A PHOTO-ELECTROCHEMICAL DETERMINATION OF THE POSITION OF THE CONDUCTION AND VALENCE BAND EDGES OF P-TYPE CUO

Lithium-doped p-type CuO is a low mobility semiconductor with an indirect band gap of 1. 35 ev and a flatband potential of plus 0. 55 v, with respect to the saturated calomel electrode (SCE), when in contact with an electrolyte at a pH of 9. 4. Its valence band lies 5. 42 ev below the vacuum level and is made up mainly from the Cu**2** plus -3d wavefunctions. An oxygen 2p type band is at 7. 33 ev, in agreement with a semi-empirical estimate. Its performance as a photoelectrode for the solar photoelectrolysis of water is rather poor, because of the presence of recombination centers in the band gap and its chemical instability. As photoelectrolysis electrodes, oxides with 3d-type valence bands may have advantages over the more common oxides with 2p-type valence bands.