Thermodynamic stabilities of semiconductor electrodes

The application of the Pourbaix diagram to the prediction and understanding of the thermodynamic stability of semiconductor materials is discussed. With the aid of flat band potential information, the thermodynamic stability of semiconductor materials under various operating conditions, types of electrodes (n- or p-) to be used, conversion efficiencies, types of redox couples to be chosen for a given semiconductor electrode material, and the proper operating pH region can be determined. It is shown from the available information that all the semiconductor materials examined, i.e., CdS, CdSe, CdTe, and GaP may be unstable with respect to anodic dissolution and that p-type electrodes may be successfully used as photocathodes for the photoassisted electrolysis of water to hydrogen. GaAs is shown to be unstable with respect to both anodic and cathodic dissolution.