Redox and Surface Chemistry vs. Electrode Decomposition

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 

Besides improving stability, a practical goal of surface modification has been to utilize redox reactions, otherwise not applicable, to yield better electrical characteristics such as higher open-circuit photovoltage, and to promote high conversion efficiencies. 

Derivatized semiconductor photoelectrodes offer a way to design photosensitive interfaces for effecting virtually any redox process. Manipulation of interfacial charge transfer processes has been demonstrated using hydrolytically unstable redox 

Organic dyes, aside from their role as sensitization agents for wide band gap semiconductors have been employed also for stabilization of narrow band gap semiconductors. The majority of such studies have considered metal or metal-free phthalocyanine films for both sensitization and electrode protection purposes [35]. 

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