1. Setting Targets for
Photoelectrochemical
Cells
Priyanka deSouza, Balasubramaniam R Kavaipatti, Rangan Banerjee
Department of Energy Science and Engineering
IIT Bombay
ICAER, IIT Bombay - 11/12/2013
Acknowledgements: IIT Bombay Seed Grant 12IRCCGS014
1

2. Setting Targets
Metric Y
Energy
available
Energy
output
Energy Conversion System
Energy
input
Metric X
Energy Conversion System  PEC system
Metric X  Stability or longevity
Metric Y  Efficiency
Constraint  embodied energy of PEC
2

3. Taking a leaf out of…
Melvin Calvin, 1982: It is time to
build an actual artificial
photosynthetic system, to learn
what works and what doesn’t
work, and thereby set the stage for
making it work better
3

4. Mimicking Nature
Single Semiconductor Liquid Junction
Two Semiconductor Liquid Junctions
A. Currao, Chimia 61
(2007) 815–819
What is the current status of this field?
4

5. Scenarios
I
III
II
CB
CB
H2/H+
CB
CB
VB
VB
H2O/O2
VB
VB
McKone, J. R., E. L. Warren, et al. (2011). Energy & Environmental Science 4(9): 3573-3583.
Cao, B. B., J. J. Chen, et al. (2009). Journal of Materials Chemistry 19(16): 2323-2327
Boettcher, S. W., E. L. Warren, et al. (2011). Journal of the American Chemical Society 133(5): 1216-1219
Spurgeon, J. M., M. G. Walter, et al. (2011). Energy & Environmental Science 4(5): 1772-1780
5

6. Viability of PEC cells?
6

7. Embedded energy calculations
Energy MJ/sq m
Si wire growth
320.07
Chamber (PVC)
252
Cover (Glass)
114.12
environmental control
200
WO3 wire array growth
166.25
Membrane (Nafion)
138.93
Membrane fabrication
82.81
Pumping
31.3
Catalyst
14.99
Other chemicals
14.52
Cleaning
9.63
Photocathode (Si)
5.15
Intervening layer
(PEDOT:PSS)
4.7
Photoanode (WO3)
0.12
Total
1354.59
Thermodynamic
Models for heating
and vacuum pumping
Econinvent
Ancillary processes from
the PV industry
Source:
http://lcacenter.org/lcaxii/dra
ft-presentations/654.pdf
7

8. Photoelectrodes – embedded
energy
Photocathodes
InP
Cu2O
Photoanodes
Fe2O3
TiO2
Calculation of embedded energy of the electrodes
1)Fabrication Energy
2)Material Energy
8

9. Photocathode - InP
Material
Embedded Energy
InP
(MJ/m2 )
171
2nm TiO2
0.4
Source
Embedded Energy
of ITO[16], another
In compound used
as a proxy as that of
InP is not known
The fabrication
energy of a 2.4 µm
photoanode is
calculated in the
previous section.
This value is scaled.
Christopher Emmott et al, 97, 14-21(2012)
9

10. Photocathode – Cuprite
Material
embedded
Energy (MJ/m2 )
Source
Lactic Acid
1
Data for poly-lactic
acid used [17]
Copper
sulphate
1.9
Data for Cu used [18]
1 mm
Stainless
Steel
substrate
2 nm TiO2
256
Stainless Steel is
32MJ/kg[19]
0.4
Scaled value used
J. Dflou et al, MRS Bulletin, 37, (2012)
T.E. Norgate and W.j. Rankin, International conference on Minerals Processing
10
and Extractive Metallurgy, 133-138 (2012)
http://web.mit.edu/2.813/www/readings/ICE.pdf, accessed 17/09/2103

11. Photoanode – Haematite
Material Embedded
Source
Energy
(MJ/m2)
Fe(CO)5
900
Data for Fe used [19]
TEOS
9923
Data for Metallurgical
grade Si used[20]
1 mm
Glass
substrate
41.3
The embedded energy of
Glass is 15.9 MJ/kg[19]
http://web.mit.edu/2.813/www/readings/ICE.pdf, accessed 17/09/2103
I. Nawaz and G.N. Tiwari, Energy Policy, 34, 3144-3152 (2006
11

12. Photoanode - Anatase
Material embedded
Energy
(MJ/m2)
Ti
3.4
Gases
0
1 mm Glass
substrate
41.3
Source
[19]
Gas pressure is
12mtorr. Vol. of a
typical chamber is
1.5 x 105 cm3 [21].
Thus moles of gas
present
is 10−5 which is very
small
The embedded
energy of Glass is
15.9 MJ/kg[19]
http://web.mit.edu/2.813/www/readings/ICE.pdf, accessed
17/09/2103
Spuutering Systems Manual- Physics at Oregon State University
12

13. Embedded energy - Summary
Electrode Fabrication Energy Material Energy Total Energy
(MJ/m2)
(MJ/m2)
(MJ/m2)
p-Si
InP
Cu2O
334.2
35421
906
5.15
172
259
339.35
35593
1165
WO3
Fe2O3
166.25
138
0.12
10864
166.37
11002
TiO2
518
45
563
Source for p-Si data: http://lcacenter.org/lcaxii/draftpresentations/654.pdf
13

14. Applied bias
• Contour lines for the lifetime primary energy requirement of hydrogen equaling 120 MJ/kg
for different photoelectrodes under bias
• The region above each contour line is the energy feasible region
Photoelectrode Efficiency
Lifetime
(days)
p-Si nanowires
0.2%
0.92
InP nanowires
14%
1
Cu2 O
0.72%
7
WO3 nanowires
0.4%
0.25
Fe2 O3
1.84%
182.5
TiO2
6.8%
365
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15. Sacrificial reagent
embedded energy of photocathode
+ sacrificial reagent energy = 120
hydrogen production x stability
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16. Photoanode-photocathode
combinations
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17. Conclusions
• Methodology to identify the feasible range of
efficiencies and lifetimes a given PEC cell must have to
be energy feasible has been developed
• Range of efficiencies and lifetimes possible for the cell
to be energy feasible
• Operation with bias seems to be infeasible
• InP photocathode use only in combination with WO3
• Improved efficiencies needed
• Longer stability times needed
• Cu2O with a sacrificial reagent offers much better range
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18. PEC cells - Current status
Target
dates
solar to
hydrogen
efficiency
durability
(hours)
project
hydrogen
cost $/kg
2005
2010
2015
7.5
9
14
1000
10000
20000
360
22
5
PEC system with GIP and Pt electrodes η = 12.4%, lifetime = 20 hours.
Methodology to set targets for PEC cells?
18