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Transcript of Bojan Tamburic & Steve DennisonSolar Hydrogen Project The Solar Hydrogen Project Steve Dennison and...
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
The Solar Hydrogen Project
Steve Dennison and Bojan Tamburic
Dr Klaus HellgardtProf 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)
4 2 2 22 4CH H O H CO
~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) Fossil Energy
Heat
Mechanical Energy
Electricity
Electrolysis
Thermolysis
Biophotolysis
Fermentation
Biomass
Chemical Conversion
Carbon dioxideHydrogen
Photoelectrolysis
4 2 2 22 4CH H O H CO
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 ProjectBiohydrogen Production
Bojan Tamburic
Prof. Geoffrey MaitlandDr. Klaus Hellgardt
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Introduction
1) Hydrogen production and utilisation– 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– Growing algal biomass– Inducing metabolic change– Measuring and optimising H2
production
4) Early experimental results and their significance– Biohydrogen lab– Algal growth– Batch reactor– Sartorius reactor (1)– Sartorius reactor (2)
5) Future outlook– Producing more H2
– Automating and scaling-up
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
“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)
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
Photosynthetic H2 production
• 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
Ferredoxin
222 22 OHOH
Ferredoxin
222 22 OHOH
Hallenbeck & Benemann (2002)
Bojan Tamburic & Steve Dennison 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• Use the model green algae
C.reinhardtiiMelis et al. (2002)
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
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– Water displacement– Injection mass
spectrometry– Membrane inlet mass
spectrometry (MIMS)
• Optimising H2 production– Grow algae to sufficient
OD– Optimise system
parameters– Determine suitable
nutrient mix
Mass spectrometerInjection
system
Helium tank
Mass flow controler
Water displacement system
Sartorius photobioreactor
H2 permeable membrane
Gaseous H2
4-way valve
Mass spectrometerInjection
system
Helium tank
Mass flow controler
Water displacement system
Sartorius photobioreactor
H2 permeable membrane
Gaseous H2
4-way valve
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
Biohydrogen laba) Culture reactorb) 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 towere) Peristaltic pumpf) Water displacement systemg) Water-proof electric plugsh) Stainless steel worktop
a)
b)
c)
d)e) f)
g)
h)
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Algal growth
• Measure optical density - correlate to chlorophyll content and cell count
• Challenge is to provide adequate and stable growth conditions
OD measurements - growing culture
0.2457
0.28950.2570
0.2201
0.1788
0.2520
0.3151
0.3947
0.3344
0.42990.4420
0.38190.3735
0.3393
0.27560.2624
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
03/0
9/08
04/0
9/08
05/0
9/08
06/0
9/08
07/0
9/08
08/0
9/08
09/0
9/08
10/0
9/08
11/0
9/08
12/0
9/08
13/0
9/08
14/0
9/08
15/0
9/08
16/0
9/08
17/0
9/08
18/0
9/08
19/0
9/08
Date of measurement
Op
tica
l d
ensi
ty (
AU
)
Sartorius run started
Sartorius run started
Brief pump failure
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Batch reactor
• Test of process parameters
• H2 detection by:
– Water displacement
– Injection mass spectrometry
• H2 production was 5.2 ml/l of culture – total of 15ml over 5 days
Hydrogen production by WT C.reinhardtii
0
1
2
3
4
5
6
0 25 50 75 100 125 150 175 200
Time after sulphur deprivation (h)
Vo
lum
e o
f h
ydro
gen
pro
du
ced
(m
l/l o
f cu
ltu
re)
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Sartorius reactor (1)
• Used dilution method of sulphur deprivation• OD rises as algae grow, then drops as algae use up
starch reserves while producing H2
Sartorius reactor - pH and OD
7
7.1
7.2
7.3
7.4
7.5
7.6
7.7
0 20 40 60 80 100 120 140 160 180 200 220
Time after dilution (h)
pH
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
OD
(A
U)
pH OD
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Sartorius reactor (2)Sartorius reactor - pO2 and H2
0
20
40
60
80
100
120
140
0 20 40 60 80 100 120 140 160 180 200 220
Time after dilution (h)
pO
2 (%
)
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
H2
pro
du
ced
(m
l/l)
pO2 H2
• 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
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 re-
insertion• 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 ProjectPhotoelectrochemical Hydrogen
Production
Steve Dennison
Prof. Geoff KelsallDr. Klaus Hellgardt
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Content
1. Background and history
2. Energetics of the semiconductor-electrolyte interface and H2 Production
3. Characterisation of the semiconductor-electrolyte 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
2 22 2 2CBH O e H OH
2 24 4 2VBOH h O H O
e-e-
h+h+
Econduction
Evalence
Eband gap
hh 1.5 eV
Semiconductor/Aqueous Solution
EFermi
Zero energy level – electrons at rest in vacuum
Workfunction
Electron affinity
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Energetics of the semiconductor-electrolyte interface
H+ / H2
O2 / H2O
e- h
1.23/1.5 V
0.3V
e- h
h+
+
h
0.4V
0.4V
Ef
e- h
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Energetics of the semiconductor-electrolyte interface
• Requirements for a photoelectrode:
– Thermodynamic energy for water: 1.23 eV
– Band bending: 0.4 eV
– Separation of ECB and EF: 0.3 eV
– Overpotential for O2: 0.4 eV
• Total: ~2.4 eV
Bojan Tamburic & Steve Dennison 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 semiconductor-Electrolyte 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
Fe2O3 by
Spray Pyrolysis
EPD Fe2O3:
Annealed
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Fe2O3: Current-potential response
-1.00E-04
1.00E-04
3.00E-04
5.00E-04
7.00E-04
9.00E-04
1.10E-03
1.30E-03
1.50E-03
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80
E / Volts vs SCE
i / A
/cm
-2
Illuminated Dark
Electrophoretically deposited Fe2O3
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
Fe2O3: Current-potential response
-2.50E-04
0.00E+00
2.50E-04
5.00E-04
7.50E-04
1.00E-03
1.25E-03
1.50E-03
1.75E-03
2.00E-03
2.25E-03
2.50E-03
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90
E / V vs SCE
i / A
cm-2
Illuminated Dark
CVD Fe2O3 (Hydrogen Solar)
Bojan Tamburic & Steve Dennison Solar Hydrogen Project
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; N-
doped 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?