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.