14/7/2016 1 Development of an artificial photosynthesis device: from nano to macro - scale. The BiVO 4 example. Simelys Hernández ,* ,1 Guido Saracco, 1,2 Nunzio Russo. 1 * E - mail: [email protected]1 DISAT, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy) 2 Center for Sustainable Futures, CSF@POLITO, Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino (Italy)
30
Embed
Development of an artificial photosynthesis device: from ... · C.so Trento 21, 10129 Torino (Italy) 2H 2O O 2 + “2H 2 ... Diana Hidalgo, Carminna Ottone, Adriano Sacco, Angelica
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
14/7/2016 1
Development of an artificial photosynthesis device: from nano to macro-scale.
1 DISAT, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy)
2 Center for Sustainable Futures, CSF@POLITO, Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino (Italy)
2H2O O2 + “2H2”
Solar EnergyLight reaction
“2H2” + CO2 (CH2O)Organic
molecules
Dark reacion
Two basic reactions of photosynthesis
UV
H++
Solar Fuels via Artificial Photosynthesis The “mimicking nature” approach:separation of the functions of light
collection and conversion from catalysis (e.g. Transition metal oxides: IrO2, Co3O4, RuO2, Mn2O3,… or Ru/ Co-
based molecular catalyst)
Many semiconductor materials (e.g.oxides, oxynitrides, oxysulfides,
oxyfluorides, and oxyfluoronitride) have been studyed to meet specific
requirements.
The direct water photo-electrolysis:
Why BiVO4 is interesting for water splitting ?
+ Good solar light absorption (band gap = 2.4 eV)
+ Conduction and Valence band edges straddling the red-ox potentials of water.
+ High chemical stability around neutral pHs
+ Earth abundant components
- Poor e- transport and limited superficial transfer properties that can lead to recombination of photo-exited charges.
Strategies to increase photo-activity of BiVO4
Study of Reaction kinetics of Water Splitting Catalysts
Evaluation of photoelectrodes
performance
9 cm2200 cm2
2500 cm2
Implementation of PEM Photo-electrolyzerfrom lab- to pilot-scale
1.6 m2
MJ-PV cell
H2 evolving PEC lab-reactor
Our work towards the Artificial Leaf…
Outline
1 cm2
Development of a system and a mathematical model to measure the actual activity of Water Oxidation Catalysts and Photo-catalysts (semiconductors) in powder form, for the water splitting reaction
Solar simulated light sourceBubbling Reactor
Clark-sensor & PH-meter
Mass Flow Controllers
Our research
Hernández S. et .al., Chem. Eng. J. 2014, 238, 17-267
Study of the kinetics for water oxidation half reactionof powder photo-catalysts
Vg
VLRO2
a)
b)
pO2
QAr+ ΦO2
pO2,analyzer
c)
d)
QAr
O2 CO2
Ag+1 Ag0
2H2O
BiVO4 Ar Bubble
hvh+
e-
4h+ + 2H2O → O2 +4H+ + 4e-
4Ag+1+ 4e- → 4Ag0
Water Oxidation
Silver Nitrate Reduction
8
RORO,O
LOR V)ε1(VH
akV)ε1(22
2
2−+⋅
−⋅=− RC
pC b
RTQV
Hak
RT εV ,O
RO,O
L,O
R2
2
22 bbb pC
pp⋅−⋅
−⋅−=
−⋅=
RTRTQ
RT V 222 O,OO
g
ppp b
)()(22 O,O ttptp analyzer ∆−=
Mathematical Model: O2 balance into the Bubbling reactor
- In the liquid phase:
- In the gaseous bubble phase:
- In the gas phase in the headspace above liquid
- In the gas phase at the analyzer:
Oxygen is formed on the catalyst surface
Actual rate of O2 evolution over time: RO2Hernández S. et .al., Chem. Eng. J. 2014, 238, 17-26
Strategies to increase photo-activity of BiVO4
BiVO4 in Powder form
14/7/2016 11
1μm
BiVO4 morphology control by Hydrothermal Synthesis
Thalluri S-M, et. al. Chem. Eng. J. 2014, 245, 124-132.
pH of the synthesis
media
Precursors: Bi(NO3)3.5H2O; NH4VO3 and (NH4)2CO3
0
2
4 - 6
8 - 10
14/7/2016 12
1μm
Thalluri M. et . al., Chem. Eng. J. 2014, 245, 124-132
BiVO4 morphology control by hydrothermal synthesis
Optimization of calcination temperature of BiVO4 powders made at pH 0
Metal-doped BiVO4 powders by hydrothermal synthesis
Thalluri, S. M.; Hernández, S.; et. al. Appl. Catal. B: Environm. 2016, 180, 630-636.
We’ve improved the state-of-the-art photo-activity
(RO2o ~ 200 to 400 μmol/gcat.h) of
Mo & W-doped BiVO4
Development of a Photo-electrochemical Device for water splitting
BiVO4 electrodes from powders: By doctor-blade
PEC tests in Na2SO4 (0,1M) pH=6.5
Max. photo-current density at 1 sun & 1.23VRHE = 0.04
mA/cm2
Preparation of electrodes from BiVO4 powders
Max. photo-current density at 1 sun & 1.23VRHE = 0.6 mA/cm2
Dip-coating:
PEC tests in Na2SO4 (0,1M) pH=6.5
Preparation of BiVO4 electrodes by in-situ synthesis
S. Hernández, et.al., Applied Catalysis A: General, 2015, 504, 266-271.
Modeling of transport properties
S. Hernández, et. al., Applied Catalysis A: General, 2015, 504, 266-271.
Limitation of use dip-coating technique with intermediate calcination steps: Decrease of activity after a certain thickness (~160nm)
trapping of charges in the surface states
charge transfer between the electrolyte and the surface states
Rct: direct charge transfer
at the semiconductor/
electrolyteinterface
BV-3: larger impedance than the other two films -> reduced quantity of the deposited material.
BV-10 and BV-15: an additional process with time constant at very large frequencies (around 5 kHz) occurs, suggesting that a charge transfer mechanism occur via surface states -> due to an imperfect interconnection between adjacent layers in the thicker films.
Rct: 540 Ω
Rct + Rtrap = 580 Ω
Procedure 1 Precursors: Bi(NO3)3 ∙5H2O - NH4VO3
C1=50 mmol L-1 (in HNO3 1 M)Calcination: T1=773 K per 2 h.2 steps spin-coating on FTO:
500 rpm-10 s/ 2000 rpm- 15 s
Procedure 3Precursors: Bi(NO3)3 ∙5H2O -
VO(AcAc)2C3 =33 mmol L-1
(in Acetic Acid & Acetilacetone)Calcination: T3=673 K per 2 h.
1 step spin-coating on FTO:500 rpm-10 s
Procedure 2Precursors: Bi(NO3)3 ∙5H2O -
NH4VO3C2=200 mmol L-1 (in HNO3 2 M)Calcination: T2=673 K per 2 h.2 steps spin-coating on FTO:
500 rpm-10 s/ 2000 rpm- 15 s
Higher stability of the solution
Spin-coating
1.23V vs. RHE under solar light illumination (100
mW/cm2) in Na-phosphate Buffer (pH=7), active area:
4cm2
(Used for dip-coating)
Preparation of BiVO4 electrodes by in-situ synthesis