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Center for Nonlinear Studies |
Computational study of multiple electronphotooxidation of Ru-complexes covalently attached to TiO2 nanoparticles
The oxidation of water, 2H2O -> O2 + 4H+ + 4e-, is a four electron process. One proposed approach to oxidize water is with a dye-sensitized solar cells, where the dye is a catalyst for water oxidation. Dye-sensitized solar cells are constructed from dye molecules attached to semiconductor nanoparticles. Photoexcited electrons are efficiently transfered from the dye to the nanoparticle creating a long-lived charge-separated state. This efficient charge separation can be used to power water oxidation catalysts. In this work, the ability to achieve multiple charge separations on a single dye (catalyst) is explored by computational modeling. Electronic structure calculations show that each subsequent charge separation results in a change in the electronic structure that disrupts the alignment and coupling of photoexcited electrons with the nanoparticle conduction band, effectively turning off the charge separation mechanism. However, if the charge separation is accompanied by loss of a proton from the dye, the alignment and coupling can be preserved. Simulations of electron dynamics are used to calculate the rate of charge separation. The electron dynamics shows that the charge separation is completed on a sub-picosecond timescale, faster than excitation recombination.