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10924 KiB

Open AccessArticle

NiO Nanofibers as a Candidate for a Nanophotocathode

by Thomas J. Macdonald, Jie Xu, Sait Elmas, Yatin J. Mange, William M. Skinner, Haolan Xu and Thomas Nann

Nanomaterials 2014, 4(2), 256-266; https://doi.org/10.3390/nano4020256 - 3 Apr 2014

Cited by 51 | Viewed by 10624

Abstract

p-type NiO nanofibers have been synthesized from a simple electrospinning and sintering procedure. For the first time, p-type nanofibers have been electrospun onto a conductive fluorine doped tin oxide (FTO) surface. The properties of the NiO nanofibers have been directly compared [...] Read more.

p-type NiO nanofibers have been synthesized from a simple electrospinning and sintering procedure. For the first time, p-type nanofibers have been electrospun onto a conductive fluorine doped tin oxide (FTO) surface. The properties of the NiO nanofibers have been directly compared to that of bulk NiO nanopowder. We have observed a p-type photocurrent for a NiO photocathode fabricated on an FTO substrate. Full article

(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)

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1899 KiB

Open AccessArticle

Composite Electrolyte Membranes from Partially Fluorinated Polymer and Hyperbranched, Sulfonated Polysulfone

by Surya Subianto, Namita Roy Choudhury and Naba Dutta

Nanomaterials 2014, 4(1), 1-18; https://doi.org/10.3390/nano4010001 - 23 Dec 2013

Cited by 30 | Viewed by 10128

Abstract

Macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF) was done with various proportions of sulfonic acid terminated, hyperbranched polysulfone (HPSU) with a view to prepare ion conducting membranes. The PVDF-co-HFP was first chemically modified by dehydrofluorination and chlorosulfonation in order to make the membrane more [...] Read more.

Macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF) was done with various proportions of sulfonic acid terminated, hyperbranched polysulfone (HPSU) with a view to prepare ion conducting membranes. The PVDF-co-HFP was first chemically modified by dehydrofluorination and chlorosulfonation in order to make the membrane more hydrophilic as well as to introduce unsaturation, which would allow crosslinking of the PVDF-co-HFP matrix to improve the stability of the membrane. The modified samples were characterized for ion exchange capacity, morphology, and performance. The HPSU modified S-PVDF membrane shows good stability and ionic conductivity of 5.1 mS cm⁻¹ at 80 °C and 100% RH for blends containing 20% HPSU, which is higher than the literature values for equivalent blend membranes using Nafion. SEM analysis of the blend membranes containing 15% or more HPSU shows the presence of spherical domains with a size range of 300–800 nm within the membranes, which are believed to be the HPSU-rich area. Full article

(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)

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668 KiB

Open AccessArticle

Effect of Nanotube Film Thickness on the Performance of Nanotube-Silicon Hybrid Solar Cells

by Daniel D. Tune and Joseph G. Shapter

Nanomaterials 2013, 3(4), 655-673; https://doi.org/10.3390/nano3040655 - 17 Dec 2013

Cited by 26 | Viewed by 7000

Abstract

The results of measurements on solar cells made from randomly aligned thin films of single walled carbon nanotubes (SWCNTs) on n-type monocrystalline silicon are presented. The films are made by vacuum filtration from aqueous TritonX-100 suspensions of large diameter arc-discharge SWCNTs. The [...] Read more.

