Pure Ionic Conductor Research Articles

Flash sintering of cationic conductive ceramics: A way to build multilayer systems

AbstractFlash Sintering (FS), that allows densifying ceramics at low furnace temperature in a few seconds, requires a reversible electrochemical reaction to enable the current flow through the electrode / material interface. For Li+ pure ionic conductors such as Li1.3Al0.3Ti1.7(PO4)3 (LATP), the best material to ensure this fast charge transfer reaction is a mixed Li+/e− conductor, eg, LiCoO2 (LCO). This paper demonstrates the feasibility of FS on LCO between two Pt electrodes and on multi‐layers systems using LCO or LATP+LCO composite as electrodes. It is shown that a composite electrode both allows the flash event to occur and prevents the delamination possibly observed with pure LCO by lowering interfacial stresses.

ϒ-Li3PO4-Type Solid Electrolytes in Li4GeO4-Li4SiO4-Li3VO4 Quasi-Ternary System with High Lithium Ionic Conductivity

Lithium superionic conductors (LISICONs) are promising materials to realize high safety, high energy all-solid-state lithium-ion batteries. Through a dual-cation-substitution strategy, we designed ternary solid solutions of Ge-Si-V derivatives with a γ-Li3PO4-type structure in the Li4GeO4-Li4SiO4-Li3VO4 quasi-ternary system, and the relationship among their compositions, phase formation, and ionic conductivity was analyzed. The samples were fabricated through a solid-state reaction at 1173 K. The crystalline phase of the samples was identified through X-ray diffraction (XRD). The crystal structure was elucidated with Rietveld refinement of Synchrotron X-ray diffraction data. The morphologies and elemental distributions of the synthesized samples were examined through scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The ionic conductivities of the synthesized samples at various temperatures were determined by AC impedance spectroscopy. An all-solid-state battery using the discovered LISICON material was fabricated in an Ar-filled glovebox. The positive and negative electrodes were composed of a mixture of LiNbO3-coated LiCoO2 with Li10GeP2S12 and Li-In metal, respectively. A charge-discharge test was conducted between 1.9 and 3.6 V at an applied current of 0.03 mA cm−1 (0.05 C rate) at 373 K. This study determined the phase-formation regions in the Li4GeO4-Li4SiO4-Li3VO4 quasi-ternary system and demonstrated relatively high ionic conductivity of the γ-Li3PO4-type phase structures.A high conductivity with low activation energy was achieved in ternary compositions compared to that in any binary system. The bulk ionic conductivity of 5.8 × 10−5 S cm−1 at 298 K was obtained for Li3.55(Ge0.45Si0.10V0.45)O4 with a low activation energy of 0.37 eV. Li3.55(Ge0.45Si0.10V0.45)O4 maintained high ionic conduction property (~10−5 S cm−1) even for the total conductivity (sum of bulk and grain-boundary contributions). Ionic conductivity of the Li4GeO4-Li4SiO4-Li3VO4 system was visualized along with the phase-identification results, as shown in the provided figure. In this color contour map (Fig. 1), relatively high ionic conductivity is confirmed around the γ-Li3PO4-type phase area (the region around sample #9); Li3VO4, Li4SiO4, and Li4GeO4 solid solutions or their mixture exhibited low ionic conductivity. Compared to any binary composition system (i.e., Li-X-Y-O), the existing tie line between the corner of this triangular ternary composition system (i.e., Li-X-Y-Z-O) has a higher ionic conductivity. Particularly, the ionic conductivity of Li3.55(Ge0.45Si0.10V0.45)O4 at #9 is slightly higher than that of Li3.6(Ge0.6V0.4)O4, which is the composition showing the highest ionic conductivity reported to date of LISICONs in the binary systems. Besides, the activation energy of Li3.55(Ge0.45Si0.10V0.45)O4 was much lower than that of Li3.6(Ge0.6V0.4)O4. The activation energy decreased by ~17.8% compared with that of the Li3.6(Ge0.6V0.4)O4 (0.45 eV). Therefore, the novel material-search concept (more complex composition) is one of the positive directions for developing the LISICON-type ionic conductors. The absolute value of 5.8 × 10−5 S cm−1 exceeded that of the reported ternary material in the Li4GeO4-Li4PO4-Li3VO4 system (5.1 × 10−5 S cm−1) (ACS Appl. Energy Mater. 2 (2019) 6608–6615). In other words, the ionic conductivity of the discovered material is higher than that of all the practically existing LISICONs, including the ternary systems. Further optimization in the ternary system or a more complex composition system could be a promising way for the subsequent material search.The high ionic conductivity property (σ) was achieved by reducing the activation energy (E a) and increasing the pre-exponential factor (σ0) through dual doping, which determines the σ value as described in the Arrhenius equation: σT = σ0exp(−E a/kBT). Li3.55(Ge0.45Si0.10V0.45)O4 functioned as a solid electrolyte in an all-solid-state cell, indicating the features of a pure lithium ionic conductor without electronic conduction. The LISICON oxide prepared via a cold-press functioned as a solid-electrolyte separator similar to sulfide solid electrolytes in all-solid-state batteries without high-temperature sintering. This demonstration could be the first step to developing room-temperature-LISICONs-based all-solid-state lithium ionic batteries. This work verified that the dual-cation-substitution strategy is beneficial for compositional and structural optimization, affording enhanced ion-conducting properties. Additionally, the substitution of more kinds of cations with larger radii into LISICONs is proposed; further enhancement in ionic conductivity could be expected in the case of the LISICON with a larger lattice size. Ternary LISICON systems using cations with larger ionic radii (e.g., Al3+, Ga3+) are an attractive candidate for future research. Figure 1

