composite with the highest loading of imidazole, Im_13.5⊂VNU-23, displays a maximum proton conductivity value of 1.58 × 10⁻² S cm⁻¹ (85% RH and 70 °C), which is ∼4476-fold higher than H⁺⊂VNU-23 under the same conditions. Remarkably, the proton conductivity of Im_13.5⊂VNU-23 exceeds the values at 85% RH for several of the reported high-performing MOF materials. Furthermore, Im_13.5⊂VNU-23 can retain a stable proton conductivity for more than 96 h, as evidenced by FT-IR and PXRD analyses. These results prove that this hybrid material possesses potential applications as a commercial proton exchange membrane fuel cell.

A series of N-heterocyclic⊂VNU-23 materials have been prepared via the impregnation procedure of N-heterocyclic molecules into VNU-23.     

Modulation of a coordination structure in a europium(iii)-based metallo-supramolecular polymer for high proton conduction

Developing high proton conducting solid materials is significant in the field of fuel cells. A europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H) was successfully synthesized by modifying the synthesis conditions. The proton conductivity was enhanced with increasing the relative humidity (RH) from 30 to 95% RH. PolyEu-H showed about 10⁴ times higher proton conductivity than the polymer with coordinated carboxylic acids (PolyEu) and about 400 times higher than the polymer without carboxylic acids (PolyEu-2). The proton conductivity of PolyEu-H reached 4.45 × 10⁻² S cm⁻¹ at 95% RH and 25 °C and 5.6 × 10⁻² S cm⁻¹ at 75 °C. The activation energy, E_a was ultralow (0.04 eV), which indicates proton conduction based on the Grotthuss mechanism. The results indicate that efficient proton conduction occurs through proton channels formed by moisture in PolyEu-H.

Developing high proton conducting solid materials is significant in the field of fuel cells. We firstly synthesized europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H), for high proton conduction.     

A proton conductor electrolyte based on molten CsH5(PO4)2 for intermediate-temperature fuel cells

Molten carbonate fuel cells have been commercialized as a mature technology. Due to the liquid electrolyte in molten carbonate fuel cells, gas seal and low contact resistance are easier to achieve than in other fuel cells. Herein, we report an investigation of the viability of a molten oxoacid salt as a novel type of fuel cell electrolyte. In comparison with molten carbonate electrolytes for MCFCs that operate at 500–700 °C, for which a ceramic support matrix is required, the molten proton conductor electrolyte has a lower working temperature range of 150–250 °C. The present study has shown that an electrolyte membrane, in which molten CsH₅(PO₄)₂ is held in a matrix made of PBI polymer and SiO₂ powder, has excellent thermal stability, good mechanical properties, and high proton conductivity. In addition, a molten proton conductor fuel cell equipped with such an electrolyte membrane operating at 200 °C showed an open-circuit voltage of 1.08 V, and a stable output voltage during continuous measurement for 150 h at a constant output current density of 100 mA cm⁻².

An proton conductor electrolyte membrane, in which molten CsH₅(PO₄)₂ is held in a matrix made of PBI polymer and SiO₂ powder, is prepared for intermediate-temperature fuel cells.     

Synthesis and performance of solid proton conductor molybdovanadosilicic acid

A molybdovanadosilicic acid H₅SiMo₁₁VO₄₀·8H₂O was synthesized and investigated in this work. The structure features and hydration degree of this acid were characterized by IR, UV, XRD and TG-DTA. Its proton conductivity was studied by electrochemical impedance spectroscopy (EIS). The EIS measurements demonstrated that H₅SiMo₁₁VO₄₀·8H₂O showed excellent proton conduction performance with proton conductivity reaching 5.70 × 10⁻³ S cm⁻¹ at 26 °C and 70% relative humidity. So, it is a new solid high proton conductor. The conductivity enhances with the increase of temperature, and it exhibits Arrhenius behavior. The activation energy value for proton conduction is 21.4 kJ mol⁻¹, suggesting that the proton transfer in this solid acid is dominated by Vehicle mechanism.

A novel Keggin-type proton conductor shows high proton conductivity, reaching 5.70 × 10⁻³ S cm⁻¹ at room conditions.     

