There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Redox‐Based Resistive Switching Memories – Nanoionic Mechanisms, Prospects, and Challenges

Electrochemical energy storage technology is based on devices capable of exhibiting high energy density (batteries) or high power density (electrochemical capacitors). There is a growing need, for current and near-future applications, where both high energy and high power densities are required in the same material. Pseudocapacitance, a faradaic process involving surface or near surface redox reactions, offers a means of achieving high energy density at high charge–discharge rates. Here, we focus on the pseudocapacitive properties of transition metal oxides. First, we introduce pseudocapacitance and describe its electrochemical features. Then, we review the most relevant pseudocapacitive materials in aqueous and non-aqueous electrolytes. The major challenges for pseudocapacitive materials along with a future outlook are detailed at the end.

https://hal.archives-ouvertes.fr/hal-01171774/document

Pseudocapacitive oxide materials for high-rate electrochemical energy storage

Approaches, Derivatives and Applications Vasilios Georgakilas,† Michal Otyepka,‡ Athanasios B. Bourlinos,‡ Vimlesh Chandra, Namdong Kim, K. Christian Kemp, Pavel Hobza,‡,§,⊥ Radek Zboril,*,‡ and Kwang S. Kim* †Institute of Materials Science, NCSR “Demokritos”, Ag. Paraskevi Attikis, 15310 Athens, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo naḿ. 2, 166 10 Prague 6, Czech Republic

Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications

In recent years, considerable attention has been focused on graphene, because it has shown to possess a wealth of exceptional properties and various promising applications. To realize this promise, reliable methods for the large-scale production of high-quality graphene are required. Epitaxial growth on polycrystalline nickel is being actively pursued, but achieving large graphene domains with uniform properties remains a challenge. The mechanical cleavage of graphite originally led to the discovery of graphene sheets and this method is the process currently used in most fundamental research on graphene. However, the low productivity of this method makes it unsuitable for synthesizing graphene on a large-scale. Instead, the chemical conversion from graphite appears to be a muchmore-efficient approach to bulk production of graphene sheets (GSs). Most chemical syntheses of GSs from graphite begin with graphite oxide (GO) and usually need a reductant. GO can be reduced by H2. [16] However, it is highly explosive and flammable. Hydrazine can also be used to reduce GO. In view of its toxicity and combustibility, precautions must be taken when large quantities of hydrazine are used to prepare GSs on a large-scale. NaBH4 is known to reduce GO in aqueous solution. Owing to its hygroscopic and flammable properties, the secure preservation of sodium borohydride is a difficult task. Furthermore, reducing GO by traditional heating systems (such as an oil bath) is time-consuming. Therefore, those methods are inefficient and not fit for preparing GSs on a large-scale. On the other hand, the thermal stability of carbon materials is an important aspect of their properties. The synthesis of graphene with good thermal stability would provide greater potential for commercial applications. A study reported by Wu et al. found that GSs synthesized by hydrogen-arc discharge exfoliation were of good thermal stability. Unfortunately, to the best of our knowledge, there are only a few papers that have investigated the thermal stability of graphene. As such, the development of a method for synthesizing GSs with good thermal stability from widely available graphite on a large-scale is of great significance. Although various methods for the synthesis of graphene under microwave irradiation have been reported, they all employed either organic solution or poisonous reagents. In this study, GSs with upper thermal stability were rapidly synthesized in aqueous media by a method based on microwave-assisted and ascorbic acid (AA) as a reductant. Microwave adsorption of GO increased its local temperature and pressure, resulting in the elevation of the thermal stability of GSs. It should be noted that the reducing time of GO by using microwave irradiation was shortened to 30 minutes and the reductant of GO was nontoxic and tractable. AA is naturally employed as a reductant in living things, and has also been used to synthesize nanomaterials. Herein, we report the use of this nontoxic and tractable reductant for the preparation of GSs. The synthesis of GSs is shown in Scheme 1. Firstly, GO was dispersed in deionized water with the help of sonication. Secondly, the temperature of the solution around the GO rose drastically under microwave irradiation, becoming evidently higher than other regions, because GO could strongly absorb the energy of microwave irradiation. With the help of a local elevated temperature, GO was reduced by AA within 0.5 hours. In addition, the local high pressure of GO resulting from microwave irradiation may contribute to the good thermal stability of the GSs. For comparison, we also prepared GSs with an oil bath (marked as GSOB). Figure 1 a shows typical FTIR spectra obtained for GO and GSs. The FTIR spectra of GO confirmed the presence of oxygen-containing groups, including C OH (nC OH = 3390 cm ), C O C (nC O C =1230 cm ), and C=O in car[a] M. Zhang , S. Liu, X. M. Yin, Z. F. Du, Q. Y. Hao, D. N. Lei, Prof. Q. H. Li, Prof. T. H. Wang Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education and State Key Laboratory for Chemo/Biosensing and Chemometrics, Hunan University Changsha 410082 (China) Fax: (+86) 0731-88823407 E-mail : thwang@hnu.cn liqiuhon2004@hotmail.com Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000776.

Fast synthesis of graphene sheets with good thermal stability by microwave irradiation.

Design and synthesis of Cr2O3@C@G composites with yolk-shell structure for Li+ storage

Mesoporous SnO2 nanospheres are obtained from an interesting self-assembly process combining the driven forces of water-evaporation and molecular interactions. The as-obtained mesoporous SnO2 nanospheres show good electrochemical characteristics in capacity retention and rate capacity.

Taihong Wang

Papers

Fast synthesis of graphene sheets with good thermal stability by microwave irradiation.

Design and synthesis of Cr2O3@C@G composites with yolk-shell structure for Li+ storage

Mesoporous SnO2 nanospheres formed via a water-evaporating process with superior electrochemical properties

Construction of complex WO3-SnO2 hollow nanospheres as a high-performance anode for lithium-ion batteries

H x MoO 3 nanobelts with better performance as anode in lithium-ion batteries