Hydrothermal Synthesis, Structural Characterization and Proton-conducting Property of a 3-D Framework Based on Zr_3Na_3-Substituted Polyoxometalate Building Blocks

A novel Zr-substituted polyoxometalate（POM） H2K3[Na6（H2O）9][Zr3Na3O3（H2O）3-（GeW9O（34））2]·12H2O（1） has been made under hydrothermal conditions. 1 was characterized by infrared spectrum, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. Crystal data are： H（50）O（95）Na9K3Ge2Zr3W（1）8, hexagonal space group P63/mmc, a = 15.2251（6）, b = 15.2251（6）, c = 25.035（2） , V = 5025.7（6） 3, Z = 2, Dc = 3.716 mg/m3, μ = 21.648 mm（-1）, F（000） = 4726, the final R = 0.0259 and w R = 0.0647 for 1487 observed reflections with I 2σ（I）. Single-crystal X-ray structure analysis reveals that 1 exhibits a 3-dimensional framework structure based on Zr3Na3-substituted polyanions [Zr3Na3O3（H2O）3（GeW9O（34））2]（11-） and [Na6（H2O）9]（6＋） clusters building blocks. UV-Vis spectrum indicates that 1 is a wide-gap semiconductor. In addition, the proton-conducting property of 1 was also investigated.

Process of Liquid Citrate Method for Synthesizing Proton-Conducting SrCe_(0.9)Y_(0.1)O_ (3-α) Powder

The liquid citrate method was used to synthesize perovskite-type SrCe0.9 Y0.1O3-α powder. SrCe09Y01O3-α membranes were prepared from the powder by sintering at 1450℃ for 10 h. The reactions in the process of the heat treatment were studied by XRD and DSC/TG. The microstructure of the powder and the membrane was observed by SEM. The results indicate that the perovskite-type SrCe0.9Y0.1 O3-α can be synthesized at 1100℃. The particle size of the synthesized SrCe0.9Y0.1O3-α powder is less than 1μm. The powder can be densified at 1450℃.

A real proton-conductive,robust,and cobalt-free cathode for proton-conducting solid oxide fuel cells with exceptional performance

The development of proton,oxygen-ion,and electron mixed conducting materials,known as triple-conduction materials,as cathodes for proton-conducting solid oxide fuel cells(H-SOFCs)is highly desired because they can increase fuel cell performance by extending the reaction active area.Although oxygen-ion and electron conductions can be measured directly,proton conduction in these oxides is usually estimated indirectly.Because of the instability of cathode materials in a reducing environment,direct measurement of proton conduction in cathode oxide is difficult.The La0.8Sr0.2Sc0.5Fe0.5O3–δ(LSSF)cathode material is proposed for H-SOFCs in this study,which can survive in an H_(2)-containing atmosphere,allowing measurement of proton conduction in LSSF by hydrogen permeation technology.Furthermore,LSSF is discovered to be a unique proton and electron mixed-conductive material with limited oxygen diffusion capability that is specifically designed for H-SOFCs.The LSSF is an appealing cathode choice for H-SOFCs due to its outstanding CO_(2)tolerance and matched thermal expansion coefficient,producing a record-high performance of 2032 mW cm^(−2)at 700℃and good long-term stability under operational conditions.The current study reveals that a new type of proton–electron mixed conducting cathode can provide promising performance for H-SOFCs,opening the way for developing high-performance cathodes.

A high-entropy spinel ceramic oxide as the cathode for proton-conducting solid oxide fuel cells

A high-entropy ceramic oxide is used as the cathode for the first time for proton-conducting solid oxide fuel cells(H-SOFCs).The Fe_(0.6)Mn_(0.6)Co_(0.6)Ni_(0.6)Cr_(0.6)O_(4)(FMCNC)high-entropy spinel oxide has been successfully prepared,and the in situ chemical stability test demonstrates that the FMCNC material has good stability against CO_(2).The first-principles calculation indicates that the high-entropy structure enhances the properties of the FMCNC material that surpasses their individual components,leading to lower O_(2)adsorption energy for FMCNC than that for the individual components.The HSOFC using the FMCNC cathode reaches an encouraging peak power density(PPD)of 1052 mW·cm^(-2)at 700℃,which is higher than those of the H-SOFCs reported recently.Additional comparison was made between the high-entropy FMCNC cathode and the traditional Mn_(1.6)Cu_(1.4)O_(4)(MCO)spinel cathode without the high-entropy structure,revealing that the formation of the high-entropy material allows the enhanced protonation ability as well as the movement of the O p-band center closer to the Fermi level,thus improving the cathode catalytic activity.As a result,the high-entropy FMCNC has a much-decreased polarization resistance of 0.057Ω·cm^(2)at 700℃,which is half of that for the traditional MCO spinel cathode without the high-entropy design.The excellent performance of the FMCNC cell indicates that the high-entropy design makes a new life for the spinel oxide as the cathode for HSOFCs,offering a novel and promising route for the development of high-performance materials for H-SOFCs.

