Resume Pinaud (PDF, 1037 KB)

UFSP Solar Light to Chemical Energy Conversion
www.lightchec.uzh.ch
LightChEC
Résumé
Technical and economic feasibility of centralized facilities for solar hydrogen
production via photocatalysis and photoelectrochemistry
B. A. Pinaud et. al., Energy Environ. Sci., 2013, 6, 1983
Main findings
This work presents the results of a technical and economic feasibility analysis conducted for
four hypothetical, centralized, large-scale hydrogen production plants based on the
photoelectrochemical water splitting technology:
1) single bed particle suspension system
2) dual bed particle suspension system
3) fixed panel array
3) tracking concentrator array
lower costs but technical feasibility and
safety concerns?
higher costs but technique more mature, costs
can be reduced by increasing efficiency and
solar concentration
A key finding is that the production costs are consistent with the Department of Energy’s
targeted threshold cost of $2.00–$4.00 per kg H2 for dispensed hydrogen, demonstrating that
photoelectrochemical water splitting could be a viable route for hydrogen production in the
future if material performance targets can be met.
--------------------------------------------------------------------------------------------------------------------------→Overall particles beds reactors cheaper than panel based but uncertainty in their
technical feasibility
→Overall costs of panel based system can be reduced by increasing efficiency and by
solar concentration.
---------------------------------------------------------------------------------------------------------------------------
Valeria Mozzetti Page 1/15
11.11.2013
UFSP LightChEC
Introduction
Actual production of H2 is 50 million tonnes / year worldwide (wikipedia 57 million in 2004
with 10% yearly increase):
•
•


for petroleum refining
for ammonia synthesis for fertilizers (50 % wikipedia)
95% from fossil fuels via steam methane reforming.
5% 1 from (partial oxidation, plasma reforming ( Kvaerner-process), from coal
(products: syngas (hydrogen and Carbon monoxide) + methane). from water splitting
(until 2007 not in use).
High temperature electrolysis of alkalyne solution commercially exploited by Sable Chemicals
(Zimbawe, however it seems from a short search on the internet that they need a lot of
electricity that they buy under a subsidized form from the government causing shortage in the
country, at least seems that the electricity comes from hydropower).
Renewable H2 production:
a) Thermal processes: reforming bio-derived fuels
b) Electrolytic processes: renewable electricity source + electrolyzer
c) Photolytic processes: molecular chromophores or semiconductor absorber
Photoelectrochemical (PEC) water splitting




1
2
1972 Fujishima and Honda PEC water splitting on TiO2 photoelectrode.
PEC cells with iii-iv group semiconductor STH 2 12-18% 3
PEC cells with multi junction silicon STH 4.7-7.8% 4
Challenges for H2 PEC production:
 Durability
 Efficiency
 Costs (material and manufacturing)
from wikipedia (http://en.wikipedia.org/wiki/Hydrogen_production)
STH Solar to Hydrogen Efficiency
O. Khaselev and J. A. Turner, Science, 1998, 280, 425–427. and S. Licht, B. Wang, S. Mukerji, T.
Soga, M. Umeno and H. Tributsch, J. Phys. Chem. B, 2000, 104, 8920–8924.
3
S. Y. Reece, J. A. Hamel, K. Sung, T. D. Jarvi, A. J. Esswein, J. J. H. Pijpers and D. G. Nocera, Science,
2011, 334, 645–648. and R. E. Rocheleau, E. L. Miller and A. Misra, Energy Fuels, 1998, 12, 3–10.
4
Valeria Mozzetti Page 2/15
11.11.2013
UFSP LightChEC
Basic principles for PEC water splitting
Photon
Excited electron-hole pair
Band bending occurs:
•
•
at the semiconductor/ electrolyte interface
at p-n junction
excited holes
electrons
surface or electrode
surface or electrode
oxygen evolution reaction (OER)
hydrogen evolution reaction (HER)
Valeria Mozzetti Page 3/15
11.11.2013
UFSP LightChEC
PEC hydrogen production via:
•
•
•
•
single photoanode
single photocatode
multiple absorber (Tandem)
suspensions of photocatalyst particles
Figure 1 Schematic band diagram showing the phenomena of photon absorption, band bending, charge
separation, as well as hydrogen and oxygen evolution on semiconductor photoanode and photocatode
surfaces. The external circuit could also be replace by a redox mediator to shuttle charges between the two
photoelectrodes.
