Electrode materials for electrochromic supercapacitors

Smart energy storage systems, such as electrochromic supercapacitor (ECSC) integrated technology, have drawn a lot of attention recently, and numerous developments have been made owing to their reliable performance. Developing novel electrode materials for ECSCs that embed two different technologies in a material is an exciting and emerging field of research. To date, the research into ECSC electrode materials has been ongoing with excellent efforts, which need to be systematically reviewed so that they can be used to develop more efficient ECSCs. This mini-review provides a general composition, main evaluation parameters and future perspectives for electrode materials of ECSCs as well as a brief overview of the published reports on ECSCs and performance statistics on the existing literature in this field.

Structural variation, magnetism and single-source deposition of lanthanide-containing polyoxotitanates

Heterometal-containing polyoxotitanates (POTs) are much-studied single-source precursors (SSPs) for doped TiO2. In this work the properties of a wide range of lanthanide-containing POTs are studied to assess their potential use as SSPs for Ln-Ti hybrid oxides. The novel cage compounds [{Ti2O(OEt)8}(EtOH·LnCl)]2 (Ln = Sm, Gd, Tb, Dy, Ho, Tm and Yb) are structurally characterised. The magnetic properties of the Ln = Dy and Ho compounds were characterised using SQUID magnetometry-in both cases, there is evidence of significant uniaxial magnetic anisotropy, but magnetic relaxation is fast and therefore no single-molecule magnetic properties are observed. Upon decomposition lanthanide-doped anatase (Ln = La) or titania/LnTi-oxide mixtures are obtained, which show efficient stabilisation of the catalytically active anatase phase up to high temperatures, making the materials of potential interest for applications in photocatalysis.

Rare Earth-Based Nanomaterials for Supercapacitors: Preparation, Structure Engineering and Application

Supercapacitors (SCs) can effectively alleviate problems such as energy shortage and serious greenhouse effect. The properties of electrode materials directly affect the performance of SCs. Rare earth (RE) is known as "modern industrial vitamins", and their functional materials have been listed as key strategic materials. In the past few years, the number of scientific reports on RE-based nanomaterials for SCs has increased rapidly, confirming that adding RE elements or compounds to the host electrode materials with various nanostructured morphologies can greatly enhance their electrochemical performance. Although RE-based nanomaterials have made rapid progress in SCs, there are very few works providing a comprehensive survey of this field. In view of this, a comprehensive overview of RE-based nanomaterials for SCs is provided here, including the preparation methods, nanostructure engineering, compounds, and composites, along with their capacitance performances. The structure-activity relationships are discussed and highlighted. Meanwhile, the future challenges and perspectives are also pointed out. This Review can not only provide guidance for the further development of SCs but also arouse great interest in RE-based nanomaterials in other research fields such as electrocatalysis, photovoltaic cells, and lithium batteries.

Heterometallic Group 4-Lanthanide Oxo-alkoxide Precursors for Synthesis of Binary Oxide Nanomaterials

In this study, an efficient procedure for the synthesis of uncommon group 4-lanthanide oxo-alkoxide derivatives was developed. Heterometallic clusters with the structures [La₂Ti₄(μ₄-O)₂(μ₃-OEt)₂(μ-OEt)₈(OEt)₆(Cl)₂(HOEt)₂] (1), [La₂Zr₂(μ₃-O)(μ-OEt)₅(μ-Cl)(OEt)₂(HOEt)₄(Cl)₄]_n (2), [La₂Hf₂(μ₃-O)(μ-OEt)₅(μ-Cl)(OEt)₂(HOEt)₄(Cl)₄]_n (3), [Nd₂Ti₄(μ₄-O)₂(μ₃-OEt)₂(μ-OEt)₈(OEt)₆(HOEt)₂(Cl)₂] (4), [Nd₄Zr₄(μ₃-O)₂(μ-OEt)₁₀(μ-Cl)₄(OEt)₈(HOEt)₁₀(Cl)₂] (5), and [Nd₄Hf₄(μ₃-O)₂(μ-OEt)₁₀(μ-Cl)₄(OEt)₈(HOEt)₁₀(Cl)₂] (6) were synthesized via the reaction of a metallocene dichloride, Cp₂M'Cl₂ (where M' = Ti, Zr, and Hf), and metallic lanthanum or neodymium in the presence of excess ethanol. This procedure gave crystalline precursors with molecular stoichiometries suitable for obtaining group 4-lanthanide oxide materials. Compounds 1-6 were examined by analytical and spectroscopic techniques and single-crystal X-ray diffraction. The magnetic properties of 5 and 6 were investigated by using direct and alternating current (dc and ac) susceptibility measurements. The results indicated weak antiferromagnetic interactions between Nd^III ions and a field-supported slow magnetic relaxation. Lanthanum-titanium compound 1 decomposed at 950 °C to give the perovskite compound La_0.66TiO₃ and small amounts of rutile TiO₂. Under the same conditions, 4 decomposed to give a mixture of Nd₄Ti₉O₂₄ and Nd_0.66TiO₃. When 4 was calcined at 1300 °C, decomposition of Nd₄Ti₉O₂₄ to Nd_0.66TiO₃ and TiO₂ was observed. Calcination of 2, 3, 5, and 6 at 950-1500 °C led to the selective formation of heterometallic La₂Zr₂O₇, La₂Hf₂O₇, Nd₂Zr₂O₇, and Nd₂Hf₂O₇ phases, respectively.

