BY: PHILIP HOF
PHOF8723@GMAIL.COM
CHICAGO-KENT, COLLEGE OF LAW
ENERGY LAW, FALL 2010
OUTLINE
1. OVERVIEW
5. CURRENT RESEARCH
2. STATE OF THE PLANET
6. SCALABILITY
3. HOW IT WORKS
7. ROLE OF CHEMISTRY
4. KEY ISSUES
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 fuelforming direction.
 For traditional fuel cells, fuels like hydrogen drive the
production of electricity.
2 PRINCIPLE ELEMENTS
 Collectors to convert solar energy to electrical energy, and
 Electrolyzers that use the electrical
energy to split water into H2 and O2
PV cells made by Sanyo used
in Universal Studios theme
park in Singapore
Industrial electrolyzer
made by NorwegianGerman company
GHW
2. STATE OF THE PLANET
PROJECTED GROWTH TRENDS
World Population (Billions) 6.145
Energy Consumption (TW/yr) 13.5
CO2 Emissions (GtC/yr)
6.57
9.4
27.6
11
10.4
43
13.3
2001
2050
Year
2100
Population
Energy
Consumption
CO2 Emissions
2000
2050
Year
2100
CO2 IS STUBBORN
 In absence of geoengineering, the effects on environment
caused by CO2 over next 40 years will persist globally for 5002,000 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 than
humankind 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
Glucose
ARTIFICIAL PHOTOSYNTHESIS
IMITATION IS THE SINCEREST FORM OF FLATTERY
• 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 oxygen
Anode (oxidation)
2 H 2O 
 4 H   4e   O2
Cathode (reduction)
4 H   4e  
 2 H 2
Overall reaction
2 H 2O 
 2 H 2  O2
H2
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


Cathode

Anode
E
TURNER’S 1998
PROTOTYPE
Hydrogen bubbles
•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
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
Energy Diagram
• Energetics - Matching
band energies with
reactions
• Electron-hole pair
recombination
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).