Chi-Chang Hu

Bio: Chi-Chang Hu is an academic researcher from National Tsing Hua University. The author has contributed to research in topics: Cyclic voltammetry & Oxide. The author has an hindex of 70, co-authored 299 publications receiving 17923 citations. Previous affiliations of Chi-Chang Hu include National Cheng Kung University & Tsinghua University.

Design and Tailoring of the Nanotubular Arrayed Architecture of Hydrous RuO2 for Next Generation Supercapacitors

Abstract: By use of the membrane-templated synthesis route, hydrous RuO2 (RuO2·xH2O) nanotubular arrayed electrodes were successfully synthesized by means of the anodic deposition technique. The desired three-dimensional mesoporous architecture of RuO2·xH2O nanotubular arrayed electrodes with annealing in air at 200 °C for 2 h simultaneously maintained the facility of electrolyte penetration, the ease of proton exchange/diffusion, and the metallic conductivity of crystalline RuO2, exhibiting unexpectedly ultrahigh power characteristics with its frequency “knee” reaching ca. 4.0−7.8 kHz, 20−40 times better than that of RuO2 single crystalline, arrayed nanorods. The specific power and specific energy of annealed RuO2·xH2O nanotubes measured at 0.8 V and 4 kHz is equal to 4320 kW kg-1 and 7.5 W h kg-1, respectively, demonstrating the characteristics of next generation supercapacitors.

A Cost-Effective Supercapacitor Material of Ultrahigh Specific Capacitances: Spinel Nickel Cobaltite Aerogels from an Epoxide-Driven Sol–Gel Process

Abstract: Adv. Mater. 2010, 22, 347–351 2010 WILEY-VCH Verlag Gm The ever worsening energy depletion and global warming issues call for not only urgent development of clean alternative energies and emission control of global warming gases, but also more advanced energy storage and management devices. Supercapacitors, offering transient but extremely high powers, are probably the most important next generation energy storage device. To boost the specific capacitance of supercapacitors, the specific surface area of the electrode materials needs to be as high as possible to promote the electric double-layer capacitances and to accommodate a large amount of superficial electroactive species to participate in faradaic redox reactions. In addition, suitable pore sizes, 2–5 nm, of the porous electrode materials are critical to ease the mass transfer of electrolytes within the pores for fast redox reactions and double-layer charging/discharging. Aerogels are a class of mesoporous materials possessing highly specific surface areas and porosities, from which promising applications in a wide range of areas have been investigated. They are composed of 3D networks of nanoparticles with an average pore size of several nanometers, adjustably falling within the optimal pore sizes of 2–5 nm. Consequently, aerogels are a promising candidate for supercapacitor applications. As to the electrode material, electroactive materials possessing multiple oxidation states/structures that enable rich redox reactions for pseudocapacitance generation are desirable for supercapacitors. Transition metal oxides are such a class of materials that have drawn extensive and intensive research attention in recent years. Among them, RuO2 is themost prominent one with a specific capacitance as high as 1580F g , probably the highest ever reported. The commercialization of RuO2 based supercapacitors, however, is not promising because of the high cost and rareness of Ru. Spinel nickel cobaltite (NiCo2O4) is a low-cost, environmentally friendly transition metal oxide, which has been employed in electrocatalytic water splitting (oxygen evolution) and lithium ion batteries. Its application in supercapacitors, however, received much less attention. Nickel cobaltite has been reported to possess a much better electronic conductivity, at least two orders of magnitude higher, and higher electrochemical activity than those of nickel oxides and cobalt oxides. It is expected to offer richer redox reactions, including contributions from both nickel and cobalt ions, than the two corresponding single component oxides and is a potential cost-effective alternative for RuO2. Based on the above considerations, one would expect nickel cobaltite aerogels, with anticipated good electronic conductivity, low diffusion resistance to protons/cations, easy electrolyte penetration, and high electroactive areas to be a promising candidate for the construction of next-generation, ultrahighperformance supercapacitors. Traditionally, aerogels are prepared with sol–gel processes by taking corresponding alkoxides as the precursors. Alkoxides are generally expensive and sensitive to moisture and heat, requiring careful handling. Recently, to tackle these drawbacks, the epoxide synthetic route, enabling the use of low-cost and stable metal salts as the precursors, was successfully developed to prepare metal oxide aerogels. In this work, we reported the first successful preparation of nickel cobaltite aerogels with the epoxide-driven sol–gel process. The effects of the post-gel-drying calcination temperature on the critical properties of the product aerogels were investigated. At a starting Ni/Co ratio of 0.5 and a post-gel-drying calcination temperature of 200 8C, an optimal combination of composition, crystallinity, specific surface area, pore volume, and pore size was achieved to afford the nickel cobaltite aerogels that showed an extremely high-specific capacitance of 1400 F g 1 under a mass loading of 0.4 mg cm 2 at a sweep rate of 25mV s 1 within a potential window of 0.04 to 0.52V in a 1 M NaOH solution. The excellent reversibility and cycle stability of the product aerogels were also demonstrated. A stoichiometric mixture of nickel and cobalt chlorides was used as the precursor for the preparation of the nickel cobaltite aerogels. After the gel is dried in supercritical carbon dioxide, a post-gel-drying calcination is generally required to acquire preferred composition and/or better crystallinity of the products. The post-gel-drying calcination temperature is thus an important processing parameter to be studied. For referring convenience, we term the product aerogels as Ni–Co–O–T, with Tdenoting the calcination temperature. The T block is omitted for as-prepared samples. Also, for comparison purposes, NiO and Co3O4 aerogels were prepared, termed as Ni–O–T and Co–O–T, respectively. Figure 1a shows the X-ray diffraction (XRD) patterns of the as-prepared product aerogels and those samples calcined at 200 and 300 8C. Surprisingly, nickel cobaltite was formed even at the as-prepared condition. The diffraction peak located at the 2u value

