Low-Temperature, Universal Synthetic Route for Mesoporous Metal Oxides by Exploiting Synergistic Effect of Thermal Activation and Plasma

Mesoporous metal oxides exhibit excellent physicochemical properties and are widely used in various fields, including energy storage/conversion, catalysis, and sensors. Although several soft-template approaches are reported, high-temperature calcination for both metal oxide formation and template removal is necessary, which limits direct synthesis on a plastic substrate for flexible devices. Here, a universal synthetic approach that combines thermal activation and oxygen plasma to synthesize diverse mesoporous metal oxides (V2O5, V6O13, TiO2, Nb2O5, WO3, and MoO3) at low temperatures (150-200 °C), which can be applicable to a flexible polymeric substrate is introduced. As a demonstration, a flexible micro-supercapacitor is fabricated by directly synthesizing mesoporous V2O5 on an indium-tin oxide-coated colorless polyimide film. The energy storage performance is well maintained under severe bending conditions.

Heterogeneous Self-Assembly of a Single Type of Nanoparticle Modulated by Skin Formation

Self-assembly of colloidal nanoparticles has generated tremendous interest due to its widespread applications in structural colorations, sensors, and optoelectronics. Despite numerous strategies being developed to fabricate sophisticated structures, the heterogeneous self-assembly of a single type of nanoparticle in one step remains challenging. Here, facilitated by spatial confinement induced by a skin layer in a drying droplet, we achieve the heterogeneous self-assembly of a single type of nanoparticle by quickly evaporating a colloid-poly (ethylene glycol) (PEG) droplet. During the drying process, a skin layer forms at the droplet surface. The resultant spatial confinement assembles nanoparticles into face-centered-cubic (FCC) lattices with (111) and (100) plane orientations, generating binary bandgaps and two structural colors. The self-assembly of nanoparticles can be regulated by varying the PEG concentration so that FCC lattices with homo- or heterogeneous orientation planes can be prepared on demand. Besides, the approach is applicable for diverse droplet shapes, various substrates, and different nanoparticles. The one-pot general strategy breaks the requirements for multiple types of building blocks and predesigned substrates, extending the fundamental understanding underlying colloidal self-assembly.

Two-Dimensional V2O5 Inverse Opal: Fabrication and Electrochromic Application

The open-layered structure of Vanadium pentoxide (V2O5) has triggered significant interest in exploring its energy-related application as lithium (Li) intercalation cathode material. Various methods are extensively studied to improve the Li diffusion using thin films or nanoarchitecture. In this work, high-quality two-dimensional (2D) inverse opal α-V2O5 films were synthesized via a modified ‘dynamic hard template’ infiltration strategy using sacrificial polystyrene spheres (PS, a diameter of 530 nm) photonic crystal as a template. The new material exhibited an excellent porous array with featured structural colors in a large area. The electrochromic behavior was explored by combining bandgap and electrochemical characterization. On the one hand, the intercalation/deintercalation of Li+ played an important role in the bandgap (Eg), and thereafter on the visible range transmittance through changing the film’s stoichiometry and the valence of vanadium ions. On the other hand, the asymmetry of the lattice due to the disordered distribution of Li+ within the V2O5 interlayer and/or the formation of an irreversible phase explained the change in transmittance with voltage.

VO2(D) hollow core–shell microspheres: synthesis, methylene blue dye adsorption and their transformation into C/VOxnanoparticles

Hollow core–shell VO₂(D) microspheres were fabricated and they exhibited excellent MB adsorption ability; and the regenerated C/VO_xnanoparticles showed enhanced adsorption performance and good reusability.

Reductive mineralization of cellulose with vanadium, iron and tungsten chlorides and access to MxOy metal oxides and MxOy/C metal oxide/carbon composites

M_xO_y and M_xO_y/C composites (M=V, Fe and W) were obtained by mineralization of cellulose with several metal chlorides. Cellulose was used both as a templating agent and as an oxygen and a carbon source. Soluble chloride molecules (VOCl₃ and WCl₆) and a poorly soluble ionic chloride compound (FeCl₃) were chosen as metal oxide precursors. In a first time, primary metal oxide/cellulose composites were obtained via a thermal treatment by reacting urea impregnated filter paper with the corresponding metal chlorides in an autoclave at 150°C after 3days. After either pyrolysis or calcination steps of these intermediate materials, interesting metal oxides with various morphologies were obtained (V₂O_5, V₂O₃, Fe₃O₄, WO_3, H_0.23WO₃), composites (V₂O₃/C) as well as carbides (hexagonal W₂C and WC, Fe₃C) This result highlight the reductive role that can play cellulose during the pyrolysis step that allows to tune the composition of M_xO_y/C composites. The materials were characterized by FTIR, Raman, TGA, XRD and SEM. This study highlights that cellulose can be used for a convenient preparation of a variety of highly demanded M_xO_y and M_xO_y/C composites with original shapes and morphologies.