An Efficient Electrochromic Supercapacitor Based on Solution-Processable Nanoporous Poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine}

A new green synthetic route to tris[4-(3,4-ethylenedioxythiophene)phenyl]amine (TEPA) monomer has been developed and the molecular structure of TEPA has been determined by using single-crystal XRD. Solution-processable nanoporous poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine} (PTEPA) is prepared by a chemical oxidative polymerization in a microemulsion. Based on the distorted structure of TEPA in the solid state, it is proposed that dendritic PTEPA has a distorted 3 D conformation with multiple twisted channels and pores that are narrowed and blocked by bifurcation and distortion of PTEPA, which is consistent with the observed hierarchical pore structure. As a cathode material, PTEPA exhibits a discharge capacity of 89.5 mAh g-1 in the initial cycle with a highly sloping two-stage discharge curve and relatively stable cycling performance. Beyond its excellent energy storage properties, PTEPA also shows relatively good electrochromic performance. Furthermore, an efficient all-solid-state electrochromic supercapacitor (ECSC) with good electrochromic performance and high energy storage capacity (13.3 mF cm-2 ) is assembled from PTEPA and nanoporous graphene films. During charge-discharge processes, the color of the ECSC changes between yellow-green and steel blue. Thus, the energy storage level of the ECSC can be monitored by the corresponding color changes. The fabricated ECSC may have practical applications, for example, in self-powered electrochromic smart windows.

Eu-phen Bonded Titanium Oxo-Clusters, Precursors for a Facile Preparation of High Luminescent Materials and Films

Incorporation of Eu complexes into various organic or inorganic matrixes is one of the acceptable strategies to obtain displaying materials having practical applications. In this work, we report a convenient approach to preparing high luminescent organic-inorganic hybrid materials and films from the europium-titanium oxo-clusters (EuTOCs) having photoactive antenna ligands. Three Eu₂Ti₄ oxo-clusters were synthesized and crystallographically characterized. They are the first reported lanthanide-TOCs coordinated with 1,10-phenanthroline (phen) and 2,2'-bipyridine (bpy) as photoactive ligands, Eu₂Ti₄O₆(phen)₂(pa)₁₀ (1) (pa = propionate), Eu₂Ti₄O₆(bpy)₂(pa)₁₀ (2), and Eu₂Ti₄O₆(phen)₂(MA)₁₀ (3) (MA = methacrylate). Benefitting from the photoactive antenna ligands and the rigid cluster structures, these clusters showed bright red luminescence with quantum yield in the range of 60-80% and long lifetime up to 3.0 ms. Unlike those physically mixed polymeric materials, the MA coordinated compound 3 can be self-polymerized to form a brilliant luminescent film. The film coated slide was used to develop a fluorescence sensor for biomolecule ascorbic acid (AA). The low detection limit and reusable properties suggest great potential for such EuTOC films in real applications.

Molecular Engineering of Metal Alkoxides for Solution Phase Synthesis of High-Tech Metal Oxide Nanomaterials

The 'bottom-up' synthesis of inorganic nanomaterials with precision at the atomic/molecular level offers many opportunities for the design and improvement of the nanomaterials for various applications. Molecular engineering during soft chemical processing for the synthesis of functional nanomaterials enables the desired chemical and physical properties of the precursors, such as solubility or volatility, clean decomposition, control of stoichiometry for multimetallic species to name a few, and leads to easy control of uniform particle size distribution, stoichiometry…. This Minireview illustrates some important aspects of the molecular engineering in light of some recent developments from the molecular synthesis of nanomaterials involving non-silicon metal alkoxide systems for high-tech applications.