Valeria Mozzetti Page 4/15
11.11.2013
UFSP LightChEC
Key requirements for semiconducting materials
•
•
•
•
•
Suitable band gap for light absorption
Proper band gap edge alignment (for redox reactions)
Long term stability in aqueous environment (in light and dark)
Cost
Material availability
Band gap
•
•
•
•
At least 1.23 eV
Large enough to split water (more than 1.23 eV calculating losses)
Small as possible to absorb the greatest portion of solar spectrum (high band gap = UV
not useful in terrestrial applications)
Possible solution: small band gap materials in parallel
Energy levels of electrons and holes
•
•
•
Higher electrochemical redox potential for HER and OER
Conduction band < 0.0 eV vs. RHE
Valence band > 1.23 eV vs. RHE
Catalysis
•
To reduce the overpotential and so the total voltage required
Charge transport
•
•
In absorber material
At electrode/electrolyte interface
Valeria Mozzetti Page 5/15
11.11.2013
UFSP LightChEC
PEC system efficiency's calculation
SOLAR TO HYDROGEN EFFICIENCY: STH EFFICIENCY*
Chemical Energy (H2)
Solar Energy Input
* OER must occur (solar energy and water must be the only inputs, no sacrifical reagents, no
half reactions)
STH Efficiency depends on:
•
•
•
•
•
Total solar irradiance
Entropic losses due to blackbody radiation and recombination
Kinetic overpotential for the two half reactions
Non-ideal band edge alignment
Series resistances from the solution or wiring
Taken into account here
Not taken into account here
Thermodynamic limits = upper bound for STH Efficiency
5
6
•
•
Single PEC 29-31% 5
Tandem PEC 40-41% 6
•
•
With multiple excition generation
With solar concentration
STH
R. T. Ross and T. L. Hsiao, J. Appl. Phys., 1977, 48, 4783–4785.
M. C. Hanna and A. J. Nozik, J. Appl. Phys., 2006, 100, 074510-1–074510-8.
Valeria Mozzetti Page 6/15
11.11.2013
UFSP LightChEC
Calculation of STH: STH = 1-2
1)
•
Maximum photocurrent under illumination for a given band gap
•
•
Kinetic overpotentials losses
Energy and entropic losses from material defects and nonradiative recombination
2)
--------------------------------------------------------------------------------------------------------------------------→ current-voltage relationship for each band gap → STH efficiency*
*7
Maximum photocurrents
calculated by summing the absorbable photons over the solar spectrum for materials of varying
band gaps assuming all photons with energy greater than the band gap are absorbed.
Open circuit voltages
were used to estimate the usable photovoltage
were calculated for each band gap taking into account entropic losses modeled after single
crystal silicon according to Ross 8
Eqn (1) is one defnition for STH efficiency, using the product of voltage and short-circuit
current to calculate the chemical power output of the PEC water splitting cell under standardstate conditions relative to the power input to the cell by 1 sun AM 1.5 G illumination, assuming
100% Faradaic conversion of water to H2 and O2.
7
8
R. T. Ross, J. Chem. Phys., 1967, 46, 4590–4593.
Valeria Mozzetti Page 7/15
11.11.2013
UFSP LightChEC
Kinetic overpotentials
•
•
•
for all possible currents
calculated assuming Butler-Volmer kinetics
for H2 and O2 evolution on platinum and ruthenium oxide, respectively.
Shunt losses
•
neglected (device dependant)
Valeria Mozzetti Page 8/15
11.11.2013
UFSP LightChEC
STH calculation's results for different PEC configurations
Configuaration
Single
photoabsorber
Dual stacked
photoabsorber
Dual side by side
photoabsorber
Info
Maximum
STH*
-
The top photoabsorber is assumed to be placed
above the bottom photoabsorber, thus only
photons with energy less than the band gap of
the former are transmitted to the latter.
The two electrodes are assumed to be placed
next to each other and can each access the full
solar spectrum.
