Cu+& O2--terminated (211) surface Stability Mechanism of p-Cu2O as Photocathode Akiko Fillinger, Chemistry Department, Ithaca College Ithaca, NY 14850 Photodecomposition to Cu We have hypothesized that the stability of electro-deposited p-Cu2O is due to the Cu-terminated (111) surface, where reduction of O2 occurs preferentially in an aqueous solution upon illumination. On the other hand, single crystal p-Cu2O undergoes decomposition to Cu because of the predominate (211) and (311) surfaces, where H+ assisted reduction of Cu2O is inevitable. We are currently further testing this hypothesis. Stable Pyramids with a four-fold symmetry axis are shown in the AFM image of an electrodeposited p-Cu2O. The four-fold symmetry axis is parallel to the [100] direction, and the four sides were identified as (111) surface by XRD. Stoichiometric Cu+- terminated pyramid O2- are exposed. Stoichiometric O2--terminated (311) surface Cu+-terminated (211) Surface. Cu+& O2--terminated (211) surface