Hybrid of NiCo2S4 and nitrogen and sulphur-functionalized multiple graphene aerogel for application in supercapacitors and oxygen reduction with significant electrochemical synergy

Abstract

The paper reports a promising hybrid of NiCo2S4 and nitrogen and sulphur-functionalized multiple graphene aerogel (N,S-MGA) for application in supercapacitors and oxygen reduction. The NiCo2S4/N,S-MGA was constructed by in-situ growth of ultrathin NiCo2S4 nanoflakes on dense and strong graphene conductive network of N,S-MGA. The resulting composite displays a well-defined three-dimensional architecture with hierarchical porous structure. The unique architecture not only enhances the structural stability of NiCo2S4 and effectively prevents the agglomeration of NiCo2S4 flakes and graphene sheets, resulting in high specific surface area of 76.3m2g−1, but also accelerates the electron transfer and electrolyte transport during the electrochemical process. The hybrid of N,S-MGA with NiCo2S4 achieves to significant synergy in the electrochemical reaction. The oxygen reduction further improves the electrode reactions, leading to an enhanced capacitance (about 23%). The NiCo2S4/N,S-MGA electrode exhibits high specific capacitance (822.6Fg−1 at the current density of 1Ag−1) and good rate-capability (556.8Fg−1 at the current density of 10Ag−1) for supercapactors, and excellent catalytic activity for oxygen reduction reaction in an O2-saturated 1.0M KOH electrolyte using a three-electrode test system. The asymmetric supercapacitor of NiCo2S4/N,S-MGA/activated carbon provides the energy density of 122Whkg−1 at the power density of 800Wkg−1 and 103.1Whkg−1 at the power density of 3200Wkg−1 in a two-electrode test system in an O2-saturated 1.0M KOH electrolyte. The energy density is much higher than that of single NiCo2S4 electrode and N,S-MGA electrode. Such a good capacitive performance make it can be used as the electrode materials for next-generation high-performance supercapacitors.