In this paper, we wish to present an overview of the research carried out in our laboratories with low-cost transition metal oxides (manganese dioxide, iron oxide and vanadium oxide) as active electrode materials for aqueous electrochemical supercapacitors. More specifically, the paper focuses on the approaches that have been used to increase the capacitance of the metal oxides and the cell voltage of the supercapacitor. It is shown that the cell voltage of an electrochemical supercapacitor can be increased significantly with the use of hybrid systems. The most relevant associations are Fe3O4 or activated carbon as the negative electrode and MnO2 as the positive. The cell voltage of the Fe3O4/MnO2 device is 1.8 V and this value was increased to 2.2 V by using activated carbon instead of Fe3O4. These two systems have shown superior behavior compared to a symmetric MnO2/MnO2 device which only works within a 1 V potential window in aqueous K2SO4. Furthermore, the activated carbon/MnO2 hybrid device exhibits a real power density of 605 W/kg (maximum power density =19.0 kW/kg) with an energy density of 17.3 Wh/kg. These values compete well with those of standard electrochemical double layer capacitors working in organic electrolytes.

http://ma.ecsdl.org/content/MA2005-01/35/1348.full.pdf

Nanostructured Transition Metal Oxides for Aqueous Hybrid Electrochemical Supercapacitors

Energy storage devices are the key components for successful and sustainable energy systems. Some of the best types of energy storage devices right now include lithium-ion batteries and supercapacitors. Research in this area has greatly improved electrode materials, enhanced electrolytes, and conceived clever designs for device assemblies with the ever-increasing energy and power density for electronics. Electrode materials are the fundamental key components for energy storage devices that largely determine the electrochemical performance of energy storage devices. Various materials such as carbon materials, metal oxides and conducting polymers have been widely used as electrode materials for energy storage devices, and great achievements have been made. Recently, metal nitrides have attracted increasing interest as remarkable electrode materials for lithium-ion batteries and supercapacitors due to their outstanding electrochemical properties, high chemical stability, standard technological approach and extensive fundamental importance. This review analyzes the development and progress of metal nitrides as suitable electrode materials for lithium-ion batteries and supercapacitors. The challenges and prospects of metal nitrides as energy storage electrode materials are also discussed.

Recent advances in metal nitrides as high-performance electrode materials for energy storage devices

Removal of heavy metal ions from wastewater is of prime importance for a clean environment and human health. Different reported methods were devoted to heavy metal ions removal from various wastewater sources. These methods could be classified into adsorption-, membrane-, chemical-, electric-, and photocatalytic-based treatments. This paper comprehensively and critically reviews and discusses these methods in terms of used agents/adsorbents, removal efficiency, operating conditions, and the pros and cons of each method. Besides, the key findings of the previous studies reported in the literature are summarized. Generally, it is noticed that most of the recent studies have focused on adsorption techniques. The major obstacles of the adsorption methods are the ability to remove different ion types concurrently, high retention time, and cycling stability of adsorbents. Even though the chemical and membrane methods are practical, the large-volume sludge formation and post-treatment requirements are vital issues that need to be solved for chemical techniques. Fouling and scaling inhibition could lead to further improvement in membrane separation. However, pre-treatment and periodic cleaning of membranes incur additional costs. Electrical-based methods were also reported to be efficient; however, industrial-scale separation is needed in addition to tackling the issue of large-volume sludge formation. Electric- and photocatalytic-based methods are still less mature. More attention should be drawn to using real wastewaters rather than synthetic ones when investigating heavy metals removal. Future research studies should focus on eco-friendly, cost-effective, and sustainable materials and methods.

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Removal of heavy metal ions from wastewater: a comprehensive and critical review

Capacitive deionization using nitrogen-doped mesostructured carbons for highly efficient brackish water desalination

Manganese dioxide (MnO2 ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO2 single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO2 -based composites via the construction of homojunctions and MnO2 /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO2 -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO2 -based materials for comprehensive environmental applications is provided.

MnO2 -Based Materials for Environmental Applications.

Improved removal capacity of magnetite for Cr(VI) by electrochemical reduction.

Remediation of heavy metal contaminated soils by organic acid extraction and electrochemical adsorption.

Birnessite is widely used as an excellent adsorbent for heavy metal ions and as active electrode materials for supercapacitors. The occurrence of redox reactions of manganese oxides is usually accompanied by the intercalation–deintercalation of cations during the charge–discharge processes of supercapacitors. In this study, based on the charge–discharge principle of the supercapacitor and excellent adsorption properties of birnessite, a birnessite-based electrode was used to remove Cd2+ from aqueous solutions. The Cd2+ removal mechanism and the influences of birnessite loading and pH on the removal performance were investigated. The results showed that Cd2+ was adsorbed on the surfaces and interlayers of birnessite, and the maximum electrosorption capacity of birnessite for Cd2+ was about 900.7 mg g–1 (8.01 mmol g–1), which was significantly higher than the adsorption isotherm capacity of birnessite (125.8 mg g–1). The electrosorption specific capacity of birnessite for Cd2+ increased with an increase in ...

Lihu Liu

Papers

Improved removal capacity of magnetite for Cr(VI) by electrochemical reduction.

Remediation of heavy metal contaminated soils by organic acid extraction and electrochemical adsorption.

Cadmium Removal from Aqueous Solution by a Deionization Supercapacitor with a Birnessite Electrode.

Enhanced adsorption removal of arsenic from mining wastewater using birnessite under electrochemical redox reactions

High-performance Cu2+ adsorption of birnessite using electrochemically controlled redox reactions.