Properties of Metal Coated p-GaP Photocathodes in Photoelectrochemical Reduction of Carbon Dioxide in Aqueous Electrolytes

Abstract

Photocurrent spectra, current-potential curves and photoelectrochemical properties of Pb, Zn or Au coated p-GaP photocathodes have been investigated to clarify their behaviors as the photocathode for photoelectrochemical reduction of carbon dioxide [CO₂] in aqueous electrolytes. In the case of Pb-p-GaP, silvery luster was observed on the electrode surface during the photoelectrolytic reduction of CO₂. Such a silvery state of the surface, probably metallic Pb, might prevent the hydrogen evolution reaction, and resulted in a remarkable increase of the faradaic efficiencies for the formation of HCOOH and CO, although the spectral photocurrents were depressed. On the other hand, Au coated p-GaP photocathode became more stable than the bare one, and the photocurrent was kept almost constant for many hours. In the aqueous solutions of tetraalkylammonium salts, the size of cation did not affect the faradaic efficiency for HCOOH formation. The larger cation, however, promoted the formation of CO.