1. l
Luke Schkeryantz

2. History of PhotoElectroChemical cells
First reported in 1972
Fujishima and Honda, Nature, 238, 37-38
Heavily invested in the 70's and 80's, progress slow
Field revitalized in 90's and continues today with separation of light absorption and redox active components of the cell

3. Dye-Sensitized PhotoElectroChemical Cells
Nearly all DSPECs use TiO2  as photoanodes
Ruthenium based dyes are most common
Improving anchoring groups of dye
J. Phys. Chem. C 2013, 117, 14526−14533

4. State of the Art Dyes Photoelectrodes
Organice pi-acceptor chromophores
J. Phys. Chem. Lett. 2015, 6, 3213−3217.
ACS Nano 2012, 6, 6185−6196
J. Phys. Chem. C. 2012, 116, 4892−4902
J. Mater. Chem. A. 2016, 4, 2969−2975

5. Problems with DSPECs Paper identifies two main problems
Degradation of dye molecule
Fast electron hole recombination time
Proposed solution
Layer of Al2O3

6. Breaking Down DSPECs Perylene-3,4-dicarboximide (PMI or dye)
IrIr (dimeric catalyst)
The mode of binding is unknown for this molecule
IrSil (monomeric catalyst)

7. Steady-State UV-Vis Absorption
ALD refers to Atomic Layer Deposition, or growth of Al2O3 layer
Blue-shift for first few cycles of ALD
Disaggregation of PMI
Red-shift for additional cycles of ALD
More rigid environment for the PMI
Degradation monitored by UV-Vis
No ALD = Major loss of PMI in 2 weeks in light and air
More ALD = Less loss
30 Full cycles = Low loss even after 3 months

8. Electrochemistry Performed with Ag/AgCl reference electrode
Pt counter electrode
All values given against NHE (normal hydrogen electrode)

9. Photoelectrochemistry
Linear sweep voltammetry (LSV) was performed to study the response of the films to an applied bias under light (420 nm)
An increased photocurrent was observed upon addition of Al2O3 indicating the charge recombination benefits outweighed the negative impact on electron injection
The photocurrent changed with addition of the catalysts
IrIr showed lower photocurrent, IrSil higher
IrIr due to faster recombination, further supported by enhanced photocurrent with more ALD
IrSil due to the long linker between the Ir metal center and the electrode surface
IrIr displays higher catalyst functionality than IrSil under purely electrochemical conditions

10. Transient Absorption Spectroscopy
Irradiated initially with 495 nm
Excitation of PMI causes ground state bleach (GSB) at nm, stimulated emission (SE) at 575nm and singlet excited state absorption (1*PMI) at 680nm
About 14% of excited PMI units do not inject electrons into TiO2 (τ1)
The rest however do inject electrons on a time scale of 1-10 ps (τ2)
Demonstrated by rapid decay of SE and (1*PMI) bands
600 nm band represents a Stark shift of PMI ground state absorption induced by electron injection
Substantially lowered in systems with ALD (approximately 1.6 times slower)
Rate slows with as little as 5 cycles of ALD and does not further slow with additional ALD
Decay of absorption at 600 nm represents charge recombination

11. Transient Absorption Spectroscopy (cont.)
Authors expected a slower electron injection rate (τ2) would also result in a longer electron recombination (τ3)
Not the case with systems with no catalyst
ALD may protect against charge recombination with solvent

12. Catalyst Kinetics
No direct observation of catalyst possible with UV-Vis (low absorption by these Ir species)
Kinetics elucidated by comparison to analogous system with no catalyst
More rapid rise of Stark shift and faster decay of 1*PMI and SE in cells with IrIr
Indicates faster electron injection and recombination
Authors argues this indicates (τ4) and (τ6) are occurring rapidly (although diminishes with greater ALD)
Potentially (τ5) is implicated in this spectra, but not conclusive
In contrast the system with IrSil are almost indistinguishable from the no catalyst cell
(τ4,τ6) is longer and non competitive with (τ2)
Pathway (τ2,τ5) is dominant in oxidation of the catalyst
(τ7) for both catalyst systems increases with additional ALD

14. Catalyst Testing
Generator-Collector Method biased by 0.51V and V respectively
Both cells with catalyst and without were tested
Illuminated by 410 nm light
Counter electrode = Pt Mesh
Faradaic efficiency of 18% and 22% w/o and with catalyst
Both catalysts performed similarly
Lack of difference between systems indicates little oxidation performed by catalyst

15. Conclusions Concerns Future Work Achievements
ALD layer of Al2O3 protects dye molecules from degradation and slows charge recombination
Concerns
Negligible improvement in catalysis yields with catalyst applied
Inconsistent reasoning on various points
Contradiction between photoelectrochemistry and catalysis
Future Work
Studying intermediate charge transfer steps further
Investigate new conditions to improve rate of catalyst oxidation