BY: PHILIP HOFPHOF8723@GMAIL.COMCHICAGO-KENT, COLLEGE OF LAWENERGY LAW, FALL 2010

OUTLINE

1.OVERVIEW

2. STATE OF THE PLANET

3. HOW IT WORKS

4. KEY ISSUES

5. CURRENT RESEARCH

6. SCALABILITY

7. ROLE OF CHEMISTRY

8. FUTURE POSSIBILITIES

1. OVERVIEW

Question of the day:

• What energy-producing technology can be envisioned today that will last for millennia and can be implemented in developing countries, in addition to the US?

Answer…

…SOLAR FUELS

Potential to solve two major problems:

• Energy security

• Carbon emissions

The key is to make energy-dense chemical fuel with minimal carbon emissions.

MOTIVATION IS ALL AROUND US Real-life leaves prove that sunlight can be

converted into fuel using only common elements

Q: Can humankind imitate this process to rescue the planet from global warming?

FUEL CELL IN REVERSE

For solar fuel, sunlight provides driving force in the fuel-forming direction.

For traditional fuel cells, fuels like hydrogen drive the production of electricity.

2 PRINCIPLE ELEMENTS

Industrial electrolyzer made by Norwegian-German company GHW

PV cells made by Sanyo used in Universal Studios theme park in Singapore

2. STATE OF THE PLANET2. STATE OF THE PLANET

PROJECTED GROWTH TRENDS

World Population (Billions) 6.145 9.4 10.4Energy Consumption (TW/yr) 13.5 27.6 43

CO2 Emissions (GtC/yr) 6.57 11 13.3

2001 2050 2100

Year

Year

CO2 IS STUBBORN

In absence of geoengineering, the effects on environment caused by CO2 over next 40 years will persist globally for 500-2,000 years

Atmospheric CO2 levels were between 210-300 ppm for last 420,000 years

We are hoping to stabilize it in the 550-650 ppm range

In order to do this, by 2050 we would need as much carbon neutral power as the amount of total energy produced today

CARBON-NEUTRAL POWER OPTIONS

Three main options• Nuclear fission• Clean coal with carbon capture and storage• Renewable sources of energy

The technology must start now and maintain a similar growth rate• Probably too late for nuclear fission and carbon

capture technologies• Look to renewables!

THE SUN HAS POTENTIAL…

The Sun is by far the largest exploitable source of energy• “The Sun pours more energy onto the Earth every hour

thanhumankind uses in a year” –Nathan

Lewis

But what about when the sun goes down? Storage?

STORE ENERGY IN CHEMICAL BONDS

Use the Sun to churn out fuel that we can burn

• To power cars,• To create heat,• To generate electricity,

And that we can store for use when the Sun goes down.

3. HOW IT WORKS

NATURAL PHOTOSYNTHESIS

• Stores solar energy as fuel by rearranging the chemical bonds of water to form O2 and NADPH, which is nature’s form of H2

• Later in the process, NADPH is used to form glucose, which is a sugar and a main basis for energy in most organisms Glucos

e

ARTIFICIAL PHOTOSYNTHESISIMITATION IS THE SINCEREST FORM OF FLATTERY

222

2

22

22

244

442

OHOH

HeH

OeHOH

• Two spatially separated electrodes coated with catalysts placed in water

• Sunlight creates a wireless current that sparks the reactions below

• Cathode produced hydrogen, and anode produces oxygenAnode

(oxidation)

Cathode (reduction)

Overall reactionH2

ENERGY DIAGRAM

Energy of light photon, E = hv, is absorbed at anode with help of catalyst

Charge separation:• Electron (e-) jumps to higher band• Hole (h+) is left behind

E

AnodeCathode

TURNER’S 1998 PROTOTYPE

•It works!

•Built by John Turner in 1998•Overall 12.4% solar to hydrogen efficiency, which is about 12x as efficient as a leaf

• But…

•Lifespan of only about 20 hours•Used expensive platinum as catalyst•Cost roughly $10,000/cm2

Hydrogen bubbles

4. KEY ISSUES

Cost of Catalysts

Thermodynamic Barriers

Corrosion

COST OF CATALYSTS

Commercial PV cells contain expensive silicon (Si) crystals

Electrolyzers use platinum (Pt), which costs $1,500 an ounce

At these prices, maybe alright for the military, but not to power civilization

• Look to cheap minerals for catalysts, like iron, cobalt, or manganese

THERMODYNAMIC BARRIERS

• Lack of efficient light

absorption

• Energetics - Matching

band energies with

reactions

• Electron-hole pair

recombination

Energy Diagram

light

CORROSION

Water splitting reaction is highly corrosive

The oxidizing power causes electrodes to degrade

Same with natural photosynthesis, but plants can rebuild• Turner’s cell lasted only 20 hours