High-performance proton-conducting solid oxide fuel cells using the first-generation Sr-doped LaMnO_(3) cathode tailored with Zn ions

Sr-doped LaMnO_(3)(LSM)which is the firstgeneration cathode for solid oxide fuel cells(SOFC;)has been tailored with Zn ions,aiming to achieve improved protonation ability for proton-conducting SOFCs(H-SOFCs).The new Sr and Zn co-doped LaMnO_(3)(LSMZ)can be successfully synthesized.The first-principle studies indicate that the LSMZ improves the protonation of LSM and decreases the barriers for oxygen vacancy formation,leading to high performance of the LSMZ cathode-based cells.The proposed LSMZ cell shows the highest fuel cell performance among ever reported LSMbased H-SOFCs.In addition,the superior fuel cell performance does not impair its stability.LSMZ is stable against CO_(2),as demonstrated by both in-situ CO_(2)corrosion tests and the first-principles calculations,leading to good long-term stability of the cell.The Zn-doping strategy for the traditional LSM cathode with high performance and good stability brings back the LSM cathode to intermediate temperatures and paves a new way for the research on the LSM-based materials as cathodes for SOFCs.

Tailoring Sr_(2)Fe_(1.5)Mo_(0.5)O_(6-δ)with Sc as a new single-phase cathode for proton-conducting solid oxide fuel cells

Sc-doped Sr_(2)Fe_(1.5)Mo_(0.5)O_(6-δ)(SFMSc)was successfully synthesized by partially substituting Mo in Sr_(2)Fe_(1.5)Mo_(0.5)O_(6-δ)(SFM)with Sc,resulting in a higher proton diffusion rate in the resultant SFMSc sample.Theoretical calculations showed that doping Sc into SFM lowered the oxygen vacancy formation energy,reduced the energy barrier for proton migration in the oxide,and increased the catalytic activity for oxygen reduction reaction.Next,a proton-conducting solid oxide fuel cell(H-SOFC)with a single-phase SFMSc cathode demonstrated significantly higher cell performance than that of cell based on an Sc-free SFM cathode,achieving 1258 mW cm^(−2)at 700℃.The performance also outperformed that of many other H-SOFCs based on single-phase cobalt-free cathodes.Furthermore,no trade-off between fuel cell performance and material stability was observed.The SFMSc material demonstrated good stability in both the CO_(2)-containing atmosphere and the fuel cell application.The combination of high performance and outstanding stability suggests that SFMSc is an excellent cathode material for H-SOFCs.

Towards high-performance tubular-type protonic ceramic electrolysis cells with all-Ni-based functional electrodes

Protonic ceramic electrolysis cells(PCECs),which permit high-temperature electrolysis of water,exhibit various advantages over conventional solid oxide electrolysis cells(SOECs),including cost-effectiveness and the potential to operate at low-/intermediate-temperature ranges with high performance and efficiency.Although many efforts have been made in recent years to improve the electrochemical characteristics of PCECs,certain challenges involved in scaling them up remain unresolved.In the present work,we present a twin approach of combining the tape-calendering method with all-Ni-based functional electrodes with the aim of fabricating a tubular-designed PCEC having an enlarged electrode area(4.6 cm^2).This cell,based on a 25μm-thick BaCe0.5Zr0.3Dy0.2O3-δ proton-conducting electrolyte,a nickelbased cermet and a Pr1.95Ba0.05NiO4+δ oxygen electrode,demonstrates a high hydrogen production rate(19 m L min^-1 at 600℃),which surpasses the majority of results reported for traditional button-or planar-type PCECs.These findings increase the scope for scaling up solid oxide electrochemical cells and maintaining their operability at reducing temperatures.

Visiting the roles of Sr-or Ca-doping on the oxygen reduction reaction activity and stability of a perovskite cathode for proton conducting solid oxide fuel cells

While double perovskites of PrBaCo_(2)O_(6)(PBC)have been extensively developed as the cathodes for proton-conducting solid oxide fuel cells(H-SOFCs),the effects of Sr-or Ca-doping at the A site on the activity and stability of the oxygen reduction reaction are yet to be fully studied.Here,the effect of A-site doping on the oxygen reduction reaction activity and stability has been studied by evaluating the performance of both symmetrical and single cells.It is shown that Ca-doped PBC(PrBa_(0.8)Ca_(0.2)Co_(2)O_(6),PBCC)shows a slightly smaller polarization resistance(0.076Ωcm^(2))than that(0.085Ωcm^(2))of Sr-doped PBC(PrBa0.8Sr0.2Co2O6,PBSC)at 700◦C in wet air.Moreover,the degradation rate of PBCC is 0.0003Ωcm^(2)h^(−1)(0.3%h−1)in 100 h,about 1/10 of that of PBSC at 700◦C in wet air.In addition,it is also confirmed that single cells with PBCC cathode show higher peak power density(1.22Wcm^(−2)vs.1.08Wcm^(−2)at 650◦C)and better durability(degradation rate of 0.1%h^(−1)vs.0.13%h^(−1))than those with PBSC cathode.The distribution of relaxation time analyses suggests that the better stability of the PBCC electrode may come from the fast and stable surface oxygen exchange process in the medium frequency range of the electrochemical impedance spectrum.

