Bojan Tamburic & Steve DennisonSolar 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

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Structure of presentation Background Biohydrogen (Bojan Tamburic) Photoelectrochemical Hydrogen (Steve Dennison) Questions

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Solar Energy Available

Bojan Tamburic & Steve DennisonSolar 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 (NH 3, methanol, etc.) A fuel for the future (in fuel cells) - towards the hydrogen economy?

Bojan Tamburic & Steve DennisonSolar 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 DennisonSolar Hydrogen Project Hydrogen Production Today Steam reformation of methane (+ other light hydrocarbons) ~5 kg carbon dioxide is produced per kg H 2 which is not sustainable!

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Routes to Hydrogen Production adapted from J.A.Turner, Science 285, 687(1999)

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Clean (CO 2 -free) Hydrogen Electrolysis (?) Photoelectrolysis Biophotolysis

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Solar Hydrogen Project Biohydrogen Production Bojan Tamburic Prof. Geoffrey Maitland Dr. Klaus Hellgardt

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Introduction 1)Hydrogen production and utilisation –Hydrogen as a fuel –Clean and green H 2 production 2)Green algal routes to solar hydrogen –Photosynthetic H 2 production –Two stage growth and hydrogen production procedure 3)Main challenges facing biohydrogen production –Growing algal biomass –Inducing metabolic change –Measuring and optimising H 2 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 H 2 –Automating and scaling-up

Bojan Tamburic & Steve DennisonSolar 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 DennisonSolar Hydrogen Project Hydrogen as a fuel Environmental concerns over: –CO 2 emissions –Vehicle exhaust gasses (SO x, NO x ) Sustainability concerns: –Peak oil –Global warming Hydrogen – transport fuel of the future Proton exchange membrane (PEM) fuel cells use H 2 to drive an electrochemical engine; the only product is water Barriers that must be overcome: –Compression of H 2 –Development of Hydrogen infrastructure –Sustainable H 2 production

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Clean and green H 2 production Bulk Hydrogen is typically produced by the steam reforming of Methane, followed by the gas-shift reaction: –CH 4 + H 2 O → CO + 3H 2 –CO + H 2 O → CO 2 + H 2 Negates many of the benefits of PEM fuel cells Renewable and sustainable H 2 production required Can be achieved by renewable electricity generation, followed by water electrolysis, but: –Low efficiency –High costs –Can use electricity directly “Photosynthetic H 2 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 DennisonSolar 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 DennisonSolar Hydrogen Project Photosynthetic H 2 production Discovered by Gaffron in 1942 Direct H 2 photoproduction –2H 2 O → 2H 2 + O 2 Solar energy absorbed by Photosystem II and used to split water Electrons transported by Ferredoxin H 2 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)

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Two-stage growth and hydrogen production procedure Hydrogenase enzyme deactivated in the presence of Oxygen – limit on volume and duration of H 2 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 H 2 and ATP –H 2 production slows after about 5 days as algae begin to die Use the model green algae C.reinhardtii Melis et al. (2002)

Bojan Tamburic & Steve DennisonSolar 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 DennisonSolar 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 H 2 production? –Without contamination? Can the growth process be scaled up?

Bojan Tamburic & Steve DennisonSolar 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 DennisonSolar Hydrogen Project Measuring and optimising H 2 production Measuring H 2 production –Water displacement –Injection mass spectrometry –Membrane inlet mass spectrometry (MIMS) Optimising H 2 production –Grow algae to sufficient OD –Optimise system parameters –Determine suitable nutrient mix

Bojan Tamburic & Steve DennisonSolar 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 DennisonSolar Hydrogen Project Biohydrogen lab a)Culture reactor b)Measuring probes and tubing connections including: Condenser for hydrogen collection Thermocouple pH, pO 2 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 a) b) c) d) e)f) g) h)

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Algal growth Measure optical density - correlate to chlorophyll content and cell count Challenge is to provide adequate and stable growth conditions

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Batch reactor Test of process parameters H 2 detection by: –Water displacement –Injection mass spectrometry H 2 production was 5.2 ml/l of culture – total of 15ml over 5 days

Bojan Tamburic & Steve DennisonSolar 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 H 2

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Sartorius reactor (2) Hydrogen production activated upon the introduction of anaerobic photosynthesis H 2 production - 3.1±0.3 ml/l of culture

Bojan Tamburic & Steve DennisonSolar 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 DennisonSolar Hydrogen Project Producing more H 2 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 H 2 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 DennisonSolar Hydrogen Project Automating and scaling-up Improve H 2 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 DennisonSolar Hydrogen Project Solar Hydrogen Project Photoelectrochemical Hydrogen Production Steve Dennison Prof. Geoff Kelsall Dr. Klaus Hellgardt

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Content 1.Background and history 2.Energetics of the semiconductor- electrolyte interface and H 2 Production 3.Characterisation of the semiconductor- electrolyte interface 4.Future Work

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Background and History Photoelectrochemistry of semiconductors –Fujishima & Honda (1972) Single crystal TiO 2 Near UV light ( ~ nm) Produced H 2 and O 2 from water without external bias

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Energetics of the semiconductor-electrolyte interface

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Energetics of the semiconductor-electrolyte interface

Bojan Tamburic & Steve DennisonSolar 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 E CB and E F : 0.3 eV –Overpotential for O 2 : 0.4 eV Total: ~2.4 eV

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Energetics of the semiconductor-electrolyte interface : possible materials Fe 2 O 3 : Eg ~ 2.2 (to 2.4) eV WO 3 : Eg ~ 2.6 eV Nitrogen-doped TiO 2 : Eg < 3.1 eV TiO 2 : Eg ~ 3.1 eV

Bojan Tamburic & Steve DennisonSolar 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 DennisonSolar Hydrogen Project Fe 2 O 3 EPD Fe 2 O 3 : As-Deposited Fe 2 O 3 by Spray Pyrolysis EPD Fe 2 O 3 : Annealed

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Fe 2 O 3 : Current-potential response Electrophoretically deposited Fe 2 O 3

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Fe 2 O 3 : Current-potential response CVD Fe 2 O 3 (Hydrogen Solar)

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Fe 2 O 3 : Photoelectrode Performance Dip CoatedElectrophoretic Deposition Spray Pyrolysis * / Acm -2 As-deposited3 x x x Annealed ‡ 1 x x * Produced at Hydrogen Solar: FeCl3/SnCl2 (1%) in EtOH ‡ 400°C in air for 30 min.

Bojan Tamburic & Steve DennisonSolar Hydrogen Project Future Work 1.Materials development: –Evaluate further materials: TiO 2 ; WO 3 ; N- doped TiO 2. –Improvements to Fe 2 O 3 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 DennisonSolar 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 DennisonSolar Hydrogen Project Any questions?