Outstanding proton conductivity over wide temperature and humidity ranges and enhanced mechanical, thermal stabilities for surface-modified MIL-101-Cr-NH_(2)/Nafion composite membranes

High-performance proton exchange membranes are of great importance for fuel cells.Here,we have synthesized polycarboxylate plasticizer modified MIL-101-Cr-NH_(2)(PCP-MCN),a kind of hybrid metal-organic framework,which exhibits a superior proton conductivity.PCP-MCN nanoparticles are used as additives to fabricate PCP-MCN/Nafion composite membranes.Microstructures and characteristics of PCP-MCN and these membranes have been extensively investigated.Significant enhancement in proton conduction for PCP-MCN around 55℃ is interestingly found due to the thermal motion of the PCP molecular chains.Robust mechanical properties and higher thermal decomposition temperature of the composite membranes are directly ascribed to strong intermolecular interactions between PCP-MCN and Nafion side chains,i.e.,the formation of substantial acid–base pairs(-SO_(3)^(-)…^(+)H–NH-),which further improves compatibility between additive and Nafion matrix.At the same humidity and temperature condition,the water uptake of composite membranes significantly increases due to the incorporation of porous additives with abundant functional groups and thus less crystallinity degree in comparison to pristine Nafion.Proton conductivity(σ)over wide ranges of humidities(30-100%RH at 25℃)and temperatures(30-98℃ at 100%RH)for prepared membranes is measured.The s in PCPMCN/Nafion composite membranes is remarkably enhanced,i.e.0.245 S/cm for PCP-MCN-3wt.%/Nafion is twice that of Nafion membrane at 98℃ and 100%RH,because of the establishment of well-interconnected proton transport ionic water channels and perhaps faster protonation–deprotonation processes.The composite membranes possess weak humidity-dependence of proton transport and higher water uptake due to excellent water retention ability of PCP-MCN.In particular,when 3 wt.%PCP-MCN was added to Nafion,the power density of a single-cell fabricated with this composite membrane reaches impressively 0.480,1.098 W/cm^(2) under 40%RH,100%RH at 60℃,respectively,guaranteeing it to be a promising proton exchange membrane.

Influences of Structure Disorder and Temperature on Properties of Proton Conductivity in Hydrogen-Bond Molecular Systems

The dynamic properties of proton conductivity along hydrogen-bonded molecular systems, for example, ice crystal, with structure disorder or damping and finite temperatures exposed in an externally applied electric-field have been numerically studied by Runge-Kutta way in our soliton model. The results obtained show that the proton-soliton is very robust against the structure disorder including the fluctuation of the force constant and disorder in the sequence of masses and thermal perturbation and damping of medium, the velocity of its conductivity increases with increasing of the externally applied electric-field and decreasing of the damping coefficient of medium, but the proton-soliton disperses for quite great fluctuation of the ＂force constant and damping coefficient. In the numerical simulation we find that the proton-soliton in our model is thermally stable in a large region of temperature of T ≤ 273 K under influences of damping and externally applied electric-field in ice crvstal. This shows that our model is available and appropriate to ice.

Synthesis,Proton Conductivity and Humidity Sensing Property ofγ-Type Zirconium Hydrogen Phosphate,Zr(HPO_4)_2·2H_2O

A γ - type of layered zirconium hydrogen phosphate, Zr(HPO 4) 2·2H 2O( γ ZrP), was synthesized under hydrothermal conditions and characterized by powder X ray diffraction and thermogravimetric analysis. The temperature dependence of the proton conductivity in γ ZrP was investigated in a temperature range of 23￣413 ℃ by ac impedance spectroscopy. The variation of the conductivity with water loss and phase transitions was observed. The best proton conductivity in γ ZrP is 6×10 -4 S·cm -1 at 60 ℃. The proton conductivities in the dehydrated sample are ￣10 -5 at 150 ℃ and ￣10 -4 S·cm -1 at 350 ℃, respectively. The conductivities as a function of humidity in the temperature range of 120￣200 ℃ were measured.

