“…12,13 In recent years, transition metal oxides such as zinc oxide (ZnO), vanadium oxide (V 2 O 5 ), cobalt oxide (Co 3 O 4 ), ruthenium oxide (RuO 2 ), and other related materials have been extensively employed as electrode materials for supercapacitors. [14][15][16][17][18][19][20][21][22][23][24][25] Among the widely studied supercapacitor electrode materials, a spinal structure (AB 2 O 4 ) of mixed transition metal oxides, comprising single-phase ternary metal oxides with two various transition metal elements has attracted much attention because of its higher electronic conductivity and electrochemical activity than the single transition metal oxides. [26][27][28] In particular, spinel nickel cobaltite (NiCo 2 O 4 [NCO]) has been broadly investigated as an electrode material in EDLC because of its advantages including large theoretical capacitance value (Z3000 F g À1 ), low cost, environmental-friendliness, etc.…”