A-site deficient semiconductor electrolyte Sr1−xCoxFeO3−δ for low-temperature (450–550 °C) solid oxide fuel cells

Fast ionic conduction at low operating temperatures is a key factor for the high electrochemical performance of solid oxide fuel cells (SOFCs). Here an A-site deficient semiconductor electrolyte Sr_1−xCo_xFeO_3−δ is proposed for low-temperature solid oxide fuel cells (LT-SOFCs). A fuel cell with a structure of Ni/NCAL-Sr_0.7Co_0.3FeO_3−δ–NCAL/Ni reached a promising performance of 771 mW cm⁻² at 550 °C. Moreover, appropriate doping of cobalt at the A-site resulted in enhanced charge carrier transportation yielding an ionic conductivity of >0.1 S cm⁻¹ at 550 °C. A high OCV of 1.05 V confirmed that neither short-circuiting nor power loss occurred during the operation of the prepared SOFC device. A modified composition of Sr_0.5Co_0.5FeO_3−δ and Sr_0.3Co_0.7FeO_3−δ also reached good fuel cell performance of 542 and 345 mW cm⁻², respectively. The energy bandgap analysis confirmed optimal cobalt doping into the A-site of the prepared perovskite structure improved the charge transportation effect. Moreover, XPS spectra showed how the Co-doping into the A-site enhanced O-vacancies, which improve the transport of oxide ions. The present work shows that Sr_0.7Co_0.3FeO_3−δ is a promising electrolyte for LT-SOFCs. Its performance can be boosted with Co-doping to tune the energy band structure.

Fast ionic conduction at low operating temperatures is a key factor for the high electrochemical performance of solid oxide fuel cells (SOFCs).     

High-performance yttrium-iron alloy doped Pt-free catalysts on graphene for hydrogen evolution

Research into the preparation and application of metal/graphene nanocomposite materials is an important issue in the field of graphene applications. Metal nanomaterials and graphene materials have many excellent properties and have been perfectly combined into metal/graphene nanocomposite materials. These offer the high catalytic activity of metal nanomaterials and the high specific surface area and favorable electrical conductivity of graphene. The unique advantages can produce synergistic effects and can significantly improve the overall performance of the composite materials. This gives the metal/graphene nanocomposite materials excellent application prospects for hydrogen evolution. Here, we report the preparation of yttrium-doped palladium/iron on graphene (Pd/YFeO₃/^GC) using a simple and efficient method. The catalytic performance of the Pd/YFeO₃/^GC nanocomposites for water electrolysis and hydrogen production was evaluated. The results show that the overpotential for the hydrogen evolution reaction at −10 mA cm⁻² is only 15 mV, which is competitive with Pt/C catalysts. The Pd/YFeO₃/^GC is highly active for hydrogen evolution with an onset potential of −8 mV in 0.5 M H₂SO₄ solution and a Tafel slope of 37 mV dec⁻¹ with a Pd loading of only 20 μg_Pd cm⁻². These results clearly demonstrated that Pd/YFeO₃/^GC is an excellent catalyst for hydrogen evolution.

Research into the preparation and application of metal/graphene nanocomposite materials is an important issue in the field of graphene applications.     

The enhancement of photocatalytic performance of SrTiO3 nanoparticles via combining with carbon quantum dots

Carbon quantum dots were prepared by a simple chemical process using activated carbon as carbon source. The as-prepared carbon quantum dots are fine with a narrow size distribution and show excellent hydrophilicity. The carbon quantum dots were combined with SrTiO₃ nanoparticles through a simple impregnation process to obtain a carbon quantum dots/SrTiO₃ nanocomposite. The photocatalytic reaction rate of carbon quantum dots/SrTiO₃ nanocomposite is about 5.5 times as large as that of pure SrTiO₃ in the degradation of rhodamine B under sunlight irradiation. The enhanced performance in the degradation of rhodamine B may be attributed to the interfacial transfer of photogenerated electrons from SrTiO₃ to carbon quantum dots, leading to effective charge separation in SrTiO₃. Carbon quantum dots show potential applications in high-efficiency photocatalyst design.

The introduction of the CQDs (electron acceptor) to the SrTiO₃ nanoparticles will facilitate the efficient separation of photogenerated e⁻–h⁺ pairs and thus enhance the photocatalytic performance.     

Enhanced capacitive performance of cathodically reduced titania nanotubes pulsed deposited with Mn2O3 as supercapacitor electrode

A facile and simple pulse electrodeposition method was employed to deposit Mn₂O₃ nanoparticles on cathodically reduced titania nanotubes (R-TNTs) at different deposition time in the range of 3–15 min to investigate the influence of mass loading of Mn₂O₃ on the electrochemical performance of Mn₂O₃/R-TNTs nanocomposite for supercapacitor application. Mn₂O₃ nanoparticles were deposited on circumference of R-TNTs as well as in the nanotubes as revealed by FESEM images for all the deposited time. XPS result confirmed the presence of MnO₂ (Mn⁴⁺) and MnO (Mn²⁺) on the Mn₂O₃/R-TNTs composite which provide pseudocapacitive behaviour for the electrode. Mass loading of Mn₂O₃ increased linearly with deposition time as confirmed by EDX analysis. The sample deposited for 12 min exhibits the highest areal capacitance of 51 mF cm⁻² (which is 22 times enhancement over R-TNTs) at a current density of 0.1 mA cm⁻² and specific capacitance of 325 F g⁻¹ at 6 A g⁻¹. The sample also show a high-rate capability by retaining 80% of its capacitance even at higher current density of 30 A g⁻¹. Interestingly, it retained 98% of the capacitance over 5000 charge discharge cycles at 10 A g⁻¹ after initial drop to 95% at 200th cycles suggesting an excellent long-term chemical stability. A considerably low equivalent series resistance (ESR) and charge transfer resistance (R_ct) of 9.6 Ω and 0.4 Ω respectively was deduced from electrochemical impedance spectroscopy (EIS) analysis indicating good conductivity and improved charge transfer efficiency of Mn₂O₃/R-TNTs nanocomposite.

