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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


Structure of presentation

• Background

• Biohydrogen (Bojan Tamburic)

• Photoelectrochemical Hydrogen (Steve Dennison)

• Questions


Solar Energy Available


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?


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.


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!


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)


Clean (CO2-free) Hydrogen

• Electrolysis (?)

• Photoelectrolysis

• Biophotolysis


Solar Hydrogen ProjectBiohydrogen Production

Bojan Tamburic

Prof. Geoffrey MaitlandDr. Klaus Hellgardt


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


Content

• Hydrogen production and utilisation

• Green algal routes to solar hydrogen

• Main challenges facing biohydrogen production

• Early experimental results and their significance

• Future outlook


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


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)


Content





• Future outlook


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)


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)


Content





• Future outlook


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?


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


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


Content





• Future outlook


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)


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


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)


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


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


Content





• Future outlook


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)


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


Solar Hydrogen ProjectPhotoelectrochemical Hydrogen

Production

Steve Dennison

Prof. Geoff KelsallDr. Klaus Hellgardt


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


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


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



H+ / H2

O2 / H2O

e- h

1.23/1.5 V

0.3V

e- h

h+

+

h

0.4V

0.4V

Ef

e- h



• 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


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


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)


Fe2O3

EPD Fe2O3:

As-Deposited

Fe2O3 by

Spray Pyrolysis

EPD Fe2O3:

Annealed


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


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)


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.


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.


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


Any questions?

[email protected]

[email protected]

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