Flexible 3D core–shell nanoforest arrays trimetal electrode for high capacitance supercapacitor

Abstract

A supercapacitor electrode with high capacitance is mainly based on the careful design of nanostructures and the intelligent hybridization of custom active materials. Herein, we designed 3D core-shell nanoforest arrays with hierarchical structure which are directly grown on carbon cloth using a two-step bracket-hydrothermal method and electrodeposition process. Due to the advantages of large specific surface area, abundant pores and active sites, the structure of Mo-Co-Ni(nanotube)@Ni-Co(nanosheet) arrays can promote electrolyte penetration and ions diffusion, further improving the electrochemical performance. The 3D core-shell nanoforest arrays electrode shows outstanding electrochemical performance: a superb areal capacitance of 9.81 F cm −2 (1998.0 F g −1 ) at the current densities of 1 mA cm −2 , as well as long cycle stability (after 3000 cycles maintains 85.4% of the highest capacitance value). This work may provide a promising method for design of flexible supercapacitor electrode materials.

Recent Progress in Core@Shell Sulfide Electrode Materials for Advanced Supercapacitor Devices

“…Nevertheless, they present some downsides, such as limited capacitance and short life cycle. Many approaches can be applied to overcome such limitations, but two stand out among them and deserves much attention: 1) the design of core@shell structured materials based on those bimetallic sulfides, as seen in the previous chapter; and 2) the incorporation of another metal ion into the sulfide structure, producing a trimetallic sulfide, [8b,10,30,58,64] for example by substituting some of its cations by Mn, [64a,b] Mo, [64d] Cu [30] or Fe [8b,64c] …”

“…Core@shell materials grown as ultrathin materials on highly conductive substrates present improved charge‐transfer and electrical conductivity. Therefore, additionally to the trimetallic sulfide‐based core@shell materials, [30] recent reports indicate hierarchical materials prepared with trimetallic sulfides as core and in situ grown mixed transition metal hydroxides shell can be an efficient strategy to exploit the relatively larger conductivity and specific capacitance of these materials, respectively [8b,64b,d] . Interestingly, since trimetallic sulfides have even higher electrochemical activity in comparison to the mono‐ and bimetallic counterparts, they are promising as shell materials along with a core prepared with an even more conductive material, such as carbon nanotube fibers (CNTF) [64a] and nickel nanocone arrays (NCA) [64c] …”

“…The superior electrochemical performance of core@shell materials with trimetallic sulfides as core can be attributed to synergistic effects encompassing: [30,64b,d,65] 1) the enhanced surface area due to the hierarchical structures, which leads to larger electrolyte/electrode interfaces and promotes facile electrolyte diffusion; 2) increased mechanical and electrochemical stability provided by the tight contact between the electrode components due to the in‐situ synthesis; 3) abundant redox active sites and rapid transport of ions/electrons, provided by numerous edge sites and the ultrathin interfaces with strong affinity for OH − ; 4) enhanced conductivity, high charge storage efficiency and rich electrochemical properties due to the multi‐metallic multivalence character (Ni 3+ /Ni 2+ , Co 3+ /Co 2+ Cu 2+ /Cu + , [30] Mn 2+ /Mn 3+ , [64a,b] Mo 4+ /Mo 5+ /Mo 6+[64d] and Fe 2+ /Fe 3+ ) [64c,65] of all reported materials in each specific case.…”

“…Only three materials that can be classified as mixed transition metal sulfide‐hydroxide core@shell materials were found in the literature: Ni 1.80 Co 0.50 Mn 0.50 S 1.52 @NiCoMn‐OH nanoneedles; [64b] 3D MoCoNi‐S@NiCo‐OH nanopine forest arrays; [64d] and hierarchical petal‐like NiFeCo‐S@NiFeCo‐TH heterogeneous ultrathin nanosheets [65] . Sanchez et al [64b] .…”

“…Lv et al ., [64d] on the other hand, explored deeply the synergistic effects of core@shell materials based on transition metal sulfides‐hydroxides. They prepared 3D MoCoNi‐S@NiCo‐OH nanopine forest arrays on carbon cloth (CC) by growing the core directly on CC by a two‐step hydrothermal method, and the shell by electrodeposition (Figure 18A–18D).…”