The Solar Hydrogen Project
Steve Dennison and Bojan Tamburic
Dr Klaus Hellgardt
Prof Geoff Kelsall
Prof Geoff Maitland
Dept of Chemical Engineering,
Imperial College, LONDON SW7 2AZ
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Structure of presentation
• Background
• Biohydrogen (Bojan Tamburic)
• Photoelectrochemical Hydrogen (Steve
Dennison)
• Questions
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Solar Energy Available
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Why Hydrogen?
• It is a good route to storage of solar
energy
• Key feedstock in petroleum refining
• Important feedstock in the chemical
industry (NH3, methanol, etc.)
• A fuel for the future (in fuel cells)
- towards the hydrogen economy?
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Solar Hydrogen Project
• Multi-department/discipline project at
Imperial (Chemistry; Biological Sciences,
Chemical Engineering, Earth Sciences).
• £4.5M, 5-year programme investigating
and developing systems for the generation
of sustainable hydrogen using solar
energy as the major energy input.
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Hydrogen Production Today
• Steam reformation of methane (+ other
light hydrocarbons)
CH4  2H2O  4H2  CO2
~5 kg carbon dioxide is produced per kg H2
which is not sustainable!
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Routes to Hydrogen Production
Nuclear Energy
Non-Fossil Energy (Solar, Water, Wind)
Heat
Photoelectrolysis
Mechanical Energy
Electricity
Fossil Energy
Biomass
Biophotolysis
Fermentation
Thermolysis
Electrolysis
Chemical Conversion
CH 4  2 H 2O  4 H 2  CO2
Hydrogen
Carbon dioxide
adapted from J.A.Turner, Science 285, 687(1999)
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Clean (CO2-free) Hydrogen
• Electrolysis (?)
• Photoelectrolysis
• Biophotolysis
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Solar Hydrogen Project
Biohydrogen Production
Bojan Tamburic
Prof. Geoffrey Maitland
Dr. Klaus Hellgardt
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Introduction
1) Hydrogen production and
utilisation
4)
– Hydrogen as a fuel
– Clean and green H2 production
–
–
–
–
–
2) Green algal routes to solar
hydrogen
– Photosynthetic H2 production
– Two stage growth and
hydrogen production procedure
3) Main challenges facing
biohydrogen production
Early experimental results
and their significance
5)
Biohydrogen lab
Algal growth
Batch reactor
Sartorius reactor (1)
Sartorius reactor (2)
Future outlook
– Producing more H2
– Automating and scaling-up
– Growing algal biomass
– Inducing metabolic change
– Measuring and optimising H2
production
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Content
• Hydrogen production and utilisation
• Green algal routes to solar hydrogen
• Main challenges facing biohydrogen
production
• Early experimental results and their
significance
• Future outlook
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Hydrogen as a fuel
• Environmental concerns over:
– CO2 emissions
– Vehicle exhaust gasses (SOx, NOx)
• Sustainability concerns:
– Peak oil
– Global warming
• Hydrogen – transport fuel of the future
• Proton exchange membrane (PEM) fuel
cells use H2 to drive an electrochemical
engine; the only product is water
• Barriers that must be overcome:
– Compression of H2
– Development of Hydrogen infrastructure
– Sustainable H2 production
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Clean and green H2 production
• Bulk Hydrogen is typically produced
by the steam reforming of Methane,
followed by the gas-shift reaction:
– CH4 + H2O → CO + 3H2
– CO + H2O → CO2 + H2
• Negates many of the benefits of PEM
fuel cells
• Renewable and sustainable H2
production required
• Can be achieved by renewable
electricity generation, followed by
water electrolysis, but:
– Low efficiency
– High costs
– Can use electricity directly
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
