Hydrogen production at intermediate temperatures with proton conducting ceramic cells:Electrocatalytic activity,durability and energy efficiency

Proton conducting ceramic cells(PCCs)are an attractive emerging technology operating in the intermediate temperature range of 500 to 700℃.In this work,we evaluate the production of hydrogen at intermediate temperatures by proton conducting ceramic cell electrolysis(PCCEL).We demonstrate a highperformance steam electrolysis owing to a composite positrode based on BaGd_(0.8)La_(0.2)Co_(2)O_(6-δ)(BGLC1082)and BaZr0.5Ce0.4Y0.1O3-δ(BZCY541).The high reliability of PCCEL is demonstrated for 1680 h at a current density as high as-0.8 A cm^(-2)close to the thermoneutral cell voltage at 600℃.The electrolysis cell showed a specific energy consumption ranging from 54 to 66 kW h kg^(-1)that is comparable to state-of-the-art low temperature electrolysis technologies,while showing hydrogen production rates systematically higher than commercial solid oxide ceramic cells(SOCs).Compared to SOCs,the results verified the higher performances of PCCs at the relevant operating temperatures,due to the lower activation energy for proton transfer comparing with oxygen ion conduction.However,because of the p-type electronic conduction in protonic ceramics,the energy conversion rate of PCCs is relatively lower in steam electrolysis.The faradaic efficiency of the PCC in electrolysis mode can be increased at lower operating temperatures and in endothermic conditions,making PCCEL a technology of choice to valorize high temperature waste heat from industrial processes into hydrogen.To increase the faradaic efficiency by optimizing the materials,the cell design,or the operating strategy is a key challenge to address for future developments of PCCEL in order to achieve even more superior techno-economic merits.

Preparation and Conducting Behavior of Amphibious Organic/Inorganic Hybrid Proton Exchange Membranes Based on Benzyltetrazole

A series of novel amphibious organic/inorganic hybrid proton exchange membranes with H3PO4 doped which could be used under both wet and dry conditions was prepared through a sol-gel process based on acrylated triethoxysilane（A-TES） and benzyltetrazole-modified triethoxysilane（BT-TES）.The dual-curing approach including UV-curing and thermal curing was used to obtain the crosslinked membranes.Polyethylene glycol（400） diacrylate（PEGDA） was used as an oligomer to form the polymeric matrix.The molecular structures of precursors were characterized by 1 H,13 C and 29 Si NMR spectra.The thermogravimetric analysis（TGA） results show that the membranes exhibit acceptable thermal stability for their application at above 200 oC.The differential scanning calorimeter（DSC） determination indicates that the crosslinked membranes with the mass ratios of below 1.6 of BT-TES to A-TES and the same mass of H3PO4 doped as that of A-TES possess the-T g s,and the lowest T g（-28.9 ℃） exists for the membrane with double mass of H3PO4 doped as well.The high proton conductivity in a range of 9.4―17.3 mS/cm with the corresponding water uptake of 19.1%―32.8% of the membranes was detected at 90 oC under wet conditions.Meanwhile,the proton conductivity in a dry environment for the membrane with a mass ratio of 2.4 of BT-TES to A-TES and double H3PO4 loading increases from 4.89×10-2 mS/cm at 30 ℃ to 25.7 mS/cm at 140 ℃.The excellent proton transport ability under both hydrous and anhydrous conditions demonstrates a potential application in the polymer electrolyte membrane fuel cells.

Proton Conducting Composite Membranes from Sulfonated Polyether Ether Ketone and SiO_2

Proton conducting composite membranes from sulfonated polyether ether ketone and SiO2 for direct methanol fuel cell （DMFC） application were prepared with sulfonated polyether ether ketone（SPEEK） and tetracethoxy silane（TEOS） by sol-gel method. The covalent crosslinking structure was formed between —SO3H of SPEEK via SiO2. The SEM images show that the interfacial compatibility of SPEEK and SiO2 is improved obviously and SiO2 disperses uniformly in the polymer matrix and the particle diameter of SiO2 does not exceed 40 nm. The proton conductivity of composite membranes decreases slightly compared with the SPEEK membrane while the methanol permeability and swelling of composite membrane are improved remarkablely owing to covalent cross-linking between —SO3H and SiO2 .