Hydrothermal Synthesis,Crystal Structure and Proton Conductivity of a Pr–Ca Heterometal-organic Framework Generated by 1,2,4,5-Benzenetetracarboxylic Acid

A heterometal-organic framework {[Pr2Ca（betc）2（H2O）7]·H2O}n（1） was prepared by the hydrothermal reaction of 1,2,4,5-benzenetetracarboxylic acid（H4betc） with Pr（NO3）3 and CaCO3, and further characterized by single-crystal X-ray structural analysis, elemental analysis, IR, thermal gravimetric, and X-ray powder diffraction. Complex 1 crystallizes in triclinic, space group P1 with a = 7.3668（12）, b = 10.1726（14）, c = 11.2264（15） A, a = 100.404（2）, b = 106.113（3）, g = 109.158（3）o, V = 728.48（19） A3, Mr = 966.26, Z = 1, F（000） = 470, Dc = 2.203 g/cm3, m（Mo Kα） = 3.585 mm-1, the final R = 0.0195 and w R = 0.0470（I 〉 2s（I））. Complex 1 is a 3D network with pcu topology with 1D porosity and rich hydrogen-bonding interactions. The proton conductivity of complex 1 was also studied under ~97% relative humidity and the different temperature conditions.

Bioinspired supramolecular macrocycle hybrid membranes with enhanced proton conductivity

Enhancing the proton conductivity of proton exchange membranes(PEMs)is essential to expand the applications of proton exchange membrane fuel cells(PEMFCs).Inspired by the proton conduction mechanism of bacteriorhodopsin,cucurbit[n]urils(CB[n],where n is the number of glycoluril units,n=6,7,or 8)are introduced into sulfonated poly(ether ether ketone)(SPEEK)matrix to fabricate hybrid PEMs,employing a nature-inspired chemical engineering(NICE)methodology.The carbonyl groups of CB[n]act as proton-conducting sites,while the host–guest interaction between CB[n]and water molecules offers extra protonconducting pathways.Additionally,the molecular size of CB[n]aids in their dispersion within the SPEEK matrix,effectively bridging the unconnected proton-conducting sulfonic group domains within the SPEEK membrane.Consequently,all hybrid membranes exhibit significantly enhanced proton conductivity.Notably,the SPEEK membrane incorporating 1 wt.%CB[8](CB[8]/SPEEK-1%)demonstrates the highest proton conductivity of 198.0 mS·cm^(−1) at 60°C and 100%relative humidity(RH),which is 228%greater than that of the pure SPEEK membrane under the same conditions.Moreover,hybrid membranes exhibit superior fuel cell performance.The CB[8]/SPEEK-1%membrane achieves a maximum power density of 214 mW·cm^(−2),representing a 140%improvement over the pure SPEEK membrane(89 mW·cm^(−2))at 50°C and 100%RH.These findings serve as a foundation for constructing continuous proton-conducting pathways within membranes by utilizing supramolecular macrocycles as fuel cell electrolytes and in other applications.

Parallelogram 3d-4f-5d heterometallic clusters based on trilacunary tungstoantimonates with excellent proton conductivity

Two 3d-4f-5d heterometallic cluster-containing polyoxometalates,formulated as Na_(22){(SbW_(9)O_(33))_(4)[La_(3)W_(6)MO_(18)(H_(2)O)_(8)(CH_(3)COO)_(4)]_(2)}·nH_(2)O(abbreviated as La_(6)M_(2),M=Co/Mn)were synthesized and structurally characterized.Single-crystal X-ray diffraction analyses reveal that the polyanions of La_(6)Co_(2)and La_(6)Mn_(2)consist of the uncommon 3d-4f-5d clusters{La_(6)W_(12)Co_(2)}and{La_(6)W_(12)Mn_(2)},which are encapsulated by four trilacunary Keggin tungstoantimonates to form the parallelogram-shaped title compounds.Additionally,the polyanions can be extended into a two-dimensional(2D)frame by the linkage of peripheral Na+ions.The inner space of the 2D layer was filled with water molecules and thus an H-bonded network was formed,which is expected to exhibit a fascinating proton conductivity.The study of water-assisted proton conduction demonstrated that La_(6)Co_(2)and La_(6)Mn_(2)were temperature-and humiditydependent proton conductors,respectively,and the proton conductivities could reach 1.3×10^(-2)and 2.3×10^(-2)S/cm at 65℃and 90%RH conditions.

