Photoelectrochemical production of H2: an example of a model system

Abstract

H2 evolution was observed from a photoelectrochemical cell using an n-type Cu20 photoelectrode under visible light irradiation. Three-electrode configuration was used in the photoelectrochemical cell to observe H2 evolution. AgCl/Ag calomel electrode and a platinum plate were used as the reference and counter electrodes, respectively. FeS04 (10'4 M) and CuS04 (10‘3 M) solutions were used as the electrolytes. H2 evolution was visible on the platinum electrode. The highest H2 generation (8x10‘2 mol Y %) appears at the potential +0.5V vs NHE in the presence of CuS04 solution as the electrolyte. Degassing the system after each 4 hour cycle, the system is irradiated again. After each cycle, a decrease of the saturated value of evolved H2 is observed. In case of FeS04 electrolyte, this decrease is due to the fact, that during the illumination, in addition to the H2 evolution, a black amorphous product is formed gradually on the Pt electrode, thus decreasing the activity of the PEC cell acting the black amorphous product as a photocatalyst. When the biasing is more negative, band bending at semiconductor-electrolyte interface is small which reduces the concentration of the photogenerated charge earners and thus decrease the H2 evolution. When the bias is more positive than +0.5V vs NHE, the band position of CB becomes more positive compared to the H2/H+ redox level that suppresses the H? evolution. V-I characteristics for the PEC were investigated. Typical V-I characteristic curves were observed under dark and illumination for a PEC with n-type semiconductor. When the applied potential is more negative than the onset potential, dark current increases rapidly. For the positive potentials (vs NHE) dark current is almost zero for some regions. Under irradiation, total current increases at positive applied potential. Onset potential occurs at +0.1 IV vs NHE