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Proton-Induced Trap States, Injection and Recombination Dynamics in Water-Splitting Dye-Sensitized Photoelectrochemical Cells
journal contribution
posted on 2016-06-13, 00:00 authored by Nicholas S. McCool, John R. Swierk, Coleen T. Nemes, Timothy P. Saunders, Charles A. Schmuttenmaer, Thomas E. MalloukWater-splitting dye-sensitized photoelectrochemical
cells (WS-DSPECs) utilize a sensitized metal oxide and a water oxidation
catalyst in order to generate hydrogen and oxygen from water. Although
the Faradaic efficiency of water splitting is close to unity, the
recombination of photogenerated electrons with oxidized dye molecules
causes the quantum efficiency of these devices to be low. It is therefore
important to understand recombination mechanisms in order to develop
strategies to minimize them. In this paper, we discuss the role of
proton intercalation in the formation of recombination centers. Proton
intercalation forms nonmobile surface trap states that persist on
time scales that are orders of magnitude longer than the electron
lifetime in TiO2. As a result of electron trapping, recombination
with surface-bound oxidized dye molecules occurs. We report a method
for effectively removing the surface trap states by mildly heating
the electrodes under vacuum, which appears to primarily improve the
injection kinetics without affecting bulk trapping dynamics, further
stressing the importance of proton control in WS-DSPECs.
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Recombination Dynamicsproton controlelectron lifetimeinjection kineticsdye molecules causesdye moleculesmetal oxidewater oxidation catalystproton intercalationwater splittingquantum efficiencyrecombination mechanismstime scalesTiO 2surface trap statesphotogenerated electronsProton intercalation forms nonmobile surface trap statesrecombination centersFaradaic efficiency
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