SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: ACS applied materials & interfaces

28

Nanoclay minerals play a promising role as additives in the liquid electrolyte to form a gel electrolyte for quasi-solid-state dye-sensitized solar cells because of their high chemical stability, unique swelling ability, ion exchange capacity and rheological properties. Here we report the improved performance of a quasi-solid-state gel electrolyte comprising a liquid electrolyte and synthetic nitrate-hydrotalcite nanoclay. Charge transport mechanism in the gel electrolyte, and nanoclay interactions with TiO2/electrolyte interface are discussed in detail. The electrochemical analysis reveals that the charge transport is solely based on physical diffusion. The calculated physical diffusion coefficient shows that the diffusion of redox ions is not much affected by the viscosity of nanoclay gel. The addition of nitrate-hydrotalcite clay in electrolyte has the effect of buffering the protonation process at TiO2/electrolyte interface, resulting in conduction band up-shift and a boost in Voc. Higher Voc with undiminished photocurrent is achieved with nitrate-hydrotalcite nanoclay gel electrolyte for organic as well as for inorganic dye (D35 and N719) systems. 10 % improvement in the efficiency for hydrotalcite clay gel electrolyte is obtained, compared to that of the liquid electrolyte. The power conversion efficiency can be achieved as high as 10.1% under 0.25 sun and 9.6% under full sun. This study demonstrates that nitrate-hydrotalcite nanoclay in the electrolyte not only solidifies the liquid electrolyte to prevent solvent leakage, but also facilitates the improvement in cell efficiency.  

Concepts: Electrochemistry, Physical chemistry, Solar cell, Titanium dioxide, Energy conversion, Energy conversion efficiency, Dye-sensitized solar cell, Thin film solar cell

28

We develop a simple approach to fabricate graphene loaded TiO2 thin films on glass substrates by spin-coating technique. Our graphene-loaded TiO2 films were highly conductive, transparent and showed enhanced photocatalytic activities. More significantly, graphene-TiO2 films displayed super-hydrophilicity within short time even under white fluorescent light bulb, as compared to a pure TiO2 film. The enhanced photocatalytic activity of graphene-TiO2 films is attributed to its efficient charge separation, owing to electrons injection from the conduction band of TiO2 to graphene. The electroconductivity of the graphene loaded TiO2 thin film also contributes to the self-cleaning function by its anti-fouling effect against particulate contaminants. The present study reveals the ability of graphene as a low cost co-catalyst instead of expensive noble metals (Pt, Pd), and further shows its capability for the application of self-cleaning coatings with transparency. The promising characteristics of (inexpensive, transparent, conductive, super-hydrophilic, and high photocatalytic active) graphene loaded TiO2 films may have the potential use in various indoor applications.

Concepts: Fluorescence, Ultraviolet, Light, Semiconductor, Fluorescent lamp, Incandescent light bulb, Thin film, Self-cleaning glass

28

We report the fabrication of a highly flexible indium tin oxide (ITO) electrode that is completely transparent to light in the visible spectrum. The electrode was fabricated via the formation of a novel ITO nanoarray structure, consisting of discrete globular ITO nanoparticles superimposed on an agglomerated ITO layer, on a heat-sensitive polymer substrate. The ITO nanoarray spontaneously assembled on the surface of the polymer substrate by a simple sputter coating at room temperature, without nanolithographic or solution-based assembly processes being required. The ITO nanoarray exhibited a resistivity of approximately 2.3 × 10(-3) Ω cm and a specular transmission of about 99% at 550 nm, surpassing all previously reported values of these parameters in the case of transparent porous ITO electrodes synthesized via solution-based processes at elevated temperatures. This novel nanoarray structure and its fabrication methodology can be used for coating large-area transparent electrodes on heat-sensitive polymer substrates, a goal unrealizable through currently available solution-based fabrication methods.

