PHOTOELECTROCHEMICAL STORAGE CELLSIn addition to photoelectrochemical cells that produce solar electricity as PV devices, PEC cells can also store solar energy as solar-
generated fuel (for example, hydrogen in a photoelectrolysis cell), or they can store electricity in a third-electrode PV cell. In a
photoelectrolysis cell (left figure), the semiconductor electrode is in contact with water and, when illuminated, it produces electron-hole
pairs that separate. In n-type semiconductor electrodes, the holes move to the surface and oxidize water to oxygen; the electrons flow
to a second metal electrode, where they reduce water to hydrogen. In p-type semiconductor electrodes, the roles of the two electrodes
are reversed, and hydrogen is produced at the semiconductor electrode. In an electrical storage cell, some of the photocurrent
generated during illumination is sent to the third storage electrode to charge it. Then, during periods of no illumination, the third
electrode discharges, thus maintaining constant power output. The electrochemical electrode reactions for this cell are illustrated in the
figure on the right.REFERENCES
E. Becquerel, Comptes Rendus 9 , 561 (1839).
D. Chapin, C. Fuller, and G. Pearson, “A New Silicon p-n Junction Photocell for Converting
Solar Radiation into Electrical Power,” J. Appl. Phys. 25 , 676 (1954).
EIA: see Energy Information Administration.
Energy Information Administration, Electric Power Monthly. U.S. Department of Energy (June
2005); available at http://www.eia.doe.gov/cneaf/electricity/epm/chap1.pdf.
M. Grätzel, “Photoelectrochemical Cells,” Nature 414 , 338 (2001).
M.A. Green, Third Generation Photovoltaics: Advanced Solar Energy Conversion. Springer-
Verlag: Berlin, Germany (2004).
A.J. Bard, M. Stratmann, and S. Licht (Eds.), Semiconductor Electrodes and
Photoelectrochemistry: Volume 6 of Encyclopedia of Electrochemistry. Wiley-VCH: Darmstadt,
Germany (2002).
PEC Cell for Fuel Production:
Photoelectrolysis of Water