Pore-filling Three-dimensionally Ordered Macroporous Polyimide Composite Proton Conducting Membranes

The silica opal templates were prepared from three silica colloids of different diameters of 230 nm, 500 nm and 1.5 mm by a filtration route. The large-scale stable opal template membranes after sintering the deposited SiO2 opal template can be successfully obtained by optimizing the pH value and NaCl concentration in silica colloidal solutions. The three-dimensionally ordered macroporous（3DOM） polyimide membranes without crack were fabricated by reproducing the structure of silica opal template. We prepared the pore-filling composite proton exchange membranes by filling the 3DOM structure with proton conducting organosilane sol. The result indicates that the composite membranes exhibit higher water uptake than pure filling organosilane gel. The proton conductivity increased with the increasing of pore cell in composite membranes.

Barium-doped Pr_(2)Ni_(0.6)Cu_(0.4)O_(4+δ) with triple conducting characteristics as cathode for intermediate temperature proton conducting solid oxide fuel cell

Proton conducting solid oxide fuel cell(H-SOFC)is an emerging energy conversion device,with lower activation energy and higher energy utilization efficiency.However,the deficiency of highly active cathode materials still remains a major challenge for the development of H-SOFC.Therefore,in this work,K_(2)NiF_(4)-type cathode materials Pr_(2-x)Ba_(x)Ni_(0.6)Cu_(0.4)O_(4+δ)(x=0,0.1,0.2,0.3),single-phase tripleconducting(e-/O^(2-)/H^(+))oxides,are prepared for intermediate temperature H-SOFCs and exhibit good oxygen reduction reaction activity.The investigation demonstrates that doping Ba into Pr_(2-x)BaxNi_(0.6)Cu_(0.4)O_(4+δ) can increase its electrochemical performance through enhancing electrical conductivity,oxygen vacancy concentration and proton conductivity.EIS tests are carried at 750℃ and the minimum polarization impedances are obtained when x=0.2,which are 0.068 Ω·cm^(2) in air and 1.336 Ω·cm^(2) in wet argon,respectively.The peak power density of the cell with Pr_(1.8)Ba_(0.2)Ni_(0.6)Cu_(0.4)O_(4+δ) cathode is 298 mW·cm^(-2) at 750℃ in air with humidified hydrogen as fuel.Based on the above results,Ba-doped Pr_(2-x)Ba_(x)Ni_(0.6)Cu_(0.4)O_(4+δ) can be a good candidate material for SOFC cathode applications.

Silk nanofibril as nanobinder for preparing COF nanosheet-based proton exchange membrane

Two-dimensional covalent organic framework nanosheets(CONs)with ultrathin thickness and porous crystalline nature show substantial potential as novel membrane materials.However,bringing CONs materials into flexible membrane form is a monumental challenge due to the limitation of weak interactions among CONs.Herein,one-dimensional silk nanofibrils(SNFs)from silkworm cocoon are designed as the nanobinder to link sulfonated CON(SCON)into robust SCON-based membrane through vacuum-filtration method.Ultrathin and large lateral-sized SCONs are synthesized via bottom-up interface-confined synthesis approach.Benefiting from high length-diameter ratio of SNF and rich functional groups in both SNF and SCON,two-dimensional(2D)SCONs are effectively connected together by physical entanglement and strong H-bond interactions.The resultant SCON/SNF membrane displays dense structure,high mechanical integrity and good stability.Importantly,the rigid porous nanochannels of SCON,high-concentration-SO3H groups insides the pores and H-bonds at SCON-SNF interfaces impart SCON/SNF membrane high-rate proton transfer pathways.Consequently,a superior proton conductivity of 365 mS cm^(-1)is achieved at 80C and 100%RH by SCON/SNF membrane.This work offers a promising approach for connecting 2D CON materials into flexible membrane as high-performance solid electrolyte for hydrogen fuel cell and may be applied in membrane-related other fields.

Efficient proton conduction in porous and crystalline covalent-organic frameworks(COFs)

To attain the objectives of carbon peaking and carbon neutrality,the development of stable and highperformance ion-conducting materials holds enormous relevance in various energy storage and conversion devices.Particularly,crystalline porous materials possessing built-in ordered nanochannels exhibit remarkable superiority in comprehending the ion transfer mechanisms with precision.In this regard,covalent organic frameworks(COFs)are highly regarded as a promising alternative due to their preeminent structural tunability,accessible well-defined pores,and excellent thermal/chemical stability under hydrous/anhydrous conditions.By the availability of organic units and the diversity of topologies and connections,advances in COFs have been increasing rapidly over the last decade and they have emerged as a new field of proton-conducting materials.Therefore,a comprehensive summary and discussion are urgently needed to provide an"at a glance"understanding of the prospects and challenges in the development of proton-conducting COFs.In this review,we target a comprehensive review of COFs in the field of proton conductivity from the aspects of design strategies,the proton conducting mechanism/features,the relationships of structure-function,and the application of research.The relevant content of theoretical simulation,advanced structural characterizations,prospects,and challenges are also presented elaborately and critically.More importantly,we sincerely hope that this progress report will form a consistent view of this field and provide inspiration for future research.

