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

Abstract

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.

MnO2 Nanowires@NiCo-LDH Nanosheet Core–Shell Heterostructure: A Slow Irreversible Transition of Hydrotalcite Phase for High-Performance Pseudocapacitance Electrode

“…Therefore, an operating potential of 0–1.55 V can be obtained for the ASC. Moreover, the activated materials mass loading for the two electrodes can be calculated by the following equation where m + and m – are the masses of the positive and negative active materials in ASC, respectively, and C s+ and C s– are the specific capacitances of the positive and negative electrode active materials, respectively. The calculated mass ratio of the MnO 2 @LDH-2 and AC materials is ca.…”

“…Therefore, an operating potential of 0−1.55 V can be obtained for the ASC. Moreover, the activated materials mass loading for the two electrodes can be calculated by the following equation 30…”

Anchoring γ-MnO2 within β-NiCo(OH)2 as an Interfacial Electrode Material for Boosting Power Density in an Asymmetric Supercapacitor Device and for Oxygen Evolution Catalysis

“…Recently, Ni- and Co-based hydroxide materials are receiving considerable attention due to their easy tunability and rich in redox activity. Most importantly, both Ni- and Co-based LDHs exist in the form of the α or β phase . Also, many efforts have been made to synthesize the different phases of bimetallic hydroxides such as α- or β-NiCo­(OH) 2 to understand the change in the electrochemical properties via the synergistic effect between individual metal hydroxides, that is, α-Ni­(OH) 2 or β-Ni­(OH) 2 or α-Co­(OH) 2 or β-Co­(OH) 2 . , For instance, Tang and Zhao et al prepared the mixture of flower-like α- and β-Ni 0.28 Co 0.72 (OH) 2 using the template-free method to exhibit the specific capacity of 174.3 mA h/g at 1 A/g.…”

“…Besides, the assembled asymmetric supercapacitor using α- and β-Ni 0.28 Co 0.72 (OH) 2 as positive electrode materials and activated carbon (AC) as a negative electrode shows the capacitance of 54.5 F/g at 0.1 A/g current density, where flower-like morphology exhibits a high surface area for fast intercalation/de-intercalation of electrolyte ions . Furthermore, Chen and Mi et al constructed the asymmetric supercapacitor of the α-Co­(OH) 2 /α-Ni­(OH) 2 //AC device to show the specific capacitance of 207.2 F/g at 1 A/g current density . Furthermore, Zhang et al used a simple hydrothermal and solvothermal route and variation in the solvent mixture to synthesize three different hierarchical α-Ni­(OH) 2 microspheres, where the water/ethanol mixture showed better specific capacitance …”

“…Most importantly, both Ni-and Co-based LDHs exist in the form of the α or β phase. 12 change in the electrochemical properties via the synergistic effect between individual metal hydroxides, that is, α-Ni(OH) 2 or β-Ni(OH) 2 or α-Co(OH) 2 or β-Co(OH) 2 . 13,14 For instance, Tang and Zhao et al prepared the mixture of flower-like αand β-Ni 0.28 Co 0.72 (OH) 2 using the template-free method to exhibit the specific capacity of 174.3 mA h/g at 1 A/g.…”