Yoshio Bando

“Protrusions” or “holes” in graphene: which is the better choice for sodium ion storage?

The main challenge associated with sodium-ion battery (SIB) anodes is a search for novel candidate materials with high capacity and excellent rate capability. The most commonly used and effective route for graphene-based anode design is the introduction of in-plane “hole” defects via nitrogen-doping; this creates a spacious reservoir for storing more energy. Inspired by mountains in nature, herein, we propose another way – the introduction of blistering in graphene instead of making “holes”; this facilitates adsorbing/inserting more Na+ ions. In order to properly answer the key question: ““protrusions” or “holes” in graphene, which is better for sodium ion storage?”, two types of anode materials with a similar doping level were designed: a phosphorus-doped graphene (GP, with protrusions) and a nitrogen-doped graphene (GN, with holes). As compared with GN, the GP anode perfectly satisfies all the desired criteria: it reveals an ultrahigh capacity (374 mA h g−1 after 120 cycles at 25 mA g−1) comparable to the best graphite anodes in a standard Li-ion battery (∼372 mA h g−1), and exhibits an excellent rate capability (210 mA h g−1 at 500 mA g−1). In situ transmission electron microscopy (TEM) experiments and density functional theory (DFT) calculations were utilized to uncover the origin of the enhanced electrochemical activity of “protrusions” compared to “holes” in SIBs, down to the atomic scale. The introduction of protrusions through P-doping into graphene is envisaged to be a novel effective way to enhance the capacity and rate performance of SIBs.

Ultra-high-resolution HVEM (H-1500) newly constructed at NIRIM: I. Instrumentation

Abstract Basic specifications and some experimental data of a new ultra-high-resolution HVEM (Hitachi H-1500), with a maximum accelerating voltage of 1300 kV, are described. A lattice fringe image of 0.07 nm is obtained from thin gold film, indicating excellent mechanical and electrical stability of the microscope. Spherical and chromatic aberration coefficients of the objective lens are 1.85 and 3.4 mm, respectively, at 1300 kV; and a theoretical point-to-point resolution, defined by the first-zero point of the contrast transfer function (CTF) curve under the Scherzer condition, is about 0.104 nm. A crystal structure image of silicon, in which each silicon site is observed as a black dot, is successfully obtained and the image agrees fairly with the results of computer simulations based on the above optical parameters.

3D network of cellulose-based energy storage devices and related emerging applications

There has recently been a major thrust toward advanced research in the area of hierarchical carbon nanostructured electrodes derived from cellulosic resources, such as cellulose nanofibers (CNFs), which are accessible from natural cellulose and bacterial cellulose (BC). This research is providing a firm scientific basis for recognizing the inherent mechanical and electrochemical properties of those composite carbon materials that are suitable for carbon-electrode applications, where they represent obvious alternatives to replace the current monopoly of carbon materials (carbon nanotubes, reduced graphene oxide, and their derivatives). Significant promising developments in this area are strengthened by the one dimensional (1D) nanostructures and excellent hydrophobicity of the CNFs, the interconnected pore networks of carbon aerogels, and the biodegradable and flexible nature of cellulose paper and graphenic fibers. Outstanding electrode materials with different dimensions (1D, 3D) are derivable by the strategic choice of cellulose sources. This development requires special attention in terms of understanding the significant impact of the cellulose morphology on the final electrochemical performance. This review article attempts to emphasize the role of the different structural forms and corresponding composites derived from different forms of cellulose, including bacterial cellulose and its varied 3D nanostructures. This article strongly highlights that cellulose deserves special attention as an extremely abundant and extensively recyclable material that can serve as a source of components for electronic and energy devices. Along with emphasizing current trends in electrochemical device components from cellulose, we address a few emerging areas that may lead in future such as enzyme immobilization, flexible electronics, modelling of cellulosic microfibrils. Finally, we have discussed some of the important future prospects for cellulose as source of materials for future.

In Situ Electrochemistry of Rechargeable Battery Materials: Status Report and Perspectives

The development of rechargeable batteries with high performance is considered to be a feasible way to satisfy the increasing needs of electric vehicles and portable devices. It is of vital importance to design electrodes with high electrochemical performance and to understand the nature of the electrode/electrolyte interfaces during battery operation, which allows a direct observation of the complicated chemical and physical processes within the electrodes and electrolyte, and thus provides real-time information for further design and optimization of the battery performance. Here, the recent progress in in situ techniques employed for the investigations of material structural evolutions is described, including characterization using neutrons, X-ray diffraction, and nuclear magnetic resonance. In situ techniques utilized for in-depth uncovering the electrode/electrolyte phase/interface change mechanisms are then highlighted, including transmission electron microscopy, atomic force microscopy, X-ray spectroscopy, and Raman spectroscopy. The real-time monitoring of lithium dendrite growth and in situ detection of gas evolution during charge/discharge processes are also discussed. Finally, the major challenges and opportunities of in situ characterization techniques are outlined toward new developments of rechargeable batteries, including innovation in the design of compatible in situ cells, applications of dynamic analysis, and in situ electrochemistry under multi-stimuli. A clear and in-depth understanding of in situ technique applications and the mechanisms of structural evolutions, surface/interface changes, and gas generations within rechargeable batteries is given here.