Accurate Regulating of Visible-Light Absorption in Polyoxotitanate-Calix[8]arene Systems by Ligand Modification

With use of a macrocyclic polyphenol, tert-butylcalix[8]arene (TBC[8]), as ligands, a series of TBC[8]-stabilized {Ti₄O₂}clusters, containing penta- and hexacoordinated Ti centers, were synthesized. Such complexes are "core-shell" shaped containing a {Ti₄O₂} core arranged in a zigzag fashion. While outer walls of the clusters are decorated by deprotonated TBC[8], their upper and lower surfaces can be modified by various O- or N-donor ligands, and the ratio of the penta- and hexacoordinated Ti(IV) centers in the {Ti₄O₂} core can be precisely regulated from 4:0, to 3:1, to 2:2, to 1:3, and finally to 0:4. The combined coordination of different ligands in the axial direction shows significant influence on the adsorption of the TBC[8]-Ti₄ system in the visible-light region, and their absorption edge can be precisely regulated from 600 to 700 nm. The above structural functionalization in the TBC[8]-Ti₄ system also tunes their photocatalytic H₂ production activities and oxidative desulfurization ability. Thus, for the first time, by confining the polyoxotitanium cluster in macrocyclic molecules, we provide an example of understanding the structure-property relationship of titanium-oxygen materials by ligand modification.

Bio-compatible fluorescent nano TiO materials prepared from titanium-oxo-cluster precursors

Using a fluorescent dye pre-coordinated titanium-oxo-cluster (TOC) as a molecular precursor, a biocompatible and fluorescent nano TiO material was prepared, which opens the door for most non-water-soluble TOCs for the applications in biosystems.

Porous Anatase-TiO2(B) Dual-Phase Nanorods Prepared from in Situ Pyrolysis of a Single Molecule Precursor Offer High Performance Lithium-Ion Storage

To overcome the problems faced by TiO₂ materials for lithium-ion batteries usage, such as easy nanoparticles agglomeration during cycling and poor cycling performance, in this study, TiO₂ nanorods with the controlled phase compositions are prepared via direct pyrolysis of single molecule precursors in combination with a simple washing process. By tuning the external cations in the single source precursors, three TiO₂ samples in a nanorod shape with the compositions of pure anatase, anatase-rutile dual phase, and anatase-TiO₂(B) dual phase are synthesized successfully. High-resolution transmission electron microscopy, X-ray powder diffraction, and Raman measurements confirm the phase structures and compositions of the three prepared samples. The electrochemical results manifest that all the three nanorod-shaped TiO₂ samples show the long-term cycling stability as negative materials for LIBs. Among them, the TiO₂ sample with the combination of the anatase and TiO₂-B phase shows the best performance, with the specific capacity of ∼184, 164, 140, 105, 80, and 60 mAh g^-1 at 0.1, 0.3, 0.5, 1.5, 3.0, and 5.0 A g^-1, respectively, and showing no capacity loss and low resistance after 1000 cycles at 1.5 A g^-1. By the analysis of the cyclic voltammetry results recorded from different scan rates, the lithium-ion storage mechanism is clarified, which is dominated by the semi-infinite linear diffusion (anatase phase) in combination with the partial surface pseudocapacitive contribution [TiO₂(B) phase]. As a result, this sample shows a great potential as a negative material for LIBs because of its electrochemical stability, high specific capacity, and superior rate capability. The proof-of-concept design of the anatase and TiO₂-B dual phase may provide a new strategy for the synthesis of high performance TiO₂-based anode material for LIBs.

Synthetic strategies, diverse structures and tuneable properties of polyoxo-titanium clusters

A review of polyoxo-titanium clusters (PTCs), with an emphasis on synthetic methodologies, diverse structures, tuneable optical properties and potential applications.

Energy transfer and photoluminescence properties of lanthanide-containing polyoxotitanate cages coordinated by salicylate ligands

The salicylate to Ti⁴⁺ charge-transfer process and energy transfer mechanisms in a series of polyoxotitanium cages are investigated, to account for their photoluminescence properties.

Conjugated hybrid films based on a new polyoxotitanate monomer

Electropolymerisation of the novel polyoxotitanate (POT) hexamer [Ti(μ₃-O)(OⁱPr)(TA)]₆ (TA = thiophene-3-acetate) with 3,4-ethylenedioxythiophene (EDOT) gives films of hybrid conjugated copolymer, Poly-(EDOT-POT)s, the morphologies of which are, uniquely, influenced by the electropolymerisation potential.