Polychalcogenide systems

In screening electrolyte redox systems for use in PEC the primary factor is redox kinetics, provided the thermodynamics is not prohibitive, while consideration of properties such as toxicity and optical transparency is important. Facile redox kinetics provided by fast one-electron outer-sphere redox systems might be well suited to regenerative applications and this is indeed the case for well-behaved couples that have yielded satisfactory results for a variety of semiconductors, especially with organic solvents (e.g., [21]). On the other hand, many efficient systems reported in the literature entail a more complicated behaviour, e.g., the above-mentioned polychalcogenide and polyiodide redox couples actually represent sluggish redox systems involving specific interactions with the semiconductor... 

The clear conclusions from these observations are that (1) metal polychalcogenides are unusually adaptable coordination systems, which is not surprising, and (2) the crystal fields in many of the solids are demonstrably distorting both the compositions and the stereochemistries. The structures of the crystals do not faithfully represent the most stable coordination chemistry. 

In 1976, the first regenerative PECs with substantial and sustained solar to electrical conversion efficiency were demonstrated. These PECs are based on n-type cadmium chalcogenide (S, Se or Te) electrodes immersed in aqueous polychalcogenide electrolytes. The cells were introduced by Hodes, Cahen, and Manassen (31), Wrighton and coworkers [32], and Heller and Miller [33] and were capable of converting up to 7% of insolation to electrical energy. Most investigations of these systems focused on solid-state and interfacial aspects of these PECs and photodriven oxidation of polysulfide at the photoelectrode was represented ... 

The Au system yields an new set of compounds with novel structures and illustrates the synthetic potential of using the polychalcogenide molten salts. 

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