Research on the electrochemistry of oxygen ion conductors in the former Soviet Union

Following previous reviews of research results on oxygen ion-conducting materials obtained in the former USSR, this article addresses the case of Bi₂O₃-based compositions. Phase formation in oxide systems with Bi₂O₃, thermal expansion, stability, bulk transport properties and oxygen exchange of bismuth oxide solid electrolytes are briefly discussed. Primary attention is focused on oxides with high ionic and mixed conductivity, including stabilized fluorite-type (δ) and sillenite (γ) phases of Bi₂O₃, γ-Bi₄V₂O₁₁ and other compounds of the aurivillius series. Another major point being addressed is on the applicability of these materials in high-temperature electrochemical cells, which is limited by numerous specific disadvantages of Bi₂O₃-based ceramics. The electrochemical properties of various electrode systems with bismuth oxide electrolytes are also briefly analyzed. Electronic Publication     

Determination of oxygen in oxides by carrier gas hot extraction analysis with simultaneous COx detection

The determination of oxygen by carrier gas hot extraction is the most popular method for oxygen analysis, but its application to high oxygen contents in oxides requires a critical look at the basic assumptions of the method. The process was studied for various oxides (Al₂O₃, Bi₂O₃, Cr₂O₃, Fe₂O₃, MoO₃, NiO, TiO₂, WO₃, Y₂O₃, and ZrO₂) using a modern analyser with IR-detectors for CO₂ and CO. There was a difference specific to oxides that must be known to get the required analytical results with high precision and accuracy. High amounts of CO₂ were formed particularly from Bi₂O₃, Fe₂O₃, MoO₃, NiO, and WO₃. The reaction rate can be controlled with delayed heating of the furnace, so that an oxide sample weight of up to 100 mg can be used. Received: 13 April 1999 / Revised: 24 June 1999 / Accepted: 28 June 1999     

Determination of oxygen in oxides by carrier gas hot extraction analysis with simultaneous COx detection

The determination of oxygen by carrier gas hot extraction is the most popular method for oxygen analysis, but its application to high oxygen contents in oxides requires a critical look at the basic assumptions of the method. The process was studied for various oxides (Al₂O₃, Bi₂O₃, Cr₂O₃, Fe₂O₃, MoO₃, NiO, TiO₂, WO₃, Y₂O₃, and ZrO₂) using a modern analyser with IR-detectors for CO₂ and CO. There was a difference specific to oxides that must be known to get the required analytical results with high precision and accuracy. High amounts of CO₂ were formed particularly from Bi₂O₃, Fe₂O₃, MoO₃, NiO, and WO₃. The reaction rate can be controlled with delayed heating of the furnace, so that an oxide sample weight of up to 100 mg can be used. Received: 13 April 1999 / Revised: 24 June 1999 / Accepted: 28 June 1999     

Research on the electrochemistry of oxygen ion conductors in the former Soviet Union. II. Perovskite-related oxides

The review is devoted to the analysis of experimental results on electrochemical and physicochemical properties of the perovskite-related oxide phases obtained at scientific centers of the former Soviet Union. The main attention is focused on oxides with high electronic conductivity, which are potentially useful as electrodes for high-temperature electrochemical cells with oxygen-ion conducting solid electrolytes and interconnectors of solid oxide fuel cells, and on mixed ionic-electronic conductors for oxygen separation membranes. Along with perovskite-like solid solutions based on LnMO_3−δ (Ln is a rare-earth element, M = Cr, Mn, Fe, Co, Ni) and SrCoO_3−δ, properties of the oxide phases Ln₂MO_4±δ (M = Cu, Ni, Co) with the K₂NiF₄-type structure are briefly reviewed. Received: 5 November 1998 / Accepted: 26 November 1998     

Proton Intercalation/De-Intercalation Dynamics in Vanadium Oxides for Aqueous Aluminum Electrochemical Cells