Development and Challenges of Electrode Ionomers Used in the Catalyst Layer of Proton-Exchange Membrane Fuel Cells:A Review

The electrode ionomer plays a crucial role in the catalyst layer(CL) of a proton-exchange membrane fuel cell(PEMFC) and is closely associated with the proton conduction and gas transport properties,structural stability,and water management capability.In this review,we discuss the CL structural characteristics and highlight the latest advancements in ionomer material research.Additionally,we comprehensively introduce the design concepts and exceptional performances of porous electrode ionomers,elaborate on their structural properties and functions within the fuel cell CL,and investigate their effect on the CL microstructure and performance.Finally,we present a prospective evaluation of the developments in the electrode ionomer for fabricating CL,offering valuable insights for designing and synthesizing more efficient electrode ionomer materials.By addressing these facets,this review contributes to a comprehensive understanding of the role and potential of electrode ionomers for enhancing PEMFC performance.

Recent advances and perspectives of fluorite and perovskite-based dual-ion conducting solid oxide fuel cells

High-temperature solid-state electrolyte is a key component of several important electrochemical devices,such as oxygen sensors for automobile exhaust control,solid oxide fuel cells(SOFCs) for power generation,and solid oxide electrolysis cells for H_(2) production from water electrolysis or CO_(2) electrochemical reduction to value-added chemicals.In particular,internal diffusion of protons or oxygen ions is a fundamental and crucial issue in the research of SOFCs,hypothetically based on either oxygen-ionconducting electrolytes or proton-conducting electrolytes.Up to now,some electrolyte materials based on fluorite or perovskite structure were found to show certain degree of dual-ion transportation capability,while in available electrolyte database,particularly in the field of SOFCs,such dual-ion conductivity was seriously overlooked.Actually,few concerns arising to the simultaneous proton and oxygen-ion conductivities in electrolyte of SOFCs inevitably induce various inadequate and confusing results in literature.Understanding dual-ion transportation behavior in electrolyte is indisputably of great importance to explain some unusual fuel cell performance as reported in literature and enrich the knowledge of solid state ionics.On the other hand,exploration of novel dual-ion conducting electrolytes will benefit the development of SOFCs.In this review,we provide a comprehensive summary of the understanding of dual-ion transportation in solid electrolyte and recent advances of dual-ion conducting SOFCs.The oxygen ion and proton conduction mechanisms at elevated temperature inside oxide-based electrolyte materials are first introduced,and then(mixed) oxygen ion and proton conduction behaviors of fluorite and perovskite-type oxides are discussed.Following on,recent advances in the development of dual-ion conducting SOFCs based on fluorite and perovskite-type single-phase or composite electrolytes,are reviewed.Finally,the challenges in the development of dual-ion conducting SOFCs are discussed and future prospects are proposed.

High-performance polymer electrolyte membranes incorporated with 2D silica nanosheets in high-temperature proton exchange membrane fuel cells

Silica nanosheets(SN)derived from natural vermiculite(Verm)were successfully incorporated into polyethersulfone-polyvinylpyrrolidone(PES-PVP)polymer to fabricate high-temperature proton exchange membranes(HT-PEMs).The content of SN filler was varied(0.1-0.75 wt%)to study its influence on proton conductivity,power density and durability.Benefiting from the hydroxyl groups of SN that enable the formation of additional proton-transferring pathways,the inorganic-organic membrane displayed enhanced proton conductivity of 48.2 mS/cm and power density of 495 mW/cm^(2) at 150℃ without humidification when the content of SN is 0.25 wt%.Furthermore,exfoliated SN(E-SN)and sulfonated SN(S-SN),which were fabricated by a liquid-phase exfoliation method and silane condensation,respectively,were embedded in PES-PVP polymer matrix by a simple blending method.Due to the significant contribution from sulfonic groups in S-SN,the membrane with 0.25 wt%S-SN reached the highest proton conductivity of51.5 mS/cm and peak power density of 546 mW/cm^(2) at150℃,48%higher than the pristine PES-PVP membranes.Compared to unaltered PES-PVP membrane,SN added hybrid composite membrane demonstrated excellent durability for the fuel cell at 150℃.Using a facile method to prepare 2D SN from natural clay minerals,the strategy of exfoliation and functionalization of SN can be potentially used in the production of HT-PEMs.

