Solar energy to fuels If a leaf can do it we can do it".

Transcription

1 Solar energy to fuels If a leaf can do it we can do it". James Barber Imperial College London Lee Kuan Yew NTU Lecture 10 th November 2008

2 Mean Global Energy Consumption Rate TW Over 85% from fossil fuel Oil Coal Biomass Nuclear Gas Hydro Renew Total: 14TW U.S.: 3.3TW

3 Map of the world based on population From M. Newman

4 Map of the world based on energy consumption From M. Newman

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6 But why not do what the leaf does? 2H 2 + CO 2 (CH 2 O) Fuel (Organic molecules)

7 But needs H 2 - Where does it come from?

8 Solar Energy 2H 2 O O 2 + 2H 2 From Water

9 Two basic reactions of photosynthesis Solar Energy 2H 2 O O 2 + 2H 2 2H 2 + CO 2 (CH 2 O) Organic molecules

10 Macroscopic Reaction Vessel Organic molecule of life 2H 2 O Sunlight O 2 + 4H + + 4e +CO 2

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12 1000 millions years to produce fossil fuels and used in ~ 1000 years 0r One year of fossil fuel consumption = one million years of photosynthesis 5 Billion Year Clock

13 Global Photosynthesis The Engine of Life

14 Solar Energy (100,000 TW) Biology adopted the perfect solution to the energy problem O 2 Cyclic photosynthesis light reactions dark reactions CO 2 2H 2 O 4H + + 4e CH 2 O Organic CO 2 molecules Energy Decreased entropy & heat respiration O 2 combustion biomass food fossil fuels 200 TW 0.2% efficiency

15 Two basic reactions of photosynthesis Solar Energy Light reactions 2H 2 O O 2 + 2H 2 2H 2 + CO 2 (CH 2 O) Organic molecules Dark reactions

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17 Thylakoid membranes (Light reactions) Stroma (Dark reactions)

18 Photosynthetic efficiency Lucky to get 2% dry matter and 0.5% starch/sugar with inputs

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20 Brazil (sugar) Bioenergy 30% of total energy ~50% of cars sold in 2005 were Flex-Fuel vehicles able to use ethanol and petrol USA (corn) 6 million cars able to use E85 But only ~2% of fuel

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22 5 tons of bioethanol/acre to be competitive at present (i.e. 5:1 conversion) Miscanthus

23 2005 USDA/DOE Report ~ 30% of the US energy requirements Currently ~ 3%

24 The big loss factor But need solar energy conversion at 10% or better

25 Solar Energy Hydrogen 2H 2 O O 2 Hydrogenase photosynthesis light reactions dark reactions 4H + + 4e CO 2 Organic molecules respiration combustion CO 2 biomass food fossil fuels O 2 For high efficiency of energy conversion use the front end of photosynthesis Light Reactions

26 Solar Land Area Requirements at 10% efficiency 6 Boxes at 3.3 TW Each

27 Ni-Fe type hydrogenase Fe-S type hydrogenase

28 Hydrogen green alga Chlamydomonas Hydrogenase e/h + O 2 H 2 O Organic substrates (CH 2 0) n

29 Solar Energy (100,000TW) O 2 The Perfect Solution Cyclic One hour of solar = annual global energy consumption 2H 2 O 2H 2 +CO 2 Liquid fuel Energy Total global (14TW) O 2 The Artificial Leaf H 2 /O 2 /H 2 O cycle driven by solar energy

30 Solar Energy Light reactions 2H 2 O O 2 + 2H 2 The Water Splitting Reaction

31 5 Billion Year Clock Oxygenic atmosphere & Ozone layer H 2 O splitting Big Bang of Evolution

32 Photosystem II (PSII) is the enzyme found in plants, algae and cyanobacteria which uses solar energy to split water into molecular oxygen and reducing equivalents

33 Redox scale ev -1 Red. Electron transfer in Photosystem II P680* Pheo - H + PQ A 0 PQ B Oxid. +1 P680 + H 2 O Tyr z (Y Z ) P680 + is highly oxidising Em ~ 1.3eV at ph 7

34 Water splitting reaction is a four photon process 2H 2 O + 2PQ O 2 + 2PQH 2 Light (4hv) PSII

35 S-state cycle Kok & Joliot dark stable state

36 Oxygen emission induced by flashes Joliot & Kok ~1969

37 Photosystem II (PSII) Water splitting rapid turnover of D1 a repair process

38 PSII 1994 SP EM 1995 From Black Box to Atomic Resolution EC X-ray 1998 Cyanobacterial PSII Plant PSII

39 Mn 4 CaO 4 Photosystem Two: The water splitting enzyme 4hv 2H 2 O O 2 + 4e + 4H + Ferreira et al Science 2004

40 Active Branch Protective Branch

41 Lumenal view of PSII monomer within the dimer

42 Oxygen Evolving Centre Anomalous diffraction for Mn (1.89A) and Ca (2.25A) bicarbonate? Ferreira et al Science 303(2004)

43 Water Splitting-Oxygen Evolving Catalytic Site A344

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45 Cubane-like Mn 3 CaO 4 cluster linked to a 4th Mn by a mono-μ-oxo bond Amino acid ligands D1 protein 1 CP43

46 Diagrammatic representation of the water splitting centre

47 S 4 Highly electrophilic oxo (or oxyl radical) H H Cl O Ca O O Mn V O Nucleophilic attack O Mn IV Mn IV MnIV O

48 Biomimetic Systems a) hv c) e - Tom Moore and colleagues ASU b) e - C60-Por-Bi-PhOH

49 From Natural to Artificial Photosynthesi s Q A Q B Acceptor N N Tyr P 680 N Ru N NH N N Me EtO 2 C N N O N N Mn O Mn N Mn O O O Mn O N Hammerstrom & Styring U. of Uppsala Me Me

50 Design of an artificial water splitting system O H B O Fe Mn V H Cl O Daniel O Nocera MIT Ca O O O IV MnIVMn Mn IV O

51 Solar Energy The Artificial Leaf O 2 2H 2 O 2H 2 +CO 2 Carbon based fuels Energy Total global O 2

52 Calvin Cycle RuBisCO +H 2 O

53 Crystal structure of RuBisCo isolated from spinach

54 Leonardo s Dream

55 Solar Energy (100,000TW) Solar Energy (100,000TW) O 2 O 2 Our Dream One hour of solar = annual global energy consumption 2H 2 O 2H 2 2H 2 O 2H 2 +CO 2 Liquid fuel Energy Total global Energy Total (14TW) global (14TW) O 2 O 2 The If a leaf can do it we can do it Artificial Leaf Its only chemistry

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57 Jules Verne s Dream (1875) I believe that water will one day be used as a fuel, because the hydrogen and oxygen which constitute it, used separately or together, will furnish an inexhaustible source of heat and light. I therefore believe that, when coal deposites are oxidised, we will heat ourselves by means of water. Water is the fuel of the future

58 I say - If the leaf can do it, we can do it