How to Achieve Maximum Utilization of Hydrous Ruthenium Oxide for Supercapacitors

Abstract: The utilization of hydrous ruthenium oxide (denoted as RuO x .nH 2 O) was promoted by annealing the oxide in air as well as by mixing it with conductive activated carbon (AC) due to the significant improvement in intra- and interparticle electronic conductivity, respectively. The maximum specific capacitance (C S,RuOx ) of RuO x .nH 2 O, 1340 F/g (measured at 25 aV/s), very close to the theoretic value, was obtained from a composite consisting of AC and RuO x .nH 2 O coated on graphite (denoted as AC-RuO x /G) with 10 wt % of sol-gel-derived RuO x .nH 2 O nanodots annealed in air at 200°C for 2 h. The UV absorption spectral features showed a shift in λ max to the red as the mean particle size of RuO x .nH 2 O nanodots was increased, attributable to the surface plasmon resonance phenomenon. The average particle size of highly uniform RuO x .nH 2 O nanodots, ranged from 2.05 to 3.01 nm, was estimated from the high-resolution transmission electron microscopy. The dependence of capacitive performance on the size and content of RuO x .nH 2 O nanodots, evidenced by cyclic voltammetry and electrical impedance spectroscopy results, revealed the important influences of interparticle electronic conductivities on the utilization of RuO x .nH 2 O. The RuO x .nH 2 O nanodots with and without annealing in air at 200°C for 2 h showed the amorphous structure from both the X-ray diffraction and electron diffraction analysis.

Materials for electrochemical capacitors

Abstract: Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

Solar Water Splitting Cells

Abstract: Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

A review of electrode materials for electrochemical supercapacitors

Abstract: In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

Carbon-based materials as supercapacitor electrodes

Abstract: This tutorial review provides a brief summary of recent research progress on carbon-based electrode materials for supercapacitors, as well as the importance of electrolytes in the development of supercapacitor technology. The basic principles of supercapacitors, the characteristics and performances of various nanostructured carbon-based electrode materials are discussed. Aqueous and non-aqueous electrolyte solutions used in supercapacitors are compared. The trend on future development of high-power and high-energy supercapacitors is analyzed.