High lithium ionic conductivity of γ-Li3PO4-type solid electrolytes in Li4GeO4−Li4SiO4–Li3VO4 quasi-ternary system

Lithium superionic conductors (LISICONs) are promising materials to realize high safety, high energy all-solid-state lithium batteries. LISICONs with a γ-Li3PO4-type structure were developed for use in the Li4GeO4−Li4SiO4–Li3VO4 ternary system, and the relationship among their composition, phase formation, and ionic conductivity was analyzed. Ionic conductivity of 5.8 ​× ​10−5 ​S ​cm−1 ​at 298 ​K, the highest value among the LISICONs reported to date, was obtained for Li3.55(Ge0.45Si0.10V0.45)O4 with a low activation energy of 0.37 ​eV. This was achieved by reducing the activation energy and increasing the pre-exponential factor through dual doping. The Ge4+, Si4+, and V5+ cations of Li3.55(Ge0.45Si0.10V0.45)O4 occupied the same site; thus, the solid-solution formation was confirmed. Li3.55(Ge0.45Si0.10V0.45)O4 functioned as a solid electrolyte in an all-solid-state cell, indicating the features of a pure lithium ionic conductor without electronic conduction. This work verified that the dual substitution strategy is beneficial for compositional and structural optimization, affording enhanced ion-conducting properties.

High oxide ion and proton conductivity in a disordered hexagonal perovskite.

Oxide ion and proton conductors, which exhibit high conductivity at intermediate temperature, are necessary to improve the performance of ceramic fuel cells. The crystal structure plays a pivotal role in defining the ionic conduction properties, and the discovery of new materials is a challenging research focus. Here, we show that the undoped hexagonal perovskite Ba7Nb4MoO20 supports pure ionic conduction with high proton and oxide ion conductivity at 510 °C (the bulk conductivity is 4.0 mS cm-1), and hence is an exceptional candidate for application as a dual-ion solid electrolyte in a ceramic fuel cell that will combine the advantages of both oxide ion and proton-conducting electrolytes. Ba7Nb4MoO20 also showcases excellent chemical and electrical stability. Hexagonal perovskites form an important new family of materials for obtaining novel ionic conductors with potential applications in a range of energy-related technologies.