A highly reduced Mo_(74) polyoxometalate featuring high proton conductivity accessed by building block strategy

Highly reduced polyoxometalates(POMs) are predicted to be used as rather high energy density materials;however,it still suffers from the limited cluster species and reduction ratio.Here we demonstrate that it is possible to employ the building block strategy to generate a highly reduced polyoxomolybdate(C_(2)H_(8)N)_(14)(NH_(4))_(4)H_(14)[Mo_(48)-ⅤMo_(26)ⅥO_(202)(OH)_(12)(SO_(4))_(6)]·46H_(2)O(Mo_(74)).The fundamental Mo-based{Mo_x}(x=4,5,and 6) building blocks,which are templated by tetra-coordinated anions{MoO_(4)}or{SO_(4)},not only lay foundation for the formation of Mo_(74) featuring an unprecedented reduction ratio of 65%,but also give rise to SBBs-mediated(secondary building blocks) supramolecular dense packing interactions among the isolated Mo_(74) clusters that are favorable for proton conduction.Remarkably,high proton conductivity(2.04×10^(-2)S cm^(-1)) had been realized at 50℃ and 90% relative humidity,revealing one of the well-known POMs-based crystalline proton conducting materials.This result highlights that this building block approach possesses great potential in producing highly reduced POM systems that can achieve controllable reduced ratio and desirable properties.

In situ protonation in a locally flexible porous coordination polymer for enhancing proton-carrier loading and proton conductivity

Designing efficient proton-conductive materials is crucial in fuel cells.Yet,it remains a substantial challenge because of the issues in proton mobility,proton-carrier amount,and orientation of proton host materials.Herein,we report an in-situ protonation strategy to produce a locally flexible porous coordination polymer(PCP)to enhance the proton-carrier loading and proton conductivity.The local dipole flipping of the ligand allows effective proton exchange with low activation energy,promoting interpore proton transport through the pore apertures and pore walls.The protonation induces substantial charges to the frameworks and enhances the interaction with proton carriers,thereby increasing the loading of the proton carriers.By this design strategy,the resulting PCP exhibits enhanced phosphoric acid loading and extraordinary proton conductivities under both aqueous and anhydrous conditions compared to its isoreticular analog that features rigidity without proton-exchange capability.Our work provides a new avenue for designing proton-conductive materials that combine structural dynamics with performance merits.

Dimensional regulation in gigantic molybdenum blue wheels featuring{(W)Mo_(5)}motifs for enhanced proton conductivity

Dimensional regulation in polyoxometalates is an effective strategy during the design and synthesis of polyoxometalates-based high proton conductors,but it is not available to date.Herein,the precise regulation of dimensionality has been realized in an unprecedented gigantic molybdenum blue wheel family featuring pentagonal{(W)Mo5}motifs through optimizing the molar ratio of Mo/W,including[Gd_(2)Mo_(124)W_(14)O_(422)(H_(2)O)62]38-(0D-{Mo_(124)W_(14)},1),[Mo_(126)W_(14)O441(H_(2)O)51]^(70-)(1D-{Mo_(126)W_(14)}n,2),and[Mo_(124)W_(14)O_(430)(H_(2)O)50]60-(2D-{Mo_(124)W_(14)}n,3).Such important{(W)Mo5}structural motif brings new reactivity into gigantic Mo blue wheels.There are different numbers and sites of{Mo2}defects in each wheel-shaped monomer in 1-3,which leads to the monomers of 2 and 3 to form 1D and 2D architectures via Mo-O-Mo covalent bonds driven by{Mo2}-mediated H_(2)O ligands substitution process,respectively,thus achieving the controllable dimensional regulation.As expected,the proton conductivity of 3 is 10 times higher than that of 1 and 1.7 times higher than that of 2.The continuous proton hopping sites in 2D network are responsible for the enhanced proton conductivity with lower activation energy.This study highlights that this dimensional regulation approach remains great potential in preparing polyoxometalates-based high proton conductive materials.