11.2%
Band Gap
for Max
STH
2.26 eV
22.8%
1.23 eV and
1.84 eV
15.5%
1.59
Table 1 STH Efficiency for different PEC configurations
* large losses due to reaction overpotential → need for better catalysts
Maximum theoretical STH graphs by different PEC configurations
Single
Dual stacked
Figure 2 Maximum theoretical solar-to-hydrogen efficiency
Dual side by side
Valeria Mozzetti Page 9/15
11.11.2013
UFSP LightChEC
Demonstrated STH
Panel based PEC configurations
•
•
•
PEC system alone
o Single absorber: disadvantage need wide band gap (ultraviolet > 2.1) for STH>
5% (Figure 2), additionally often materials with band edge potentials for both
half reactions have a valence band edge significantly more positive than the
water oxidation potential (SrTiO3 and KTaO4 oxides) 9
o Dual PEC (2 coupled low band gap) 10: STH > 8% but stability is an issue
PEC junction + external phtovoltaic (PV) device
o until 12.4% STH but stability is an issue 11
PV + electrolyzer
→Overall 15% STH efficiency is achievable but availability and costs remain an issue
Particle based PEC configurations
→These configurations have much lower efficiencies and STH were not calculated an
alternative measure of efficiency is used (EQY*) which does not take into consideration the
voltage of a particular reaction or product: Overall energy efficiency is not accounted for.
•
•
•
Single particle / single photon water splitting
o highest EQY with wider band gap systems (but these are UV)
o EQY of 2.5% at 420 nm with Rh2-yCryO3-loaded(Ga1-xZnx)(N1-xOx) 12
2 particles / 2 photons water splitting (Z-scheme): need twice as many photons but
higher voltage and more material choiches (in paper many examples p. 6)
half reaction water splitting with sacrifical reagent/non water photocatalyst (may be
useful for photocatalytic decomposition of organic pollutants).
J. G. Mavroides, J. A. Kafalas and D. F. Kolesar, Appl. Phys. Lett., 1976, 28, 241–243. and A. B.
Ellis, S. W. Kaiser and M. S. Wrighton, J. Phys. Chem., 1976, 80, 1325–1328.
9
10
11
R. C. Kainthla, B. Zelenay and J. O. Bockris, J. Electrochem.Soc., 1987, 134, 841–845.
O. Khaselev and J. A. Turner, Science, 1998, 280, 425–427.
K. Maeda, K. Teramura, L. Daling, T. Takata, N. Saito, Y. Inoue and K. Domen, Nature, 2006,
440, 295.
12
Valeria Mozzetti Page 10/15
11.11.2013
UFSP LightChEC
EQY = External Quantum Yeld
where n is the number of electrons transferred per product
molecule.
Cost calculation for 4 hypothetical reactor types
Cost was calculated for a working plant with a net 1 Tonne per day hydrogen output including
all costs (material and operating).
Aqueous reactor beds with
suspended particles
Multilayer absorber planar
arrays in aqueous electrolyte
1
Single bed particle suspension
1.60$
3
Fixed panel array
10.40$
2
4
Dual bed particle suspension
Tracking concentrator array
3.20$
4.00$
Valeria Mozzetti Page 11/15
11.11.2013
UFSP LightChEC
Figure 3 Four reactor types
Valeria Mozzetti Page 12/15
11.11.2013
UFSP LightChEC
Sensitivity analysis results for the different hypothetical reactors
Figure 4 Effect of efficiency, particle or panel cost, and component lifetime on the cost of hydrogen from each
reactor design. Each calculation represents the variation of a single parameter from the base case to a higher
and lower value as indicated on the left axis.
Valeria Mozzetti Page 13/15
11.11.2013
UFSP LightChEC
Aqueous reactor beds with suspended particles
Type 1 and 2
•
•
•
Type 1
•
Type 2
•
Cheaper but uncertain technological feasibility
Efficiency has strong impact on costs
Technical feasibility?
o particles with photovoltage for H2O splitting & use of a wide portion of the solar
spectrum needed
o compression of H2 and O2 gases needed
Separation of H2 and O2 gases needed most probably technically feasible but
nevertheless a huge safety concern
Technical feasibility ? of:
o membrane bridges
o circulation system
o effective use of redox mediator
o development of separate particles for O2 and H2 evolution
Type 3 and 4
•
Type 4
•
•
•
All parameters have an influence on costs:
o efficiency
o cell cost
o durability
More cost effectiveness from solar concentration (1:10)
Important to research into the effects of increased light intensity on photoabsorber
materials
Efficiency is a key parameter:
Valeria Mozzetti Page 14/15
11.11.2013
UFSP LightChEC
o
with a theoretical efficiency of 25% the costs will drop to 2.90$ (a 22%
efficiency is achievable in a tandem structure (Table 1)
--------------------------------------------------------------------------------------------------------------------------→Overall particles beds reactors cheaper than panel based but uncertainty in their
technical feasibility
→Overall costs of panel based system can be reduced by increasing efficiency and by
solar concentration.
---------------------------------------------------------------------------------------------------------------------------
Valeria Mozzetti Page 15/15
11.11.2013

Download Report