Water induced phase segregation in hydrocarbon proton exchange membranes

Proton exchange membranes （PEMs） are a key material for proton exchange membrane fuel cells （PEM-FCs）, Non-fluorinated hydrocarbon PEMs are low-cost alternatives to Nation, but limited by the low pro-ton conductivity, because of the weak phase segregation structure and narrow ion-transport channels.Various efforts have been taken to improve the performance of hydrocarbon PEMs, but mostly with com-plex methodologies. Here we demonstrate a simple, yet very efficient method to create phase segrega-tion structure inside a typical hydrocarbon PEM, sulfonated poly（ether ether ketone） （SPEEK）. By sim-ply adding appropriate amounts of water into the DMF solvent, the resulting SPEEK membrane exhibitswidened ion-transport channels, with the phase size of 2.7 nm, as indicated by both molecular dynamic（MD） simulations and transmission electron microscope （TEM） observations, and the proton conductivityis thus improved by 200%. These findings not only further our fundamental understanding of hydrocarbonPEMs, but are also valuable to the development of low-cost and practical fuel cell technologies.

Preparation and properties of composite membrane of bisphenol A-based sulfonated poly(arylene ether sulfone)and phosphotungstic acid for proton exchange membranes

A series of bi A-SPAES(Ds=0.4)/phosphotungstic acid(PWA/bi A-SPAES)composite membranes with various contents of PWA were prepared and characterized by FT-IR.Scanning electron microscopy(SEM)images indicated the PWA were well dispersed within polymer matrix.These composite membranes were evaluated for proton exchange membranes(PEM)in direct methanol fuel cell(DMFC).These membranes showed good thermal stability.It was found that the water uptake of these membranes increased with the increase of the PWA content in the hybrid membranes.Meanwhile,the introduction of inorganic particles increased both the proton conductivity and the methanol permeability.The proton conductivities of composite membranes were increased from 0.017 S/cm to 0.045 S/cm at 20 ℃ and from 0.054 S/cm to 0.093 S/cm at 100 ℃ with the increase of PWA content from 0 to 50 %.Especially,all the methanol diffusion coefficients(4.20×10-8-1.05×10-7cm2/s)of bi A-SPAES/PWA hybrid membranes are much lower than that of Nafion 117 membrane(2.1×10-6 cm2/s).Bi A-SPAES/PWA hybrid membranes were therefore proposed as candidates of material for PEM in DMFC.

Modified silicon carbide whisker reinforced polybenzimidazole used for high temperature proton exchange membrane

Polybenzimidazole containing ether bond（OPBI） was reinforced with silicon carbide whisker（m Si C） modified by 3-aminopropyltriethoxysilane（KH550）, and then doped with phosphoric acid（PA） to obtain OPBI/m Si C/PA membranes. These OPBI/m Si C/PA membranes have excellent mechanical strength and oxidative stability and can be used for high temperature proton exchange membrane（HT-PEM）. The tensile strength of OPBI/m Si C/PA membranes ranges from 27.3 to 36.8 MPa, and it increases at first and then decreases with the increase of m Si C content. The high m Si C content and PA doping level contribute to improving the proton conductivity of membranes. The proton conductivity of PBI/m Si C-10/PA membrane is 27.1 m S cm-1 at 170℃ without humidity, with an increase of 55.7% compared with that of OPBI/PA membrane. These excellent properties make OPBI/m Si C/PA membranes promising membrane materials for HT-PEM applications.

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.

Synthesis，Proton Conductivity and High－Temperature Humidity Sensing Property of Zr（HPO_4）_2·H_2O and Its Aluminium－substituted Compositions

A series of aluminium-containing α-type hydrated zirconium hydrogen phosphates,Zr_(1-x)Alx (H_(1+x/2)PO_4 )_2 with x=0-0.06,were hydrothermally synthesized and characterizedby means of X-ray diffraction,differential thermal analysis and thermogravimetric analysis.The proton conductivity,1.2×10￣(-4) S·cm￣(-1)at 180℃ was found in Zr_(0.98)Al_(0.02)(H_(1.01)PO_4)_2·H_2O.Humidity-sensing measurements were carried out at 120℃ and 140℃ respectively.Even a limited substitution of Al for Zr can enhance both proton conductivity and humidity sensitivity.

