Which Is Easier to Reduce, Cu[sub 2]O or CuO?

Chronopotentiometry (CP) using as the electrolyte has been most frequently used for selective determination of cuprous and cupric oxides ( and ) formed on copper surfaces. However, there are conflicting views regarding the order of reduction of the oxides. This study was carried out to settle this problem. Differently prepared samples of Cu-duplex oxide films were partially reduced by means of CP with and then submitted to X-ray diffractometry and also linear sweep voltammetry using a strongly alkaline electrolyte in which reduction peaks of and could be obtained with good separation. The results clearly demonstrated that was first reduced in , followed by the reduction of . However, the reductions of both oxides were found to occur simultaneously, to a greater or lesser extent, in . It was also revealed that was reduced to metal Cu in one step and that a partially reduced Cu-duplex oxide sample had an expected sandwich structure.