“Photosynthetic H2
production by green algae
may hold the promise of
generating renewable fuel
from nature’s most plentiful
resources – sunlight and
water” – Melis et al. (2007)
Content
• Hydrogen production and utilisation
• Green algal routes to solar hydrogen
• Main challenges facing biohydrogen
production
• Early experimental results and their
significance
• Future outlook
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Photosynthetic H2 production
2 H 2O  2 H 2  O2
Ferredoxin
Hallenbeck & Benemann (2002)
Bojan Tamburic & Steve Dennison
• Discovered by Gaffron in 1942
• Direct H2 photoproduction
– 2H2O → 2H2 + O2
• Solar energy absorbed by Photosystem II
and used to split water
• Electrons transported by Ferredoxin
• H2 production governed by the
Hydrogenase enzyme – a natural
catalyst
• Anaerobic photosynthesis required
• Process provides ATP – energy source
• No toxic or polluting bi-products
• Potential for value-added products
derived from algal biomass
Solar Hydrogen Project
Two-stage growth and hydrogen
production procedure
• Hydrogenase enzyme deactivated in
the presence of Oxygen – limit on
volume and duration of H2 production
• Two-stage process developed by
Melis et al. (2000)
– Grow algae in oxygen-rich conditions
– Deprive algae of sulphur
– Photosystem II protons cannot
regenerate their genetic structure
– Algae use up remaining oxygen by
respiration and enter anaerobic state
– Algae produce H2 and ATP
– H2 production slows after about 5
days as algae begin to die
Melis et al. (2002)
Bojan Tamburic & Steve Dennison
• Use the model green algae
C.reinhardtii
Solar Hydrogen Project
Content
• Hydrogen production and utilisation
• Green algal routes to solar hydrogen
• Main challenges facing biohydrogen
production
• Early experimental results and their
significance
• Future outlook
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Growing algal biomass
• Micro-algal cultivation units from Aqua Medic
• TAP growth medium, sources of light and agitation
• Store algal cultures after they are grown in Biology
– Several wild type strains of C.reinhardtii
– Dum24 & other mutants
• Algal growth can be measured by
– Counting number of cells (microscopy)
– Chlorophyll content
– Optical density (OD)
• Can we grow algae:
– Quickly and efficiently?
– To the OD required for H2 production?
– Without contamination?
• Can the growth process be scaled up?
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Inducing metabolic change
• Hydrogen production is induced by sulphur deprivation
• Centrifugation
– Typically used in Biology
– Culture spun-down until pellet of algal cells forms
– Procedure time consuming and results in loss of cells
• Dilution
– TAP-S inoculated (~10% v/v) with growing culture sample
– Remaining sulphur used up as algae grow; anaerobic conditions
established
– Inefficient to ‘re-grow’ biomass
• Ultrafiltration
– Cross-flow system with backwash of algal cake
– Similar challenges as with centrifugation, but easier to scale-up
• Nutrient control
– Investigate algal growth kinetics
– Algae should run out of sulphur as they reach optimal OD
– Concerns over biological variations
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Measuring and optimising H2
production
• Measuring H2 production
Mass
spectrometer
Injection
system
4-way valve
– Water displacement
– Injection mass
spectrometry
– Membrane inlet mass
spectrometry (MIMS)
Gaseous H2
• Optimising H2 production
H2 permeable
membrane
Helium tank
Mass flow
controler
Sartorius
photobioreactor
Bojan Tamburic & Steve Dennison
Water displacement
system
Solar Hydrogen Project
– Grow algae to sufficient
OD
– Optimise system
parameters
– Determine suitable
nutrient mix
Content
• Hydrogen production and utilisation
• Green algal routes to solar hydrogen
• Main challenges facing biohydrogen
production
• Early experimental results and their
