Interface metal-sulfur

The polysulfides, thiosulfate and sulfite, which are generally metastable relative to sulfate, are most abundant near groundwater redox interfaces where they can complex with borderline or soft metal cations (cf. Barnes 1979 Daskalakis and Helz 1992). Many sedimentary and hydrothermal ore deposits are found at redox interfaces where the breakdown and formation of such complexes may have locally caused metal precipitation and remobilization (cf. Granger and Warren 1969 Boulegue and Michard 1979 Barnes 1979). Similar metal-sulfur species mobilization may also occur in the vicinity of some toxic metal-organic waste sites. 

The life-limiting increase of resistance and decrease of capacity of cycled cells is usually attributed to the deteriorating effects of corrosion of the positive current collector— the cell container in the case of sodium core cells or a rod in the case of sulfur core cells. Apart from consuming the active material, corrosion may lead to the deposition of poorly conductive layers at the current collector surface, thus interrupting the contact of the inert electrode fibers with the current collector. Corrosion products may also deposit and block both the solid electrolyte and the electrode surface. The thermodynamic instability of metals in polysulfide melts severely limits the choice of materials interfacing the sulfur electrode.A fully satisfactory solution has not yet been reported. 

Actually, it is recognized that two different mechanisms may be involved in the above process. One is related to the reaction of a first deposited metal layer with chalcogen molecules diffusing through the double layer at the interface. The other is related to the precipitation of metal ions on the electrode during the reduction of sulfur. In the first case, after a monolayer of the compound has been plated, the deposition proceeds further according to the second mechanism. However, several factors affect the mechanism of the process, hence the corresponding composition and quality of the produced films. These factors are associated mainly to the com-plexation effect of the metal ions by the solvent, probable adsorption of electrolyte anions on the electrode surface, and solvent electrolysis. 

The discovery in 1973 that polysulfur nitride (SN)X, a polymer comprised only of non-metallic elements, behaves as a superconductor at 0.26 K sparked widespread interest in sulfur-nitrogen (S-N) chemistry. In the past 30 years, the field of inorganic S-N chemistry has reached maturity and interfaces with other areas of chemistry, e.g., theoretical chemistry, materials chemistry, organic synthesis, polymer chemistry and biochemistry, have been established and are under active development. This interest has been extended to Se-N and, to a lesser extent, Te-N systems. 

The function of zinc ions may be either catalytic or stractural. Enzymes with a co-catalytic center of two or even three zinc ions in close proximity are also known. In a new type of zinc-binding site, the protein interface, zinc ions are fixed at the interface of two proteins with the aid of amino acid residues. The ligand residues are usually His, Asp, Glu or Cys, which interact via nitrogen, oxygen or sulfur donors with the metal ion. In catalytic binding sites. His coordination dominates and an additional reactive water molecule is bound. 

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