A Multifunctional Protein Coating for Self-Assembled Porous Nanostructured Electrodes

Creation of three-dimensional (3D) porous nanostructured electrodes with controlled conductive pathways for both ions and electrons is becoming an increasingly important strategy and is particularly of great interest for the development of high-performance energy storage devices. In this article, we report a facile and environmentally friendly self-assembly approach to fabricating advanced 3D nanostructured electrodes. The self-assembly is simply realized via formation of a multifunctional protein coating on the surface of electrode nanoparticles by using a denatured soy protein derived from the abundantly prevalent soybean plant. It is found that the denatured protein coating plays three roles simultaneously: as a surfactant for the dispersion of electrode nanoparticles, an ion-conductive coating for the active materials, and a binder for the final electrode. More importantly, it is interestingly found that being a unique surfactant, the surface protein coating enables the self-assembly behavior of the electrode nanoparticles during the evaporation of aqueous dispersion, which finally results in 3D porous nanostructured electrodes. In comparison with the most classic binder, poly­(vinylidene fluoride), the advantages of the 3D nanostructured electrode in terms of electrochemical properties (capacity and rate capability) are demonstrated. This study provides an environmentally friendly and cost-effective self-assembly strategy for fabrication of advanced nanostructured electrodes using electrode nanoparticles as the building block

Charge Transport Properties in TiO₂ Network with Different Particle Sizes for Dye Sensitized Solar Cells

The charge transport properties in the TiO₂ nanoparticle networks with the different TiO₂ nanoparticle sizes were investigated by means of electrochemical impedance spectroscopy (EIS) with consideration of morphological aspects of mesoporous TiO₂ network including particle size (<i>d</i>_p), coordination number (<i>N</i>_n), neck diameter (<i>d</i>_n), and effective surface area (<i>S</i>_e). The morphological analysis of the network revealed that the particle size and surface area would be factors exerting an impact on the charge transport properties, while the coordination number and neck diameter seemed to be consistent with the nanoparticle size. As a result, the electron transport along with the TiO₂ network was predominantly affected by the particle size in terms of the mean free path; the bigger particle size provides both long travel distance and less collision chance with the boundary. Surface area seems to exert a strong influence on the recombination when it is in contact with an electrolyte, suggesting that pore size distribution determining penetration of an electrolyte has to be considered in terms of the effective surface area (<i>S</i>_e). Due to the low transport resistance, high recombination resistance, and low chemical capacitance, the largest particle showed the longest diffusion length (<i>L</i>_n). However, the highest efficiency observed in 15 nm TiO₂ nanoparticle photoanode indicated that the compensating characteristics of the morphological factors of the network for light harvesting efficiency (LHE) (surface area) and charge collection efficiency (η_c, particle size) should be balanced in designing a nanostructured network for high performance DSCs

Elucidating the Role of Defects for Electrochemical Intercalation in Sodium Vanadium Oxide

Na_{1.25+<i>x</i>}V₃O₈ (with <i>x</i> < 0, = 0, and > 0) was synthesized via a wet chemical route involving the reduction of V₂O₅ in oxalic acid and NaNO₃ followed by calcination. It was possible to control the sodium composition in the final product by adjusting the amount of sodium precursor added during synthesis. It was revealed that deficient and excessive sodium contents, with respect to the ideal stoichiometry, are accommodated or compensated by the respective generation of oxygen vacancies and partial transition metal reduction, or cation disordering. When examined as NIB electrode material, the superior performance of the cation disordered material with excessive sodium was clearly demonstrated, with more than 50% higher storage capacity and superior rate capacity and cyclic stability. The formation of oxygen vacancies initially seemed promising but was coupled with stability issues and capacity fading upon further cycling. The disparity in electrochemical performance was attributed to variations in the electronic distribution as promoted through Na–ion interactions and the direct influence of such on the oxygen framework (sublattice); these factors were determined to have significant impact on the migration energy and diffusion barriers

Polyol-Mediated Solvothermal Synthesis and Electrochemical Performance of Nanostructured V₂O₅ Hollow Microspheres

Hollow vanadyl glycolate nanostructured microspheres were synthesized via a highly scalable and template-free polyol-induced solvothermal process. Subsequent calcination transformed the precursor material into vanadium pentoxide, a well-studied transition metal oxide. The vanadyl glycolate nanoparticles were synthesized through a self-seeding process and then aggregated around N₂ microbubbles formed during the reaction that acted as “quasi-micelles” due to the large polarization discrepancy between nitrogen and water. The proposed formation mechanism provides a firm understanding of the processes leading to the observed hollow microsphere morphology. The thermally treated material was tested as a cathode for lithium-ion battery and showed excellent cycle stability and high rate performance. The exceptional electrochemical performance was attributed to the relatively thin-walled structure that ensured fast phase penetration between the electrolyte and active material and shortened lithium-ion migration distance. The prolonged cycling stability is ascribed to the inherent morphological void that can readily accommodate volume expansion and contraction upon cycling

General Strategy for Designing Core–Shell Nanostructured Materials for High-Power Lithium Ion Batteries

