In-situ growth of binder-free Cr/NiO thin film electrodes via co-sputtering for asymmetric supercapacitors

•Binder-free Cr/NiO electrodes prepared by single-step magnetron sputtering.•Synergistic effect of Cr in NiO is highlighted in asymmetric supercapacitor.•Cr doped NiO showed an excellent supercapacitive performance (429 mF cm−2).•Remarkable cycling stability performance over 5,000 cycles.•Aging effect of coin cell was examined after 720 h.•Cr/NiO electrodes can utilized for portable and miniaturized electronic devices.