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- Electrodeposited manganese oxide on tailored 3D bimetallic nanofoams for energy storage applicationsPublication . Siwek, Katarzyna; Eugénio, Sónia; Moura E Silva, Teresa; M.F. MontemorThree-dimensional (3D) electrode design has great advantages over its two-dimensional (2D) counterparts, including higher mass loading of active material, enhanced ion diffusion, and electron charge transfer. Commercial 3D porous structures (i.e., Ni foams) do not fit the purpose of the ideal 3D electrode for supercapacitors, in which surface area (per cm(2)) is more important than large pore volume. These characteristics, however, can be tuned by the dynamic hydrogen bubble template (DHBT) electrodeposition, a route that is used to tailor 3D nanostructured (multi-) metallic porous surfaces. In addition to the higher surface area and tailored porosity, these 3D nanostructures can be subsequently functionalized with different species such as metal oxides or other compounds. Therefore, a facile two-step electrochemical fabrication of 3D composite electrode composed of a bimetallic foam functionalized with manganese (Mn) oxide is proposed. The effect of applied current densities on the distribution and structure of Mn oxide (MnOx) electrodeposited over the bare foam is discussed. The results demonstrate that this route paves the way to design high-surface-area architectures for charge storage electrodes with enhanced electrochemical performance (194Fg(-1) mg(-1) of electrodeposited MnOx at 0.5Ag(-1)) and high charge-discharge rate capabilities (91% capacitance retention at 20Ag(-1)) for supercapacitor applications.
- Hydrothermally grown Ni0.7Zn0.3O directly on carbon fiber paper substrate as an electrode material for energy storage applicationsPublication . Upadhyay, Kush; Eugénio, Sónia; Della Noce, Rodrigo; Morais Silva, Teresa; M.J. Carmezim; M.F. MontemorNickel oxides because of their excellent electrochemical performance have been considered attractive materials for electrochemical energy storage. However, their application as active material for redox supercapacitor electrodes has been limited by poor electrical conductivity. In order to improve this property, herein we synthesized a nanonet of Ni
Zn-mixed oxide, by facile hydrothermal route, directly on the substrate. The Zn-modified oxide material showed good electrochemical performance, displaying specific capacitance of 770 F g−1 at 1 A g−1 and almost 120% capacitance retention after 2000 cycles of charge discharge at 2 A g−1 in 2 M KOH. Electrochemical impedance results revealed that the Ni0.7Zn0.3O mixed oxide displayed increased conductivity compared to the single NiO material.
- One-step process to form a nickel-based/carbon nanofoam composite supercapacitor electrode using Na2SO4 as an eco-friendly electrolytePublication . Della Noce, Rodrigo; Eugénio, Sónia; Boudard, M.; Rapenne, Laetitia; Moura E Silva, Teresa; Carmezim, Maria; Donne, S. W.; MONTEMOR, FATIMAIn this work, NiOx is anodically electrodeposited onto carbon nanofoam (CNF) to form a composite electrode devoted to supercapacitor applications. The use of NiSO4 as precursor in electrodeposition results in the formation of NiO and NiOOH species, as confirmed by XPS analysis, by means of a one-step anodic process. The presence of both NiO and NiOOH suggests the existence of pseudocapacitance, as observed in MnO2 and RuO2 materials. By employing Na2SO4, an eco-friendly electrolyte, the resulting composite delivers a specific capacitance of 150 F g(-1) at 1 A g(-1) considering the total mass of the electrode (deposit plus substrate). In addition, this composite electrode can operate in a very broad potential window, as high as 2.2 V, suggesting its application in high energy density electrochemical supercapacitors.
- Electrochemical response of a high-power asymmetric supercapacitor based on tailored MnOx/Ni foam and carbon cloth in neutral and alkaline electrolytesPublication . Aldama, Ivan; Siwek, K. I.; Amarilla Alvarez, Jose Manuel; Rojo, Jose M.; Eugénio, Sónia; Moura E Silva, Teresa; MONTEMOR, MARIATailored 3D Ni foams with smaller macropores and larger surface areas than commercial Ni foams are prepared by electrodeposition under the dynamic hydrogen bubble template on stainless steel substrates. These Ni foams are functionalized with electrodeposited manganese oxide (MnOx), resulting in MnOx/Ni foam composites. The electrochemical performance of the composites is studied in aqueous Na2SO4 and KOH electrolyte. Moreover, asymmetric cells, combining the MnOx/Ni foam composites as positive electrodes and carbon cloths as negative electrodes, are tested in the presence of the two electrolytes. Despite the significant number of papers dealing with asymmetric supercapacitors, there is still the need of understanding the electrolyte role for optimizing their electrochemical response. The cell potential window is broader in neutral electrolyte, 1.6 V, compared to the alkaline one, 1.2 V, but the cell capacitance is lower in the neutral electrolyte, 37 F g(-1), than in the alkaline one, 49 F g(-1). The energy density is similar for the two electrolytes, ca. 10 Wh kg(-1). The power density reaches 1-3.10(4) W kg(-1), which is among the highest values reported for asymmetric cells in aqueous electrolytes. The stability of the cells on cycling, floating and self-discharge are compared for the two electrolytes.