Proton conductivity performance and its correlation with physiochemical properties of proton exchange membrane(PEM)

Graphene oxide(GO)filler containing diversified Nafion-based proton exchange membrane(PEM)is studied to know the unique physical and chemical properties and performances of PEM.Nafion-SPEEK 1%-GO 0.75%(NSG-0.75%)composite shows the highest proton conductivity of 0.327 S·cm^(-1) at 90℃ and 100%RH(relative humidity)among all the PEM investigated.The descending order of significant proton conductivity is found as;Nafion-sPGO(1%)0.306 S·cm^(-1)>Nafion/ZIF-8@GO 0.280 S·cm^(-1)>Nafion/PGO(2%)0.277 S·cm^(-1)>Nafion/GO-sulfur(3%)0.232 S·cm^(-1)>Nafion/GO-poly-SPM-co-PEGMEMA(1%)0.229 S·cm^(-1)>Nafion/Ce-sPGO(1%)0.215 S·cm^(-1).The proton conductivity,water uptake capacity and ion exchange capacity,hydration number,thermal and oxidative stability,mechanical integrity(tensile strength),maximum power,and current density are found to be increased while activation energy and fuel crossover show a decrement as GO or modified GO is incorporated in the Nafion matrix.Principal component analysis(PCA)predicted a significant correlation between the proton conductivity and the properties;the water uptake capacity,ion exchange capacity,hydration number,maximum power density,and maximum current density are 0.598%,0.688%,0.894%,0.980%,and 0.852%accordingly.A multiple linear model equation of proton conductivity is defined with the parameters of water uptake capacity,ion exchange capacity,hydration number,maximum power density,and maximum current density whereas the regression coefficient is 0.9923.

Superhigh intrinsic proton conductivity in densely carboxylic covalent organic framework

Herein,we developed for the first time two carboxylic acid based intrinsic proton conductors(COOHCOF-1 and COOH-COF-2)via pre-assembly approach.The obtained COOH-COF-1 and COOH-COF-2 not only show outstanding chemical and thermal stabilities,but also exhibit superhigh intrinsic proton conductive behaviors.Especially,the intrinsic proton conductivity of COOH-COF-2 is up to 2.6×10^(−3) S/cm at 353 K and 98%RH,which is the highest value among all the reported acid functionalized COFs.This work lights up the way for the rational design of functional COFs with remarkably intrinsic proton conducting performance and related practical applications.

Enhanced proton conductivity of viscose-based membranes via ionic modification and dyeing processes for fuel cell applications

Proton exchange membranes(PEMs),which are crucial fuel cell parts,play an important role in the field of energy science.However,the further development of conventional PEMs based on synthetic polymers is greatly limited by high energy consumption and difficult degradation.In this work,we reported the fabrication of a novel viscose-based PEM via cationic modification and dyeing treatment with the reactive dyes KE-7B1.High-efficiency proton transmission channels can be constructed due to the for-mation of the complex internal three-dimensional network of the as-prepared viscose-based PEM.Hþconductivity(sHþ)and water uptake are intensively investigated by changing the cationic agents and KE-7B1,and the maximum sHþreaches 44.19 mS/cm at 80℃and 98%relative humidity(RH).Furthermore,the prepared membrane shows the lowest calculated activation energy value(12.25 kJ/mol),indicating that both Grotthuss and Vehicle mechanisms play an important role in ionic transport.The membrane chemical structure and micromorphology are analyzed and the proton transmission modes are explored in detail,supplemented with research on the hydrophilic/hydrophobic characteristics and crystallinity of the membranes.The application stability of the membranes is also evaluated analyzing the thermal,mechanical,and oxygen resistance properties,and the results show that all the prepared membranes can maintain good thermal stability within 200℃.The maximum tensile strength reaches 42.12 MPa,and the mass losses of the membranes soaked in 30%(in mass,same below)H_(2)O_(2)solution for 120 h can be restricted to 10%.Therefore,as a novel PEM,the obtained dye viscose-based membranes show great potential for application in fuel cells.

Two-in-one tecton strategy to construct single crystalline hydrogen-bonded organic framework with high proton conductivity above 100℃

By tactically integrating two different kinds of proton donors and acceptors into one supramolecular tecton, a new crystalline hydrogen-bonded organic framework(HOF-SXU-1) has been developed. HOF-SXU-1 features a remarkable proton conductivity as high as 6.32 mS cm^(-1) and an extremely low activation energy of 0.16 eV at 160℃ under anhydrous N_(2) conditions.By contrast, under identical conditions, the organic precursors of HOF-SXU-1 only exhibit negligible proton conduction performance, demonstrating that the formation of HOF is crucial for excellent proton conduction performance.