K-doped BaCo_(0.4)Fe_(0.4)Zr_(0.2)O_(3−δ) as a promising cathode material for protonic ceramic fuel cells

Slow oxygen reduction reaction(ORR)involving proton transport remains the limiting factor for electrochemical performance of proton-conducting cathodes.To further reduce the operating temperature of protonic ceramic fuel cells(PCFCs),developing triple-conducting cathodes with excellent electrochemical performance is required.In this study,K-doped BaCo_(0.4)Fe_(0.4)Zr_(0.2)O_(3−δ)(BCFZ442)series were developed and used as the cathodes of the PCFCs,and their crystal structure,conductivity,hydration capability,and electrochemical performance were characterized in detail.Among them,Ba_(0.9)K_(0.1)Co_(0.4)Fe_(0.4)Zr_(0.2)O_(3−δ)(K10)cathode has the best electrochemical performance,which can be attributed to its high electron(e^(−))/oxygen ion(O^(2−))/H^(+)conductivity and proton uptake capacity.At 750℃,the polarization resistance of the K10 cathode is only 0.009Ω·cm^(2),the peak power density(PPD)of the single cell with the K10 cathode is close to 1 W·cm^(−2),and there is no significant degradation within 150 h.Excellent electrochemical performance and durability make K10 a promising cathode material for the PCFCs.This work can provide a guidance for further improving the proton transport capability of the triple-conducting oxides,which is of great significance for developing the PCFC cathodes with excellent electrochemical performance.

Preparation and Properties of Hybrid Silane-crosslinked Sulfonated Poly(aryl ether ketone)s as Proton Exchange Membranes

A series of novel organic-inorganic hybrid proton-conducting electrolyte membranes with silane-crosslinked sulfonated poly(aryl ether ketone)(SC-SPAEK) networks was prepared via a simple procedure that includes solution casting and acid treatment. The organosilicon pendants of the silane-grafted SPAEK, which were expected to serve as coupling and crosslinking agents, were found to play a key role in the homogenous dispersion of inorganic particles and improved the performance of hybrid membranes. The hybrid membranes exhibited enhanced proton conductivity, and SC-SPAEK/TiO2-4 showed an extremely high proton conductivity of 0.1472 S/cm at 100℃. The crosslinked hybrid membranes also demonstrated good chemical resistance, oxidative stability, and mechanical properties. The crosslinked hybrid membranes with excellent comprehensive performance may be a promising material for proton exchange membrane fuel cells.

High proton conductivity in metalloring-cluster based metalorganic nanotubes

Two novel anionic single-walled metal-organic nanotubes(MONTs),[(CH_(3))_(2)NH_(2)][ln(cdc)(thb)].2DMF.9.5H_(2)O(FJU-105)and[(CH_(3))_(2)NH_(2)][ln(cdc)(H-btc)]-2DMA·11H_(2)O(FJU-106)(H_(2)cdc=9H-carbazole-3,6-dicarboxylic acid,H_(2)thb=2,5-thiophene dicarboxylic acid,H3btc=1,3,5-benzene tricarboxylic acid),are achieved by employing[ln_(6)(cdc)_(6)]^(6+)metalloring cluster with largest diameter as the secondary building blocks(SBUs).The inner surface of FJU-106 is functionalized by uncoordinated-COOH groups of the H-btc linkers,leading to a higher proton conduction than FJU-105.At 70℃,FJU-106 displays the proton conduction performances among MONTs,up to 1.80×10^(-2)S·cm(^-1).And FJU-105 and FJU-106 are the first examples of MONT proton conductors operating at subzero temperature.

Synthesis,structure and properties of three novel transition-metal-containing tantalum-phosphate clusters

Peroxide ligation of aqueous metal-oxo clusters provides rich speciation and structural diversity.Here,three novel transition-metal derivatives of polyoxometalate anions,[Ni_(2)(H_(2)O)_(10){P_(4)Ta_(6)(O_(2))_(6)O_(24)}]^(6-)(1a),[Zn(H_(2)O)_(4){P_(4)Ta_(6)(O_(2))_(6)O_(24)}]^(8-)(2a)and[Cd(H_(2)O)_(4){P_(4)Ta_(6)(O_(2))_(6)O_(24)}]^(8-)(3a),have been successfully synthesized by adopting a one-pot reaction strategy.All of these hexatantalates are built from a new-type phosphorus-incorporated hexatantalates.We investigated the solution behaviors,and the peak assignments of the MS spectra indicated some degree of stability of them in water.Furthermore,the proton-conducting ability of compound 1a was also explored and it has shown well conductivity at high relative humidities,with conductivity achieved 1.22×10^(-3) S/cm(85℃,90%RH).