Solid State Ionics最新文献

In this paper, carbon-coated Mn₃O₄ nanoparticles were synthesized by sintering the gel containing manganese acetate, PAN and DMF. Being heated to 500 °C in air at a heat rate of 13 °C/min, and then taken out immediately from the furnace, the gel converted to carbon-coated Mn₃O₄ nanoparticles with 20–30 nm sized Mn₃O₄ nanoparticles encapsulated in PAN-derived carbon. Unlike electrospinning and subsequent sintering the electrospun precursor in an inert atmosphere to synthesize metal oxide/carbon composite fibers, carbon-coated Mn₃O₄ nanoparticles with the low carbon content of 8.9 % were produced by sintering the gel precursor in air. As a cathode material for ZIBs, carbon-coated-Mn₃O₄ nanoparticles exhibit a high capacity of 557 mAh g⁻¹ at a current density of 0.1 A g⁻¹ after 300 cycles and good capacity retention performance during cycling. Its high capacity and good capacity retention performance are attributed to its low carbon content and porous PAN-derived carbon coating. Its low carbon content minimizes the negative impact of PAN-derived carbon on its capacity; its porous PAN-derived carbon coating prevents the cracking of Mn₃O₄ nanoparticles during charging-discharging and improves the electronic conductivity of Mn₃O₄ nanoparticles. The simple conducted technology synthesizes the carbon-coated Mn₃O₄ nanoparticles with a high capacity and good capacity retention performance, which makes it a promising route in the commercial production of cathode materials for ZIBs.

The REBa₂Fe₃O_8+δ (RE = Nd, Sm, Pr) perovskites are investigated as potential cobalt-free electrodes in symmetrical solid oxide fuel cells (SOFCs). After the preparation of samples by a soft chemistry route, we first characterized the intrinsic properties and then determined the electrochemical performance after the deposition of porous electrodes to obtain symmetrical cells. Analytical techniques such as X-ray diffraction (XRD) at room and high temperatures, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), dilatometry (TEC), and 4-probe conductivity measurements were employed to characterize exhaustively structural, thermal and electrical properties of the samples. The electrochemical characterization was further investigated through electrochemical impedance spectroscopy (EIS) as well as fuel cell testing conducted on electrolyte-supported symmetrical cells. XRD showed that all samples have a cubic structure with the $\mathrm{Pm}\overline{3}m$ space group. However, during TEM experiments, it was observed that SmBa₂Fe₃O_8+δ presents a quintuple nano-ordering perovskite structure. Pr-based sample shows the highest electrical conductivity (68 S cm⁻¹ at 500 °C), while NdBa₂Fe₃O_8+δ presents the lowest area specific resistance in air (0.47 Ω cm² at 600 °C) revealing that the disordered perovskite structure is more efficient than the quintuple nano-ordered phase of SmBa₂Fe₃O_8+δ in the oxygen reduction reaction (ORR). The use of NdBa₂Fe₃O_8+δ as electrodes in symmetrical cells has been demonstrated between 500 °C and 600 °C.

Interface construction must provide electrochemical compatibility between solid electrolyte (oxide) and cathode/anode materials for all-solid-state batteries (ASSBs). Layered rock-salt oxides (cathode) have good compatibility with LISICON compound Li_3.5Ge_0.5V_0.5O₄. The crystal structures of layered rock-salt cathode and LISICON solid electrolyte solid remain almost unchanged even after co-firing at 973 K. Furthermore, mixtures after co-firing exhibited electrochemical activity closely resembling that of pristine cathodes. Based on these findings from experimentation, a green sheet process was conceived with cathode/electrolyte stacking layers prepared by tape casting, stacking, and co-sintering. The obtained laminated cathode/electrolyte composites were evaluated with a half-cell configuration using polymer electrolyte on the Li anode side at 333 K and 0.01C current density, revealing charge-discharge profiles closely resembling those of cathodes in an ordinary liquid electrolyte battery. The areal capacity increased almost in direct proportion to cathode particle loading, reaching approximately ∼1.2 mAhcm⁻². The Li ionic conductivity of the LISICON electrolyte is less than approximately 10⁻⁴ Scm, indicating that the solid electrolyte particles with LLZO garnet core and LISICON shell can be specially designed as a solid electrolyte with higher ionic conductivity. Using them as the electrolyte in laminated composites, we conducted brief charge-discharge experiments.

