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Electron injection dynamics in high-potential porphyrin photoanodes
Rebecca L Milot1, Charles A Schmuttenmaer1
1Department of Chemistry and Energy Sciences Institute, Yale University, 225 Prospect Street, P.O. Box 208107, New Haven, Connecticut 06520-8107, United States.
Accounts of Chemical Research
|May 5, 2015
Summary
Researchers used terahertz spectroscopy to study solar fuel production, finding that tin oxide nanoparticles improve electron injection efficiency. Water-stable anchoring groups like hydroxamate also show promise for artificial photosynthesis.
Area of Science:
- Materials Science
- Photochemistry
- Spectroscopy
Background:
- Solar energy addresses the need for carbon-neutral power sources.
- Artificial photosynthesis aims to store solar energy in chemical bonds (solar fuels).
- Water oxidation is a critical step in artificial photosynthesis, mimicking natural processes.
Purpose of the Study:
- To investigate electron injection dynamics in potential solar fuel devices using terahertz spectroscopy.
- To compare dye-sensitized solar cell (DSSC) technology for electricity generation with its adaptation for water splitting.
- To identify and address challenges in adapting DSSC technology for solar fuel production, focusing on energy level matching and anchoring group stability.
Main Methods:
- Time-resolved terahertz spectroscopy (TRTS) was employed to analyze electron injection rates and efficiencies on a sub-picosecond timescale.
- Studies involved bio-inspired pentafluorophenyl porphyrins as sensitizers and various metal oxide nanoparticles (TiO2, SnO2).
- Evaluation of different anchoring groups (carboxylate, phosphonic acid, hydroxamic acid, acetylacetone, boronic acid) for their stability and impact on electron injection.
Main Results:
- Electron injection was inefficient into TiO2 but more efficient into SnO2 nanoparticles.
- SnO2 electron injection timescales were influenced by the porphyrin's central substituent and excited-state deactivation.
- Heavy or paramagnetic metal ions in porphyrins increased electron injection timescales due to triplet state involvement.
- Hydroxamate anchoring groups demonstrated stability and comparable performance to carboxylates in water oxidation conditions.
- Incorporating an iridium-based precatalyst decreased electron injection efficiency despite increased photocurrent.
Conclusions:
- TRTS is a powerful tool for studying ultrafast electron transfer crucial for solar fuel development.
- SnO2 offers a promising platform for efficient electron injection in artificial photosynthesis.
- Water-stable anchoring groups are essential for robust solar fuel devices.
- Further research is needed to optimize catalyst integration and overcome challenges in artificial photosynthesis.
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