A novel Sn0.9Ni0.1P2O7/KPO3 composite electrolyte with improved electrical properties for intermediate temperature fuel cells

In this study, a novel Sn0.9Ni0.1P2O7/KPO3 composite electrolyte was prepared by a mechanical mixing method. The Raman spectrum and X-ray diffraction of Sn0.9Ni0.1P2O7/KPO3 indicated that the main microstructure is pyrophosphate phase and KPO3 mainly exists in amorphous state in the composite. The intermediate temperature (400–700 °C) electrical properties of Sn0.9Ni0.1P2O7/KPO3 were studied by means of electrochemical impedance spectroscopy. The maximum conductivity of Sn0.9Ni0.1P2O7/KPO3 was 6.1 × 10−2 S cm−1 in a dry nitrogen atmosphere at 700 °C. The log σ ～ log (pO2) results showed that Sn0.9Ni0.1P2O7/KPO3 is a pure ionic conductor in an oxidizing atmosphere and a hybrid conductor of proton and electron hole under a reductive atmosphere. The maximum power density of Sn0.9Ni0.1P2O7/KPO3 (thickness: 1.2 mm) was 434 mW cm−2 at 700 °C.

Pressure-induced ionic to mixed ionic and electronic conduction transition in solid electrolyte LaF3.

The ionic transport properties of solid electrolyte LaF3 were systematically studied under high pressures up to 30.6 GPa with alternate-current impedance spectra measurements and first-principles calculations. From the impedance spectra measurements, LaF3 was found to transform from pure ionic conduction to mixed ionic and electronic conduction at 15.0 GPa, which results from the pressure-induced structural phase transition from a tysonite-type structure to an anti-Cu3Ti-type structure. F- ion migration can be suppressed by pressure, causing a decrease of the ionic conductivity of LaF3. By first-principles calculations, the pressure-dependent diffusion behaviors of the F- ions can be understood. The increased overlap of electron clouds at the interstitial site between rigid La3+ and liquid F- lattices leads to the appearance of electronic conduction in anti-Cu3Ti-type structured LaF3.

Impact of the support on the catalytic activity of Ag nanoparticles for soot combustion

This study investigates the catalytic activity for soot combustion of Ag nanoparticles dispersed on various supports showing different redox properties. Temperature programmed soot oxidation and isotopic exchange experiments were performed to assess the impact of the soot/catalyst contact, the oxygen partial pressure and the ageing toward activity. Three different contact modes have been used to clearly highlight the catalytic performances: loose, tight and supertight. Whatever the support, in both loose and tight contact modes, the catalytic performances are linked with the Ag surface concentration which was found to be high on zirconia-based catalysts and low on ceria-zirconia. The ignition of the soot combustion process occurs on Ag nanoparticles except for catalysts supported on Yttria-Stabilized Zirconia (YSZ), a pure oxygen ionic conductor, where Ag nanoparticles only promote the run-away of the reaction at higher temperatures. Catalysts based on SiO2, ZrO2 and YSZ exhibit a remarkable hydrothermal stability as performances in tight contact mode are fairly similar after the hydrothermal ageing.

Emergence of electronic conduction in bismuth oxide eletrolyte under high pressure

The ionic transport properties of bismuth oxide (Bi2O3) were investigated under high pressures with impedance spectrum and Raman spectrum measurements. It was found that Bi2O3 is a pure ionic conductor below 9.0 GPa. Its pressure-dependent ionic conduction is determined by the diffusion rate of O2− ions. Above 9.0 GPa, the number of O2− ions that participate in electrical transportation are reduced rapidly by the pressure-induced distortion of crystal lattice, which becomes the essential factor to affect the ionic conduction. Most importantly, electronic conduction began to appear in the transportation process and coexist with the ionic conduction at 9.0 GPa indicating a few of originally localized electrons are involved in the electrical transportation due to the enhancement in distorted intension of Bi polyhedrons. Meanwhile, from the impedance spectra studies, it was also known that the electrical transport behaviors of Bi2O3 can be tuned by the frequency of input signals. At high frequencies, Bi2O3 behaves like an ionic solid electrolyte, but at low frequencies, it behaves like an electronic resistor.

