Theories of Homogeneous and Electrochemical Electron Transfer in Complex Media

Project: Research project

Description

Both the need to curb the level of carbon dioxide in the atmosphere and to produce hydrogen or other fuels contribute to the urgency to design effective schemes for separation of charge with solar energy. This is a global problem, which grows more important on a daily basis and it will soon become the dominant scientic issue. Solar photochemistry research is often driven by empirical approaches searching for optimum combination of parameters, while theories guiding new laboratory approaches are insufficiently developed. The prevailing paradigms suggest that molecules are not
the best materials for building photosynthetic conversion systems, and solid
semiconductors should be used instead. On the other hand, natural systems based on combinations of molecules with nanoscale interfaces have achieved significant efficiency gains where evolutionary pressure forced them to do so. Natural photosynthesis provides an example of complex interfacial systems where complex dynamics couples with non-trivial energetics affecting electronic states of photosynthetic cofactors. The development of solar photochemistry in recent years seems to re-trace nature's steps by employing increasingly complex solvents and interfaces. While these new systems offer significant advantages for efficient solar energy conversion, they also present challenges for rational design since their properties are not well understood and hard to measure. There is also little from the established general theory that can guide the researcher in what to expect in terms of charge-transfer rates when certain conditions and/or design components change. This proposal aims to address these challenges by developing predictive theoretical
formalisms to model rates of charge transfer in non-traditional solvents and at electrodes (electrochemistry).

We propose: (i) to develop theories of electron transfer in non-dipolar
solvents, (ii) to extend the analysis of cyclic voltammetry to dynamically
complex media, including room-temperature ionic liquids, and (iii) to de-
velop analytical formalisms for the analysis of charge-transfer band shapes.
Our main goal is to arrive at computational algorithms which can be used
by practitioners without significant investment in theory.

Description

The need to curb the level of carbon dioxide in the atmosphere and to produce fuels contribute to the urgency to design eective schemes for separation of charge with solar energy. Solar photochemistry research is often driven by empirical approaches searching for optimum combination of parameters, while theories guiding new practical design are insufficiently developed. The recent focus has been on extending the computational capabilities for material research into the realm of high-performance computing. While significant advances by using parallel computer architectures have in-
deed been achieved, there is an urgent need to translate the results of computations into reliable theoretical formalisms cast in terms of measurable material properties which practitioners can use for predictive exploration of the parameters affecting solar energy conversion. This is especially true with the current shift of the field toward the use of complex materials and interfaces. While these new systems offer significant advantages for tunability of material properties, they also present challenges for rational design since their properties are not well understood and hard to measure.

The present proposal makes the next step in developing practical theories of charge transfer in complex media and interfaces. We propose to build on our initial success in the previous research cycle and to continue developing models of charge transfer in ionic liquids in the bulk and in contact with electrodes. The development of formal model will be supported by extensive simulations of model ionic liquids to provide the theory with the microscopic structural information. We next propose to take advantage of enormous polarizability of photoexcited quantum dots to use polarizability as a new
parameter to control and improve the eciency of charge separation. Both a general theory will be developed and specific calculations performed to connect theory to new experiments recently reported in the literature. Finally, we propose to develop a unified theory of asymmetric voltammetric curves in electrochemistry. Recent advances in the data analysis have shown that such phenomena are much more abundant than previously thought. No consistent theory of volmammetric asymmetry currently exists and we will bridge this gap and connect our results with experiment.
StatusActive
Effective start/end date6/1/168/31/19

Funding

  • DOE: Office of Science (OS): $456,608.00

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Charge transfer
Ionic Liquids
Solar energy
Electrons
Photochemical reactions
Curbs
Electrochemistry
Energy conversion
Carbon Dioxide
Materials properties
Electrodes
Molecules
Computer architecture
Photosynthesis
Electronic states
Semiconductor quantum dots
Cyclic voltammetry
Hydrogen
Experiments
Temperature