Free-standing Nano Research Articles

Review on Hydrogen Storage Performance of MgH2: Development and Trends

AbstractHydrogen storage technology is related to the process of hydrogen energy market. Efficient and safe hydrogen storage materials have always been the goal pursued by people. In the past few years, oceans of materials for hydrogen storage have been researched, MgH2 is considered to be one of the most potential hydrogen storage materials due to its high hydrogen storage capacity, good reversibility and price advantage. However, its development has been limited by its good thermodynamic stability and slow dehydrogenation kinetics. In this paper, the improvement of hydrogen storage performance of MgH2 is summarized from catalyst doping, MgH2 nanosizing, alloying and the construction of composite system. In particular, catalyst doping and MgH2 nanosizing will be more effective modification strategies. With the development of nanotechnology, monatomic catalyst will also become a research hotspot. In view of the changes in thermodynamic properties caused by the nanofabrication of MgH2, the loadless freestanding nano MgH2 will undoubtedly receive more attention.

Towards free-standing graphane: atomic hydrogen and deuterium bonding to nano-porous graphene

Graphane is formed by bonding hydrogen (and deuterium) atoms to carbon atoms in the graphene mesh, with modification from the pure planar sp2 bonding towards an sp3 configuration. Atomic hydrogen (H) and deuterium (D) bonding with C atoms in fully free-standing nano porous graphene (NPG) is achieved, by exploiting low-energy proton (or deuteron) non-destructive irradiation, with unprecedented minimal introduction of defects, as determined by Raman spectroscopy and by the C 1s core level lineshape analysis. Evidence of the H- (or D-) NPG bond formation is obtained by bringing to light the emergence of a H- (or D-) related sp3-distorted component in the C 1s core level, clear fingerprint of H–C (or D–C) covalent bonding. The H (or D) bonding with the C atoms of free-standing graphene reaches more than 1/4 (or 1/3) at% coverage. This non-destructive H-NPG (or D-NPG) chemisorption is very stable at high temperatures up to about 800 K, as monitored by Raman and x-ray photoelectron spectroscopy, with complete healing and restoring of clean graphene above 920 K. The excellent chemical and temperature stability of H- (and D-) NPG opens the way not only towards the formation of semiconducting graphane on large-scale samples, but also to stable graphene functionalisation enabling futuristic applications in advanced detectors for the β-spectrum analysis.

GHz-range resonant ultrasound spectroscopy for a free-standing nano film studied by picosecond ultrasonics

Progress in the wireless communication requires higher frequency bandpass filters, and the bulk acoustic-wave filter is especially the key device for the GHz-range communication. Its resonance frequencies depend on the elastic constants of individual layers, but it is never straightforward to measure them. In this study, we apply resonant ultrasound spectroscopy to a GHz-range free-standing AlN/Ru/Cr resonator to simultaneously determine the elastic constant of each layer. Using picosecond ultrasonics, we measure free-vibration resonance frequencies up to ∼70 GHz and inversely determine it. The obtained values are reasonable as thin films elasticity, confirming the applicability of the proposed method.

Design and synthesis of a free-standing carbon nano-fibrous web electrode with ultra large pores for high-performance vanadium flow batteries

A highly porously free-standing nano fibrous web electrode has been designed and fabricated for VFB through a novel horizontally-opposed blending electrospinning method in this study.

Direct Growth of Freestanding ZnO Tetrapod Networks for Multifunctional Applications in Photocatalysis, UV Photodetection, and Gas Sensing.

Growth of freestanding nano- and microstructures with complex morphologies is a highly desired aspect for real applications of nanoscale materials in various technologies. Zinc oxide tetrapods (ZnO-T), which exhibit three-dimensional (3D) shapes, are of major importance from a technological applications point of view, and thus efficient techniques for growth of different varieties of tetrapod-based networks are demanded. Here, we demonstrate the versatile and single-step synthesis of ZnO-T with different arm morphologies by a simple flame transport synthesis (FTS) approach, forming a network. Morphological evolutions and structural intactness of these tetrapods have been investigated in detail by scanning electron microscopy, X-ray diffraction, and micro-Raman measurements. For a deeper understanding of the crystallinity, detailed high-resolution transmission electron microscopic studies on a typical ZnO tetrapod structure are presented. The involved growth mechanism for ZnO tetrapods with various arm morphologies is discussed with respect to variations in experimental conditions. These ZnO-T have been utilized for photocatalytic degradation and nanosensing applications. The photocatalytic activities of these ZnO-T with different arm morphologies forming networks have been investigated through the photocatalytic decolorization of a methylene blue (MB) solution under UV light illumination at ambient temperature. The results show that these ZnO-T exhibit strong photocatalytic activities against MB and its complete degradation can be achieved in very short time. In another application, a prototype of nanoelectronic sensing device has been built from these ZnO-T interconnected networks and accordingly utilized for UV detection and H2 gas sensing. The fabricated device structures showed excellent sensing behaviors for promising practical applications. The involved sensing mechanisms with respect to UV photons and H2 gas are discussed in detail. We consider that such multifunctional nanodevices based on ZnO tetrapod interconnected networks will be of interest for various advanced applications.

Versatile Growth of Freestanding Orthorhombic α-Molybdenum Trioxide Nano- and Microstructures by Rapid Thermal Processing for Gas Nanosensors

We demonstrate a new technique that requires a relatively low temperature of 670–800 °C to synthesize in 10–20 min high crystalline quality MoO3 nano- and microbelts and ribbons. The developed technological process allows rapid synthesis of large amounts of MoO3 nano- and microsheets, belts, and ribbons, and it can be easily scaled up for various applications. Scanning electron microscopy (SEM) studies revealed that the MoO3 nano- and microbelts and ribbons are synthesized uniformly, and the thickness is observed to vary from 20 to 1000 nm. The detailed structural and vibrational studies on grown structures confirmed an excellent agreement with the standard data for orthorhombic α-MoO3. Also, such freestanding nano- and microstructures can be transferred to different substrates and dispersed individually. Using focused ion beam SEM, MoO3-based 2D nano- and microsensors have been integrated on a chip and investigated in detail. The nanosensor structures based on MoO3 nano- and microribbons are quite stable...

Nanoscale membrane electrolyte array for solid oxide fuel cells

This paper presents a fabrication method for a low temperature micro-solid oxide fuel cell (μ-SOFC), featuring a large number of free-standing nano thin film electrolyte membranes. The μ-SOFC was fabricated by simple silicon-based MEMS processes to create a membrane array structure that renders high surface area density and mechanically stable support for yttria-stablized zirconia (YSZ) with only 70nm in thickness. A total number of 765 to 6885 circular YSZ electrolyte membranes with a diameter of 50μm were enclosed within 2mm to 6mm square arrays. The active membrane area density on a silicon wafer surface was increased up to 20 times higher than that of previously reported structures. A 2mmμ-SOFC array was tested at 350, 400, and 450°C, and maximum power outputs of 1.78mW, 2.43mW, and 2.98mW were obtained, respectively. Total power output of the high performance micro-SOFCs was increased from microwatts up to the milliwatt scale, and can be easily scaled up further for higher power output by this method.