Carbon dioxide reduction on gallium arsenide electrodes

Abstract

Studies of carbon dioxide reduction by conduction band electrons from gallium arsenide single-crystal electrodes were undertaken, to determine the degree of product selectivity. It was found that a reinterpretation of the reduction process is necessary. The most striking result was the detection of open circuit (dark) reduction of carbon dioxide to methanol. This occurred at the rate of 0.1 ..mu..mol/(h cm/sup 2/) on the As face of the heavily doped p-type GaAs. A slightly higher rate (50%) was observed for moderately doped n-type crystal. Some formaldehyde production was also seen but at a much smaller rate (1/5). It was determined that this rate is constant with surface area and time. A measurement on the opposite face (Ga) showed very little methanol production. It was also determined that damaging the surface greatly reduced methanol production while increasing the amount of formaldehyde. Closed circuit measurements under cathodic bias showed reduction of carbon dioxide as indicated by the disappearance of hydrogen bubbles when the carbon dioxide gas was introduced. The product was almost certainly formic acid as no additional methanol or formaldehyde (over the open circuit results) was detected at either high current (10 mA) or low current (0.2 mA). 25 references, 5more » figures, 1 table.« less