SLicht@GWU.edu, The George Washington University

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

High Temperature

Carnot limited

generator

Electricity – 6% grid losses!

Nuclear solarwindwater

mechanical

limited

generator

photovoltaic

generation

Vehicle Electrification

SLicht@GWU.edu, The George Washington University

Fueling future transportation: 2) prior solar fuel options were inefficient

Solar Thermal

Status: solar to H2 < 10%

-losses: high T, multi-step

& back reactions,

separation losses.

Solar Concentrator

High Temp

Multi-step Reactions

Hydrogen

Gas Separation

Solar PV

Status: solar H2: 10-20%

-efficiency constrained by

visible sunlight.

-solar thermal not used &

is detrimental to PVs.

Photovoltaics

Electricity

Hydrogen

Water Electrolysis

Biofuels

Status: solar to fuel < 10%

-photosynthesis &

separation limited.

-food & forest versus fuel.

Photosynthesis

Algae or Plant

Fuel Separation

Alcohol, CH4, etc

SLicht@GWU.edu, The George Washington University

Fueling future transportation: 3) STEP generation of solar fuel

Solar Thermal Electrochemical Photo conversion of solar energy

Electrolysis (electrochemical reaction): ex water or CO2 splitting

Sunlight is concentrated & excess thermal is split from visible sunlight

Energetic Chemical Products: ex: H2 or synthetic solar diesel

PV ElectricityHeat reactants

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

STEP is a synergy, which can capture

more sunlight than individual

technologies by making use of both the

visible and thermal portions of sunlight.

The STEP (Solar Thermal, Electrochemical and Photo) process

In STEP processes solar thermal energy

decreases the electrolysis energy.

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

2002: First STEP- theory that even a small bandgap semiconductor, such as Si, can drive water splitting.*

STEP hydrogen generation

Today with our friends at Lynntech, Inc., a

STEP type hydrogen generator is in

development for the air force.

High Temperature

Electrolyzer

Photovoltaic cell

Beam

splitter

Sunligh

t

Hydrogen Oxygen

hnOverall reaction: H2O H2(g) + ½

O2(g)

2003: First STEP-experiment that i) a Si solar

cell alone can drive H2 from water, and ii)

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.

Why?

SLicht@GWU.edu, The George Washington University

*"STEP generation of energetic molecules:

A solar chemical process to end anthropogenic global warming,” J. of Phys. Chem., C, 113 (2009).

The energy to electrolyze CO2 into

carbon monoxide falls even more

rapidly with temperature than that of

water.

The energy decrease, provides

opportunities for high STEP solar

conversion efficiencies.

Can this be accomplished experimentally?

In 2009 STEP was extended from H2 to the general formation of energetic chemicals.*

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

Baohui Wang, Susanta Ghosh, Hina Ayub, Olivia Chityat, Andrew

Dick, Harry Bergmann, Dimitry Sanchez, and Nabila Gasmi

Acknowledgements Licht Group - STEP Participants

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

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.