ZnO/CoS heterostructured nanoflake arrays vertically grown on Ni foam for high-rate supercapacitors

Hybrid supercapacitors using metal-organic framework derived nickel-sulfur compounds

HYPOTHESIS

Metal-organic frameworks (MOFs) are highly suitable precursors for supercapacitor electrode materials owing to their high porosity and stable backbone structures that offer several advantages for redox reactions and rapid ion transport.

EXPERIMENTS

In this study, a carbon-coated Ni9S8 composite (Ni9S8@C-5) was prepared via sulfuration at 500 ℃ using a spherical Ni-MOF as the sacrificial template.

FINDING

The stable carbon skeleton derived from Ni-MOF and positive structure-activity relationship due to the multinuclear Ni9S8 components resulted in a specific capacity of 278.06 mAh·g-1 at 1 A·g-1. Additionally, the hybrid supercapacitor (HSC) constructed using Ni9S8@C-5 as the positive electrode and the laboratory-prepared coal pitch-based activated carbon (CTP-AC) as the negative electrode achieved an energy density of 69.32 Wh·kg-1 at a power density of 800.06 W·kg-1, and capacity retention of 83.06 % after 5000 cycles of charging and discharging at 5 A·g-1. The Ni-MOF sacrificial template method proposed in this study effectively addresses the challenges associated with structural collapse and agglomeration of Ni9S8 during electrochemical reactions, thus improving its electrochemical performance. Hence, a simple preparation method is demonstrated, with broad application prospects in supercapacitor electrodes.

MOF-derived NiCo-LDH Nanocages on CuO Nanorod Arrays for Robust and High Energy Density Asymmetric Supercapacitors

Layered double hydroxide (LDH) is widely explored in supercapacitors on account of its high capacity, adjustable composition and easy synthesis process. Unfortunately, solitary LDH still has great limitations as an electrode material due to its shortcomings, such as poor conductivity and easy agglomeration. Herein, nanoflakes assembled NiCo-LDH hollow nanocages derived from a metal-organic framework (MOF) precursor are strung by CuO nanorods formed from etching and oxidation of copper foam (CF), forming hierarchical CuO@NiCo-LDH heterostructures. The as-synthesized CuO@NiCo-LDH/CF shows a large capacitance (5607 mF cm^-2 at 1 mA cm^-2 ), superior rate performance (88.3 % retention at 10 mA cm^-2 ) and impressive cycling durability (93.1 % capacitance is retained after 5000 cycles), which is significantly superior to control CuO/CF, CuO@ZIF-67/CF, NiCo-LDH/CF and Cu(OH)₂ @NiCo-LDH/CF electrodes. Besides, an asymmetrical supercapacitor consists of CuO@NiCo-LDH/CF and activated carbon displays a maximum energy density of 47.3 Wh kg^-1 , and its capacitance only declines by 6.8 % after 10000 cycles, demonstrating remarkable cycling durability. The advantages of highly conductive and robust CuO nanorods, MOF-derived hollow structure and the core-shell heterostructure contribute to the outstanding electrochemical performance. This synthesis strategy can be extended to design various core-shell heterostructures adopted in versatile electrochemical energy storage applications.

Design and Construction of Cu(OH)2/Ni3S2 Composite Electrode on Cu Foam by Two-Step Electrodeposition

A Cu(OH)2/Ni3S2 composite has been designed and in situ constructed on Cu foam substrate by facile two-step electrodeposition. Cu(OH)2 is achieved on Cu foam by galvanostatic electrodeposition, and the subsequent coating of Ni3S2 is realized by cyclic voltammetric (CV) electrodeposition. The introduction of Cu(OH)2 provides skeleton support and a large specific surface area for the Ni3S2 electrodeposition. Benefiting from the selection of different components and preparation technology, the Cu(OH)2/Ni3S2 composite exhibits enhanced electrochemical properties with a high specific capacitance of 4.85 F cm−2 at 2 mA cm−2 and long-term cyclic stability at 80.84% (4000 cycles).

Facile hydrothermal synthesis of cobaltosic sulfide nanorods for high performance supercapacitors

With high reactivity, electrical conductivity, theoretical specific capacitance and well redox reversibility, transition metal sulfides are considered as a promising anode material for supercapacitors. Hence, we designed a simple two-step hydrothermal process to grow Co₄S₃ nanorod arrays in situ on flexible carbon cloth substrates. Benefited from the larger specific surface area of nanoarrays, the binder-free Co₄S₃ electrode demonstrates a higher specific capacity of 1.97 F cm⁻² at a current density of 2 mA cm⁻², while the Co₃O₄ electrode has a capacity of only 0.07 F cm⁻² at the same current density. Surprisingly, at a high scan rate of 200 mV s⁻¹, the synthesized Co₄S₃ electrode still maintains almost 100% of its initial capacitance after 5000 cycles. Moreover, when using the prepared Co₄S₃ and MnO₂ electrode as the anode and cathode, the fabricated flexible supercapacitor obtains a high volumetric energy density of 0.87 mW h cm⁻³ (power density of 0.78 W cm⁻³) and a peak power density of 0.89 W cm⁻³ (energy density of 0.50 mW h cm⁻³). The excellent electrochemical properties imply that there is a large market for the prepared materials in flexible energy storage devices.

With high reactivity, electrical conductivity, theoretical specific capacitance and well redox reversibility, transition metal sulfides are considered as a promising anode material for supercapacitors.