In-situ electrodeposition of bimetal Ni-Co selenides for high performance asymmetric supercapacitor

Transition-metal selenides have recently attracted increasing interest in supercapacitors (SCs) owning to their fascinating electrochemical properties. Here, binary metal selenides (NiCoSe2, NiCo2Se4, NiCo2Se4) are designed as novel electrode materials according to the reported NiSe and CoSe via a one-step electrodeposition process. The effects of different Ni/Co ratio on pseudo-capacitive properties of the binary metal selenides are investigated accordingly. Obviously, the designed binary metal selenides can combine the advantages of both metal selenides. As a result, the NiCoSe2 sample exhibits an optimized performance with a high specific capacity (334.2 mAh g-1, 1 A g-1), good rate capability, and excellent durability (90.7%, 5000 cycles). Most notably, the NiCoSe2//AC asymmetric SC (ASC) exhibits an excellent energy density of 41.7 Wh kg-1 at 800 W kg-1. Hence, a variety of ions with complementary advantages can be combined by electrodeposition, which provides an efficient way to synthesize excellent materials with various properties.