Interfacial PCET

PCET can also play an important role in interfadal charge transfer processes. Electrochemical PCET have recently been explored, both theoretically and experimentally. Hammes-Schiffer et al. have applied their theoretical framework to model systems where the proton transfer occurs within solvated hydrogen-bonded solute complexes while the electron is transferred between that solute complex and an immersed electrode Costentin et al. have investigated the mechanistic details of PCET in the oxidation of phenols, as model systems of central processes in oxygenic photosynthesis. The same groups have explored the experimental and theoretical aspects of PCET in model systems with proton relay networks.  

Another important example of interfacial PCET can occur between semiconductor surfaces and adsorbate molecules, and is particularly relevant for some of the current energy conversion strategies, such as dye-sensitised solar cells (DSSC) or photoelectrochemical (PEC) water splitting cells. A simple proof of the involvement of PCET in interfacial redox processes is the dependence of the conduction and valence band potentials of semiconducting metal oxides, such as Ti02, with pH. The nature of the surface terminal groups (typically O or OH in metal oxides) will have a strong influence in the thermodynamics and kinetics of the system. 

Interfacial electron transfer at solid-liquid interfaces, photoinduced and/or in the presence of an applied potential bias, as in the case of water oxidation on semiconducting metal oxide electrodes involves, as will be discussed in the next section, multiple electron and proton transfer steps. The energy cost associated with charge transfer across the interface will translate into overpotentials for driving the (photo)electrochemical reactions. This is particularly significant in 

Petek and co-workers have investigated ultrafast interfacial inner sphere PCET dynamics, where the presence of strong potential gradients will subject electrons and protons to opposite forces within a spatial region.This is the case for water oxidation on semiconductor photoelectrodes, and therefore with potential impact in the context of artificial photosynthesis. 

Splitting water into molecular oxygen and hydrogen, and reduction of carbon dioxide into carbohydrates are multielectron processes 

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