NiS/NiO heterojunction anchored on N-doped carbon nanosheet aerogels for dual-ion hybrid supercapacitors.

As a member of transition metal sulfides, NiS has been reported as one type of the effective pseudocapacitive electrode materials for supercapacitors, due to its good electrical conductivity and high electrochemical activity. To further improve the energy density of the NiS-based supercapacitors, we propose a novel approach to the NiS/NiO heterojunction anchored on N-doped carbon nanosheet aerogels (NiS/NiO@N-CNA), which is used as the cathode for Zn-ion hybrid supercapacitors with the dual-ion electrolytes. The NiS/NiO@N-CNA samples can be prepared through the bubble-templated polymerization of pyrrole and the carbonization of the polypyrrole nanosheet hydrogel/Ni. The NiS/NiO@N-CNA cathode is immersed into the Li-ion catholyte for Li storage, while the Zn foil anode is immersed into the Zn-ion anolyte for Zn storage. Electrochemical kinetic analysis of the dual-ion hybrid supercapacitor indicates its evident capacitance characteristic. Additionally, theoretical calculations reveal that the NiS/NiO heterojunction can facilitate the adsorption and dehydration of a hydrated Li ion to further play a great role in the enhancement of pseudocapacitance. Based on the novel strategy of the alkaline dual-ion electrolytes, this dual-ion hybrid supercapacitor with the high energy density (64.2 Wh kg) opens up a new avenue to develop high-performance Zn-ion hybrid supercapacitors.