Yb₂O₃ Doped Zr0.92Y0.08O2-α(8YSZ) and Its Composite Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells.

Yb3+ and Y3+ double doped ZrO2 (8YSZ+4Yb2O3) samples were synthesized by a solid state reaction method. Moreover, 8YSZ+4Yb2O3-NaCl/KCl composites were also successfully produced at different temperatures. The 8YSZ+4Yb2O3, 8YSZ+4Yb2O3-NaCl/KCl (800 °C), and 8YSZ+4Yb2O3-NaCl/KCl (1000 °C) samples were characterized by x–ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that a dense composite electrolyte was formed at a low temperature of 800 °C. The maximum conductivities of 4.7 × 10−2 S·cm−1, 6.1 × 10−1 S·cm−1, and 3.8 × 10−1 S·cm−1 were achieved for the 8YSZ+4Yb2O3, 8YSZ+4Yb2O3-NaCl/KCl (800 °C), and 8YSZ+4Yb2O3-NaCl/KCl (1000 °C) samples at 700 °C, respectively. The logσ~log (pO2) plot result showed that the 8YSZ+4Yb2O3-NaCl/KCl (800 °C) composite electrolyte is a virtually pure ionic conductor. An excellent performance of the 8YSZ+4Yb2O3-NaCl/KCl (800 °C) composite was obtained with a maximum power density of 364 mW·cm−2 at 700 °C.

SrCe0.9Sm0.1O3-α Compounded with NaCl-KCl as a Composite Electrolyte for Intermediate Temperature Fuel Cell.

SrCeO3 and SrCe0.9Sm0.1O3-α were synthesized using a high-temperature solid-state reaction method using Sm2O3, SrCO3, CeO2 as precursors, then the SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte was fabricated by compounding SrCe0.9Sm0.1O3-α with NaCl-KCl and sintering it at a lower temperature (750 °C) than that of a single SrCeO3 material (1540 °C). The phase and microstructure of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The conductivities of the samples were measured in dry nitrogen atmosphere using electrochemical analyzer. The conductivities of the SrCeO3, SrCe0.9Sm0.1O3-α and SrCe0.9Sm0.1O3-α-NaCl-KCl at 700 °C were 2.09 × 10−5 S·cm−1, 1.82 × 10−3 S·cm−1 and 1.43 × 10−1 S·cm−1 respectively. The conductivities of SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte are four orders of magnitude higher than those of SrCeO3 and two orders of magnitude higher than those of SrCe0.9Sm0.1O3-α. The result of logσ ~ logpO2 plot indicates that SrCe0.9Sm0.1O3-α-NaCl-KCl is almost a pure ionic conductor. The electrolyte resistance and the polarization resistance of the H2/O2 fuel cell based on SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte under open-circuit condition were 1.0 Ω·cm2 and 0.2 Ω·cm2 respectively. Further, the obtained maximum power density at 700 °C was 182 mW·cm−2.

Electrical property investigations and microstructure characterization of a nuclear borosilicate glass ceramic

The electrical properties of a borosilicate glass ceramic used as a conditioning matrix for nuclear waste management are investigated by impedance spectroscopy over frequency and temperature ranges from 1 Hz to 1 MHz and from room temperature to 500 °C respectively. The microstructure of the glass ceramic was studied by scanning electron microscopy which revealed a phase separation phenomenon. The single circle arcs obtained from a complex impedance plot (−Z''(ω)vsZ'(ω)) indicate a pure ionic conduction mechanism and no Maxwell-Wagner-Sillars (MWS) polarization effect. The dependence of ac conductivity on frequency follows Jonscher's power law (known as the UDR: Universal Dielectric Response) very well. The plateau at low frequency corresponding to dc conductivity (σdc or σ0) is mainly associated with the long-distance motion of alkali ions and increases linearly with temperature in Arrhenius coordinates. Scaling of both conductivity and dielectric properties were performed to avoid electrode polarization contribution and to provide better understanding of the relaxation behaviour in this sample. The master curves obtained from Summerfield scaling and normalized peaks (Z''(ω)/Zmax'' and M''(ω)/Mmax'') formalism suggest a conductivity due to short and long range mobility for the lowest temperatures and only a long-range mechanism associated with a non-Debye relaxation process at higher temperatures.

