Stuart Licht, GW Professor of Chemistry, presented at the GW Solar Institute symposium on April 19, 2010. More information available at: solar.gwu.edu/Symposium.html

1. Stuart Licht, Department of Chemistry
SLicht@GWU.edu, The George Washington University

2. STEP
A new solar energy conversion process
(Solar Thermal Electrochemical Photo) conversion
SLicht@GWU.edu, The George Washington University

3. STEP
A new solar energy conversion process
(Solar Thermal Electrochemical Photo) conversion
"STEP generation of energetic molecules:
A solar chemical process to end anthropogenic global warming,”
Stuart Licht, Journal of Physical Chemistry, C, 113, 16283 (2009):
SLicht@GWU.edu, The George Washington University

4. Fueling future transportation: 1) the electric option
Burning coal,
oil, natural gas Nuclear water wind solar
    
High Temperature
 mechanical
limited
photovoltaic
generation
Carnot limited generator
generator
 

Electricity – 6% grid losses!

Vehicle Electrification
SLicht@GWU.edu, The George Washington University

5. Fueling future transportation: 2) prior solar fuel options were inefficient
Biofuels Solar Thermal Solar PV
Photosynthesis Solar Concentrator Photovoltaics
  
Algae or Plant High Temp Electricity
  
Multi-step Reactions Water Electrolysis
Fuel Separation
 

Gas Separation Hydrogen
Alcohol, CH4, etc 
Hydrogen
Status: solar to fuel < 10% Status: solar H2: 10-20%
-photosynthesis & Status: solar to H2 < 10% -efficiency constrained by
separation limited. -losses: high T, multi-step visible sunlight.
-food & forest versus fuel. & back reactions, -solar thermal not used &
separation losses. is detrimental to PVs.
SLicht@GWU.edu, The George Washington University

6. Fueling future transportation: 3) STEP generation of solar fuel
Solar Thermal Electrochemical Photo conversion of solar energy
Sunlight is concentrated & excess thermal is split from visible sunlight
 
Heat reactants PV Electricity
 
Electrolysis (electrochemical reaction): ex water or CO2 splitting

Energetic Chemical Products: ex: H2 or synthetic solar diesel
SLicht@GWU.edu, The George Washington University

7. A new synergestic solar energy conversion process evolved from our solar H2 studies
SLicht@GWU.edu, The George Washington University

8. The STEP (Solar Thermal, Electrochemical and Photo) process
STEP is a synergy, which can capture
In STEP processes solar thermal energy more sunlight than individual
decreases the electrolysis energy. technologies by making use of both the
visible and thermal portions of sunlight.
This forms an energetically allowed
pathway to drive solar electrolyses, such
as water splitting to form H2 fuel.
SLicht@GWU.edu, The George Washington University

9. STEP hydrogen generation
2002: First STEP- theory that even a small bandgap semiconductor, such as Si, can drive water splitting.*
Hydrogen Oxygen Photovoltaic cell
Sunligh
t
High Temperature
Beam
Electrolyzer
splitter
hn
Overall reaction: H2O  H2(g) + ½
O2(g)
Today with our friends at Lynntech, Inc., a
2003: First STEP-experiment that i) a Si solar STEP type hydrogen generator is in
cell alone can drive H2 from water, and ii) development for the air force.
demonstration of STEP synergy: that a 26% Si
CPV, can form H2 at > 30% solar efficiency.**
*Licht, "Efficient solar generation of hydrogen fuel - a fundamental analysis,"
Electrochemistry Communications, 4/10, 789-794 (2002).
**Licht, Halperin, Kalina, Zidman "Electrochemical Potential Tuned Solar Water Splitting" Chem. Comm. (2003).
SLicht@GWU.edu, The George Washington University

10. Envisioning a STEP Hydrogen refueling center
In 2008,
Zweibel & Mason
assessed costs of conventional
PV driven water splitting and determined:
Solar H2 cost $6/kg & ~100 miles2 plant to fuel
106 fuel cell vehicles. With STEP H2 costs decrease > 2X
and the solar plant area is 6X smaller.
SLicht@GWU.edu, The George Washington University
Why?

11. In 2009 STEP was extended from H2 to the general formation of energetic chemicals.*
The energy to electrolyze CO2 into The energy decrease, provides
carbon monoxide falls even more opportunities for high STEP solar
rapidly with temperature than that of conversion efficiencies.
water.
Can this be accomplished experimentally?
*"STEP generation of energetic molecules:
A solar chemical process to end anthropogenic global warming,” J. of Phys. Chem., C, 113 (2009).
SLicht@GWU.edu, The George Washington University

12. Yes, in preliminary results, we drive a conventional
molten carbonate fuel cell in reverse mode:
generating fuel from electricity, instead of electricity
from fuel.
Carbon monoxide is efficiently formed, at low voltage
in accord with STEP,
in a molten carbonate bath fed by carbon dioxide.
cathode: CO2(g) +2e-  CO3=(molten) +CO(g)
anode: CO3=(molten)  CO2(g) +1/2O2(g) +2e-
cell: CO2(g)  CO(g) +1/2O2(g)
Why is the ability to
generate H2 and CO
efficiently from solar
energy at low
electrolysis voltage
significant?
SLicht@GWU.edu, The George Washington University

13. South Africa began to convert coal to synthetic diesel fuel, using the Fischer Tropsch
process, which arose from Nazi Germany’s search for an oil alternative.
Today, the majority of South Africa’s diesel is made using coal to generate CO and H2
for the Fischer Tropsch process: 2C + 2H2O  CO + 2H2 + CO2
FT: (2n+1)H2 + nCO  CnH(n+2) + nH2O
-Synthetic diesel are straight-chained C10-C15 alkanes, and are less expensive than
conventional diesel, when oil costs over $43/barrel.*
-Carbon dioxide’s contribution to global warming represents the primary drawback to
the Fischer-Tropsch process when using coal as a feedstock.*
STEP can form CO and H2 to feed Fischer Tropsch without CO2 generation.
The process, from CO2 conversion to synthetic diesel consumption is carbon neutral.
*Fisher-Tropsch Fuels from coal, natural gas & biomass. A. Andrews, J. Logan,
Congressional Research Service Report for Congress, March 27, 2008, 30 pages, available at:
http://www.policyarchive.org/handle/10207/19952
SLicht@GWU.edu, The George Washington University

14. Direct, efficient solar generation of fuels from sunlight,
ranging from H2 to synthetic diesel,
is an important alternative to vehicle electrification
powered by grid distributed renewable energy.
Acknowledgements Licht Group - STEP Participants
Baohui Wang, Susanta Ghosh, Hina Ayub, Olivia Chityat, Andrew
Dick, Harry Bergmann, Dimitry Sanchez, and Nabila Gasmi
S Licht is grateful for ongoing collaborations with:
Ken Zweibel, GWU Solar Institute
and Chris Rhodes, Lynntech, Inc.
and support of this research by:
The George Washington University Solar and Energy Institutes
SLicht@GWU.edu, The George Washington University