Evaluation of Solvents used to Extract Chlorophyll for Photovoltaic CellsChelsie Johnson and Jim Bidlack

Department of Biology, University of Central Oklahoma, Edmond, Oklahoma 73034, USA

Abstract

An experiment was conducted to evaluate several solvents used to extract chlorophyll from spinach for eventual use in photovoltaic cells. These cells were constructed with tin-oxide coated plates; the cathode was treated with graphite and the anode contained chlorophyll extracts embedded in titanium dioxide. Once treated with titanium dioxide, each anode was soaked in chlorophyll preparations made with one of three different solvents including ethanol, acetone, and water, for a period of 4 to 10 days. After air-drying anodes, complete photovoltaic cells were assembled with a drop of iodine / potassium iodide conducting solution, sandwiched between the plates. The cells were first tested to ensure that they produced significantly higher voltage in the presence of light compared to complete darkness. Power curves (in light) were then constructed for these cells using a resistance replacement box and maximum power was used to determine which resistance should be used for cells to measure voltage over a period of 10 to 30 days. Preliminary results demonstrated that photovoltaic cells constructed with acetone-extracted and ethanol-extracted chlorophyll can produce up to 350 millivolts, whereas cells constructed with water-extracted chlorophyll are unstable and, generally produce about 298 millivolts. We are currently in the process of evaluating the longevity of these cells and whether or not the same treatment differences exist over a longer period of time.

Materials and Methods Photovoltaic Cells were constructed at the University of Central Oklahoma. Procedures for constructing cells were derived from a Nanocrystalline Solar Kit purchased from the Institute of Chemical Education at the University of Wisconsin in Madison, Wisconsin. Homemade cells were constructed using tin lined glass plates . Solvents including ethanol, acetone, and water saturated with sucrose are used to treat cells. Results were recorded using a voltage meter and a RIO Stat or Resistance Replacement Box (Figure 1) to put resistance on a closed circuit cells. Construction of the cells begin with the coating of each plate with exactly five grams of titanium dioxide and then baked at five hundred degrees Celsius for a period of three to five minutes. When baked, the titanium dioxide goes through a chemical change and will turn black then turn white again. This is how it is know that the titanium dioxide has bonded to the tin coated glass plate (Figure 3). Each solvent was combined with whole spinach leaves and ran as a blank to act as controls. To make the test solutions, exactly five milliliters of chloroplast where combined with twenty milliliter of each solvent. Three cells are placed in a blank, solvent with leaves, and chloroplast mixture to soak for a period of four to ten days in total and complete darkness. After a period of four to ten days, each cell is combined with a blank tin coated plate covered in graphite from pencil lead (anode). Potassium Iodide is put between the two plates to conduct electricity and super glue is put along the edges to hold the two plates together. The anode and cathode are then connected to the RIO Stat and a volt meter. By multiplying current by voltage, the power max of a cell can be calculated. From these calculations, power curves can be constructed.

Methods and Materials Continued

The two cells that are the most consistent and close in voltage readings are put into the environmental chamber for a period of thirty days. Once in the environmental chamber, voltage will be read ever twenty minutes during a 12 hour day and 12 hour night period under lights that range in intensity from 20,000 to 30,000 lumens.

Results and Discussion

There are no results for this experiment because the experiment is still ongoing and longevity is still being determined while cells are in the environmental chamber. Preliminary power curves showed that cells treated with the chloroplast mixed with water saturated with sucrose produced the highest power curves (Figure 2). These cells had an average max power of 298 millivolts. Those cells treated with isolated chloroplasts suspended in acetone and ethanol had considerable lower readings with an average voltage of 218 millivolts. Solvent mixed with leaves for all three solvents were relatively low, but stayed constant throughout the experiment with power averaging between 200 and 300 millivolts. Blanks of all three solvents spike at the beginning of the experiment with powers between 200 to 400 millivolts, but drop quickly within a week to values of between 100 and 200 millivolts. More research is currently being done to increase and test the longevity of the cells so they can be applied to pre-made cells.

References

EPA. “Manufacture of Photovoltaic Solar Cells Ucing Plant Chlorophyl” 29 08 2008. <http://cfpub.epa.gov/si/si_public_record_Report.cfm?dirEntryId=187266>.

FitzSimons, T.R. 2010. Harnessing solar energy using photosynthetic and organic pigments. Master’s Thesis. University of Central Oklahoma, Edmond, OK. USA. 160 pp.

Leung, Issac. "Spinach-based solar cell extracts energy from chlorophyll protein." 12 04 2012. www.electronicsnews.com. 14 01 2013 <http://www.electronicsnews.com.au/news/spinach-based-solar-cell-extracts-energy-from-chlo>.

Rouzer, C. A. (2010, March 10). Nature's Approach to Solar Power. Retrieved January 25, 2012, from http://www.vanderbilt.edu/vicb/discoveriesachives/solar_power.html/

Acknowledgements Funding for this project was provided by the Office of Research & Grants at the University of Central Oklahoma. Also thanks to Brett Jones, and Hunter Porter for their help in evaluating and guiding research methodologies.

Figure 3: Titanium Dioxide coated plates soaked in chloroplasts isolated form spinach and t with water saturated with sucrose.

Figure 2: RIO Stat or Resistance Replacement connected to a closed circuit cell to provide resistance that is read with a volt meter.