Porous cobalt oxides/carbon foam hybrid materials for high supercapacitive performance

Pseudocapacitive Deionization of Saltwater by Mn3O4@C/Activated Carbon

Capacitive deionization (CDI), a m ethod with notable advantages of relatively low energy consumption and environmental friendliness, has been widely used in desalination of saltwater. However, due to the weak electrical double-layer electrosorption of ions from water, CDI has suffered from low throughput capacity that may limit its commercial applications. Thus, it is of importance to develop a high-efficiency and engineering-feasible CDI process. Manganese and cobalt and their oxides, being faradic materials, have a relatively high pseudocapacitance, which can cause an increase of positive and negative charges on opposing electrodes. However, their low conductivity properties limit their electrochemical applications. Pseudocapacitive Mn₃O₄ nanoparticles encapsulated within a conducting carbon shell (Mn₃O₄@C) were prepared to enhance charge transfer and capacitance for CDI. Desalination performances of the Mn₃O₄@C (5-15 wt %) core-shell nanoparticles on activated carbon (AC) (Mn₃O₄@C/AC) serving as CDI electrodes have thus been investigated. The pseudocapacitive Mn₃O₄@C/AC electrodes with relatively low diffusion resistances have much greater capacitance (240-1300 F/g) than the pristine AC electrode (120 F/g). In situ synchrotron X-ray absorption near-edge structure spectra of the Mn₃O₄@C/AC electrodes during CDI (under 1.2 and -1.2 V for electrosorption and regeneration, respectively) demonstrate that reversible faradic redox reactions cause more negative charges on the negative electrode and more positive charges on the positive electrode. Consequently, the pseudocapacitive electrodes for CDI of saltwater ([NaCl] = 1000 ppm) show much better desalination performances with a high optimized salt removal (600 mg/g·day), electrosorption efficiency (48%), and electrosorption capacity (EC) (25 mg/g) than the AC electrodes (288 mg/g·day, 23%, and 12 mg/g, respectively). The Mn₃O₄@C/AC electrode has a maximum EC of 29 mg/g for CDI under +1.2 V. Also, the Mn₃O₄@C/AC electrodes have much higher pseudocapacitive electrosorption rate constants (0.0049-0.0087 h^-1) than the AC electrode (0.0016 h^-1). This work demonstrates the feasibility of high-efficiency CDI of saltwater for water recycling and reuse using the low-cost and easily fabricated pseudocapacitive Mn₃O₄@C/AC electrodes.

Current Methods for Synthesis and Potential Applications of Cobalt Nanoparticles: A Review

Cobalt nanoparticles (CoNPs) are promising nanomaterials with exceptional catalytic magnetic, electronic, and chemical properties. The nano size and developed surface open a wide range of applications of cobalt nanoparticles in biomedicine along with those properties. The present review assessed the current environmentally friendly synthesis methods used to synthesize CoNPs with various properties, such as size, zeta potential, surface area, and magnetic properties. We systematized several methods and provided some examples to illustrate the synthetic process of CoNPs, along with the properties, the chemical formula of obtained CoNPs, and their method of analysis. In addition, we also looked at the potential application of CoNPs from water purification cytostatic agents against cancer to theranostic and diagnostic agents. Moreover, CoNPs also can be used as contrast agents in magnetic resonance imaging and photoacoustic methods. This review features a comprehensive understanding of the synthesis methods and applications of CoNPs, which will help guide future studies on CoNPs.

Recent Advance in Co3O4 and Co3O4-Containing Electrode Materials for High-Performance Supercapacitors

Among the popular electrochemical energy storage devices, supercapacitors (SCs) have attracted much attention due to their long cycle life, fast charge and discharge, safety, and reliability. Transition metal oxides are one of the most widely used electrode materials in SCs because of the high specific capacitance. Among various transition metal oxides, Co3O4 and related composites are widely reported in SCs electrodes. In this review, we introduce the synthetic methods of Co3O4, including the hydrothermal/solvothermal method, sol-gel method, thermal decomposition, chemical precipitation, electrodeposition, chemical bath deposition, and the template method. The recent progress of Co3O4-containing electrode materials is summarized in detail, involving Co3O4/carbon, Co3O4/conducting polymer, and Co3O4/metal compound composites. Finally, the current challenges and outlook of Co3O4 and Co3O4-containing composites are put forward.

CoNi2S4 nanosheets on nitrogen-doped carbon foam as binder-free and flexible electrodes for high-performance asymmetric supercapacitors

Flexible electrode materials show many advantages and hold great prospects for energy storage application. But, the synthesis processes of these kind of materials are always complicated, are low in efficiency and high in cost. Here, we propose a facile and cost-effective two-step synthesis strategy of a flexible electrode by growing ultrathin and vertical CoNi₂S₄ nanosheets on nitrogen-doped carbon foam (CoNi₂S₄ NSs@NCF). The NCF is obtained by direct carbonization of the melamine foam. When evaluated as binder-free electrode material for supercapacitor in three-electrode system, the CoNi₂S₄ NSs@NCF exhibits an excellent specific capacitance of 1576.8 F g^-1 and a superior cycling stability (91.5% capacitance retention at the 5000th cycle). Then, an asymmetrical supercapacitor was fabricated using the as-synthesized material as the positive electrode and activated carbon as the negative electrode, which delivers a high energy density of 42.8 Wh kg^-1 at a power density of 399.7 W kg^-1, remarkable rate capability and satisfactory cycling stability (85.3% capacitance retention at the 5000th cycle). In brief, our work offers a low-cost and facile approach to prepare promising flexible electrode materials for high-performance supercapacitors.