Controllable Fabrication of Two-Dimensional Patterned VO2 Nanoparticle, Nanodome, and Nanonet Arrays with Tunable Temperature-Dependent Localized Surface Plasmon Resonance

A universal approach to develop various two-dimensional ordered nanostructures, namely nanoparticle, nanonet and nanodome arrays with controllable periodicity, ranging from 100 nm to 1 μm, has been developed in centimeter-scale by nanosphere lithography technique. Hexagonally patterned vanadium dioxide (VO₂) nanoparticle array with average diameter down to sub-100 nm as well as 160 nm of periodicity is fabricated, exhibiting distinct size-, media-, and temperature-dependent localized surface plasmon resonance switching behaviors, which fits well with the predication of simulations. We specifically explore their decent thermochromic performance in an energy saving smart window and develop a proof-of-concept demo which proves the effectiveness of patterned VO₂ film to serve as a smart thermal radiation control. This versatile and facile approach to fabricate various ordered nanostructures integrated with attractive phase change characteristics of VO₂ may inspire the study of temperature-dependent physical responses and the development of smart devices in extensive areas.

Color-Coded Batteries - Electro-Photonic Inverse Opal Materials for Enhanced Electrochemical Energy Storage and Optically Encoded Diagnostics

For consumer electronic devices, long-life, stable, and reasonably fast charging Li-ion batteries with good stable capacities are a necessity. For exciting and important advances in the materials that drive innovations in electrochemical energy storage (EES), modular thin-film solar cells, and wearable, flexible technology of the future, real-time analysis and indication of battery performance and health is crucial. Here, developments in color-coded assessment of battery material performance and diagnostics are described, and a vision for using electro-photonic inverse opal materials and all-optical probes to assess, characterize, and monitor the processes non-destructively in real time are outlined. By structuring any cathode or anode material in the form of a photonic crystal or as a 3D macroporous inverse opal, color-coded "chameleon" battery-strip electrodes may provide an amenable way to distinguish the type of process, the voltage, material and chemical phase changes, remaining capacity, cycle health, and state of charge or discharge of either existing or new materials in Li-ion or emerging alternative battery types, simply by monitoring its color change.

2D and 3D photonic crystal materials for photocatalysis and electrochemical energy storage and conversion

This perspective reviews recent advances in inverse opal structures, how they have been developed, studied and applied as catalysts, catalyst support materials, as electrode materials for batteries, water splitting applications, solar-to-fuel conversion and electrochromics, and finally as photonic photocatalysts and photoelectrocatalysts. Throughout, we detail some of the salient optical characteristics that underpin recent results and form the basis for light-matter interactions that span electrochemical energy conversion systems as well as photocatalytic systems. Strategies for using 2D as well as 3D structures, ordered macroporous materials such as inverse opals are summarized and recent work on plasmonic-photonic coupling in metal nanoparticle-infiltrated wide band gap inverse opals for enhanced photoelectrochemistry are provided.

Electrodeposited Structurally Stable V2O5 Inverse Opal Networks as High Performance Thin Film Lithium Batteries

High performance thin film lithium batteries using structurally stable electrodeposited V2O5 inverse opal (IO) networks as cathodes provide high capacity and outstanding cycling capability and also were demonstrated on transparent conducting oxide current collectors. The superior electrochemical performance of the inverse opal structures was evaluated through galvanostatic and potentiodynamic cycling, and the IO thin film battery offers increased capacity retention compared to micron-scale bulk particles from improved mechanical stability and electrical contact to stainless steel or transparent conducting current collectors from bottom-up electrodeposition growth. Li(+) is inserted into planar and IO structures at different potentials, and correlated to a preferential exposure of insertion sites of the IO network to the electrolyte. Additionally, potentiodynamic testing quantified the portion of the capacity stored as surface bound capacitive charge. Raman scattering and XRD characterization showed how the IO allows swelling into the pore volume rather than away from the current collector. V2O5 IO coin cells offer high initial capacities, but capacity fading can occur with limited electrolyte. Finally, we demonstrate that a V2O5 IO thin film battery prepared on a transparent conducting current collector with excess electrolyte exhibits high capacities (∼200 mAh g(-1)) and outstanding capacity retention and rate capability.