typical singals of Ni2p and P2p were detected from the survey scan of Ni-P; and typical singals of Ni2p,
Co2p and O1 s were detected from the survey scan of NiCo2O4; whereas typical singals of Ni2p, Co2p, P2p and O1 s were detected from the survey scan of Ni-P@NiCo2O4composite. The XPS results further confirm the formation of Ni-P@NiCo2O4composite