Because of its extreme safety and outstanding cycle life, Li₄Ti₅O₁₂ has been regarded as one of the most promising anode materials for next-generation high-power lithium-ion batteries. Nevertheless, Li₄Ti₅O₁₂ suffers from poor electronic conductivity. Here, we develop a novel strategy for the fabrication of Li₄Ti₅O₁₂/carbon core–shell electrodes using metal oxyacetyl acetonate as titania and single-source carbon. Importantly, this novel approach is simple and general, with which we have successfully produce nanosized particles of an olivine-type LiMPO₄ (M = Fe, Mn, and Co) core with a uniform carbon shell, one of the leading cathode materials for lithium-ion batteries. Metal acetylacetonates first decompose with carbon coating the particles, which is followed by a solid state reaction in the limited reaction area inside the carbon shell to produce the LTO/C (LMPO₄/C) core–shell nanostructure. The optimum design of the core–shell nanostructures permits fast kinetics for both transported Li⁺ ions and electrons, enabling high-power performance

Design and Tailoring of a Three-Dimensional TiO₂–Graphene–Carbon Nanotube Nanocomposite for Fast Lithium Storage

Nanocrystalline TiO₂ grown on conducting graphene nanosheets (GNS) and multiwalled carbon nanotubes (CNTs) via a solution-based method to form a three-dimensional (3D) hierarchical structure for fast lithium storage. CNTs in the unique hybrid nanostructure not only prevent the restacking of GNS to increase the basal spacing between graphene sheets but also provides an additional electron-transport path besides the graphene layer underneath of TiO₂ nanomaterials, increasing the electrolyte/electrode contact area and facilitating transportation of the electrolyte ion and electron into the inner region of the electrode. Such a 3D TiO₂–GNS–CNT nanocomposite had a large specific surface area of 291.2 m² g^–1 and exhibited ultrahigh rate capability and good cycling properties at high rates

Surface Engineering of Quantum Dots for Remarkably High Detectivity Photodetectors

Ternary alloyed CdSe_<i>x</i>Te_1–<i>x</i> colloidal QDs trap-passivated by iodide-based ligands (TBAI) are developed as building blocks for UV–NIR photodetectors. Both the few surface traps and high loading of QDs are obtained by in situ ligand exchange with TBAI. The device is sensitive to a broad wavelength range covering the UV–NIR region (300–850 nm), showing an excellent photoresponsivity of 53 mA/W, a fast response time of ≪0.02s, and remarkably high detectivity values of 8 × 10¹³ Jones at 450 nm and 1 × 10¹³ Jones at 800 nm without an external bias voltage. Such performance is superior to what has been reported earlier for QD-based photodetectors. The photodetector exhibits excellent stability, keeping 98% of photoelectric responsivity after 2 months of illumination in air even without encapsulation. In addition, the semitransparent device is successfully fabricated using a Ag nanowires/polyimide transparent substrate. Such self-powered photodetectors with fast response speed and a stable, broad-band response are expected to function under a broad range of environmental conditions

Salami-like Electrospun Si Nanoparticle-ITO Composite Nanofibers with Internal Conductive Pathways for use as Anodes for Li-Ion Batteries

We report novel salami-like core–sheath composites consisting of Si nanoparticle assemblies coated with indium tin oxide (ITO) sheath layers that are synthesized via coelectrospinning. Core–sheath structured Si nanoparticles (NPs) in static ITO allow robust microstructures to accommodate for mechanical stress induced by the repeated cyclical volume changes of Si NPs. Conductive ITO sheaths can provide bulk conduction paths for electrons. Distinct Si NP-based core structures, in which the ITO phase coexists uniformly with electrochemically active Si NPs, are capable of facilitating rapid charge transfer as well. These engineered composites enabled the production of high-performance anodes with an excellent capacity retention of 95.5% (677 and 1523 mAh g^–1, which are based on the total weight of Si-ITO fibers and Si NPs only, respectively), and an outstanding rate capability with a retention of 75.3% from 1 to 12 C. The cycling performance and rate capability of core–sheath-structured Si NP-ITO are characterized in terms of charge-transfer kinetics

Novel Photoanode for Dye-Sensitized Solar Cells with Enhanced Light-Harvesting and Electron-Collection Efficiency

A novel photoanode structure modified by porous flowerlike CeO₂ microspheres as a scattering layer with a thin TiO₂ film deposited by atomic layer deposition (ALD) is prepared to achieve a significantly enhanced performance of dye-sensitized solar cells (DSSCs). The light scattering capability of the photoanode with the porous CeO₂ microsphere layer is considerably improved. The interconnection of particles and electrical contact between bilayer and conducting substrate is further enhanced by an ALD-deposited TiO₂ film, which effectively reduces the electron recombination and facilitates electron transport and thus enhances the charge collection efficiency of DSSCs. As a result, the overall efficiency of the obtained TiO₂–CeO₂-based cells reaches 9.86%, which is 31% higher than that of the DSSCs with a conventional TiO₂ photoanode

Continuous Size Tuning of Monodispersed ZnO Nanoparticles and Its Size Effect on the Performance of Perovskite Solar Cells

ZnO has been demonstrated to be a promising candidate to fabricate high efficiency perovskite solar cells (PSCs) in terms of its better electron extraction and transport properties. However, the inability of synthesis of ZnO nanoparticles (NPs) with minimal surface defects and agglomeration remains a great challenge hindering the fabrication of highly efficient PSCs. In this work, highly crystalline and agglomeration-free ZnO NPs with controlled size were synthesized through a facile solvothermal method. Such ZnO NPs were applied in the fabrication of meso-structured PSCs. The solar cells with ∼40 nm ZnO NPs exhibit the highest power conversion efficiency (PCE) of 15.92%. Steady-state and time-resolved photoluminescence measurements revealed the faster injection and lower charge recombination at the interface of ∼40 nm ZnO NPs and perovskite, resulting in significantly enhanced <i>J</i>_SC and <i>V</i>_OC