“…When compared to simple metal oxides, mixed metal oxides exhibit high electrical conductivity due to lower activation energy for electron transfer between cations [3,18]. A number of single phase binary metal oxide systems such as CuFe 2 O 4 [19], NiMn 2 O 4 [20], MnFe 2 O 4 [21,22], ZnCo 2 O 4 [23], MnCo 2 O 4 [24], CoFe 2 O 4 [25,26], NiCo 2 O 4 [27,28], and their composites CoFe 2 O 4 /graphene [29], NiFe 2 O 4 /PANI [30], NiCo 2 O 4 /graphene [31,32], NiCo 2 O 4 /CNT [33] and NiCo 2 O 4 /carbon cloth [34] have been reported. Among these oxides, the spinel NiCo 2 O 4 has been emerging as high performance electrode material for ECs.…”