Self-formed porous Ni(OH)2 on Ni3S2/Ni foam during electrochemical cycling for high performance supercapacitor with ultrahigh areal capacitance

Enhanced faradic activity by construction of p-n junction within reduced graphene oxide@cobalt nickel sulfide@nickle cobalt layered double hydroxide composite electrode for charge storage in hybrid supercapacitor

The intrinsic faradic reactivity is the uppermost factor determining the charge storage capability of battery material, the construction of p-n junction composing of different faradic components is a rational tactics to enhance the faradic activity. Herein, a reduced graphene oxide@cobalt nickle sulfide@nickle cobalt layered double hydroxide composite (rGO@CoNi₂S₄@NiCo LDH) with p-n junction structure is designed by deposition of n-type nickle cobalt layered double hydroxide (NiCo LDH) around p-type reduced graphene oxide@cobalt nickle sulfide (rGO@CoNi₂S₄), the charge redistribution across the p-n junction enables enhanced faradic activities of both components and further the overall charge storage capacity of the resultant rGO@CoNi₂S₄@NiCo LDH battery electrode. As expected, the rGO@CoNi₂S₄@NiCo LDH electrode can deliver high specific capacity (C_s, 1310 ± 26 C g^-1 at 1 A g^-1) and good cycleability (77% C_s maintaining ratio undergoes 5000 charge-discharge cycles). Furthermore, the hybrid supercapacitor (HSC) based on the rGO@CoNi₂S₄@NiCo LDH p-n junction battery electrode exports high energy density (E_cell, 57.4 Wh kg^-1 at 323 W kg^-1) and good durability, showing the prospect of faradic p-n junction composite in battery typed energy storage.

2D nanosheet/3D cubic framework Ni-Co sulfides for improved supercapacitor performance via structural engineering

The construction of multi-dimensional structured battery-type electrode materials is a promising strategy to develop high performance electrodes for supercapacitors. Herein, a series of battery-type Ni3S2@Co3S4 electrodes with different morphologies are synthesized by controlling the hydrothermal reaction time. Owing to the unique structure with independent but interconnected 2D nanosheets and 3D cubic frameworks, NCS-60 displays high conductivity, numerous active sites and good wettability behavior. It can deliver a high specific capacity of 388.9 mA h g-1 (3500 F g-1) at 1 A g-1, an outstanding rate capacity of maintaining 88.6% at 10 A g-1 and long cycle stability. The battery-type supercapacitor hybrid (BSH) device with active carbon (AC) as the negative electrode delivers an energy density of 41.8 W h kg-1 at the power density of 800 W kg-1. This study provides a feasible route for regulating the morphologies of in situ growth materials that improve the electrochemical performance of supercapacitors.

MOF-assisted construction of a Co9S8@Ni3S2/ZnS microplate array with ultrahigh areal specific capacity for advanced supercapattery

Transition metal sulfides are important candidates of battery-type electrode materials for advanced supercapatteries due to their high electric conductivity and electrochemical activity. The Co9S8@Ni3S2/ZnS composite microplate array was prepared by a metal-organic framework-assisted strategy because the electrochemical properties of composite arrays are governed by the synergistic effects of their diverse structures and compositions. As a battery-type material, the Co9S8@Ni3S2/ZnS electrode expressed an ultrahigh areal specific capacity of 8192 C cm-2 at the current density of 2 mA cm-2, and excellent cycling stability of 79.7% capacitance retention after 4000 cycles. An assembled supercapattery device using the Co9S8@Ni3S2/ZnS microplate array as a positive electrode and active carbon as the negative electrode delivered a high energy density of 0.377 mW h cm-2 at a high power density of 1.517 mW cm-2, and outstanding retention of 95.2% after 5000 cycles. As a result, the obtained Co9S8@Ni3S2/ZnS shows potential for applications in high-performance supercapattery.

Heterojunction α-Co(OH)2/α-Ni(OH)2 nanorods arrays on Ni foam with high utilization rate and excellent structure stability for high-performance supercapacitor

The practical implementation of supercapacitors is hindered by low utilization and poor structural stability of electrode materials. Herein, to surmount these critical challenges, a three-dimensional hierarchical α-Co(OH)₂/α-Ni(OH)₂ heterojunction nanorods are built in situ on Ni foam through a mild two-step growth reaction. The unique lamellar crystal structure and abundant intercalated anions of α-M(OH)₂ (M = Co or Ni) and the ideal electronic conductivity of α-Co(OH)₂ construct numerous cross-linked ion and electron transport paths in heterojunction nanorods. The deformation stresses exerted by α-Co(OH)₂ and α-Ni(OH)₂ on each other guarantee the excellent structural stability of this heterojunction nanorods. Using nickel foam with a three-dimensional network conductive framework as the template ensures the rapidly transfer of electrons between this heterojunction nanorods and current collector. Three-dimensional hierarchical structure of α-Co(OH)₂/α-Ni(OH)₂ heterojunction nanorods provides a large liquid interface area. These result together in the high utilization rate and excellent structure stability of the α-Co(OH)₂/α-Ni(OH)₂ heterojunction nanorods. And the capacitance retention rate is up to 93.4% at 1 A g⁻¹ from three-electrode system to two-electrode system. The α-Co(OH)₂/α-Ni(OH)₂//AC device also present a long cycle life (the capacitance retention rate is 123.6% at 5 A g⁻¹ for 10000 cycles), a high specific capacitance (207.2 F g⁻¹ at 1 A g⁻¹), and high energy density and power density (72.6 Wh kg⁻¹ at 196.4 W kg⁻¹ and 40.9 Wh kg⁻¹ at 3491.8 W kg⁻¹), exhibiting a fascinating potential for supercapacitor in large-scale applications.