In protonic ceramic fuel cells using Ba(Zr,M)O_3-δ (M: trivalent dopant elements) as the electrolyte, the precipitation of BaM₂NiO₅ due to Ni diffusion from the co-sintered NiO-based electrode causes degradation of protonic ceramic fuel cells. However, BaM₂NiO₅ itself has been little studied, and even possible stable crystal structures and compositions have not been fully characterized. In this study, we investigated the dynamic and energetic stability of BaM₂NiO₅ for various trivalent M elements by using first-principles calculations. First, dynamically stable crystal structures were determined for all compositions from phonon dispersion analysis. The formation energies showed negative values in the case of M = lanthanide elements, B, Ga, Tl and Y. The contribution of vibrational entropy to the formation energy of BaM₂NiO₅ was insignificant, and the internal energy was dominant. The chemical bonding analysis revealed that in BaM₂NiO₅, the covalent nature of the M-O bond and the ionic nature of the BaO bond are dominant in the stability of the crystal structure. Precipitation of BaM₂NiO₅ in Ba(Zr,M)O_3-δ was suggested to be dominated by a specific threshold value of formation energy. The validity of that assumption was discussed in terms of the relationship between the factors involved in precipitation and the ionic radius of M element. The formation energy of BaM₂NiO₅ in M = lanthanide elements and Y showed a downward convex tendency with M = Pm as the minimum value. The reason for this was discussed in terms of the characteristics of the crystal structure of BaM₂NiO₅, suggesting that the tensile strain in the M-O bonds and the compressive strain in the NiO and BaO bonds relax with the ionic radius of the M element.

The compound Cs₂(HSeO₄)(H₂PO₄) is of interest due to its high conductivity in its superprotonic state. In the present work, in situ X-ray diffraction studies, simultaneous thermal analysis, and AC impedance spectroscopy, each performed under controlled value of steam partial pressure (pH₂O), were carried out to elucidate the crystallographic features of the transformation and resolve the conductivity in the high temperature phase. The studies reveal that the material transforms to a cubic phase at a temperature of approximately 116 °C, that the activation energy for proton transport in the cubic phase is 0.304(2) eV, and the magnitude of the conductivity is comparable to that of Cs₂(HSO₄)(H₂PO₄). Despite differences in the room temperature structures of Cs₂(HSeO₄)(H₂PO₄), Cs₂(HSO₄)(H₂PO₄), and CsH₂PO₄, each has a monoclinic to cubic transformation entropy of approximately 23 J/mol(CsH_xXO₄)/K. Under pH₂O = 0.05 atm, the cubic phase of Cs₂(HSeO₄)(H₂PO₄) is stable to approximately 250 °C. Under elevated pH₂O (0.3 atm), exsolution of a trigonal phase, with structure analogous to that of Cs₃H(SeO₄)₂, was found to accompany the transformation to the cubic phase. While the driver for this transformation is not fully known, the cell volumes of both the exsolved and matrix phases indicate they are chemically distinct, respectively, from Cs₃H(SeO₄)₂ and Cs₂(HSeO₄)(H₂PO₄), suggesting additional chemical levers for control of transformation behavior.

All-solid-state batteries with sulfur-based positive electrode active materials have been attracting much attention regarding their safety and long cycle life. The Li₂S−V₂S₃−LiI system with high ionic and electronic conductivity is a promising positive electrode material for sulfide-based all-solid-state batteries. Such cells using Li₂S−V₂S₃−LiI in the positive electrode layer operate without conductive carbons and solid electrolytes. In particular, cells using 90(0.75Li₂S·0.25V₂S₃)·10LiI (mol %) exhibit a high capacity and cycle durability even after 100 cycles. To clarify the charge-discharge mechanism of Li₂S−V₂S₃−LiI, we investigated microstructural changes during charge-discharge cycles via transmission electron microscopy (TEM). The microstructure of 90(0.75Li₂S·0.25V₂S₃)·10LiI before charge-discharge measurement was characterized by LiVS₂ and Li₂S−LiI nanocrystallites in an amorphous matrix. In the Li₂S−LiI domain, the Li₂S−LiI nanocrystallites with an antifluorite-type crystal structure amorphized after charging and reprecipitate as Li₂S−LiI nanocrystallites after discharging. As for LiVS₂, Li deintercalation and intercalation occurred during the charge-discharge processes. Ex-situ TEM observations demonstrated that the structural reversibility of LiVS₂ and Li₂S−LiI in an amorphous matrix contributes to high cycle performance.