Understanding cation (H⁺, Li⁺, Na⁺, Al³⁺, etc.) intercalation/de-intercalation chemistry in transition metal compounds is crucial for the design of cathode materials in aqueous electrochemical cells. Here we report that orthorhombic vanadium oxides (V₂O₅) supports highly reversible proton intercalation/de-intercalation reactions in aqueous media, enabling aluminum electrochemical cells with extended cycle life. Empirical analyses using vibrational and x-ray spectroscopy are complemented with theoretical analysis of the electrostatic potential to establish how and why protons intercalate in V₂O₅ in aqueous media. We show further that cathode coatings composed of cation selective membranes provide a straightforward method for enhancing cathode reversibility by preventing anion cross-over in aqueous electrolytes. Our work sheds light on the design of cation transport requirements for high-energy reversible cathodes in aqueous electrochemical cells.     

Proton Intercalation/De‐Intercalation Dynamics in Vanadium Oxides for Aqueous Aluminum Electrochemical Cells

Understanding cation (H⁺, Li⁺, Na⁺, Al³⁺, etc.) intercalation/de‐intercalation chemistry in transition metal compounds is crucial for the design of cathode materials in aqueous electrochemical cells. Here we report that orthorhombic vanadium oxides (V₂O₅) supports highly reversible proton intercalation/de‐intercalation reactions in aqueous media, enabling aluminum electrochemical cells with extended cycle life. Empirical analyses using vibrational and x‐ray spectroscopy are complemented with theoretical analysis of the electrostatic potential to establish how and why protons intercalate in V₂O₅ in aqueous media. We show further that cathode coatings composed of cation selective membranes provide a straightforward method for enhancing cathode reversibility by preventing anion cross‐over in aqueous electrolytes. Our work sheds light on the design of cation transport requirements for high‐energy reversible cathodes in aqueous electrochemical cells.     

Phosphorus and Halogen Co‐Doped Graphene Materials and their Electrochemistry

Doping of graphene materials with heteroatoms is important as it can change their electronic and electrochemical properties. Here, graphene is co‐doped with n‐type dopants such as phosphorus and halogen (Cl, Br, I). Phosphorus and halogen are introduced through the treatment of graphene oxide with PX₃ gas (PCl₃, PBr₃, and PI₃). Graphene oxides are prepared through chlorate and permanganate routes. Detailed chemical and structural characterization demonstrates that the graphene sheets are covered homogeneously by phosphorus and halogen atoms. It is found that the amount of phosphorus and halogen introduced depends on the graphene oxide preparation method. The electrocatalytic effect of the resulting co‐doped materials is demonstrated for industrially relevant electrochemical reactions such as the hydrogen evolution and oxygen reduction reactions.     

Relationship between transport properties and phase transformations in mixed-conducting oxides

To elucidate the relationship between transport properties and phase transformations in mixed-conducting oxides, Sr_0.9Ca_0.1Co_0.89Fe_0.11O_3−δ (SCCFO) and SrCoO_3−δ (SCO) were chosen as the model materials and have been investigated in detail. Oxygen permeation measurements verified that both oxides are well permeable to oxygen at elevated temperatures, e.g., at 900 °C during a cooling procedure, oxygen permeation rates as large as 1.5 and 2.0 mL/min/cm² could be obtained with disk-shaped SCCFO and SCO membranes of thickness 1.5 mm, respectively. But when cooled to critical temperatures, the oxygen permeability of these kinds of oxides diminished sharply, which could be recovered by increasing the temperature again to certain values. Abrupt changes on electrical conductivity were also observed for both oxides around the same region of temperature as that of oxygen permeability. As indicated by high-temperature X-ray diffraction and thermal analysis, the SCCFO and SCO systems undergo phase transformation between a low-temperature orthorhombic brownmillerite structure (B) or a hexagonal 2H-type structure (H) and a high-temperature cubic perovskite structure (C), respectively. The present results suggest the observed abrupt changes in transport properties versus temperature are attributed to such phase transformation, which may be directly associated with the order-disorder transition of oxygen vacancies. Moreover, compared to the B/C transformation that mainly involves an order-disorder transition on the oxygen sublattice, the H/C one necessarily also involves the cooperative long-range reorganization on the cation sublattice. Therefore it occurs at a higher temperature and absorbs more heat quantity than those of B/C transformation.     

