In the case of -1.8 and -2.3 V, the oxygen content is above original GO. In addition, the sp 2 C fraction obtained from C1s peak in Figure and shows that the GO is reduced at < -1.1 V. Consequently, the increased oxygen content at < -1.8 V indicates that Cr2O3 is electrochemically synthesized within the rGO stack. When the GO/Ag was replaced by a pure Ag substrate no Cr signal was found in the XPS result under the same electrochemical conditions.