Concepts: Light, Solar cell, Indium tin oxide, Liquid crystal display, Indium(III) oxide, Indium, Transparent electrodes, Sputter deposition

28

Si has the highest theoretical capacity among all known anode materials, but it suffers from the dramatic volume change upon repeated lithiation and delithiation processes. In order to overcome the severe volume change, Si nanoparticles were first coated with a polymer-driven carbon layer, and then dispersed in a CNT network. In this unique structure, the carbon layer can improve electronic conductivity and buffer the severe volume change; while the tangled CNT network is expected to prevent the crack and pulverization, maintain the integrity of electrodes, stabilize the electronic conductive network, and eventually lead to better cycling performance. Electrochemical test result indicates the carbon-coated Si nanoparticles dispersed in CNT networks show a capacity retention of 70% after 40 cycles, which is much better than the carbon-coated Si nanoparticles without CNTs.

Concepts: Electrochemistry, Carbon, Carbon nanotube, Graphite, Materials science, Battery, Electrolyte, Rechargeable battery

28

The applicability of gallium-based liquid metal alloy has been limited by the oxidation problem. In this paper, we report a simple method to remove the oxide layer on the surface of such alloy to recover its non-wetting characteristics, using hydrochloric acid (HCl) vapor. Through the HCl vapor treatment, we successfully restored the non-wetting characteristics of the alloy and suppressed its viscoelasticity. We analyzed the change of surface chemistry before and after the HCl vapor treatment using x-ray photoelectron spectroscopy (XPS) and low energy ion scattering spectroscopy (LEIS). Results showed that the oxidized surface of Galinstan® (Ga2O3 and Ga2O) was replaced with InCl3 and GaCl3 after the treatment. Surface tension and static contact angle on a Teflon®-coated glass of the HCl vapor treated Galinstan® were measured to be 523.8 mN/m and 152.5°. A droplet bouncing test was successfully carried out to demonstrate the non-wetting characteristics of the HCl vapor treated Galinstan®. Finally, the stability of the transformed surface of the HCl vapor treated Galinstan® was investigated by measuring contact angle and LEIS spectra after re-oxidation in ambient environment.

Concepts: Hydrogen, Zinc, Liquid, Surface tension, Materials science, Chlorine, X-ray photoelectron spectroscopy, Surface chemistry

28

A relatively new and efficient method is reported here for the purification and arrangement of high-aspect-ratio gold nanorods (AuNRs) using an amphiphilic dendrimer, Bis-(amidoethylcarbamoylethyl) octadecylamine (C18N3), which strongly adsorbs to the surface of AuNRs. The adsorbed layers of dendrimer on AuNRs exhibit the ability to de-aggregate AuNPs at low pH in aqueous medium and to promote their aggregation at high pH. By regulating the pH of the dispersion medium, a well-ordered arrangement of 99% monodisperse AuNRs was obtained, having dimensions of approximately 18 nm in diameter, 353 nm in length, and an area of several dozens of μm2, which is much larger than what has been reported in the literature. A very strong optical absorption in the near-infrared region (NIR) of as-prepared AuNRs assemblies was shown. This strategy of using pH responsive amphiphilic dendrimers to mediate both the homogenization in shape and the arrangement of nanoparticles provides a new methodology for the formation of nanoparticle assemblies.

Concepts: Nanoparticle, Electromagnetic radiation, Nanotechnology, Colloid, Adsorption, PH, Gold, Greenhouse effect

28

Effect of positioning of the cyanoacrylic acid anchoring group on ring periphery of phenothiazine dye on the performance of dye-sensitized solar cells (DSSCs) is reported. Two types of dyes, one having substitution on the C-3 aromatic ring (Type 1) and another through the N-terminal (Type 2), have been synthesized for this purpose. Absorption and fluorescence studies have been performed to visualize the effect of substitution pattern on the spectral coverage and electrochemical studies to monitor the tuning of redox levels. B3LYP/6-31G* studies are performed to visualize the frontier orbital location and their significance in charge injection when surface modified on semiconducting TiO(2). New DSSCs have been built on nanocrystalline TiO(2) according to traditional two-electrode Grätzel solar cell setup with a reference cell based on N719 dye for comparison. The lifetime of the adsorbed phenothiazine dye is found to be quenched significantly upon immobilizing on TiO(2) suggesting charge injection from excited dye to semiconducting TiO(2). The performances of the cells are found to be prominent for solar cells made out of Type 1 dyes compared to Type 2 dyes. This trend has been rationalized on the basis of spectral, electrochemical, computational, and electrochemical impedance spectroscopy results.

