The Solar Hydrogen Project
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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. Structure of presentation. Background Biohydrogen (Bojan Tamburic)

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The solar hydrogen project

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


Structure of presentation

Structure of presentation

Background

Biohydrogen (Bojan Tamburic)

Photoelectrochemical Hydrogen (Steve Dennison)

Questions


Solar energy available

Solar Energy Available


Why hydrogen

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

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

Hydrogen Production Today

Steam reformation of methane (+ other light hydrocarbons)

~5 kg carbon dioxide is produced per kg H2 which is not sustainable!


Routes to hydrogen production

Routes to Hydrogen Production

adapted from J.A.Turner, Science 285, 687(1999)


Clean co 2 free hydrogen

Clean (CO2-free) Hydrogen

Electrolysis (?)

Photoelectrolysis

Biophotolysis


Solar hydrogen project biohydrogen production

Solar Hydrogen ProjectBiohydrogen Production

Bojan Tamburic

Prof. Geoffrey Maitland

Dr. 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)

Future outlook

Producing more H2

Automating and scaling-up

Introduction


Content

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

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 h 2 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)


Content1

Content

  • Hydrogen production and utilisation

  • Green algal routes to solar hydrogen

  • Main challenges facing biohydrogen production

  • Early experimental results and their significance

  • Future outlook


Photosynthetic h 2 production

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

Hallenbeck & Benemann (2002)


Two stage growth and hydrogen production procedure

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.reinhardtii

Melis et al. (2002)


Content2

Content

  • Hydrogen production and utilisation

  • Green algal routes to solar hydrogen

  • Main challenges facing biohydrogen production

  • Early experimental results and their significance

  • 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?

Growing algal biomass


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

Inducing metabolic change


Measuring and optimising h 2 production

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


Content3

Content

  • Hydrogen production and utilisation

  • Green algal routes to solar hydrogen

  • Main challenges facing biohydrogen production

  • Early experimental results and their significance

  • Future outlook


Biohydrogen lab

Biohydrogen lab

  • Culture reactor

  • Measuring probes and tubing connections including:

    • Condenser for hydrogen collection

    • Thermocouple

    • pH, pO2 and OD sensors

    • MIMS system

  • Main vessel of the Sartorius photobioreactor (PBR)

  • Sartorius PBR control tower

  • Peristaltic pump

  • Water displacement system

  • Water-proof electric plugs

  • Stainless steel worktop

a)

b)

g)

c)

d)

e)

f)

h)


Algal growth

Algal growth

  • Measure optical density - correlate to chlorophyll content and cell count

  • Challenge is to provide adequate and stable growth conditions


Batch reactor

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


Sartorius reactor 1

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 2

Sartorius reactor (2)

  • Hydrogen production activated upon the introduction of anaerobic photosynthesis

  • H2 production - 3.1±0.3 ml/l of culture


Content4

Content

  • Hydrogen production and utilisation

  • Green algal routes to solar hydrogen

  • Main challenges facing biohydrogen production

  • Early experimental results and their significance

  • Future outlook


Producing more h 2

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

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 project photoelectrochemical hydrogen production

Solar Hydrogen ProjectPhotoelectrochemical Hydrogen Production

Steve Dennison

Prof. Geoff Kelsall

Dr. Klaus Hellgardt


Content5

Content

Background and history

Energetics of the semiconductor-electrolyte interface and H2 Production

Characterisation of the semiconductor-electrolyte interface

Future Work


Background and history

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

Energetics of the semiconductor-electrolyte interface


Energetics of the semiconductor electrolyte interface1

Energetics of the semiconductor-electrolyte interface


Energetics of the semiconductor electrolyte interface2

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


Energetics of the semiconductor electrolyte interface possible materials

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

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)


Fe 2 o 3

Fe2O3

EPD Fe2O3:

As-Deposited

EPD Fe2O3:

Annealed

Fe2O3 by

Spray Pyrolysis


Fe 2 o 3 current potential response

Fe2O3: Current-potential response

Electrophoretically deposited Fe2O3


Fe 2 o 3 current potential response1

Fe2O3: Current-potential response

CVD Fe2O3 (Hydrogen Solar)


Fe 2 o 3 photoelectrode performance

Fe2O3: Photoelectrode Performance

* Produced at Hydrogen Solar: FeCl3/SnCl2 (1%) in EtOH

‡ 400°C in air for 30 min.


Future work

Future Work

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

Complete (high-throughput) photocurrent spectrometer and full thin-film semiconductor characterisation system

Develop identification of new materials, using theoretical and empirical approaches.


Future work1

Future Work

Evaluation of particulate semiconductor systems and comparison with electrochemical systems.

Development of a photoelectrochemical reactor(10 x 10 cm scale): design, modelling and optimisation

Leading, ultimately, to a demonstrator system


Any questions

Any questions?

[email protected]

[email protected]


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