V vs. Ag/AgCl electrode No clathrates V vs. Ag/AgCl

Daniel DeCiccio*$, Francisco Schunk*, Steven Ahn$, Sugat Sen$, Tayhas Palmore$, Christoph Rose-Petruck*

*Department of Chemistry, Brown University, $ School of Engineering, Brown University

Introduction

We aim to develop new technology that captures and converts carbon

dioxide (CO2) into valuable products such as ethylene. Currently, the

chemical industry uses oil, a non-sustainable carbon source, to

makes billions of pounds of these products. The replacement of oil by

CO2 as a carbon source is a promising alternative because of the

great abundance of CO2.

We attacked the problem in a new way by first capturing the CO2 in

clathrate hydrates and then reducing the CO2 electrochemically. By

first using clathrates to capture and sequester carbon dioxide we

created the first processes for capturing and converting carbon

dioxide into hydrocarbons. We are the first group to both capture and

convert the carbon dioxide.

Water-solvated gases with molecular diameters between 0.35nm and

0.75nm can transform into inclusion compounds under suitable

thermodynamic conditions. Gas solute molecules occupy sites in

aqueous cage structures formed by the water molecules. The guest

molecules do not chemically bind to the water molecules but stabilize

the clathrates cages. These inclusion compounds are known as

clathrate hydrates. Clathrate hydrates allow the storage of huge

volumes of gas, up to more than an order of magnitude more than

would usually be soluble in a solution.

Clathrates usually form at high pressure and low temperature. The

pressure required to form clathrate hydrates can be reduced by

adding solute molecules, such as tetrahydrofuran, to the liquid water.

The clathrates form a slushy like solution which can selectively uptake

different gasses based on the temperature we set the reactor to.

Experimental

Conclusion

We use a copper foam working electrode (cathode) to increase surface

area available to reduce CO2.

Clathrate Hydrates of Natural Gases, E. D. Sloan, 2 ed. (Jr. Marcel

Dekker, Inc, New York, 1998).

Conversion of Carbon Dioxide into

Hydrocarbons using Clathrates Hydrates

References

We Performed cyclic voltammetry to characterize the electrochemical

properties of the copper foam and chronopotentiometry to reduce the CO2.

Gaseous products were quantified with gas chromatograph and liquid

products with gas chromatography

Clathrate Hydrates

Custom Batch Reactor

Clathrate Slurry

Electrochemical Cell

Electron micrographs of copper foam electrodes

We built a custom batch reactor to make up to 2L of clathrate slurry at

a time. The reactor is chilled and under constant slight positive CO2

pressure. The Clathrate hydrates are then loaded into an electrochemical

cell to perform electrolysis.

Manometer

showing

positive

pressure

Cyclic Voltammogram of

copper foam showing the

onset potential where the

bottom part of the curve

begins to drop at ~-1.0V

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

120%

-1.8 -1.7 -1.6 -1.5 -1.4 -1.3 -1.2 -1.1 -1 -0.9

Fara

dai

c Ef

fici

ency

(%

)

V vs. Ag/AgCl electrode

With clathratesTotalH2COHCOOH

0%

1%

2%

3%

-1.8 -1.7 -1.6 -1.5 -1.4 -1.3 -1.2 -1.1 -1 -0.9

Fara

dai

c Ef

fici

ency

(%

)

V vs. Ag/AgCl electrode

With clathratesCH4

C2H4

C2H6

C3H6

C3H8

C4H8 ?

C4H10 ?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

120%

-1.8 -1.7 -1.6 -1.5 -1.4 -1.3 -1.2 -1.1 -1 -0.9

Fara

dai

c Ef

fici

ency

(%

)

V vs. Ag/AgCl electrode

No clathratesTotal

H2

CO

HCOOH

0%

1%

2%

3%

-1.8 -1.7 -1.6 -1.5 -1.4 -1.3 -1.2 -1.1 -1 -0.9

Fara

dai

c Ef

fici

ency

(%

)

V vs. Ag/AgCl electrode

No clathratesCH4

C2H4

C2H6

C3H6

C3H8

C4H8 ?

C4H10 ?

When clathrate hydrates were used as a source of carbon dioxide, we

saw

Greater carbon monoxide production at -1V vs Ag/AgCl, 70% vs

10%

Greater formic acid production at -1.3 and -1.7V vs Ag/AgCl

Less hydrogen production at all potentials

We demonstrated the first use of

clathrate hydrates as a gas supply to an

electrochemical reaction. This is the

first work to incorporate both carbon

capture and conversion technology into

one overall process.

This is a first step to creating an

artificial carbon cycle in which carbon

dioxide may be captured and converted

into usable products such as formic

acid and carbon monoxide

We have begun investigating the use of

clathrate hydrates with a variety of other

catalysts.

Results