Properties of cerium-zirconium mixed oxides partially substituted by neodymium: Comparison with Zr-Ce-Pr-O ternary oxides

CeO₂ doped with praseodymium, neodymium and/or zirconium atoms were prepared by coprecipitation and by the sol-gel method. Structural properties were investigated by in situ XRD and Raman spectroscopy while oxygen storage capacity (OSC) was measured by transient CO oxidation. All the compounds, except pure Nd₂O₃, have a fluorite-type structure as well as a Raman band at 560 cm⁻¹ characteristic of the oxygen vacancies involving non-stoichiometric oxides. The lattice parameter under hydrogen, being dependent on the temperature, revealed two reduction mechanisms: one at a low temperature at the surface and another at a high temperature in the bulk. Ce-Nd binary oxides show a strong tendency towards crystallite aggregation, which reduces accessibility to gases and OSC properties. Zirconium improves the thermal resistance to sintering of both Ce-Nd and Ce-Pr oxides. The Zr-Ce-Pr-O followed by Zr-Ce-Nd-O compounds displaying high oxygen mobility at a low temperature, appear to be very promising for practical applications such as OSC materials.     

黄铜矿及其复合材料在电化学储能领域的研究进展

黄铜矿(CuFeS₂)是一种具有特殊金色光泽的天然矿物,具有四方结构,其中Fe、Cu离子与晶格中的硫形成四面体配位,相较于其他硫化物和其相对应的氧化物,CuFeS₂具有较高的电导率和优异的电化学性能,且拥有成本低廉、存在天然矿物且自然储量丰富、无毒等优势,使其具有应用于电化学储能体系电极材料的潜能。本文详细介绍了CuFeS₂的物理化学性质、几种简单的不同形貌的合成方法以及其作为电化学储能电极材料方面的研究,并对CuFeS₂材料未来的研究方向进行了展望。     

Recent advances of transition metal oxalate-based micro- and nanomaterials for electrochemical energy storage: a review

A key challenge in the development of electrochemical energy storage (EES) is the design and engineering of electrode materials for electrochemical reactions. Transition metal oxalates (TMOxs) have been widely used in various EES applications due to their low cost, simple synthesis, and excellent electrochemical performance. In this review, the recent advances in the design and engineering of transition metal oxalate-based micro- and nanomaterials for EES are summarized. Specifically, the survey will focus on three types of micro- and nano-scale TMOxs (monometallic, bimetallic, and trimetallic TMOxs), their composites (TMOx-metal oxide, TMOx-hydroxide, TMOx-GO, and TMOx-MOFs composites), and derivatives, including transition metal oxides (TiO₂, V₂O₅, Mn_xO_y, Co₃O₄, NiO, CuO, and Nb₂O₅), multi-transition metal oxides (MCo₂O₄ (M = Ni, Cu, and Zn), NiMn₂O₄, and N_xO_y-M_xO_y), transition metal sulfide (NiS₂), and carbon materials (ordinary carbon, GO and their composites), within the context of their intrinsic structure and corresponding electrochemical performance. A range of experimental variables will be carefully analyzed, such as sample synthesis, crystal structure, and electrochemical reaction mechanism. The applications of these materials as EES electrodes are then featured for supercapacitors (SCs) and lithium-ion batteries (LIBs). We conclude the review with a perspective of future research prospects and challenges.     

