Photoelectrochemical water splitting with a solar photovoltaic cell provides for the direct conversion of solar energy into a practical chemical fuel such as hydrogen. Current devices however suffer from the high cost, low efficiency and limited lifetime of the electrodes, in particular the photoanode. We investigate here the effect of various surface modification procedures for Si and Ti oxide surfaces on the photoelectrochemical production of hydrogen.
Pt nanoclusters were deposited on Si by electrodeposition, electroless deposition and from water-in-oil microemulsions, in order to control and thus optimize the average diameter, dispersion and density of Pt clusters. Pt islands with smallest dimensions (20-40 nm) and narrow size distribution were best obtained from reversed micellar solutions. Conversion efficiency is found to depend on light intensity (10 - 100 mW/cm²); at high intensity, only Pt islands with small size were capable to maintain photoconversion efficiency as high as 20%.
Arrays of Ti oxide nanotubes with diameters 100-200 nm were obtained by electrochemical anodization of sputtered Ti films; surface modification by carbon or nitrogen, achieved by thermal annealing in suitable atmospheres or electrochemical charging in suitable solutions, were found to decrease the energy gap of the titania and to provide for an increased photoconversion efficiency under simulated solar light.