“…Compared with the strong peak intensity of Ni, weak peaks at 19.31°, 31.26°, 36.85°, 38.38°, 44.64°, 55.27°, 59.34°, and 65.17°, which were assigned to the (111), (220), (311), (222), (400), (422), (511), and (440) lattice planes of Co 3 O 4 (JCPDS No. 42-1467), respectively (Figure ), could be detected for the Co 3 O 4 - x /Ni binder-free electrode. , The main reason for the weak intensity could be attributed to the limited amount of Co 3 O 4 and the strong background of Ni foam. Almost no impurity peaks could be found with increasing hydrothermal time, indicating the reaction time did not obviously affect the crystallization behavior of Co 3 O 4 .…”