Effect of the preparation method of the cathode material LiNi<Subscript>0.33</Subscript>Mn<Subscript>0.33</Subscript>Co<Subscript>0.33</Subscript>O<Subscript>2</Subscript> on the electrochemical characteristics of a lithium ion cell

Complex metal oxides with the composition LiNi_0.33Mn_0.33Co_0.33O₂ prepared by various methods: sol–gel method, solid-phase method, and thermal destruction of metal-containing compounds in oil were studied. The results of elemental analysis, TGA/DSC, powder X-ray diffraction, SEM, TEM, as well as the results of electrochemical testing of the cathodes based on the obtained materials are presented. The complex metal oxides LiNi_0.33Mn_0.33Co_0.33O₂ prepared by sol–gel processes and thermal destruction of metal-containing compounds in oil consist of primary nanosized crystallites with an average size of 90 nm covered by a nanometer carbon layer, which improves the electrochemical characteristics of lithium ion batteries.     

Effect of the Synthesis Method on the Functional Properties of Lithium-Rich Complex Oxides Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript>

Layered Li-rich transition metal oxides are considered among the most promising cathode materials for high energy density lithium-ion batteries. It was studied how the method and conditions of synthesis of Li-rich oxides Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ affect their electrochemical properties. Coprecipitation methods and modified Pechini process were used. It was shown that it is necessary to carefully choose the synthesis conditions when using the modified Pechini method because of their significant effect on the morphology of Li-rich oxides. Samples were obtained with high electrochemical characteristics: capacity discharge of 260–270 mAh/g (16 mA/g) and 60–70 mAh/g (988 mA/g) within the voltage range of 2.5–4.8 V.     

Enhanced electrochemical reduction of rare earth oxides in simulated oxide fuel via co-reduction of NiO in Li2O–LiCl salt

Rare earth oxides in spent oxide fuel from nuclear plants have poor reducibility in the electrochemical reduction process due to their high oxygen affinity and thermodynamic stability. Here, we demonstrate that the extent of their reduction can be enhanced via co-reduction of NiO in a Li₂O–LiCl electrolyte for the electrochemical reduction of a simulated oxide fuel (simfuel). First, the electrochemical behaviors of Nd₂O₃, NiO, and Nd₂O₃–NiO were studied by cyclic voltammetry and voltage control electrolysis. Then, the electrochemical reduction of the simfuel containing UO₂ and rare earth oxides (Nd₂O₃, La₂O₃, and CeO₂) was conducted in molten LiCl salt with 1 wt.% Li₂O via the co-reduction of NiO. The extent of reduction of the rare earth oxides was found to be significantly improved.     

Reversible Anionic Redox Activities in Conventional LiNi1/3Co1/3Mn1/3O2 Cathodes

Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium‐excessive layered‐oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi_1/3Co_1/3Mn_1/3O₂. The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high‐capacity lithium‐ion batteries.     

Prediction of transport properties of new functional materials based on lanthanum-strontium cuprates: Molecular mechanics calculations

The method of molecular dynamics is used for prediction of properties of new functional materials based on lanthanum-strontium cuprates La_{2 ? x} Sr _x CuO_{4 ? δ} as new materials of the solid state ionics. The most interesting phases are synthesized to test the obtained calculation data and their electrophysical and thermomechanical characteristics are studied. It is shown that the high values of the oxygen diffusion coefficients are obtained in the La_{2 ? x} Sr _x CuO_{4 ? δ} solid solutions with a high replacement degree of Sr → La (up to x = 1). The calculated values of lattice cell parameters, thermal expansion coefficients and oxygen diffusion coefficients agree with the experimental data. The observed anisotropy of anionic transport for all the studied compositions corresponds to the regularities of crystal structure of complex oxides. Using the molecular dynamics method allows tracing the contribution of separate types of oxygen ions (equatorial and apical) into ionic transport at the microscopic level and also confirming directly that oxygen diffusion occurs according to the usual jump mechanism, mainly in (CuO₂) layers.     