Proton conducting ceramics are promising solid electrolytes for protonic ceramic fuel cells. However, the presence of cracks remains a challenge before successful commercialization of the proton ceramic devices. This study investigates the impact of internal strain and lattice distortion on the crack formation in BaZr_0.8Y_0.2O_3-δ. During sintering, pellets are covered with controlled amount of sacrificial powder 2 or 3 times of the pellet mass, and the effects of adding BaCO₃ in the sacrificial powder is studied. The pellets sintered with 2 times sacrificial powder remain intact when dried, yet 53 % show cracks after hydration in 0.03 atm water vapor pressure. All pellets fracture into pieces when sintered with additional BaCO₃ in sacrificial powder, in which 0.07 mol% excessive Ba is observed in the actual composition. These Ba excess pellets show larger lattice constant compared to those prepared under other conditions. Strain analysis indicates that 0.14 % to 0.15 % micro strain is observed in the batches with cracks. Raman spectra reveal higher degree of lattice distortion in the BO₆ octahedra in the cracked batches. The findings highlight the role of lattice distortion in internal strain, and crack formation. This work may contribute to the processing of solid electrolytes in protonic ceramic fuel cells.

Direct production of pressurized hydrogen through polymer exchange membrane (PEM) water electrolysis without the usage of the external compressor is an industrially important approach to maximize energy efficiency. An additional challenge in conventional water electrolyzers is the lack of separation of the generated gases, hydrogen and oxygen, from water. In this report, we demonstrate the operation of a new water electrolysis cell at high inlet water pressure with the assistance of a hydrophobic gas diffusion layer (hydrophobic-GDL). This configuration allows the gas/water separation to take place at the electrode so that pressurized water-free gases can be the output due to water being injected directly into the membrane as a source of electrolysis for a continuous supply of water it prevents membrane dehydration. Another important feature is also the cell can be operable in a reversible operation by combining with fuel cell operation. The membrane electrode assemblies (MEAs) were prepared using the hydrophobic-GDL, a Nafion membrane, and Pt-C/IrO₂ catalysts. Electrolysis experiments were performed at different temperatures with pressurized water (ΔP = 0.05–0.4 MPa based on atmospheric pressure) resulting output was pressurized (0.05–0.4 MPa) hydrogen and oxygen gases. The current densities at 1.6 V of electrolysis voltage were 117, 188, 262 mA cm⁻² at 25, 60, and 80 °C, respectively, and the hydrogen and oxygen gas evolution rates were consistent with theoretical values. It was found that increasing water pressure is beneficial to the electrode kinetics and there was an increase in water transport to the electrode surface as well as efficient gas separation and the production of pressurized gases.

Exploring high energy density electrode material and superionic conductors are of great significance in fields such as lithium-ion batteries (LIBs). Here, two new 2D materials, i.e., Li₃CrMnS₄ and Li₃CrMnO₄, are proposed. Theoretical capacities of Li₃CrMnS₄ and Li₃CrMnO₄ are 314 mAh/g and 419 mAh/g, respectively. The calculations of phonon spectra show that both the materials are dynamical stable. The first-principles molecular dynamics simulations also show that they have thermodynamic stability at room temperature. The calculations on the electronic structures suggest that both materials are semiconductors, and their band gaps are 1.33 eV and 1.67 eV, respectively. The ground states of Li₃CrMnS₄ and Li₃CrMnO₄ are ferromagnetic and antiferromagnetic, respectively. In order to explore the possibility of these two materials as superionic conductors, the diffusion properties of Li ions are emphasized. The diffusion coefficients of Li ions in both materials reach 10⁻⁵ cm²s⁻¹, for the Li₃CrMnS₄, two Li-ions concerted migration has the highest diffusion coefficient. The minimum migration energy barriers of Li ions in Li₃CrMnS₄ and Li₃CrMnO₄ are 0.16 eV and 0.12 eV, respectively. The Li ions migration is dominated by the Li ions between the octahedral layers.

Active and durable catalytic material for ammonia (NH₃) decomposition reaction is attracting attentions for utilization of NH₃ as an innovative hydrogen carrier. In this study, diverse single metal and alloy nano catalysts are prepared via in-situ exsolution method and their NH₃ decomposition properties are evaluated. Transition metal cations (Ni, Co, Fe ions) are doped into the La_0.43Ca_0.37M_xN_yTi_1-(x+y)O_3-δ (LCMNT) perovskite oxide structure and exsolved on its surface as supported nano particles under reduction condition. The maximum doping level and chemical composition of exsolution catalysts are investigated to optimize their NH₃ decomposition activity. The exsolution catalyst demonstrates improved NH₃ decomposition characteristics compared to conventionally prepared infiltration catalysts, indicating higher conversion efficiency and H₂ production rate. The exsolved nano catalysts also exhibit great thermochemical stability against catalyst agglomeration or surface nitriding. The results obtained in this study suggest the potential utilization of exsolution catalysts for on-site production of H₂ through NH₃ decomposition catalysis.