Crystal Face Dependence of p-Cu[sub 2]O Stability as Photocathode

Previously we hypothesized that the reported stability of electrodeposited p-Cu 2 O films is attributed to the predominant Cu + -terminated (111) surface, where the Cu + -supported O 2 reduction occurs and the H + -assisted Cu 2 O reduction, which is the decomposition of Cu 2 O , does not happen. The well-known instability of single-crystal Cu 2 O is attributed to predominant (211) and (311) surfaces, where the photodecomposition into Cu is inevitable at the exposed O 2 − sites. To examine our hypothesis, the stability and photochemical behavior were compared between electrodeposited Cu 2 O films with predominantly Cu + -terminated surfaces and ones with predominantly O 2 − -terminated surfaces. When used as photocathodes, the predominantly Cu + -terminated films did not deteriorate as readily as the predominantly O 2 − -terminated films did. Also, when oxygen was removed from the aqueous solution, the predominantly Cu + -terminated films generated photocurrents one order of magnitude smaller compared to the predominantly O 2 − -terminated films, indicating the stability of the Cu + -terminated surface against photodecomposition into Cu. These results confirmed our hypothesis on the crystal face dependence of p-Cu 2 O stability as a photocathode.