Conversion of Solar Radiation into Chemical Energy

E. Reguera CICATA-IPN, Unidad Legaria

Semana de la Ciencia en el IPN, 2013

“The struggle for survival is the struggle for the energy availability”.

Ludwig Boltzmann

Outline__________________________________________

• From Solar Radiation to Chemical Energy

• Natural Photosynthesis Process

• From Natural Photosynthesis to Fossil Fuels

• Renewable Energies

• Artificial Photosynthesis (APh) Products

• Different Approaches

• Use of Materials of Low Cost for APh

• Summary

165,000 TeraWatts of sunlight hit the earth every day

We only need to capture .02-.04% of solar radiation!

Lots of ‘big, fast & efficient’ problems• Light harvesting• Energy conversion• Energy transport• Energy storage ….Nanotech will play a major role in meeting all of these!

Current Global Energy Comsuption: 13 TW

Sugar from Sunlight + CO2 + H2O

Natural Photosynthesis

Natural Photosynthesis is a very complex process; its artificial reproduction involves large difficulties !!!

2H2O 4H+ + 4e- +O2

DG = 237 kJ/mole

Natural Photosynthesis: Process in presence of light

4Mn(II) 4Mn(III) + 4e-

Process in absence of light

• The Natural Photosynthesis was already developed about 3 billions of years ago;

• The Natural Photosynthesis was first established in the aqueous medium;

• The evolved oxygen contributes to the formation of the ozone shielding for UV radiation and to the appearance of an oxygen rich atmosphere of our planet.

Photosynthesis is also important for the environment preservation; it consumes CO2 and releases O2

Fossil Fuels:> 400 millions of years of solar into chemical energy conversion through Natural Photosyntesis

That huge volume of accumulated chemical energy will be consumed by the human civilization in about 300 years !!!

1900 1925 1950 1975 2000 2025 2050 2075 2100 2125 2150 2175 2200 2225 2250 2275 23000

50

100

150

200

250

300

Coal Energy Crude-Oil Energy Natural-Gas EnergyTotal Fossil Fuels Energy

year

10

^9

MB

tu

1980

2025

The Availability of Fossil Fuels: Global Scenario

Assumes that 75% of each fossil fuel is burned for energy.

2065

Peaks at about 2025

Shale gas and oil shift the peak about 50 years

190019251950197520002025205020752100212521502175220022252250227523000

1

2

3

4

5

6

7

8

0

50

100

150

200

250

300

350Population Fit to Energy

Population Projection (10^9) Population Fit Total Fossil Fuels Energy

year

10

^9 p

eo

ple

10

^9 M

Btu

Population without renewable energy

Fossil Fuels Energy

12 kW/person

World Population Projection

Fit of population to available fossil-fuels energy 1950-2006.

Population with renewable energy

Renewable Energy Technologies: A Global Urgency

Variable Character Energy Storage Media are Required

All these Sources are of Solar Nature

How Much Land is Needed?

12 kW/person x 8.3 billion people = 96 x 1012 watts ≈ 100 terawatts. Current = ~15 TW.)

Solar energy = ~342 watts/m2 at surface. Land area needed at 10% efficiency = ~2.8 x 106

km2. Earth land area is ~1.48 x 108 km2. So, ~2% of land is needed. Use roofs of buildings,

parking lots, highways & railways (1.1 x 105 km2) for solar and use agriculture land and offshore sites for wind.

http://arts.bev.net/RoperLDavid/

Artificial Photosynthesis is the Solar into Chemical Energy Conversion

2H2O + hu 4H2 +O2

“CO2 + 2H2O + hu CH4 + 2O2”

“CO2 + 2H2O + hu CH3OH + 3/2O2”

“2CO2 + 3H2O + hu C2H5OH + 5/2O2”All these processes consume energy which is accumulated in the obtained products

H2O

2e-

2H+ +1/2O2 2H+ H2

NC O

N C H3

NN

NN

HHH

CO2

H2, CH4

CH3OH

H2O

O2

H2O H2 + (1/2)O2 Eo = 1.23 eVH2O + CO2 (1/6)C6H12O6 Eo = 1.24 eV

H2 production involves the 99% of the harvested energy!!

Why Artificial Photosynthesis is Needed?