Nanocomposite Membranes based on Perfl uorosulfonic Acid/Ceramic for Proton Exchange Membrane Fuel Cells

Perfl uorosulfonic acid/ceramic nanocomposite membranes were investigated as electrolytes for polymer electrolyte membrane fuel cell applications under low relative humidity. Different nanosized ceramics（SiO2, ZrO2, TiO2） with diameters in the range of 2-6 nm were synthesized in situ in Nafion solution through a sol-gel process and the formed nanosized ceramics were well-dispersed in the solution.The nanocomposite membranes were formed through a casting process. The nanocomposite membrane showes enhanced water retention ability and improved proton conductivity compared to those of pure Nafi on membrane. The mechanical strength of the formed nanocomposite membranes is slightly less than that of pure Nafi on membrane. The experimental results demonstrate that the polymer ceramic nanocompsite membranes are potential electrolyte for fuel cells operating at elevated temperature.

Sulfonated fluorinated multi-block copolymer hybrid containing sulfonated(poly ether ether ketone) and graphene oxide: A ternary hybrid membrane architecture for electrolyte applications in proton exchange membrane fuel cells

A ternary hybrid membrane architecture consisting of sulfonated fluorinated multi-block copolymer （SFMC）, sulfonated （poly ether ether ketone） （SPEEK） and I or 5 wt% graphene oxide （GO） was fabricated through a facile solution casting approach. The simple, but effective monomer sulfonation was performed for SFMC to create compact and rigid hydrophobic backbone structures, while conventional random sulfonation was carried-out for SPEEK. Hydrophilic-hydrophobic-hydrophilic structure of SFMC enhances the compatibility with SPEEK and GO and allows for an unprecedented approach to alter me- chanical strength and proton conductivity of ternary hybrid membrane, as verified from universal test machine （UTM） curves and alternating current （AC） impedance plots. The impact of GO integration on the morphology and roughness of hybrid membrane was scrutinized using field emission scanning electron microscope （FE-SEM） and atomic force microscope （AFM）. Ternary hybrid showed uniform intercalation of GO nanosheets throughout the entire surface of membrane with an increased surface roughness of 8.91 nm. The constructed ternary hybrid membrane revealed excellent water absorption, ion exchange capacity and gas barrier properties, while retaining reasonable dimensional stability. The well-optimized ternary hybrid membrane containing 5 wt% GO revealed a maximum proton conductivity of 111.9 mS/cm, which is higher by a factor of two-fold with respect to that of bare SFMC membrane. The maximum PEMFC power density of 528.07mW/cm2 was yielded by ternary hybrid membrane at a load current density of 1321.1 mA/cm2 when operating the cell at 70 ℃ under 100% relative humidity （RH）. In comparison, a maximum power density of only 182.06 mW/cm2 was exhibited by the bare SFMC membrane at a load current density of 455.56 mA/cm2 under same operating conditions.

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

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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.

Proton dynamics in phosphotungstic acid impregnated mesoporous silica proton exchange membrane materials

Phosphotungstic acid is an excellent proton conductor that can be incorporated into porous supports, and nanocomposite proton exchange membrane materials made from mesoporous silica impregnated with phosphotungstic acid have been suggested for use in fuels cells operating> 100 ℃. In this work, quasielastic neutron scattering was used to study proton self-diffusion in mesoporous disordered and P6 mm symmetry silica impregnated with two concentrations of phosphotungstic acid. Overall, the silica structure had a significantly greater effect on proton conduction and diffusion than phosphotungstic acid concentration, with higher proton conduction occurring for the P6 mm symmetry silica samples. Quasielastic neutron scattering revealed two populations of protons diffusing through each sample, and that proton conduction is limited by the slower of these populations, which diffuse via a jump-diffusion mechanism. Whilst the fundamental jump-diffusion mechanism by which these slower protons moved was found to be similar for both silica supports and phosphotungstic acid concentrations, the faster diffusion occurring in P6 mm structured silica arises from a lower residence time of protons moving between sites in the jump-diffusion model, suggesting a lower energy barrier.