5. CURRENT RESEARCH

Many researchers are trying to make this technology more efficient, affordable, and more durable

Two notable researchers are Nathan Lewis and Daniel Nocera

Nathan Lewis, Caltech

Daniel Nocera, MIT

IMPROVING THE COLLECTOR

Lewis has devised a collector made of silicon nanowires embedded in a transparent plastic film

Practical ability to roll and unroll like a blanket

The light to electric energy efficiency of nanowires at 3% is much less than the 20% of commercial solar cells• But it might be acceptable if cheap enough

FINDING A BETTER CATALYST

In 2008, Nocera hit on an inexpensive combination of phosphate and cobalt that can catalyze the production of O2

Used an electrode made of inert indium tin oxide in phosphate-buffered water containing cobalt ions

Many similarities to natural photosynthesis• Catalyst that forms in situ from earth-abundant materials

• Generates O2 in neutral water under ambient conditions

Highlights a new era of exploration

6. SCALABILITY

Must be able to scale up cheaply into thin flexible solar-fuel films that roll off high-speed production

lines the way newsprint does

THE SCALE IS DAUNTING

We would have to split more than 1015 mol H2O/year to meet the current US energy demand

Solar devices would have to convert 10% of light energy into fuel and cover an area the size of South Carolina

Would literally need to use rocks as catalysts

WHAT ABOUT COSTS?

As for cost, it would have to be as cheap as wall-to-wall carpeting, less than $1 per sq. foot

“We need to think potato chips, not silicon chips” – Harry Atwater, Jr., Caltech

7. ROLE OF CHEMISTRY

JULY 2010 DOE GRANT

$122 M over 5 years to a team of scientists to explore solar technologies, including solar fuels

Team consists of researchers at:• Colorado School of Mines, University of

Colorado, University of Wisconsin, Switzerland, Mexico, Armenia, Sweden, and Japan

One of the targets is a solar device with a 10,000 hour service life

8. POSSIBILITIES FOR THE FUTURE

HOW AMBITIOUS ARE WE?

Could produce pure water for the municipal water supply• Pure water is a by-product of burning hydrogen• Could use ocean water to create hydrogen, then burn

the hydrogen at a power plant to produce electricity for the grid and clean water• It’s a win-win!

In theory, could combine Sun, water and basic atmospheric gases like carbon dioxide, nitrogen, and oxygen to create• Not only fuels, electricity, and pure water, but also • Polymers , food, and almost everything else we need!

HOW CLOSE ARE WE?

Will Americans soon be cooking up hydrogen for their cars using affordable backyard equipment?

Many solar-fuel experts maintain that the research has decades to go

Considering the challenges, they might be right

THE END

SOURCES Oscar Khaselev & John Turner, A Monolithic Photovoltaic-Photoelectrochemical

Device for Hydrogen Production via Water Splitting, SCIENCE, April 17, 1998, at 425-27.

John Turner, A Realizable Renewable Energy Future, SCIENCE, July 30, 1999, at 687-89.

Antonio Regalado, Reinventing the Leaf: The ultimate fuel may come not from corn or algae but directly from the sun itself, SCIENTIFIC AMERICAN, October 2010, at 32-35.

Matthew Kanan & Daniel Nocera, In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+ , SCIENCE, Aug. 22, 2008, at 1072-75.

Harry Gray, Powering the Planet with Solar Fuel, Nature Chemistry, April 2009, at 7. Nathan Lewis & Daniel Nocera, Powering the Planet: Chemical Challenges in Solar

Energy Utilization, PNAS, Oct. 24, 2006, at 15729-35. $122 Million Granted to Solar Fuel Research, CALFINDER (July 26, 2010),

http://solar.calfinder.com/blog /solar-research/122-million-solar-fuel-research/ . Solar Fuel Starting Up, CALFINDER (April 30, 2010),

http://solar.calfinder.com/blog/news/solar-fuel-starting-up/ Sunlight Advances Hydrogen-Production Technology, ENERGY INNOVATIONS:

SCIENCE AND TECHNOLOGY, Winter 2010 (published by National Renewable Energy Laboratory).