Use of Chloroplasts and Anthocyanin in Photovoltaic Cells
Hunter Porter, Brian Tetreault, and Jim Bidlack
Department of Biology, University of Central Oklahoma, Edmond, OK 73034
An experiment was designed to determine the viability of using chloroplasts and
concentrated anthocyanin in dye-sensitized solar (photovoltaic) cells. These cells
were made using glass plates with a film of tin oxide; one coated with titanium
dioxide embedded with pigment to serve as the anode and another coated with
graphite to serve as the cathode. Anodes were soaked with chloroplasts extracted
from spinach (Spinacia oleracea), or anthocyanin derived from the leaves of purple
heart (Tradescantia pallida) or anthocyanin from red cabbage (Brassica oleracea),
in order to embed pigments within the titanium dioxide. A KI/I2 electrolyte
solution was sandwiched between the anode and cathode cells and opposing ends
were connected to a voltmeter which recorded output over time using a Pico
Recorder. Use of chloroplasts in anodes showed promising results, with some cells
yielding over 800 millivolts per cell, whereas application of concentrated
anthocyanin to anodes produced an average of 400 to 600 millivolts. Both
chloroplasts and anthocyanin treatments produced voltages that were significantly
above control counterparts, which averaged about 100 millivolts per cell. A
preliminary longevity test of anthocyanin showed a voltage increase over a period
of 15 days. Longevity tests for chloroplast and concentrated anthocyanin cells are
currently being investigated.
Solar Cell Construction
Cells were constructed from mostly hand-made components, beginning with two glass
plates coated with SnO. Coated plates were then taped down, leaving a window of
space in the center. A TiO2 solution, consisting of 1.5 g of titanium(IV) oxide
nanopowder, 3 mL of dilute acetic acid solution, .75 mL of Triton-X 100, and .3g of
p-dihydroxybenzene, was then added to the cell and made into a smooth layer using a
glass rod. Coated cell sides were then fired at 500 degrees Celsius to anneal the TiO2
and create a nano-crystalline structure. Cathodes were then made by coating an
alternate SnO glass plate with a graphite lattice. Treatment cells had a specific solution
applied to the white titanium layer on the anode, while controls received no coloration.
A drop of Lugol’s solution was added as an electrolyte. Glass plates were lastly fastened
together using rubber band, finishing the cell construction.
Electrical Measurement and Recording
Constructed solar cells were attached to a voltmeter by clips and tested for output in
millivolts (Fig. 3). A circuit was then created to test power output using a rheostat to
apply variable resistance and power curves were generated for each cell (Fig. 4). The
average Pmax corresponding resistance was then chosen as the standard resistor for all
trials.
Data recording used a random block design, assigning cells randomly to one of two
recording racks. The racks were affixed with 100k ohm resistors (determined as
described previously), wires to a computer recorder, and clips to hold PV cells in place
(Fig. 5). Voltage was recorded for a period of 30 days using Pico Log Recorder.
0.000002
0.0000015
Series1
T2 – K
0.000001
Treatment Isolation and Application
Multiple things were used as treatments, but chloroplasts isolated from spinach
(Spinacia oleracea) were the main treatment condition. Chloroplasts were isolated by
homogenizing 5 grams of finely diced spinach leaves in a sugar grinding solution,
which was then centrifuged multiple times to pellet chloroplasts and allow removal of
other cell parts. Chloroplasts were examined under light microscope to ensure limited
damage and lack of free pigments (Fig. 1).
0.0000005
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Voltage (Volts)
Figure 3 (above):Voltmeter reading from cell
Introduction
Chloroplast Cell Power Curve
0.0000025
Power (Amperes)
Abstract
Materials and Methods
Figure 4 : Power Curve Example – Chloroplast Cell
Figure 5 (right): PV cells on testing rack
“Gratzel’s cell is a remarkable innovation [which] … closely mimics natural
photosynthesis” (Jayaweera, et al. 2007). Other projects have been conducted, such
as using the energy generated by microorganisms, in sea water, breaking down
carbon in the sediment to create electricity (Tender, et al. 2002). Dye-sensitized
solar cells (DSSCs) have been proven to harness solar energy into useable
electricity. The University of Central Oklahoma has specifically focused on
creating DSSCs using organic pigments instead of man-made pigments. However,
the application of living cells performing photosynthesis to a DSSC and its effects
still require testing. The goal of the research is to determine whether or not living
photosynthetic energy can be used to create more efficient DSSCs and if those cells
can be maintained over a long period of time.