Design and synthesis of phosphomolybdate coordination compounds based on {P_(4)Mo_(6)} structural units and their proton conductivity

Developing new low-cost and efficient proton-conducting materials remains an attractive and challenging task.Herein,sodium molybdate dihydrate is used as the source of molybdenum,mixed with transition metal chloride and 2-methylimidazole(2-MI),using the "one-pot method" to synthesize two crystalline proton conducting materials based on {P4Mo6} units:H14[C4H6N2]2[M(H_(2)O)5][M(H_(2)O)_(2)]_(2){M[(PO_(3))_(3)(PO_(4))Mo_(6)O_(15)]_(2)}·4H_(2)O(M=Co and Fe)(1-2).Different from the common{P4Mo_(6)},we use H3PO3to adjust the pH value,resulting in two different coordination modes of P atoms in the crystal structure.The structure is expanded into three-dimensional network by metal ions.At 75℃ and 98% relative humidity,the proton conductivity of compounds 1 and 2 are 1.33 ×10^(-2)S·cm^(-1)and 1.03×10^(-2)S·cm^(-1),respectively.The high proton conductivity is mainly attributed to the free state of 2-methylimidazole as the proton carrier,which has a fast migration rate.At the same time,2-methylimidazole,coordination water,and {P4Mo6} anion form a hydrogen bond network to provide multiple pathways for the transmission of protons.

Free-standing polymer-metal-organic framework membrane with high proton conductivity and water stability

As a new class of porous material,polymer-metal-organic framework(polyMOF)has attracted tremendous interests owing to their combined advantages of polymer and crystalline MOF.However,the poor film-forming ability of polyMOF limits its widespread application,especially in membrane separation area.Herein,for the first time,we demonstrate the fabrication of freestanding polyMOF membrane.The polyMOF nanosheets are synthesized by a polymer-assisted self-inhibition crystal growth strategy.Followed by self-assembly through vacuum filtration,a 20μm-thick free-standing polyMOF membrane is constructed.Benefiting from the inclusion of polymer with hydrophobic backbone and the continuously distributed non-coordinated hydrophilic groups along polymer chain,the polyMOF membrane attains excellent structure stability against water,as well as superior proton transfer property.Proton conductivity as high as 112 and 25.6 mS·cm^(–1)is obtained by this polyMOF membrane at 100%and 20%relative humidity(RH),respectively,which are two orders of magnitude higher than those of pristine MOF.The conductivity under low humidity(20%RH)is even over 8 times higher than that of commercial Nafion membrane(3 mS·cm^(–1)).This study may provide some guidance on the development of polyMOF membranes.

Expanding the dimensionality of proton conduction enables ultrahigh anhydrous proton conductivity of phosphoric acid-doped covalent-organic frameworks

It is of great significance to develop high-temperature anhydrous proton conducting materials.Herein,we report a new strategy to significantly enhance the proton conductivity of covalent organic frameworks(COFs)through expanding the dimensionality of proton conduction.Three COF-based composites,COF-1@PA,COF-2@PA,and COF-3@PA(PA:phosphoric acid),are prepared by PA doping of three COFs with similar pore sizes but different amounts of hydrophilic groups.With the increase of hydrophilic groups,COFs can load more PA because of the enhanced hydrogen–bonding interactions between PA and the frameworks.powder X-ray diffraction(PXRD),scanning electron microscopy(SEM),and two-dimensional(2D)solid-state nuclear magnetic resonance(NMR)analyses show that PA can not only enter the channels of COF-3,but also insert into its 2D interlayers.This expands the proton conduction pathways from one-dimensional(1D)to three-dimensional(3D),which greatly improves the proton conductivity of COF-3.Meanwhile,the confinement effect of 1D channels and 2D layers of COF-3 also makes the hydrogen-bonded networks more orderly in COF-3@PA-30(30μL of PA loaded on COF-3).At 150℃,COF-3@PA-30 exhibits an ultrahigh anhydrous proton conductivity of 1.4 S·cm−1,which is a record of anhydrous proton conductivity reported to date.This work develops a new strategy for increasing the proton conductivity of 2D COF materials.

