(73a) Electrochemical Reduction of CO2 On Modified Gold Surfaces

Electrochemical Reduction of CO₂
on Modified Gold Surfaces

Etosha
Cave, Kendra Kuhl, David Abram, and Thomas F. Jaramillo

Dept.
of Chemical Engineering, Stanford University

381
North-South Mall, Stanford, CA 94305 USA

The
efficient electrochemical reduction of CO₂ to fuels could be a viable
means to store electricity generated by renewable technologies such as solar
cells or wind turbines. Almost all metals have the ability to electrochemically
reduce carbon dioxide at low temperatures, however, most do so with low current
efficiencies for carbon based fuels or at high overpotentials [1].
Gold has previously been shown to produce carbon monoxide with faradaic
efficiencies around 90%, as well as formate with ~1% faradaic efficiency [2].  CO₂
reduction, as with many electrochemical reactions, is often dependent upon the
electrode surface structure and preparation. Thus, this presentation will focus
on enhancement of the activity and product selectivity of CO₂
reduction on gold by changing the topology of a polycrystalline gold surface.

In
this study, the surfaces of gold foils were roughened and then tested for the
electrochemical reduction of carbon dioxide. Testing was performed in a
3-electrode, 2-compartment compression cell separated by an anion exchange
membrane. Gas product analysis was achieved by a gas chromatograph, liquid
products by NMR. 

The
gold foils were characterized by their roughness. A variety of methods were
employed: surface roughness was calculated with charge transfer measurements and
electrochemical activity was studied using cyclic voltammetry in a 3-electrode
electrochemical compression cell. CO₂ reduction activities were
measured with a continuous flow of CO₂ in a CO₂ saturated
0.1M potassium bicarbonate solution at 23°C. An anion exchange membrane was
used to prevent liquid products from being oxidized at the counter electrode
which consisted of a platinum foil.  A Ag/AgCl reference electrode was used
during experimentation. Potentials were adjusted post experimentation to the
reversible hydrogen electrode (RHE). Potentials were also adjusted 100% for uncompensated
resistance.

Hydrogen
and carbon monoxide were the main products formed from the electrochemical
reduction of CO₂ on gold. We will describe our efforts to modify the
surface of gold and how such modifications translate to differences in activity
and selectivity for CO₂ reduction.  We will also discuss the
physical and chemical properties of the surface that could give rise to such
changes.

REFERENCES

[1]           M.
Azuma, K. Hashimoto, M. Hiramoto, M. Watanabe and T. Sakata, Journal of The
Electrochemical Society 137 (1990) 1772.

[2]           Y. Hori, H. Wakebe, T. Tsukamoto and O. Koga,
Electrochimica Acta 39 (1994) 1833.