Hierarchical Design of Cross‐Linked NiCo₂S₄ Nanowires Bridged NiCo‐Hydrocarbonate Polyhedrons for High‐Performance Asymmetric Supercapacitor

Abstract

Engineering core‐shell materials with rationally designed architectures and components is an effective strategy to fulfill the high‐performance requirements of supercapacitors. Herein, hierarchical candied‐haws‐like NiCo2S4@NiCo(HCO3)2 core‐shell heterostructure (NiCo2S4@HCs) is designed with NiCo(HCO3)2 polyhedrons being tightly strung by cross‐linked NiCo2S4 nanowires. This rational design not only creates more electroactive sites but also suppresses the volume expansion during the charge–discharge processes. Meanwhile, density functional theory calculations ascertain that the formation of NiCo2S4@HCs heterostructure simultaneously facilitates OH− adsorption/desorption and accelerates electron transfer within the electrode, boosting fast and efficient redox reactions. Ex situ X‐ray diffraction and Raman measurements reveal that gradual phase transformations from NiCo(HCO3)2 to NiCo(OH)2CO3 and then to highly‐active NiCoOOH take place during the cycles. Therefore, NiCo2S4@HCs demonstrates an ultrahigh capacitance of 3178.2 F g−1 at 1 A g−1 and a remarkable rate capability of 2179.3 F g−1 at 30 A g−1. In addition, the asymmetric supercapacitor NiCo2S4@HCs//AC exhibits a high energy density of 69.6 W h kg−1 at the power density of 847 W kg−1 and excellent cycling stability with 90.2% retained capacitance after 10 000 cycles. Therefore, this novel structural design has effectively manipulated the interface charge states and guaranteed the structural integrity of electrode materials to achieve superior electrochemical performances.

An urchin-like Co-doped NiS2/C nanorod array with enriched sulfur vacancies for asymmetric supercapacitors

“…50 The deconvolutions of Co 2p 3/2 peaks show that Co-O and Co-S are located at 795.0 and 794.6 eV, and the Co 2p 1/2 peaks are located at 780.5 and 778.9 eV, respectively. 5 Also, two satellite peaks around 786.3 and 803.0 eV are observed for all four samples. In Fig.…”

“…7c, mainly consists of a small semicircle in the high-frequency region and a straight line in the low-frequency region, representing charge transfer resistance ( R ct ) and diffusion resistance ( R s ), respectively. 5,37 As shown in Tab. S3,† the R ct and R s of Co-NiS 2 /C are 0.49 and 0.53 Ω, indicating a lower charge-transfer resistance and a higher ion diffusion rate.…”

“…3,4 Transition metal suldes, especially bimetallic Ni-Co suldes, have attracted considerable scientic and technical interest due to their excellent electrochemical performance. [5][6][7] Bimetallic Ni-Co suldes have higher electron transfer efficiency than monometallic suldes due to redox pairs of Co 3+ /Co 2+ and Ni 3+ / Ni 2+ and the electron jumps between different valence states. 7 However, their electrochemical activity and stability are severely restricted by their poor conductivity and large charge-discharge deformation.…”

Hollow nanotube arrays of nickle–cobalt metal sulfide for high energy density supercapacitors

“…6b. At a lower scanning rate of 2 mV s −1 , a pair of significant redox peaks are observed near 0.37 and 0.22 V, which indicates that the specific capacity is mainly attributed to the following typical reaction process: 44,45 NiCo 2 S 4 + OH − + H 2 O ↔ NiS (4−4 x ) OH + 2CoS 2 x OH + e − CoS 2 x OH + OH − ↔ CoS 2 x O + H 2 O + e − CoS 2 x + OH − ↔ CoS 2 x OH + e − NiS (4−4 x ) + OH − ↔ NiS (4−4 x ) OH + e − With the increase of scanning rate, the oxidation peak and reduction peak move to higher potential and lower potential, respectively.…”

“…6b. At a lower scanning rate of 2 mV s −1 , a pair of signicant redox peaks are observed near 0.37 and 0.22 V, which indicates that the specic capacity is mainly attributed to the following typical reaction process: 44,45…”