Carbazole Based Anionic MOF for Proton Conductivity

A non-interpenetrated anionic In-MOF(FJU-302)based on a linear H2 bpdc and an angled H2 cdc as dual-ligands was characterized by FT-IR,TGA and X-ray single-crystal/powder diffraction.FJU-302 crystallizes in the monoclinic system and I4_(1)/amd space group with a=27.1274(8),b=27.1274(8),c=29.788(3)Å,V=21921(2)Å^(3),Z=16,M_(r)=608.32,D_(c)=0.737 g/cm^(3),F(000)=4848,μ(Cu Kα)=3.659 mm^(–1),R=0.0800 and wR=0.1911 for 5703 observed reflections(I>2s(I)),and R=0.1470 and w R=0.2342 for all data.In this work,a carbazole based anionic In-MOF(FJU-302)was designed and synthesized,and the proton conductivity from subzero temperature(–30℃)to 70℃ was measured without additional humidity.FJU-302 presents a max proton conductivity of 6.47×10^(–4) S·cm^(–1) at 70℃,and it can maintain 5.88×10^(–7) S·cm^(–1) at–30℃.This work reports a first carbazole based MOF for proton conductivity at subzero temperature conditions.

Photogated proton conductivity of ZIF-8 membranes co-modified with graphene quantum dots and polystyrene sulfonate

Smart proton conductive metal-organic framework(MOF) membranes with dynamic remote control over proton conduction show high potential for use in advanced applications, such as sensors and bioprocesses. Here, we report a photoswitchable proton conductive ZIF-8 membrane by coencapsulating polystyrene sulfonate and graphene quantum dots into a ZIF-8 matrix(GQDs-PSS@ZIF-8) via a solidconfined conversion process. The proton conductivity of the GQDs-PSS@ZIF-8 membrane is 6.3 times higher than that of pristine ZIF-8 and can be reversibly switched by light due to photoluminescence quenching and the photothermal conversion effect, which converts light into heat. The local increase in temperature allows water molecules to escape from the porous channels, which cuts off the proton transport pathways and results in a decrease in proton conductivity. The proton conductivity is restored when the light is off owing to regaining water molecules, which act as proton carriers, from the surroundings. The GQDs-PSS@ZIF-8 membrane responds efficiently to light and exhibits an ON/OFF ratio of 12.8. This photogated proton conduction in MOFs has potential for the development and application of MOF-based protonic solids in advanced photoelectric devices.

Light enhanced proton conductivity in a terbium phosphonate photochromic chain complex

Crystalline complexes that exhibited light switchable proton conductivity are of great interest but still a challenge in material science.Herein,a terbium phosphonate chain complex was synthesized through assembly of electron-rich phosphonate units,electron-deficient polypyridine components and paramagnetic Tb^(3+)ions.Via light irradiation and heat treatment,the photogenerated radicals could simultaneously and reversibly tune the photochromic,luminescent and magnetic properties.Originating from the abundant hydrogen bonding networks formed between PO_3 groups and lattice water molecules,proton conductive behaviour was explored with high proton conductivity of(1.74±0.19)×10^(-3)S cm^(-1)at 80°C and 100%relative humidity.Importantly,accompanied with the colorless sample changed to blue,the proton conductivity increased about 20%after room temperature light illumination,implying that light irradiation could act as an external stimulus to enhance the conductive properties of original material.This work innovatively realized the light responsive conductive property in the electron transfer photochromic materials,providing a novel strategy for the construction of smart materials.

Researches into the Proton Conductivity of Molybdovanadophosphoric Acids with Wells－Dawson Structure

Five kinds of molybdovanadophosphoric acids H_7[P_2Mo_(17)VO_(62)],H_8[P_2Mo_(16)·V_2O_(62)],H_9 [P_2Mo_(15)V_3O_(62)],H_8[P_2Mo_(14)V_4O_(61)(H_2O)]and H_9[P_2Mo_(13)V_5O_(61)(H_2O)]have been synthesized.Their protop conductivities(C) have been measured.The effects of three main factors (frequency,hydration numbers,temperature)on the conductivity have been investigated.In some degree,heteropoly compounds with different structures give a different conductivity.