SLIDE 1
Nano-wire Photoelectrochemical cell
For water splitting Yude Su
SID: 24045922 Peidong Yang’s group
Outline
- 1. Motivation of PEC
- 2. Mechanism of PEC
- 3. Some examples
- 4. Future direction
Nano-wire Photoelectrochemical cell For water splitting Yude Su - - PowerPoint PPT Presentation
Nano-wire Photoelectrochemical cell For water splitting Yude Su - - PowerPoint PPT Presentation
Nano-wire Photoelectrochemical cell For water splitting Yude Su SID: 24045922 Peidong Yangs group Outline 1. Motivation of PEC 2. Mechanism of PEC 3. Some examples 4. Future direction Motivation Renewable Energy replace Fossil Fuel
SLIDE 2
SLIDE 3
Motivation
- Renewable Energy replace Fossil Fuel
264 GW (2008) 70 GWe (2011) Car running on Biomass (WW II) Car running on Solar (2012)
SLIDE 4
Photochemical cell Photovoltaic cell
H2O Photocatalyst H2 and O2
Motivation
η1>20%
Electricity
η2>80% η3<<1%
SLIDE 5
Overall picture of a PEC cell PEC
PV Device + Electrochemical Reaction
- Chem. Rev. 1992, 92, 411-433
SLIDE 6
6
qM qS q ECB EVB EFM EFS before contact qM qS q ECB EVB EFM EFS after contact qVi qVi qB W
A i
qN V W 2
+ + + +
- - -
Schottky contact: M/pS with M < S
SLIDE 7
7
qM qS q ECB EVB EFM EFS before contact qM qS q ECB EVB EFM EFS after contact + + + +
- -
Ohmic contact: M/nS with M > S
SLIDE 8
8
light emission from semiconductors
- - - - - -
+ + + + + + CB VB excitation
- - -
- -
+ + + + + + + + +
- -
- +
- transient emission
excitation off
- - - - - -
+ + + + + + + + + + + +
- - -
- - -
+
- steady emission
after time
SLIDE 9
Electrode Kinetics
Butler-Volmer Equation Current-Overpotential link
/ (1 ) / 1
[ ] ( 0) ( 0)
nF RT nF RT
J J e e J k FC x C x
η: over-potential, defined by E-Eeq J0: exchange current density K0: the standard rate constant, defined by the activation energy when kO=kR α: the transfer coefficient
SLIDE 10
Cathode Counter Electrode O R R O Mass transport E1 E2 EEq EC
Equivalent Circuit for a PEC cathode
V E2 Butler-Volmer Term Behave as a Series Resistance in the PEC Equivalent Circuit!
( )/ ( )/2 / ( 1) /
( 1) ( 1) ( ) / [ ]
q V KT q V KT s RG sh L nF RT nF RT
I I e I e V R I I e e
SLIDE 11
How to define the efficiency of a PEC cell?
- 0.2
- 0.1
0.1 0.2 0.3 0.4 0.5
- 20
- 15
- 10
- 5
5 Voltage(V vs Solution) Current(mA) Roughness factor=100 Red: Methyl Viologen Purple: H2 evolution 100%Pt coating Blue: H2 evolution 50%Pt coating Green: H2 evolution 10%Pt coating Cyan-blue: H2 evolution 1%Pt coating Yellow: H2 evolution 0.1%Pt coating Brown: H2 evolution 0.01%Pt coating
VOC: Open circuit voltage ISC: Short circuit current FF: Fill factor=
/ *
Max OC SC
P V I
/
Max input
P P
SLIDE 12
Why to choose Nanowire as the PEC electrode?
- 1. Larger surface area, more catalytic sites
(Surface chemistry)
- Y. J. Hwang, et. al., Nano Lett., 2009, 9, 410
- 2. Strong scattering increases light path
(Optical absorption)
- M. D. Kelzenberg, et. al., Nature Mater., 2010, 9, 239
- 3. Orthogonalize absorption and charge collection
(Charge transport)
- J. M. Foley, et. al., Energy Environ. Sci., 2012, 5, 5203
Resultant improvement of photoelectrode
- K. Sivula, et. al., ChenSusChem, 2011, 4, 432
SLIDE 13
Nanowire for PEC cathode
Si
- S. W. Boettcher, et. al., Science, 2010, 327, 185
- M. D. Kelzenberg, et. al., Nature Mater., 2010, 9, 239
GaP
- J. Sun, et. al., J. Am. Chem. Soc., 2011, 133, 19306
Nanowire for PEC anode
TiO2
- B. Liu, et. al., J. Am. Chem. Soc., 2009, 131, 3985
- I. S. Cho, et. al., Nano Lett., 2011, 11, 4978
- M. Xu, et. al., Nano Lett., 2012, 12, 1503
ZnO
- X. Yang, et. al., Nano Lett., 2009, 9, 2331
- H. M. Chen, et. al., Angew. Chem. Int. Ed, 2010, 49, 5966
SLIDE 14
Cathode and anode integration
Z-scheme
Energy Diagram Current matching
SLIDE 15
Future direction
- 1. Develop earth-abundant semiconductor material
- 2. Improve the efficiency of photo-anode
- 3. Further increase the light absorption
- 4. Decrease the synthesis price