significance
• Future outlook
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Biohydrogen lab
a)
b)
g)
c)
d)
e)
f)
h)
Bojan Tamburic & Steve Dennison
a) Culture reactor
b) Measuring probes and tubing
connections including:
• Condenser for hydrogen
collection
• Thermocouple
• pH, pO2 and OD sensors
• MIMS system
c) Main vessel of the Sartorius
photobioreactor (PBR)
d) Sartorius PBR control tower
e) Peristaltic pump
f) Water displacement system
g) Water-proof electric plugs
h) Stainless steel worktop
Solar Hydrogen Project
Algal growth
OD measurements - growing culture
0.50
0.4420
0.4299
0.45
Optical density (AU)
0.3947
0.40
0.35
0.30
0.2895
0.2624
0.2570
0.2457
0.2756
0.2520
Sartorius run
started
0.2201
0.25
0.3819
0.3735
0.3344
0.3393
0.3151
0.1788
0.20
Sartorius run
started
0.15
Brief pump
failure
0.10
0.05
/0
8
/0
9
19
/0
8
/0
8
/0
9
18
/0
8
/0
9
17
/0
8
/0
9
16
/0
9
15
/0
8
/0
8
/0
9
14
/0
8
/0
9
13
/0
8
/0
9
12
11
/0
9
/0
8
/0
8
/0
9
10
/0
8
/0
9
09
/0
8
/0
9
08
/0
9
/0
8
07
/0
9
06
/0
8
/0
8
/0
9
05
/0
9
04
03
/0
9
/0
8
0.00
Date of measurement
• Measure optical density - correlate to chlorophyll
content and cell count
• Challenge is to provide adequate and stable
growth conditions
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Batch reactor
• Test of process
parameters
• H2 detection by:
Hydrogen production by WT C.reinhardtii
Volume of hydrogen produced
(ml/l of culture)
6
5
– Water
displacement
– Injection mass
spectrometry
4
3
2
1
0
0
25
50
75
100
125
150
175
200
Time after sulphur deprivation (h)
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
• H2 production was
5.2 ml/l of culture –
total of 15ml over 5
days
Sartorius reactor (1)
Sartorius reactor - pH and OD
OD
0.6
7.6
0.5
7.5
0.4
7.4
0.3
7.3
0.2
7.2
0.1
7.1
0.0
pH
7.7
7
0
20
40
60
80
100
120
140
160
180
200
Time after dilution (h)
• Used dilution method of sulphur deprivation
• OD rises as algae grow, then drops as algae use up
starch reserves while producing H2
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
-0.1
220
OD (AU)
pH
Sartorius reactor (2)
Sartorius reactor - pO2 and H2
H2
140
3.50
120
3.00
100
2.50
80
2.00
60
1.50
40
1.00
20
0.50
0
0
20
40
60
80
100
120
140
160
180
200
0.00
220
Time after dilution (h)
• Hydrogen production activated upon the introduction of
anaerobic photosynthesis
• H2 production - 3.1±0.3 ml/l of culture
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
H2 produced (ml/l)
pO2 (%)
pO2
Content
• Hydrogen production and utilisation
• Green algal routes to solar hydrogen
• Main challenges facing biohydrogen
production
• Early experimental results and their
significance
• Future outlook
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Producing more H2
• Need to expand our understanding of the process
• Improve photochemical efficiency or increase algal
lifetime
• Different algal strains
–
–
–
–
Dum24 (no cell wall)
Stm6 (genetically engineered for H2 production)
New mutants from Biology
Alternative wild type strains, marine species
• Optimising process parameters
– Initial optical density
– Light intensity, temperature, agitation and pH
– Nutrient content
• Sulphur re-insertion (increasing lifetime)
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Automating and scaling-up
• Improve H2 measurement technique
• Develop continuous S-deprivation
process
• Use natural light (or solar simulator)
• Develop ultrafiltration system
• Prolong algal lifetime by sulphur reinsertion
• Cycle algal cultures and nutrients
• Investigate cheaper nutrients and
circulation systems
• Collect produced hydrogen (membrane)
• Connect to PEM fuel cell system
• Ultimate aim is ~20l outdoor reactor
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Solar Hydrogen Project
Photoelectrochemical Hydrogen
Production
Steve Dennison
Prof. Geoff Kelsall
Dr. Klaus Hellgardt
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Content