Novel Composite Electrolytes of Zr0.92Y0.08O2-α(8YSZ)-Low Melting Point Glass Powder for Intermediate Temperature Solid Oxide Fuel Cells.

In this study, Zr0.92Y0.08O2-α(8YSZ) powders were synthesized by the sol-gel method. The chemical physics changes and phase formation temperature of 8YSZ crystal were determined by thermogravimetry analysis and differential scanning calorimetry (TGA-DSC). 8YSZ-low melting point glass powder (8YSZ-glass) composite electrolytes with various weight ratios were prepared and calcined at different temperatures. The X-ray diffraction (XRD) patterns of the composite electrolytes were tested. The effects of synthesis temperature, weight ratio, test temperature, and oxygen partial pressure on the conductivities of 8YSZ-glass composite electrolytes, were also investigated at 400–800 °C. The result of the logσ ~ log(pO2) plot indicates that the 8YSZ-20% glass (700 °C) is almost a pure ionic conductor. The oxygen concentration discharge cell illustrates that the 8YSZ-20% glass (700 °C) composite electrolyte is a good oxygen ion conductor.

Nanostructured all-solid-state supercapacitors based on NASICON-type Li1.4Al0.4Ti1.6(PO4)3 electrolyte

Lithium aluminum titanium phosphate (LATP), a NASICON-type (structure of Na1 + xZr2SixP3 − xO12, 0 < x < 3) lithium ionic conductor, possesses high ionic conductivity at ambient temperature and sufficiently high electrochemical stability compared to well-established types of solid electrolytes. This ensures LATP being potentially used as solid electrolyte for all-solid-state supercapacitors. In the pure ionic conductors like LATP, the stoichiometry change under work potential for energy storage is not possible. Therefore, it is essential to produce heterophase contacts, at which the compositional changes could occur. Carbon nanotube (CNT), an excellent electronical conductor, has been consequently mixed with LATP. The all-solid-state supercapacitors with this LATP/CNT mixture have been manufactured in sandwich structure—two mixture layers separated by a pure LATP layer as separator. And the impedance behavior as well as supercapacitance dependent on various CNT weight percentages (1–7.5%) has been investigated by electrochemical impedance spectroscopy and cyclic voltammetry. The results clearly prove that electrical double layer could be formed at the heterophase contacts indicating the supercapacitance behavior of the device, especially when the high contents of CNTs are used. The capacitance of specimen without CNT shows only a value of 0.52 mF/cm3, which is strongly promoted to 11.59 mF/cm3 when CNT content increases to 7.5%.

Novel SrCe1 − xYbxO3 − α-(Na/K)Cl composite electrolytes for intermediate temperature solid oxide fuel cells

In this study, novel SrCe1−xYbxO3−α (x=0, 0.05, 0.10, 0.15)-(Na/K)Cl composite electrolytes were synthesized at low temperature (750°C). The structural and microstructural properties of the composite electrolytes are observed by X–ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the upper doping limit of Yb3+ in SrCeO3 is 15mol%. The XRD results shown that no chemical reactions take place between SrCe1−xYbxO3−α (x=0, 0.05, 0.10, 0.15) and NaCl/KCl. The SEM images revealed that NaCl/KCl is coated on the surface of SrCe1−xYbxO3−α (x=0, 0.05, 0.10, 0.15) act as a binder. The electrical conductivity is determined by impedance spectroscopy. The log σ~log (pO2) plots results indicate that the composites are almost pure ionic conductors. Finally, the excellent performance of SCYb15-NK is obtained with a maximum power density of 615mW·cm−2 at 700°C.