Results and Discussion
Quantitative Results
While long term tests showed no significant difference (p>.05), voltage output
difference between controls and anthocyanin cells at construction were significant
(p<.05). Also, differences between chloroplast cells and controls at construction were
significant (p<.05) (Fig. 6).
Discussion
Figure 1 : Chloroplast Extraction – 400x magnified
Chloroplasts were then applied to cells using a drip method, depositing roughly 50
microliters of solution at a time and leaving to dry. Drip-coating was done daily for a
week. The applied chloroplasts thoroughly colored the white titanium substrate (Fig. 2).
Half of cells constructed (treatments; controls are assumed to follow) did not
function. The difference was starkly noticeable in treatment cells; however, the
differences were not noticed in controls. The reason for malfunction has yet to be
ascertained. It is suspected to be a result of the cells being handmade and thusly
subject to considerable human error on construction; more testing is required to
confirm the hypothesis. A more easily repeatable procedure is under development,
but was not ready in time for these trials.
Titanium(IV) nanopowder forms large conglomerations which effect the ability to
produce a quality nanocrystalline film. Options for higher quality particles are being
investigated.
Chloroplasts applied to factory made cells with less porous titanium structures did
not adhere well and resulted in weak coloration. This prompted the use of homemade
cells with potentially more human error over their mass produced alternative.
Determining why roughly half of the created cells do not function is a priority. In
order to advance research in this field, that level of failure is unacceptable past the
early research phase. Many other organic pigments could be tested, as well as
chloroplasts from different plant species or even cyanobacteria. So far, testing with
other green vegetation has shown large differences in chloroplast concentration upon
extraction. However, this data is not complete and requires further observations.
Acknowledgements
Figure 2 : TiO2 treated with chloroplast solution – 400x magnified
An aqueous anthocyanin solution was also used as a treatment, obtained from either
purple heart (Tradescantia pallida) or from red cabbage (Brassica oleracea). Purple
heart anthocyanin extractions were performed by boiling leaf tissue and then filtering
out other materials, while red cabbage was pureed and then filtered. Both extracted
solutions were boiled down to increase pigment concentration until a saturated solution
was formed.
Anthocyanin was applied to cells via the same drop method as the aforementioned
chloroplast treatments. Some cells were also coated by soaking for a period of 3 days.
Anthocyanin produced either reddish-purple (purple heart) or blue (red cabbage)
colored substrates.
Funding for this project was provided by a Research, Creative, and Scholarly Activities
(RCSA) grant from the Office of Research and Grants at the University of Central Oklahoma.
Literature Cited
Bidlack, James E. 2012. Plant Physiology Laboratory Manual Spring 2012.
Jayaweera, P.V.V., Perera, A.G.U., Tennakone, K. 2007. Why Gratzel’s Cells Work So Well.
Inorganica Chimica Acta.
Tender, Leanord M., Reimers, Clare E., Stecher III, Hilmar A., Holmes, Dawn E., Bond,
Daniel R., Lowy, Daniel A., Pilobella, Kanoelani, Fertig, Stephanie J., Lovley, Derek R
2002. Harnessing microbially generated power on the seafloor.
Average
Voltage
(mV)
Lowest
Voltage
(mV)
Highest
Voltage
(mV)
Anthocyanin Chloroplast
Control
500 (+/- 100) 400 (+/- 60)
120 (+/- 50)
0
~600
Longest
Lived Cell 3+ months
(ongoing)
0
0
~990
~5 months
~250
~1 month
Figure 6 : Table 1 – Data from cell construction