Multiple band gap devices for
solar water splitting
Tfy-56.5141 Special Course in Advanced Energy
Technologies
Priit Jaanson
Contents
• Direct PV (photovoltaic) electrolysis vs PEC
(photo electrochemical cell) electrolysis
• PEC challenges
• Biasing the PEC
• Examples
Direct PV electrolysis
vs PEC electrolysis
• Direct PV electrolysis
– Expensive?
– High current densities ->
overpotential -> lower
efficiency
– Not compact?
• PEC electrolysis
– Lower current densities ->
higher electrolysis
efficency
– All in one package: cheap,
compact.
L. Minggu et al. An overview of photocells and photoreactors for photoelectrochemical water splitting, International Journal of Hydrogen Energy, Vol. 35, 11, 2010
5233-5244.
PEC challenges
• Visible light absorption
• Stability against photocorrosion
– Metal oxides: Charge transfer kinetics > anodic
decomposition rate
– Non-oxides: thin oxide layer formation, dissolving.
• Suitable band gap and band edge energies.
Bandgap matching
• Oxidation
covered
• Reduction
challenging
• Need for
external bias
Solar hydrogen production with nanostructured metal oxides, Roel van de Krol , Yongqi Liang and Joop Schoonman, J. Mater. Chem., 2008,18, 2311-2320
Biasing
• Grid biased
– Fossil fuels
• pH biased
– More
consumables
• PV or DSSC
biased
• Internal biased
L. Minggu et al. An overview of photocells and photoreactors for photoelectrochemical water splitting, International Journal of Hydrogen Energy, Vol. 35, 11, 2010
5233-5244.
Internal-biased systems - PV/PEC
• Solar to hydrogen
efficiency 0.7 %
• Estimated to be
improved to ~10 %
with thicker oxide
layer
Eric L. Miller, Daniela Paluselli, Bjorn Marsen, Richard E. Rocheleau, Development of reactively sputtered metal oxide films for hydrogen-producing hybrid
multijunction photoelectrodes, Solar Energy Materials and Solar Cells, Volume 88, Issue 2, 15 July 2005, Pages 131-144.
Internal-biased systems - PV/PV
• STH efficiency
16.5%
• STE efficiency
28.5%
O. Khaselev, A. Bansal, J.A. Turner, High-efficiency integrated multijunction photovoltaic/electrolysis systems for hydrogen production, International Journal of
Hydrogen Energy, Volume 26, Issue 2, February 2001, Pages 127-132,
Internal-biased systems - PV/PV
• STH efficiency
7.8%
• STE efficiency
9%
Internal-biased systems - PEC/PEC
• Efficiency 5%
1)
2)
3)
4)
Glass sheet
Aqueous electrolyte
Meseporous oxide film
TCO (transparent
conducting oxide)
5) Electrical connection
6) Dye sensitized
meseoporous TiO2
7) Electrolyte
8) CE
9) Same as 2)
10) Catalytic cathode
11) Glass frit
Gratzel, M. and Augustynski, J. 2005. Tandem cell for water cleavage by visible light. Patent no. US 6936143.
Conclusions
• Highest STH efficiency achieved is 18.3 % with
a multi bandgap PV/PV PEC
• Theoretically over 30% possible.
Future:
• Emerging hybrid thermal electrical systems
utilizing wider range of solar spectrum
promise up to 50% efficiency.