Preparation and conductive properties of single phase Ba1–xKxCe0.8Y0.2O3–δ perovskite oxides

A series of single phase Ba1–xKxCe0.8Y0.2O3–δ (x=0,0.1,0.2,0.3) perovskite oxides were fabricated with 60% potassium excess at 1000°C for 3h and further sintered at 1500°C for 4h via a citrate-nitrate combustion process. ICP-OES and AAS were used to verify the accurate composition. Conductivities of the perovskite oxides were measured under the atmosphere of 3%O2 and 4.75kPa H2O/Ar by using AC impedance spectroscopy technique. The bulk conductivity was significantly higher than the grain boundary conductivity, and the total conductivities increased with the increase of the measuring temperature. Among the perovskite oxides studied, Ba0.9K0.1Ce0.8Y0.2O3–δ displayed the highest total conductivity. Additionally, the transport numbers of proton, oxide ion and electron were measured by oxygen and water concentration cell. The results indicated that Ba1–xKxCe0.8Y0.2O3–δ were almost pure ionic conductors at 300-450°C and mixed protonic-oxide ionic- electronic conductors at 450-900°C under wet oxygen atmosphere, and Ba0.7K0.3Ce0.8Y0.2O3–δ displayed the highest protonic transport number.

Importance of the Formation of Dy4+ in BaZr0.9Dy0.1O3-δ proton-Conducting Ceramics in Oxidizing Atmospheres

Yttrium doped barium zirconate, BaZr1-xYxO3-δ, has been one of the most studied high temperature proton conductors for the last two decades [1]. Several research groups focused on the choice of the trivalent dopant, which is necessary to create the oxygen vacancies required for the hydration of the material. Han et al. studied for example Sc, Sm, Eu and Dy dopants [2-4] and reported the presence of Dy4+in oxidizing atmospheres. In this work, we are interested in the comparison of structural and electrical properties between the well-known BZY10 (BaZr0.9Y0.1O3-δ) and BZDy10 (BaZr0.9Dy0.1O3-δ). A wide combination of experiments was used to confirm the presence of Dy4+ in oxidizing atmosphere, including high temperature X-ray diffraction, Raman spectroscopy, SQUID magnetometry and electron spin resonance (ESR or EPR). Figure 1 summarizes the BZDy10 lattice parameter in dry oxidizing atmosphere as a function of temperature and shows a decrease in the lattice parameter when increasing the oxygen partial pressure. This is explained by the difference in Dy radii in VI coordination: 0.78 Å and 0.912 Å for Dy4+ and Dy3+respectively. Conductivity measurements as a function of pO2in dry and moist conditions were performed for both BZY10 and BZDy10. The two materials behaved quite similarly in moist reducing atmosphere (i.e., pure ionic conduction), while significant differences were noticed in oxidizing atmospheres. [1] Fabbri E., Pergolesi D. and Traversa E., “Materials challenges toward proton-conducting oxide fuel cells: a critical review ”, Chem. Soc. Rev 39, 4355-4369 (2010) [2] D. Han, K. Shinoda, T. Uda, Dopant site occupancy and chemical expansion in rare earth-doped barium zirconate, J. Am. Ceram. Soc. 97 (2014) 643-650 [3] D. Han, T. Uda, Y. Nose, T. Okajima, H. Murata, I. Tanaka and K. Shinoda, Tetravalent Dysprosium in a Perovskite-Type Oxide, Advanced Materials 24 (2012) 2051-2053 [4] D. Han, K. Shinoda, S. Sato, M. Majima, T. Uda, Correlation between electroncutive and structural properties of proton conductive acceptor doped barium zirconate, J. Mater. Chem. A, 13 (2015) 1243-1250 Figure 1