Chemical Energy (H2, CH4, CH3OH, C2H5OH) represents an Energy Storage support;

The available mobile technologies are easily adaptable to Chemical Energy, e. g. using Fuel Cell devices;

The captured CO2 from environmental emissions can be reduced, using sunlight and water, to CH4, CH3OH, C2H5OH;

Bio-fuels must be ignored as an energy source option if potential foods are used in their production.

Inverse Engineering of the Photosynthesis Process

Mn

MnMn

Mn

O

OO

O

OO

Mn

Mn

MnMn

O

OO

O

2H2O 4H+ + 4e-

cubanePSII

Water splitting in plants - photosynthesis

2H2O + hv → 4H+ + 4e- + O2

Wu, Dismukes et al, Inorg, Chem 43, 5795 (2004)Ferreira, et al, Science 303: 1831 (2004).

H2 e-

H+

N Hd+O

OFe

S

FeS S

CC

CC C

Cys

[4Fe4S]

Od+HN

H2 e-

H+

N Hd+O

OFe

S

FeS S

CC

CC C

Cys

[4Fe4S]

Od+HN

Tard et al, Nature 433, 610 (2005)Justice, Rauchfuss et al, J. Am. Chem. Soc.126, 13214 (2004)

Alper, Science 299, 1686 (2003)

bacteria - hydrogenasecatalyst for

2 H+ + 2e- H2

10 µchlamydomonas moewusii

Modify the biochemistry of plants and bacteria

- improve efficiency by a factor of 5–10 - produce a convenient fuel methanol, ethanol, H2, CH4

Bio-Mimetic

Approaches in Progress for an Artificial Leaf:

2H2O + hu 4H2 +O2

“CO2 + 2H2O + hu CH4 + 2O2”

“CO2 + 2H2O + hu CH3OH + 3/2O2”

“2CO2 + 3H2O + hu C2H5OH + 5/2O2”

1) Hydrogen production from water splitting;

2) A complex process involving both water splitting and CO2 capture and reduction:

H2 Production using Sunlight

Semiconductor base principle

Creation of an analogue of Cubane for the OEC

D. G.Nocera, Acc. Chem. Res. 2012

Mn oxides and related nanostructures

In addition to PSII, Mn nanostructures are found in bacterial and fungal redox reactions; as ocean and freshwater nodules, coatings on rock surfaces, hydrothermal veins, and dendrites

Iron oxides for water splitting: scope and limitations

Hematite (Fe2O3) and other iron oxides are earth-abundant with

perspectives for artificial photosynthesis;

Limitations:

1) Its conduction band is too low to drive H2 production;

2) The application of a bias potential is required to drive

the oxidation reaction;

3) Ultrashort lifetime for the charge recombination process.

Ternary Semiconductors:

N-Ba5Ta4O15

Tantalates, Vanadates, Oxinitrides, ….

Ba5Ta4O15; BiVO4, N:Ta:TiO2

H2O

H2

2H+ 2H+ +1/2O2

2e-

Co3[Fe(CN)6]2

(Co2+)3-x(Co3+)x[(FeIII)2-x(FeII)x(CN)12]

(Co2+)(Co3+)2[FeII(CN)6]2

Example:

TA – L- TB

hu ne-

Use of MVS Coordination Compounds for Water Splitting

Possible combinations: Mn, Fe, CoMn2+ Mn3+, Mn4+

Fe2+ Fe3+, Fe4+

Co2+ Co3+

Engineering the photosynthesis process

D. G.Nocera, Acc. Chem. Res. 2012

An Artificial Leaf Eff.: 5 %

In Summary:

Nanostructures containing Mn, Fe and Co probably have the major opportunities in Artificial Photosynthesis;

Ternary semiconductors (tantalates, vanadates, ….) are gaining interest by their response to visible light;

Ru, Ir and Pt based materials must be considered as model systems;

Efforts are required in materials science to obtain low cost semiconductor nanostructures conjugated to antenna compounds for an efficient solar radiation energy harvesting and their use for water splitting.

Thank you for the attention!!!

Thanks to the Organizing Committee for the opportunity to talk about this interesting subject.

The Artificial Photosynthesis is a big challenge but also a great opportunity to do basic and applied science