The results of measurements on solar cells made from randomly aligned thin films of single walled carbon nanotubes (SWCNTs) on n-type monocrystalline silicon are presented. The films are made by vacuum filtration from aqueous TritonX-100 suspensions of large diameter arc-discharge SWCNTs. The dependence of the solar cell performance on the thickness of the SWCNT film is shown in detail, as is the variation in performance due to doping of the SWCNT film with SOCl₂. Full article

(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)

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1371 KiB

Open AccessArticle

Fabrication and Characterization of SnO₂/Graphene Composites as High Capacity Anodes for Li-Ion Batteries

by Abirami Dhanabalan, Xifei Li, Richa Agrawal, Chunhui Chen and Chunlei Wang

Nanomaterials 2013, 3(4), 606-614; https://doi.org/10.3390/nano3040606 - 15 Nov 2013

Cited by 42 | Viewed by 8317

Abstract

Tin-oxide and graphene (TG) composites were fabricated using the Electrostatic Spray Deposition (ESD) technique, and tested as anode materials for Li-ion batteries. The electrochemical performance of the as-deposited TG composites were compared to heat-treated TG composites along with pure tin-oxide films. The heat-treated [...] Read more.

Tin-oxide and graphene (TG) composites were fabricated using the Electrostatic Spray Deposition (ESD) technique, and tested as anode materials for Li-ion batteries. The electrochemical performance of the as-deposited TG composites were compared to heat-treated TG composites along with pure tin-oxide films. The heat-treated composites exhibited superior specific capacity and energy density than both the as-deposited TG composites and tin oxide samples. At the 70th cycle, the specific capacities of the as-deposited and post heat-treated samples were 534 and 737 mA·h/g, respectively, and the corresponding energy densities of the as-deposited and heat-treated composites were 1240 and 1760 W·h/kg, respectively. This improvement in the electrochemical performance of the TG composite anodes as compared to the pure tin oxide samples is attributed to the synergy between tin oxide and graphene, which increases the electrical conductivity of tin oxide and helps alleviate volumetric changes in tin-oxide during cycling. Full article

(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)

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2572 KiB

Open AccessArticle

Synthesis of Microspherical LiFePO₄-Carbon Composites for Lithium-Ion Batteries

by Linghui Yu, Dandan Cai, Haihui Wang and Maria-Magdalena Titirici

Nanomaterials 2013, 3(3), 443-452; https://doi.org/10.3390/nano3030443 - 22 Jul 2013

Cited by 17 | Viewed by 8692

Abstract

This paper reports an “all in one” procedure to produce mesoporous, micro-spherical LiFePO₄ composed of agglomerated crystalline nanoparticles. Each nanoparticle is individually coated with a thin glucose-derived carbon layer. The main advantage of the as-synthesized materials is their good performance at high [...] Read more.

This paper reports an “all in one” procedure to produce mesoporous, micro-spherical LiFePO₄ composed of agglomerated crystalline nanoparticles. Each nanoparticle is individually coated with a thin glucose-derived carbon layer. The main advantage of the as-synthesized materials is their good performance at high charge-discharge rates. The nanoparticles and the mesoporosity guarantee a short bulk diffusion distance for both lithium ions and electrons, as well as additional active sites for the charge transfer reactions. At the same time, the thin interconnected carbon coating provides a conductive framework capable of delivering electrons to the nanostructured LiFePO₄. Full article

(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)

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Review

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2316 KiB

Open AccessReview

Work Function Engineering of Graphene

by Rajni Garg, Naba K. Dutta and Namita Roy Choudhury

Nanomaterials 2014, 4(2), 267-300; https://doi.org/10.3390/nano4020267 - 3 Apr 2014

Cited by 256 | Viewed by 42817

Abstract

Graphene is a two dimensional one atom thick allotrope of carbon that displays unusual crystal structure, electronic characteristics, charge transport behavior, optical clarity, physical & mechanical properties, thermal conductivity and much more that is yet to be discovered. Consequently, it has generated unprecedented [...] Read more.