Oxygen-Excess-Type Ionic Conducting Thin Film for Fuel Cell Application

Oxygen-excess-type lanthanum silicate (LSO) is a promising electrolyte material for intermediate-temperature SOFCs because of its high ion conductivity and low activation energy for conduction. In this study, the anode-supported solid electrolyte cell based on Mg-doped LSO, La9.8(Si5.7Mg0.3)O26.4(MDLS), was developed, and its electrical properties and fuel cell performances were evaluated. The MDLS film was applied on top of the Ni-MDLS substrate by spin coating using nano-sized MDLS printable paste. The half cell obtained was then coated with (La0.6Sr0.4)(Co1-y Fe y )O3-δ cathode material. The open circuit voltage of the cell was about 1.1 V, indicating that MDLS is a pure ionic conductor, and good gas-tight electrolyte was obtained. The ohmic and polarization resistances of the cell at 873 K were 3.2 and 3.1 Ω cm2, respectively. Both were able to be reduced with optimizing preparation conditions of MDLS, and inserting an interlayer between cathode and MDLS. As a result, the cell performance was largely improved, and the cell showed the power density of 855 and 97 mW cm-2 at 1073 and 873 K, respectively. It is expected that high performance intermediate-temperature SOFCs will be constructed using LSO-based electrolyte.

(Invited) Multi-Element-Doped Ceria-Based Metal Oxides for Advanced Proton Conducting SOFCs

The ability of solid oxide fuel cells (SOFC) to convert the chemical energy of various kinds of fuels into electricity at high efficiency, and with reduced environmental impacts makes them an attractive technology for current and future plans for clean power generation. State-of-the-art yttria-stabilised ZrO2 (YSZ) electrolyte shows high conductivity (10-2 S/cm) at about 1000 °C [1]. However, the high operating temperature leads to durability and cost issues and hinders its full market implementation. Operating temperature of SOFCs can be lowered by employing ceramic proton conducting electrolytes based on doped- BaCeO3 which exhibits high proton conductivity (10-2 S/cm) in the intermediate temperature (IT, 400-700 °C) range [2]. However, the poor chemical stability of doped-BaCeO3 under SOFC by-products CO2, and H2O limits its use as stable electrolyte [2]. Here we report, perovskite–type Ba0.5Sr0.5Ce1-x-y-z Zr x Gd y Y z O3-δ as proton conductors for IT-SOFCs [3]. A-and B-site of BaCeO3 were doped by more electronegative elements to improve its chemical stability under H2O and CO2 at elevated temperature. In terms of chemical stability and conductivity, Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ seems to be the optimal composition with conductivity of 10-3 S/cm at 700 °C in 3% H2O/H2. Open circuit voltage of 1.15 V at 700 °C for H2-air cell suggests pure ionic (proton) conduction in Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ [3]. The effect of sintering temperature on bulk and grain boundary conductivity of these oxides was investigated using dielectric loss spectroscopy [4]. Moreover, the difference in the relaxation times in the current study suggests that short-range and long-range proton dynamics seems to be differing to previous studies on Y-doped BaZrO3 systems [5]. Additionally, layered perovskite-type Gd0.5Pr0.5BaCo2O5+δ were characterised as cathode for H-SOFCs [6]. Symmetrical cell measurements under air and wet air gave an area specific resistance of 2.4 Ω cm2 and 1.9 Ω cm2 for oxygen reduction reaction at 700 °C [6]. The effect of phase purity and synthesis methods on the electrochemical performance of Ni+Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3 -δ anode composites was investigated through symmetrical cell measurements in 3% H2O/H2. References 1) J. W. Fergus, R. Hui, X. Li, D. P. Wilkinson, J. Zhang, Solid Oxide Fuel Cells: Materials Properties and Performance, CRC Press, New York (2009). 2) K. D. Kreuer, Annu. Rev. Mater. Res. 33 (2003) 333. 3) R. Kannan, K. Singh, S. Gill, T. Fürstenhaupt, V. Thangadurai, Sci. Reports. 3 (2013) 2138. 4) K. Singh, A. Baral, V. Thangadurai, J. Am. Ceram. Soc. 99 (2016) 866. 5) Y. Yamazaki, F. Blanc, Y. Okuyama, L. Buannic L, J. C. Lucio-Vega, C. P. Grey, S. M. Haile, Nat. Mater. 12 (2013) 647. 6) K. Singh, A. K. Baral, V. Thangadurai, Solid State Ionics (2016) DOI:10.1016/j.ssi.2015.12.010.

