자연주의적 탐구조사(Naturalistic Inquiry)

Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

New materials hold the key to fundamental advances in energy conversion and storage, both of which are vital in order to meet the challenge of global warming and the finite nature of fossil fuels. Nanomaterials in particular offer unique properties or combinations of properties as electrodes and electrolytes in a range of energy devices. This review describes some recent developments in the discovery of nanoelectrolytes and nanoelectrodes for lithium batteries, fuel cells and supercapacitors. The advantages and disadvantages of the nanoscale in materials design for such devices are highlighted.

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Nanostructured materials for advanced energy conversion and storage devices

Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li-air (O(2)) and Li-S. The energy that can be stored in Li-air (based on aqueous or non-aqueous electrolytes) and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li-air and Li-S justify the continued research effort that will be needed.

Li-O2 and Li-S batteries with high energy storage.

Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials.

Materials for fuel-cell technologies

The reduction of gaseous oxygen on carbon-supported platinum electrodes has been studied at 150 C with polarization and potential decay measurements. The electrolyte was either 100 weight percent phosphoric acid or that acid with a fluorinated additive, potassium perfluorohexanesulfonate (C{sub 6}F{sub 13}SO{sub 3}K). The pseudo-Tafel curves of the overpotential vs log (ii{sub L}/(i{sub L}{minus}i)) show a two-slope behavior, probably due to different adsorption mechanisms. The potential relaxations as functions of log (t+r) and log({minus}d{eta}/dt) have been plotted. The variations of these slopes and the dependence of the double-layer capacitance on the overpotential depended on the electrode manufacture and the kind of electrolyte (whether containing the fluorinated additive or not).

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Oxygen Reduction on Gas‐Diffusion Electrodes for Phosphoric Acid Fuel Cells by a Potential Decay Method

Lower oxidation states of tellurium. Tellurium(II) in chloroaluminate melts

Chloro Complexes in Molten Salts. III. Raman Study of the Chloro Complexes Formed in the Molten KCl-AlCl3-TeCl4 System

A series of modified phosphoric acid electrolytes containing fluorinated carbon compounds and silicone fluids as additives are disclosed The modified electrolytes can improve the fuel cell performance due to the enhanced oxygen reduction kinetics These additives are, preferably, potassium perfluorohexanesulphonate (C6 F13 KO3 S), potassium nonafluorobutanesulphonate (C4 F9 KO3 S), perfluorotributylamine [(C4 F9)3 N] and polymethylsiloxanes [(--Si(CH3)2 O--)n ] The additives are added in an amount of 01-5 wt % with respect to the phosphoric acid electrolyte

Phosphoric acid fuel cell

The system LiCl-KCl-KF-1 mole percent K 2 NbF 7 (molar ration F/Nb = 8) has been investigated in the temperature range 370 to 725°C by cyclic and square wave voltammetry In the temperature range from 370 to 520°C Nb(V) was reduced to Nb(III) in two reversible steps: Nb(V) → Nb(IV) → Nb(III) At these temperatures subvalent halides of niobium were formed at more negative potentials At temperatures above 660°C metallic niobium was formed during reduction When oxide (molar ratio O 2 /Nb = 11) was introduced in the melt at 725°C only minor changes were observed in the voltammograms It is suggested that oxide addition mainly leads to precipitation of oxide containing compounds

/pdf/electrochemical-investigation-on-the-redox-chemistry-of-53i08y8wbr.pdf

Niels J. Bjerrum

Papers

Oxygen Reduction on Gas‐Diffusion Electrodes for Phosphoric Acid Fuel Cells by a Potential Decay Method

Lower oxidation states of tellurium. Tellurium(II) in chloroaluminate melts

Chloro Complexes in Molten Salts. III. Raman Study of the Chloro Complexes Formed in the Molten KCl-AlCl3-TeCl4 System

Phosphoric acid fuel cell

Electrochemical investigation on the redox chemistry of niobium in LiCl-KCl-KF-Na2O melts