Structural and Optical Interplay of Palladium-Modified TiO₂ Nanoheterostructure

The electronic structure and optical properties of Pd-modified TiO₂ nanotubes (NTs) with a vertically aligned nanotubular structure grown by a two-step electrochemical anodization method have been studied using X-ray spectroscopy. X-ray absorption near-edge structure (XANES) at the Ti L_3,2- and O K-edges was used to investigate the TiO₂ NTs before and after Pd modification. It was found that Pd nanoparticles (NPs) are uniformly coated on the NT surface. The Pd L₃-edge of the deposited Pd NPs shows a more intense whiteline and a blue shift for the Pd L₃-edge absorption threshold relative to Pd metal, indicating charge depletion from the Pd 4d orbital as a result NP formation. The lattice of Pd is slightly contracted upon NP formation, although it remains fcc as revealed by extended X-ray absorption fine structure (EXAFS) analysis at the Pd K-edge. X-ray-excited optical luminescence (XEOL) together with XANES with element and site specificity was used to study the optical luminescence from TiO₂ NTs. It was found that the defect-originated XEOL intensity dropped noticeably in the Pd NP-coated NTs, suggesting a Pd NP–TiO₂-interaction-mediated reduction in the radiative recombination of electrons and holes. Further evidence is provided by Ti 2p resonant inelastic X-ray scattering (RIXS), in which no low-energy loss features (d–d transitions) were observed. The implications of these results are discussed

Photocatalytic Color Switching of Transition Metal Hexacyanometalate Nanoparticles for High-Performance Light-Printable Rewritable Paper

Developing efficient photoreversible color switching systems for constructing rewritable paper is of significant practical interest owing to the potential environmental benefits including forest conservation, pollution reduction, and resource sustainability. Here we report that the color change associated with the redox chemistry of nanoparticles of Prussian blue and its analogues could be integrated with the photocatalytic activity of TiO₂ nanoparticles to construct a class of new photoreversible color switching systems, which can be conveniently utilized for fabricating ink-free, light printable rewritable paper with various working colors. The current system also addresses the phase separation issue of the previous organic dye-based color switching system so that it can be conveniently applied to the surface of conventional paper to produce an ink-free light printable rewritable paper that has the same feel and appearance as the conventional paper. With its additional advantages such as excellent scalability and outstanding rewriting performance (reversibility >80 times, legible time >5 days, and resolution >5 μm), this novel system can serve as an eco-friendly alternative to regular paper in meeting the increasing global needs for environment protection and resource sustainability

Tracking the Local Effect of Fluorine Self-Doping in Anodic TiO₂ Nanotubes

We report herein a study in which we reveal the role of F^– incorporated in the very anodic TiO₂ nanotubes prepared electrochemically from a Ti foil using a fluoride based electrolyte. X-ray absorption near edge structure (XANES), resonant X-ray emission spectroscopy (RXES), and X-ray photoelectron spectroscopy (XPS) have been used to examine the as-prepared and the annealed TiO₂ nanotubes. It is found that the additional electron resulting from the substitution of O^2– by self-doped F^– in the TiO₂ lattice is localized in the t_2g state. Consequently, a localized Ti³⁺ state can be tracked by a d–d energy loss peak with a constant energy of 1.6 eV in the RXES, in contrast to TiO₂ nanostructures where this peak is hardly noticeable when F^– is driven out of the lattice upon annealing

Thiophene Fused Azacoronenes: Regioselective Synthesis, Self-Organization, Charge Transport and Its Incorporation in Conjugated Polymers

A regioselective synthesis of an azacoronene fused with two peripheral thiophene groups has been realized through a concise synthetic route. The resulting thienoazacoronene (TAC) derivatives show high degree of self-organization in solution, in single crystals, in the bulk, and in spuncast thin films. Spuncast thin film field-effect transistors of the TACs exhibited mobilities up to 0.028 cm² V^–1 S^–1, which is among the top field effect mobilities for solution processed discotic materials. Organic photovoltaic devices using TAC-containing conjugated polymers as the donor material exhibited a high open-circuit voltage of 0.89 V, which was ascribable to TAC’s low-lying highest occupied molecular orbital energy level

X‑ray Absorption Spectroscopic Characterization of the Synthesis Process: Revealing the Interactions in Cetyltrimethylammonium Bromide-Modified Sulfur–Graphene Oxide Nanocomposites

We have investigated the chemical bonding interaction of S in a CTAB (cetyltrimethylammonium bromide, CH₃(CH₂)₁₅N⁺(CH₃)₃Br^–)-modified sulfur–graphene oxide (S–GO) nanocomposite used as the cathode material for Li/S cells by S K-edge X-ray absorption spectroscopy (XAS). The results show that the introduction of CTAB to the S–GO nanocomposite and changes in the synthesis recipe including alteration of the S precursor ratios and the sequence of mixing ingredients lead to the formation of different S species. CTAB modifies the cathode materials through bonding with Na₂S_<i>x</i> in the precursor solution, which is subsequently converted to C–S bonds during the heat treatment at 155 °C. Moreover, GO bonds with CTAB and acts as the nucleation center for S precipitation. All these interactions among S, CTAB, and GO help to immobilize the sulfur in the cathode and may be responsible for the enhanced cell cycle life of CTAB–S–GO nanocomposite-based Li/S cells

High-Rate, Ultralong Cycle-Life Lithium/Sulfur Batteries Enabled by Nitrogen-Doped Graphene

Nitrogen-doped graphene (NG) is a promising conductive matrix material for fabricating high-performance Li/S batteries. Here we report a simple, low-cost, and scalable method to prepare an additive-free nanocomposite cathode in which sulfur nanoparticles are wrapped inside the NG sheets (S@NG). We show that the Li/S@NG can deliver high specific discharge capacities at high rates, that is, ∼1167 mAh g^–1 at 0.2 C, ∼1058 mAh g^–1 at 0.5 C, ∼971 mAh g^–1 at 1 C, ∼802 mAh g^–1 at 2 C, and ∼606 mAh g^–1 at 5 C. The cells also demonstrate an ultralong cycle life exceeding 2000 cycles and an extremely low capacity-decay rate (0.028% per cycle), which is among the best performance demonstrated so far for Li/S cells. Furthermore, the S@NG cathode can be cycled with an excellent Coulombic efficiency of above 97% after 2000 cycles. With a high active S content (60%) in the total electrode weight, the S@NG cathode could provide a specific energy that is competitive to the state-of-the-art Li-ion cells even after 2000 cycles. The X-ray spectroscopic analysis and ab initio calculation results indicate that the excellent performance can be attributed to the well-restored C–C lattice and the unique lithium polysulfide binding capability of the N functional groups in the NG sheets. The results indicate that the S@NG nanocomposite based Li/S cells have a great potential to replace the current Li-ion batteries

Safe and Durable High-Temperature Lithium–Sulfur Batteries via Molecular Layer Deposited Coating

Lithium–sulfur (Li–S) battery is a promising high energy storage candidate in electric vehicles. However, the commonly employed ether based electrolyte does not enable to realize safe high-temperature Li–S batteries due to the low boiling and flash temperatures. Traditional carbonate based electrolyte obtains safe physical properties at high temperature but does not complete reversible electrochemical reaction for most Li–S batteries. Here we realize safe high temperature Li–S batteries on universal carbon–sulfur electrodes by molecular layer deposited (MLD) alucone coating. Sulfur cathodes with MLD coating complete the reversible electrochemical process in carbonate electrolyte and exhibit a safe and ultrastable cycle life at high temperature, which promise practicable Li–S batteries for electric vehicles and other large-scale energy storage systems