Licht - Solar Fuels for Transportation

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

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

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

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

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

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

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

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

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

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?

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

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

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

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

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Licht - Solar Fuels for Transportation

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