Synthesis,characterization and electrochemical behavior of LiNi1−xBaxO2 (x = 0.0, 0.1, 0.2, 0.3 and 0.5) cathode materials

LiNiO₂ and Ba-doped LiNiO₂ were synthesized by a simple solid state reaction, and used as cathode active materials for lithium rechargeable batteries. Physical properties of the synthesized products are discussed in the light of structural (TG/DTA, XRD, TEM, SEM with EDAX) and spectroscopic (FTIR) measurements. XRD results show that the compounds are similar to LiNiO₂ in structure. TEM and SEM analyses were used to examine the particle size, nature and morphological aspects of the synthesized oxides. The composition of the materials was explored by EDAX analysis. Performances of lithiated oxides as cathode materials in lithium-ion batteries and substitutive effect on electrochemical properties have been investigated by cyclic voltammetry and galvanostatic charge–discharge cycling. By substitution of Ni with Ba, in LiNi_0.8Ba_0.2O₂ has yielded better cycling results compared to all other materials revealed through charge–discharge studies.     

有机物单层分散在相关材料制备中的应用

与无机氧化物和盐类在载体表面自发单层分散相类似, 许多有机物也可以在载体表面自发单层分散.有机物在载体表面单层分散行为和分散后的存在状态与有机物分子形状和结构特点及载体表面性质和孔结构有关. 利用有机物在载体表面的单层分散, 可以设计制备具有优异性能的材料. 本文简要综述了近年来这方面研究工作取得的相关进展, 主要介绍了有机物单层分散在碳/氧化物复合物、氧化物和薄壁中孔碳材料的制备和织构调控方面的一些应用实例. 单层分散的有机物热分解后可在载体表面形成均匀的薄碳层, 以无机多孔氧化物为载体可制备出包覆均匀碳薄层的碳/氧化物复合物, 这种碳/氧化物复合物在染料吸附、催化剂载体和光催化方面显现出好的性能. 以溶胶-凝胶法制备氧化物时, 分散的有机物可以隔离溶胶颗粒, 从而制备出高比表面积的氧化物并可对孔容进行调控, 以此方法制备的γ-氧化铝比表面积可达506 m²·g^-1. 在惰性气氛中加热上述碳/氧化物复合物, 碳层可抑制氧化物的相变; 而在氧气中, 碳层燃烧发热会促进相变, 由此可快速制备超细α-氧化铝. 包覆均匀碳薄层的氧化物载体对碳起支撑作用, 在将氧化物溶解去除后, 可便捷制得高比表面积、大孔容、高中孔率的薄壁中孔碳材料, 碳材料的形貌、孔径分布等可通过选用不同织构的氧化物载体进行调控.     

钴基双金属氧化物的制备及其在电化学储能领域的应

钴基双金属氧化物MCo₂O₄（M=Ni、Zn、Mn等）既继承了单一钴金属氧化物（Co₃O₄、CoO等）高比容量的优点,又引入了新的改性金属元素用于改善其导电性差、倍率性能不佳等缺点,是一种潜在的新型电化学储能材料。本文分类介绍了NiCo₂O₄、ZnCo₂O₄、MnCo₂O₄等钴基双金属氧化物及其复合物的现有研究（包括制备方法、形貌结构、颗粒尺寸及其电化学性能）,阐述了改性手段的可能性机理,并对钴基双金属氧化物后续研究提出了一些看法。     

钴基双金属氧化物的制备及其在电化学储能领域的应用

钴基双金属氧化物MCo₂O₄（M=Ni、Zn、Mn等）既继承了单一钴金属氧化物（Co₃O₄、CoO等）高比容量的优点,又引入了新的改性金属元素用于改善其导电性差、倍率性能不佳等缺点,是一种潜在的新型电化学储能材料。本文分类介绍了NiCo₂O₄、ZnCo₂O₄、MnCo₂O₄等钴基双金属氧化物及其复合物的现有研究（包括制备方法、形貌结构、颗粒尺寸及其电化学性能）,阐述了改性手段的可能性机理,并对钴基双金属氧化物后续研究提出了一些看法。