Research

Artificial Photosynthetic Assemblies  |  Next Generation Solar Cells

Artificial Photosynthetic Assemblies

Natural photosynthetic systems utilize the sun’s energy to transform carbon dioxide and water into carbohydrates, nature’s stored solar fuel. Artificial photosynthetic assemblies need to be able to absorb sunlight, transfer absorbed energy, transport charge, oxidize water and reduce carbon dioxide to a fuel source. Metal-Organic Frameworks (MOFs) can be functionalized to provide an efficient, heterogeneous system for artificial photosynthesis.

 

Water Oxidation

Ruthenium based water oxidation catalysts are common in the field of homogenous catalysis. These single site catalysts can achieve high turnover frequencies but suffer from the typical drawbacks of homogeneous catalysis, primarily rapid catalyst deactivation. Zirconium-based MOFs such as the UiO series can be used to incorporate ruthenium catalysts into the MOF backbone while retaining catalytic activity. The Morris group has shown that these loaded MOFs result in higher catalytic production on a per area basis and greater stability in comparison to the homogeneous analog.

Light Absorption and Energy Transfer

One of the most important components of an artificial photosynthetic system is the light absorbing antenna which has ability to absorb solar energy and direct it towards catalytic centers. Porphyrin-based MOFs have been investigated as a possible antenna system due to their abilities to absorb light and act as an energy cascade system when incorporated into an ordered system. MOFs allow for the ordered spacing and arrangement of porphyrins to study energy transfer properties for use as an antenna system.

Charge Transport

The Morris group uncovered the fundamental mechanism of charge transport through MOFs, termed redox hopping, in early work. We now are interested in understanding how molecular and structural MOF properties change the efficiency of the process. Ultimately, through systematic variations of the molecular species in the MOFs, redox electrolytes, and MOF pores/channels, the Morris group is developing a set of design rules for sufficient charge transport through MOFs to facilitate artificial photosynthetic catalysis.

CO2 Reduction and Fixation

Although many types of CO2 reduction catalysts exist, metal cyclams have the potential to be highly selective, efficient catalysts. The Morris group recently reported a new zirconium-based MOF, VPI-100 with metallo-cyclams incorporated. These MOFs are active for CO2 reduction similar to that observed for cyclams in homogeneous solution. Additionally, CO2 can be added to strained epoxides to produce useful industrial chemicals, rather than saturating the market with carbon-based fuels.

 

Next Generation Solar Cells

The Morris group works on a class of titanium dioxide sensitized solar cells, specifically quantum dot sensitized solar cells. We use fundamental electrochemistry to study the charge transfer properties of alternative redox mediators at the electrode/electrolyte interface for use in liquid junction photovoltaics. This project involves the study of electron transfer rate constants at sensitized interfaces, as well as the fabrication and testing of solar cells for efficiency measurement.