Photo-electrochemical Production
of Hydrogen with Solar Energy
C.K Ong*, A. Hankin,
G.H Kelsall
Department of Chemical Engineering
Imperial College London
[email protected]
Outline
1. Motivation of H2 production using solar energy
2. Background to photo-electrochemical water splitting
3. Photo-electrochemical reactor operation
4. Process intensification
5. Summary and future work
The Grand Challenge
Energy supply < Energy demand
Renewables
Solar Energy
Energy storage
Hydrogen
Climate change
H2 + CO2
Electrochemical reduction of
CO2
Ectrolysis
of H2O
e- + H2O + CO2
Chemical
reduction
of CO2
Other
renewable
electricity
Sunlight + H2O + CO2
PV
Photoelectrolysis
of H2O
CO2 capture
Carbon-based fuels
Fuel utilisation
Photoelectrochemical reduction of
CO2
H2 as an important ingredient in CO2 cycle
CO2
Recycle
Photoelectrochemical H2 Production using Solar
Energy
Semiconductor + hν
Semiconductor (h+ + e-)
Econduction
hn
Eband gap
he+Evalence
Photoanode
Membrane
Cathode
Photoelectrochemical H2 Production using Solar
Energy
Semiconductor (h+ + e-)
Semiconductor + hν
2H2O + 4h+
O2 + 4H+
2H2
4H+ + 4eO2
e-
O2
Econduction
O2
hn
O2
Eband gap
O2 O2
O2
H2
H2 H2
H2 H2
H2 H2
H2 H2 H2
H2
h+
Evalence
Photoanode
Membrane
Cathode
Photoelectrochemical H2 Production using Solar
Energy
Semiconductor (h+ + e-)
Semiconductor + hν
2H2O + 4h+
O2 + 4H+
2H2
4H+ + 4eO2
e-
O2
Econduction
O2 O2
hn
O 2 O2
O2 O2 O2
O2 O 2
Eband gap
H2
H2 H2
e-
H2 H2
H2 H2
H2 H2 H2
H2 H2
h+
Evalence
Photoanode
Membrane
Cathode
Photo-anode material
Cheap /
abundent
IDEAL
Efficient
Stable
Photo-anode material : Fe2O3
Advantages
• Absorbs in the visible light spectrum
• Cheap and abundent
• Stable under oxygen evolution reaction
Disadvantages:
• Required external bias to drive water
splitting process
CV of Fe2O3 in NaOH illuminated under white Xe
lamp
0.80
Current Density A m-2
0.70
Light
0.60
0.50
0.40
0.30
0.20
0.10

4OH   4hVB

 O2  2 H 2O
EO2
H 2O
vs. HgO Hg  0.303 V
0.00
Dark
-0.10
-0.4 -0.3 -0.2 -0.1
0
0.1 0.2 0.3 0.4 0.5
Electrode Potential (vs HgO|Hg) / V
0.6
0.7
0.8
Process Intensification – Increase Light Intensity
• Illuminated Area = 16 mm x 25 mm
• Light intensity adjusted with current
supplied to solar simulator and
distance
between
Fresnel lens
reactor
and
Photoelectrochemical H2 Production Reactor
Solar Simulator
Mirror
Reactor Fresnel
Lens
Process Intensification – Increase Light Intensity
Predicted Current Density / A m-2
5
4.5
4
Model prediction
3.5
Experimental data
3
2.5
2
1.5
Fe2O3 | 0.1 M NaOH
0.4 V vs. HgO/Hg
1
0.5
0
0
1000
2000
3000
Light Intensity / W m-2
4000
Effect of temperature on dark CV
1.2
Current density / A m-2
1
0.8
25.5°C
0.6
29.1°C
33.6°C
0.4
39°C
46°C
0.2
0
-0.2
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Electrode potential (vs. HgO|Hg) / V
Effect of temperature on light CV
1.8
1.6
1.4
Current density / A m-2
1.2
1
0.8
0.6
0.4
0.2
0
25.5°C
29.1°C
33.6°C
39°C
46°C
-0.2
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Electrode potential (vs. HgO|Hg) / V
Effect of temperature on PEC water splitting
0.9
-3.6
-4
0.85
0.8
-4.2
0.75
-4.4
0.7
-4.6
-4.8
Ln (jdark) = -3569.6 T-1 + 7.2776
0.65
-5
0.6
3.10E-03 3.15E-03 3.20E-03 3.25E-03 3.30E-03 3.35E-03 3.40E-03
T-1 / K-1
Ln (current density / A m-2)
Ln (current density / A m-2)
-3.8
Ln (jlight) = 856.16 T-1 – 2.0164
Summary
• PEC water splitting has future potential to solve energy problem.
• Increasing light intensity increases photo-current generated.
• Increasing temperature would increase charge recombination.
• Future work on materials development is required.
• More development in reactor design, and reactor scale-up is
required
Acknowledgement
Prof. Geoff Kelsall
Dr. Klaus Hellgardt
Dr. Steve Dennison
Dr. Anna Hankin
Thank you for your attention
Questions ?

HLN-Kolloquium WS 2016/17