Formation of nickel-cobalt sulphide@graphene composites with enhanced electrochemical capacitive properties

Porous Carbon-Based Supercapacitors Directly Derived from Metal-Organic Frameworks

Numerously different porous carbons have been prepared and used in a wide range of practical applications. Porous carbons are also ideal electrode materials for efficient energy storage devices due to their large surface areas, capacious pore spaces, and superior chemical stability compared to other porous materials. Not only the electrical double-layer capacitance (EDLC)-based charge storage but also the pseudocapacitance driven by various dopants in the carbon matrix plays a significant role in enhancing the electrochemical supercapacitive performance of porous carbons. Since the electrochemical capacitive activities are primarily based on EDLC and further enhanced by pseudocapacitance, high-surface carbons are desirable for these applications. The porosity of carbons plays a crucial role in enhancing the performance as well. We have recently witnessed that metal-organic frameworks (MOFs) could be very effective self-sacrificing templates, or precursors, for new high-surface carbons for supercapacitors, or ultracapacitors. Many MOFs can be self-sacrificing precursors for carbonaceous porous materials in a simple yet effective direct carbonization to produce porous carbons. The constituent metal ions can be either completely removed during the carbonization or transformed into valuable redox-active centers for additional faradaic reactions to enhance the electrochemical performance of carbon electrodes. Some heteroatoms of the bridging ligands and solvate molecules can be easily incorporated into carbon matrices to generate heteroatom-doped carbons with pseudocapacitive behavior and good surface wettability. We categorized these MOF-derived porous carbons into three main types: (i) pure and heteroatom-doped carbons, (ii) metallic nanoparticle-containing carbons, and (iii) carbon-based composites with other carbon-based materials or redox-active metal species. Based on these cases summarized in this review, new MOF-derived porous carbons with much enhanced capacitive performance and stability will be envisioned.

Synergistic effect of microwave heating and hydrothermal methods on synthesized Ni2CoS4/GO for ultrahigh capacity supercapacitors

A simple and efficient strategy that takes advantages of the synergistic effect of microwave heating method and hydrothermal method is used to synthesize Ni₂CoS₄/graphene oxide (MH-Ni₂CoS₄/GO). Firstly, Ni₂CoS₄ nanoparticles are observed to grow uniformly on the surface of GO. Then the obtained MH-Ni₂CoS₄/GO electrode is tested and it demonstrates ultrahigh specific capacitance of 2675.0 F g^-1 at the current densities of 2 A g^-1, fantastic stability of 95.0% even after 2000 cycles at 30 A g^-1 and excellent rate capability of 89.7% with current density increasing from 2 A g^-1 to 30 A g^-1. Moreover, the assembled AC//MH-Ni₂CoS₄/GO asymmetric supercapacitor also delivers a good specific capacitance of 126.5 F g^-1 at 0.5 A g^-1, outstanding stability of 97.0% after 2000 cycles at 5.0 A g^-1, and an ultrahigh energy density of 59.6 Wh kg^-1 at power density of 497.6 W kg^-1. This work provides an approach to synthesize electrode materials with superior excellent performances and it can be easily scaled up for practical applications in supercapacitors.

2D nanoporous Ni(OH)2 film as an electrode material for high-performance energy storage devices

A two-dimensional (2D) nanoporous Ni(OH)₂ film was successfully developed from triethanolamine (TEA) as the alkali source and soft template using a scalable hydrothermal technique. The nanostructured Ni(OH)₂ film was flexible and translucent, and could be directly compressed on a current collector. Owing to the uniform well-defined morphology and stable structure, the Ni(OH)₂ film binder-free electrode displayed a high specific capacity, exceptional rate capability, and admirable cycle life. The specific capacitance was 453.6 mA h g⁻¹ (1633 F g⁻¹) at 0.5 A g⁻¹. The assembled Ni(OH)₂//activated carbon (AC) asymmetric supercapacitor (ASC) device had an energy density of 58.7 W h kg⁻¹ at a power density of 400 W kg⁻¹. These prominent electrochemical properties of Ni(OH)₂ were attributed to the high electrical conductivity, high surface area, and unique porous architecture. Free tailoring, binder-free, and direct pressing were the most significant achievements of the Ni(OH)₂ film in the development of high-performance energy storage devices.

A two-dimensional (2D) nanoporous Ni(OH)₂ film was successfully developed from triethanolamine (TEA) as the alkali source and soft template using a scalable hydrothermal technique.