“…From the survey of XPS spectra in Figure 3 C, N 1s peak at 398 eV was only observed in the spectra of CuO@Cu 2 O/NrGO and CuO@Cu 2 O/PNrGO; C 1s, O 1s, and Cu 2p peaks can be found in all the samples. N species comes from the urea, and the N 1s spectra shown in Figure S5 can be split into four peaks centered at 398.1, 399.6, 401.1, and 402.6 eV, which are attributed to the pyridinic-N, pyrrolic/pyridone-N, graphitic-N, and N-oxide, 36 , 37 respectively. For CuO@Cu 2 O-bare and CuO@Cu 2 O/rGO, no N 1s spectrum was found due to the absence of nitrogen source during hydrothermal treatment.…”