First Synthesis of Continuous Mesoporous Copper Films with Uniformly Sized Pores by Electrochemical Soft Templating

Although mesoporous metals have been synthesized by electrochemical methods, the possible compositions have been limited to noble metals (e.g., palladium, platinum, gold) and their alloys. Herein we describe the first fabrication of continuously mesoporous Cu films using polymeric micelles as soft templates to control the growth of Cu under sophisticated electrochemical conditions. Uniformly sized mesopores are evenly distributed over the entire film, and the pore walls are composed of highly crystalized Cu.

Reduction Mechanism of Dislocation Density in GaAs Films on Si Substrates

Significant reduction of dislocation densities in GaAs films grown on Si substrates have been demonstrated. High-quality GaAs films on Si with average etch-pit density on the order of 104 cm-2 have been obtained by combining the low-temperature growth technique and the atomic hydrogen irradiation. The reduction mechanism of dislocation density in GaAs on Si as well as possible growth kinetics have been discussed based on reflection high-energy electron diffraction (RHEED) and transmission electron microscope (TEM) observations. Most of the threading dislocations have annihilated in the low-temperature grown GaAs layers by forming closed loops. As a consequence of the dislocation density reduction, the electron mobilities of GaAs films on Si have been improved.

Morphosynthesis of nanoporous pseudo Pd@Pt bimetallic particles with controlled electrocatalytic activity

Nanoporous pseudo Pd@Pt bimetallic particles were prepared using a facile one-step synthetic approach. The morphologies of the resultant particles are changed from spheres to cubes by increasing the molar ratio of the Pd/Pt precursor solution. Compared to commercially available Pt black and Pt/C-20%, the nanoporous pseudo Pd@Pt bimetallic particles were up to 7 times and 2.1 times more active for the methanol oxidation reaction on the basis of equivalent Pt, respectively. This excellent electrocatalytic activity is caused by a combination of the high surface area of the nanoporous architecture in addition to the bimetallic synergetic effect. Through this work, we demonstrate a general approach for the creation of nanoporous bimetallic Pt-based particles with controlled shape, composition and size for enhanced catalytic activity.

Strategic synthesis of mesoporous Pt-on-Pd bimetallic spheres templated from a polymeric micelle assembly

Core–shell–corona type triblock copolymer poly(styrene-b-2-vinylpyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) micelles have been selected here to direct the synthesis of mesoporous Pt-on-Pd spheres, consisting of a Pd concentrated core and a Pt shell, as established by elemental mapping. It is important to note that the size of the PS core determines the resultant size of the mesopores. A self-evaporation method has been developed to prepare swollen micelles, so as to further enlarge the pore size (∼40 nm). Compared with commercially available catalysts (e.g., Pt black or Pt, 20 wt% on carbon black), good oxygen reduction reaction performance on the mesoporous Pt-on-Pd spheres is observed, due to the exposure of the most active Pt (111) planes and the synergistic effects from Pt and Pd in the pseudo core–shell structure.

Superior electrocatalytic activity of mesoporous Au film templated from diblock copolymer micelles

Mesoporous Au films consisting of a network of interconnected Au ligaments around ultra-large pores were found to exhibit a promising electrocatalytic activity towards sluggish reactions. Mesoporous Au films with pore sizes up to 25 nm were successfully fabricated using a polymeric micelle approach. A superior catalytic activity of the mesoporous Au films towards methanol oxidation was confirmed, which was thoroughly analyzed and compared with that of other Au materials. An intrinsic investigation on the high catalytic activity revealed that the superior performance of the as-prepared mesoporous Au film was related to its unique atomic structures around the mesopores with well-crystallized facets and several step/kink sites on the Au surfaces. These findings showcase a strategic and feasible design for preparing highly active Au-based catalysts that could be used as promising candidates in electrocatalytic applications.

BN Nanosheet/Polymer Films with Highly Anisotropic Thermal Conductivity for Thermal Management Applications

The development of advanced thermal transport materials is a global challenge. Two-dimensional nanomaterials have been demonstrated as promising candidates for thermal management applications. Here, we report a boron nitride (BN) nanosheet/polymer composite film with excellent flexibility and toughness prepared by vacuum-assisted filtration. The mechanical performance of the composite film is highly flexible and robust. It is noteworthy that the film exhibits highly anisotropic properties, with superior in-plane thermal conductivity of around 200 W m-1 K-1 and extremely low through-plane thermal conductivity of 1.0 W m-1 K-1, making this material an excellent candidate for thermal management in electronics. Importantly, the composite film shows fire-resistant properties. The newly developed unconventional flexible, tough, and refractory BN films are also promising for heat dissipation in a variety of applications.