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Honeycomb-like Ni(OH)2/Ni3S2/Ni foam (NF) was fabricated via a two-step hydrothermal process and subsequent alkalization. Ni3S2 with a honeycombed structure was in-situ synthesized on the NF surface by a hydrothermal process. MOF-derived Ni(OH)2 nanosheets were then successfully grown on the Ni3S2/NF surface by a second hydrothermal process and alkaline treatment, and a large number of nanosheets were interconnected to form a typical honeycomb-like structure with a large specific surface area and porosity. As a binder-free electrode, the prepared honeycomb-like Ni(OH)2/Ni3S2/NF exhibited a high specific capacitance (2207 F·g−1 at 1 A·g−1, 1929.7 F·g−1 at 5 mV·s−1) and a remarkable rate capability and cycling stability, with 62.3% of the initial value (1 A·g−1) retained at 10 A·g−1 and 90.4% of the initial value (first circle at 50 mV·s−1) retained after 5000 cycles. A hybrid supercapacitor (HSC) was assembled with Ni(OH)2/Ni3S2/NF as the positive electrode and activated carbon (AC) as the negative electrode and exhibited an outstanding energy density of 24.5 Wh·kg−1 at the power density of 375 W·kg−1. These encouraging results render the electrode a potential candidate for energy storage. [ABSTRACT FROM AUTHOR]

Honeycomb-like Ni(OH)2/Ni3S2/Ni foam (NF) was fabricated via a two-step hydrothermal process and subsequent alkalization. Ni3S2 with a honeycombed structure was in-situ synthesized on the NF surface by a hydrothermal process. MOF-derived Ni(OH)2 nanosheets were then successfully grown on the Ni3S2/NF surface by a second hydrothermal process and alkaline treatment, and a large number of nanosheets were interconnected to form a typical honeycomb-like structure with a large specific surface area and porosity. As a binder-free electrode, the prepared honeycomb-like Ni(OH)2/Ni3S2/NF exhibited a high specific capacitance (2207 F·g−1 at 1 A·g−1, 1929.7 F·g−1 at 5 mV·s−1) and a remarkable rate capability and cycling stability, with 62.3% of the initial value (1 A·g−1) retained at 10 A·g−1 and 90.4% of the initial value (first circle at 50 mV·s−1) retained after 5000 cycles. A hybrid supercapacitor (HSC) was assembled with Ni(OH)2/Ni3S2/NF as the positive electrode and activated carbon (AC) as the negative electrode and exhibited an outstanding energy density of 24.5 Wh·kg−1 at the power density of 375 W·kg−1. These encouraging results render the electrode a potential candidate for energy storage.

Nickel/cobalt hydroxide is a promising battery-type electrode material for supercapacitors. However, its low cycle stability hinders further applications. Herein, Ni 0.7 Co 0.3 (OH) 2 core-shell microspheres exhibiting extreme-prolonged cycling life are successfully synthesized, employing Ni-Co-metal-organic framework (MOF) as the precursor/template and a specific hydrolysis strategy. The Ni-Co-MOF and KOH aqueous solution are separated and heated to 120 °C before mixing, rather than mixing before heating. Through this hydrolysis strategy, no MOF residual exists in the product, contributing to close stacking of the hydroxide nanoflakes to generate Ni 0.7 Co 0.3 (OH) 2 microspheres with a robust core-shell structure. The electrode material exhibits high specific capacity (945 C g -1 at 0.5 A g -1 ) and unprecedented cycling performance (100% after 10 000 cycles). The fabricated asymmetric supercapacitor delivers an energy density of 40.14 Wh kg -1 at a power density of 400.56 W kg -1 and excellent cycling stability (100% after 20 000 cycles). As far as is known, it is the best cycling performance for pure Ni/Co(OH) 2 ., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)