Substrate Effects on the Cycleability of Metallic Sodium Electrode in Organic Electrolyte

Sodium (Na) shares similar chemical properties with lithium (Li) in many aspects, and Na has more positive potential, so it should be able to be used in the majority of the organic electrolytes which have been used in Li ion batteries. More importantly, Na is one of the most abundant elements in the Earth’s crust. Therefore rechargeable sodium batteries are the ideal alternative to LIBs [1-3] in many applications. Na-ion batteries (NIBs) consist of sodium intercalation materials for both positive and negative electrodes, which are electronically separated by electrolyte as a pure ionic conductor. Na ions are cycled back and forth from host electrodes, which is similar to LIBs. This design avoids the use of reactive metallic Na. So the research of NIBs is mainly focused on the development of the cathode materials, and the study of the metallic Na electrode has drawn few attentions in the past. As the Li+ deposition-stripping is crucial to LIBs, the nature of the metallic Na, especially electro-deposition-stripping characteristics, is also worthy of in-depth and systematic research. In this work, the electrodeposition and stripping characteristics of metallic Na in the electrolyte of 1 mol L-1 NaClO4/EC+DMC (1:1 vol. %) were studied and the deposition-stripping behavior of Na+ on Cu and Sn substrates were compared. The deposition-stripping cycling performances of Na on the substrates were studied through galvanostatic charge-discharge method and cyclic voltammetry. The morphologies of the substrates before and after Na+ deposition were investigated through digital video microscopy. The kinetics of the Na+ electrodeposition on the different substrates was studied through galvanostatic pulse method. The solid electrolyte interface films of Na+ deposits on the substrates were characterized via electrochemical impedance spectroscopy. The results indicate that the nature of the substrate can significantly affect the electrodeposition characteristics of Na+. The high reactivity of metallic sodium with the organic electrolyte solvents and the dendrite formation during metallic Na deposition are even more problematic than metallic Li anodes. Sn is a more suitable substrate than Cu for Na+ electrodeposition due to the formation of Na—Sn alloy during the deposition of Na+.

Synthesis and characterization of Al3+ and M (M = W6+, In3+, Nb5+, Mg2+) co-doped lanthanum silicate oxy-apatite electrolytes

Apatite-type La10Si5Al0.9M0.1O27−δ (M = W6+, In3+, Nb5+ or Mg2+) are successfully synthesized by the high-temperature solid state reaction method. The composition, microstructure and electrical conduction performance of the samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS), respectively. The dense co-doped lanthanum silicates electrolytes with pure hexagonal apatite-type structure are obtained after sintered at 1873 K for 6 h. La10Si5Al0.9W0.1O26.65 has the highest total conductivity among the co-doped samples in the temperature range of 673–1073 K. The influences of the co-doped W6+ content on the properties of the La10Si5Al1−xWxO27±δ (0 ≤ x ≤ 1) are investigated. It is found that with increasing the W6+ content, the equiaxed apatite-type grains are replaced gradually by the rod-like grains, accompanied by the formation of impurity phases (La6W2O15, La2SiO5 and La2Si2O7) in the samples. The La10Si5Al0.9W0.1O26.65 exhibits the highest conductivity of 3.03 × 10−2 S cm−1 at 1073 K. The oxygen pressure independency of the total conductivity suggests that La10Si5Al0.9W0.1O26.65 remains an almost pure oxygen ionic conductor. La10Si5Al0.9W0.1O26.65 also shows good stability in 20% H2/Ar, wet Ar and pure CO2 atmospheres, respectively.