“…O1s peaks, representing byproducts of copper oxide synthesis, of three samples are presented in Fig. 8(c); the inset indicates the distributable energy band of oxide (O 2− ), hydroxide, or hydroxyl groups (OH − ), as well as water (H 2 O) [22]. The O1s spectrum in the control sample was composed of two overlapping peaks corresponding to O 2− and OH − .…”