p-n photoelectrolysis cells

The efficiency of photoelectrolysis with solar radiation can be greatly enhanced by using simultaneously illuminated n- and p-type electrodes. An energy level scheme for heterotype and homotype p-n photoelectrolysis cells is presented which explains the enhanced efficiency. Data are presented for the homotype n-GaP/p-GaP and the heterotype n-TiO2/p-GaP systems which support the energy model. H2 and O2 are produced in the n-TiO2/p-GaP cell without the need of an external anodic bias.