Concepts: Protein, Spectroscopy, Electrochemistry, Quantum dot, Solar cell, Photovoltaics, Energy conversion, Dye-sensitized solar cell

28

Cadmium sulfide (CdS)-decorated zinc oxide (ZnO) nanorod heterostructures have been grown by a combination of hydrothermal and pulsed laser deposition techniques. Hybrid photovoltaic devices have been fabricated with CdS modified and unmodified ZnO nanorods blended separately with regioregular poly(3-hexylthiophene) (P3HT) polymer as the active layer. The solar cell performance has been studied as a function of ZnO concentration and the casting solvent (chlorobenzene, chloroform, and toluene) in the unmodified ZnO:P3HT devices. The power conversion efficiency is found to be enhanced with the increase of ZnO concentration up to a certain limit, and decreases at a very high concentration. The surface modification of ZnO nanorods with CdS leads to an increase in the open circuit voltage and short-circuit current, with enhanced efficiency by 300% over the unmodified ZnO:P3HT device, because of the cascaded band structure favoring charge transfer to the external circuit.

Concepts: Zinc, Cadmium, Solar cell, Titanium dioxide, Band gap, Cadmium telluride, Cadmium oxide, Zinc sulfide

28

Porous SnO(2)/graphene composite thin films are prepared as anodes for lithium ion batteries by the electrostatic spray deposition technique. Reticular-structured SnO(2) is formed on both the nickel foam substrate and the surface of graphene sheets according to the scanning electron microscopy (SEM) results. Such an assembly mode of graphene and SnO(2) is highly beneficial to the electrochemical performance improvement by increasing the electrical conductivity and releasing the volume change of the anode. The novel engineered anode possesses 2134.3 mA h g(-1) of initial discharge capacity and good capacity retention of 551.0 mA h g(-1) up to the 100th cycle at a current density of 200 mA g(-1). This anode also exhibits excellent rate capability, with a reversible capacity of 507.7 mA h g(-1) after 100 cycles at a current density of 800 mA g(-1). The results demonstrate that such a film-type hybrid anode shows great potential for application in high-energy lithium-ion batteries.

Concepts: Electron, Rechargeable battery, Lithium-ion battery, Lithium, Lithium battery, Lithium-ion polymer battery, Electric car, Nickel-metal hydride battery

28

Imidazolium and quaternary ammonium-functionalized poly(fluorenyl ether ketone sulfone)s were synthesized successfully with the same degree of cationic functionalization and identical polymer backbones for a comparative study of anion exchange membranes (AEMs) for solid-state alkaline membrane fuel cells (AMFCs). Both anion exchange membranes were synthesized using a new methyl-containing monomer that avoided the use of toxic chloromethylation reagents. The polymer chemical structures were confirmed by (1)H NMR and FTIR. The derived AEMs were fully characterized by water uptake, anion conductivity, stability under aqueous basic conditions, and thermal stability. Interestingly, both the cationic groups and the polymer backbone were found to be degraded in 1 M NaOH solution at 60 °C over 48 h as measured by changes of ion exchange capacity and intrinsic viscosity. Imidazolium-functionalized poly(fluorenyl ether ketone sulfone)s had similar aqueous alkaline stability to quaternary ammonium-functionalized materials at 60 °C but much lower stability at 80 °C. This work demonstrates that quaternary ammonium and imidazolium cationic groups are not stable on poly(arylene ether sulfone) backbones under relatively mild conditions. Additionally, the poly(arylene ether sulfone) backbone, which is one of the most common polymers used in ion exchange membrane applications, is not stable in the types of molecular configurations analyzed.

Concepts: Electron, Chemistry, Polymer, Ion, Monomer, Ammonium, Cation exchange capacity, Alkali anion exchange membrane