1. Background and history
2. Energetics of the semiconductorelectrolyte interface and H2 Production
3. Characterisation of the semiconductorelectrolyte interface
4. Future Work
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Background and History
• Photoelectrochemistry of semiconductors
– Fujishima & Honda (1972)
• Single crystal TiO2
• Near UV light ( ~ 390-400 nm)
• Produced H2 and O2 from water without external
bias
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Energetics of the semiconductor-electrolyte
interface
Zero energy level – electrons at rest in vacuum
Work
function
Electron affinity
Semiconductor/Aqueous Solution
Econduction
e-
EFermi
h
1.5 eV
Eband gap
Evalence
Bojan Tamburic & Steve Dennison

2H2O  2eCB

 H2  2OH 

4OH   4hVB

O2  2H2O
h+
Solar Hydrogen Project
Energetics of the semiconductor-electrolyte
interface
eh
0.4V
-
e
h
0.3V
Ef
eH+ / H2
h
1.23/1.5 V
h
O2 / H2O
0.4V
h+
+
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Energetics of the semiconductor-electrolyte
interface
• Requirements for a photoelectrode:
–
–
–
–
Thermodynamic energy for water:
Band bending:
Separation of ECB and EF:
Overpotential for O2:
• Total:
Bojan Tamburic & Steve Dennison
1.23 eV
0.4 eV
0.3 eV
0.4 eV
~2.4 eV
Solar Hydrogen Project
Energetics of the semiconductor-electrolyte
interface: possible materials
• Fe2O3:
Eg ~ 2.2 (to 2.4) eV
• WO3:
Eg ~ 2.6 eV
• Nitrogen-doped TiO2: Eg < 3.1 eV
• TiO2:
Eg ~ 3.1 eV
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Characterisation of the semiconductorElectrolyte Interface
• Current-voltage response, under dark and
illuminated conditions (analysis of general
response)
• a.c. impedance, in the dark (probe of
interfacial energetics: flat-band potential,
dopant density)
• Photocurrent spectroscopy (IPCE, Incident
Photon to Current Efficiency)
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Fe2O3
EPD Fe2O3:
As-Deposited
Bojan Tamburic & Steve Dennison
EPD Fe2O3:
Annealed
Fe2O3 by
Spray Pyrolysis
Solar Hydrogen Project
Fe2O3: Current-potential response
1.50E-03
Dark
Illuminated
1.30E-03
1.10E-03
i / A/cm -2
9.00E-04
7.00E-04
5.00E-04
3.00E-04
1.00E-04
-1.00E-04
0.00
0.10
0.20
0.30
0.40
0.50
0.60
E / Volts vs SCE
Electrophoretically deposited Fe2O3
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
0.70
0.80
Fe2O3: Current-potential response
2.50E-03
Illuminated
Dark
2.25E-03
2.00E-03
1.75E-03
i / Acm -2
1.50E-03
1.25E-03
1.00E-03
7.50E-04
5.00E-04
2.50E-04
0.00E+00
-2.50E-04
0.00
0.10
0.20
0.30
0.40
0.50
0.60
E / V vs SCE
CVD Fe2O3 (Hydrogen Solar)
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
0.70
0.80
0.90
Fe2O3: Photoelectrode Performance
Dip Coated
Electrophoretic
Deposition
Spray Pyrolysis *
/ Acm-2
/ Acm-2
/ Acm-2
As-deposited
3 x 10-6
6 x 10-4
1.22 x 10-3
Annealed ‡
1 x 10-6
7 x 10-5
-
* Produced at Hydrogen Solar: FeCl3/SnCl2 (1%) in EtOH
‡ 400°C in air for 30 min.
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Future Work
1. Materials development:
– Evaluate further materials: TiO2; WO3; Ndoped TiO2.
– Improvements to Fe2O3 deposition
– Development of fabrication techniques
(CVD, cold plasma deposition)
– Texturing of semiconductor films
2. Complete (high-throughput) photocurrent
spectrometer and full thin-film semiconductor
characterisation system
3. Develop identification of new materials, using
theoretical and empirical approaches.
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Future Work
4. Evaluation of particulate semiconductor
systems and comparison with
electrochemical systems.
5. Development of a photoelectrochemical
reactor(10 x 10 cm scale): design,
modelling and optimisation
6. Leading, ultimately, to a demonstrator
system
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project
Any questions?
Bojan.Tamburic@imperial.ac.uk
s.dennison@imperial.ac.uk
Bojan Tamburic & Steve Dennison
Solar Hydrogen Project