INFLUENCE OF SURFACE-TREATMENT OF THE P-GAP PHOTOCATHODE ON THE PHOTOELECTROCHEMICAL REDUCTION OF CARBON-DIOXIDE

Effects of the surface treatments of p-GaP electrodes with various etchants on the photoelectroreduction of CO2 were investigated in 0.1 mol dm-3 KHCO3 aqueous solution. The catalytic activities for CO2 photoelectroreduction of p-GaP electrodes depended on the etchants and also their crystallographic orientations, (100) or (111) faces. The reduction products were only HCOO- and CO from CO2, and H-2 as a by-product. Aqua regia was prefer to produce HCOO- on both faces. Conc. HCl was effective for HCOO- formation on the (111) face. Although the alkaline potassium hexacyanoferrate(III) solution was effective for reducing the overpotential and increase the photocurrent, the main product was H-2. Conc. HNO3 was not effective.