Graphene is a two dimensional one atom thick allotrope of carbon that displays unusual crystal structure, electronic characteristics, charge transport behavior, optical clarity, physical & mechanical properties, thermal conductivity and much more that is yet to be discovered. Consequently, it has generated unprecedented excitement in the scientific community; and is of great interest to wide ranging industries including semiconductor, optoelectronics and printed electronics. Graphene is considered to be a next-generation conducting material with a remarkable band-gap structure, and has the potential to replace traditional electrode materials in optoelectronic devices. It has also been identified as one of the most promising materials for post-silicon electronics. For many such applications, modulation of the electrical and optical properties, together with tuning the band gap and the resulting work function of zero band gap graphene are critical in achieving the desired properties and outcome. In understanding the importance, a number of strategies including various functionalization, doping and hybridization have recently been identified and explored to successfully alter the work function of graphene. In this review we primarily highlight the different ways of surface modification, which have been used to specifically modify the band gap of graphene and its work function. This article focuses on the most recent perspectives, current trends and gives some indication of future challenges and possibilities. Full article

(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)

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4641 KiB

Open AccessReview

Numerical Modeling of Sub-Wavelength Anti-Reflective Structures for Solar Module Applications

by Katherine Han and Chih-Hung Chang

Nanomaterials 2014, 4(1), 87-128; https://doi.org/10.3390/nano4010087 - 29 Jan 2014

Cited by 89 | Viewed by 15198

Abstract

This paper reviews the current progress in mathematical modeling of anti-reflective subwavelength structures. Methods covered include effective medium theory (EMT), finite-difference time-domain (FDTD), transfer matrix method (TMM), the Fourier modal method (FMM)/rigorous coupled-wave analysis (RCWA) and the finite element method (FEM). Time-based solutions [...] Read more.

This paper reviews the current progress in mathematical modeling of anti-reflective subwavelength structures. Methods covered include effective medium theory (EMT), finite-difference time-domain (FDTD), transfer matrix method (TMM), the Fourier modal method (FMM)/rigorous coupled-wave analysis (RCWA) and the finite element method (FEM). Time-based solutions to Maxwell’s equations, such as FDTD, have the benefits of calculating reflectance for multiple wavelengths of light per simulation, but are computationally intensive. Space-discretized methods such as FDTD and FEM output field strength results over the whole geometry and are capable of modeling arbitrary shapes. Frequency-based solutions such as RCWA/FMM and FEM model one wavelength per simulation and are thus able to handle dispersion for regular geometries. Analytical approaches such as TMM are appropriate for very simple thin films. Initial disadvantages such as neglect of dispersion (FDTD), inaccuracy in TM polarization (RCWA), inability to model aperiodic gratings (RCWA), and inaccuracy with metallic materials (FDTD) have been overcome by most modern software. All rigorous numerical methods have accurately predicted the broadband reflection of ideal, graded-index anti-reflective subwavelength structures; ideal structures are tapered nanostructures with periods smaller than the wavelengths of light of interest and lengths that are at least a large portion of the wavelengths considered. Full article

(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)

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1047 KiB

Open AccessReview

Multiple Exciton Generation in Colloidal Nanocrystals

by Charles Smith and David Binks

Nanomaterials 2014, 4(1), 19-45; https://doi.org/10.3390/nano4010019 - 24 Dec 2013

Cited by 82 | Viewed by 16501

Abstract

In a conventional solar cell, the energy of an absorbed photon in excess of the band gap is rapidly lost as heat, and this is one of the main reasons that the theoretical efficiency is limited to ~33%. However, an alternative process, multiple [...] Read more.

In a conventional solar cell, the energy of an absorbed photon in excess of the band gap is rapidly lost as heat, and this is one of the main reasons that the theoretical efficiency is limited to ~33%. However, an alternative process, multiple exciton generation (MEG), can occur in colloidal quantum dots. Here, some or all of the excess energy is instead used to promote one or more additional electrons to the conduction band, potentially increasing the photocurrent of a solar cell and thereby its output efficiency. This review will describe the development of this field over the decade since the first experimental demonstration of multiple exciton generation, including the controversies over experimental artefacts, comparison with similar effects in bulk materials, and the underlying mechanisms. We will also describe the current state-of-the-art and outline promising directions for further development. Full article

(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)

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