The mass loading of Mn₂O₃ by pulse electrodeposition (PED) onto reduced titania nanotubes (R-TNTs) greatly influences the electrochemical performance of the composite.     

New ferrocenyl-containing organic hole-transporting materials for perovskite solar cells in regular (n-i-p) and inverted (p-i-n) architectures

Three triphenylamine derivatives containing ferrocenyl groups (JW6, JW7 and JW8) were synthesized by facile syntheses. Their HOMO levels match the valence band energy of CH₃NH₃PbI₃. The introduction of ferrocenyl was aimed to obtain hole transporting materials with high mobility for perovskite solar cells. JW7 shows higher hole mobility (4.2 × 10⁻⁴ cm² V⁻¹ s⁻¹) than JW6 (1.3 × 10⁻⁴ cm² V⁻¹ s⁻¹) and JW8 (1.5 × 10⁻⁴ cm² V⁻¹ s⁻¹). Their film-forming properties are affected by their molecule structures. The methoxyl and N,N-dimethyl terminal substituents of JW7 and JW8 are beneficial for having better solubility than JW6. The regular mesoporous TiO₂-based perovskite solar cells (n-i-p) and the inverted planar heterojunction perovskite solar cells (p-i-n) fabricated using JW7 show the highest power conversion efficiency of 9.36% and 11.43% under 100 mW cm⁻² AM1.5G solar illumination. For p-i-n cells, the standard HTM PEDOT-based cell reaches an efficiency of 12.86% under the same conditions.

New ferrocene-containing organic HTMs for fabricating perovskite solar cells.     

Utilization of mesoporous phosphotungstic acid in nanocellulose membranes for direct methanol fuel cells

Nanocellulose (NC) composite membranes containing novel ternary materials including NC, imidazole (Im), and mesoporous phosphotungstic acid (m-PTA) were successfully fabricated by a phase inversion method. The single-particle size of NC was 88.79 nm with a spherical form. A m-PTA filler with a mesopore size of 4.89 nm was also successfully synthesized by a self-assembly method. Moreover, the fabricated membrane NC/Im/m-PTA-5 exhibited the best performances towards its proton conductivity and methanol permeability at 31.88 mS cm⁻¹ and 1.74 × 10⁻⁶ cm² s⁻¹, respectively. The membrane selectivity was 1.83 × 10⁴ S cm⁻³.

A NC/Im/m-PTA membrane was fabricated for direct methanol fuel cell applications.     

Arrangement of water molecules and high proton conductivity of tunnel structure phosphates,KMg1−xH2x(PO3)3·yH2O

A fast proton conductor was investigated in a mixed-valence system of phosphates with a combination of large cations (K⁺) and small cations (Mg²⁺), which resulted in a new phase with a tunnel structure suitable for proton conduction. KMg_1−xH_2x(PO₃)₃·yH₂O was synthesized by a coprecipitation method. A solid solution formed in the range of x = 0–0.18 in KMg_1−xH_2x(PO₃)₃·yH₂O. The structure of the new proton conductor was determined using neutron and X-ray diffraction measurements. KMg_1−xH_2x(PO₃)₃·yH₂O has a tunnel framework composed of face-shared (KO₆) and (MgO₆) chains, and PO₄ tetrahedral chains along the c-direction by corner-sharing. Two oxygen sites of water molecules were detected in the one-dimensional tunnel, one of which exists as a coordination water of K⁺ sites. Multi-step dehydration was observed at 30 °C and 150 °C from thermogravimetric/differential thermal analysis measurements, which reflects the different coordination environments of the water of crystallization. Water molecules are connected to PO₄ tetrahedra by hydrogen bonds and form a chain along the c-axis in the tunnel, which would provide an environment for fast proton conduction associated with water molecules. The KMg_1−xH_2x(PO₃)₃·yH₂O sample with x = 0.18 exhibited high proton conductivity of 4.5 × 10⁻³ S cm⁻¹ at 150 °C and 7.0 × 10⁻³ S cm⁻¹ at 200 °C in a dry Ar gas flow and maintained the total conductivity above 10⁻³ S cm⁻¹ for 60 h at 150 °C under N₂ gas atmosphere.

A fast proton conductor exhibiting high proton conductivity of 7.0 × 10⁻³ S cm⁻¹ at 200 °C in a dry Ar gas flow was developed by designing water chains in a rigid tunnel framework.