Browsing by Author "Siwek, K. I."
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- 3D nickel foams with controlled morphologies for hydrogen evolution reaction in highly alkaline mediaPublication . Siwek, K. I.; Eugénio, S.; Santos, Diogo; Moura E Silva, Teresa; MONTEMOR, FATIMAWater electrolysis is the cleanest method for hydrogen production, and can be 100% green when renewable energy is used as electricity source. When the hydrogen evolution reaction (HER) is carried out in alkaline media, nickel (Ni) is a low cost catalyst and an interesting alternative to platinum. Still, its performance has to be enhanced to meet the high efficiency of the nobler metals, an objective that requires further tailoring of the surface area and morphology of Ni-based electrode materials. Unlike commercially available porous Ni, these features can be easily controlled via electrodeposition, a one-step process, taking advantage of the dynamic hydrogen bubble template (DHBT). Generally, changes in surface porosity and morphology have been mainly achieved by altering the main parameters, such as the current density or the deposition time. However, very scarce work has been done on the role of supporting electrolyte (i.e., its concentration and composition) in tailoring the foam features and consequently their catalytic activity. Hence, this approach paves the way to optimum design of metallic foam structures that can be obtained only with modifications in the electrolytic bath. In this work, 3D Ni foams are obtained from different composition baths by galvanostatic electrodeposition in the hydrogen evolution regime on stainless steel current collectors. Their porosity and morphology are analysed by optical microscopy and SEM. The electrochemical performance is evaluated by cyclic voltammetry, while catalytic activity towards HER and materials' stability in 8 M KOH are tested using polarisation curves and chronoamperometry measurements, respectively. The recorded high currents and extended stability of the Ni foams with dendritic morphology demonstrate its outstanding performance, making it an attractive cathode material for HER in highly alkaline media. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
- Direct electrodeposition of hydrogenated reduced graphene oxide from unsonicated solution and its electrochemical responsePublication . Noce, R.D.; Eugenio, S.; Siwek, K. I.; Moura E Silva, Teresa; Carmezim, Maria; Sakita, A. M. P.; Lavall, R.L.; Montemor, M.F.Reduced graphene oxide (rGO) is successfully electrodeposited from a graphene oxide-containing suspension under stirring and no sonication onto Ni foam by applying -1.5 V/SCE. The electrodeposited material is characterized by X-Ray Diffraction (XRD), Scanning electron microscopy (SEM), Raman spectroscopy, Fourier Transform Infra-Red spectroscopy (FTIR) and Thermogravimetric analysis (TGA). FTIR and TGA results indicate the formation of hydrogenated rGO after electrodeposition. In addition, the electrochemical response of the rGO/Ni electrode is evaluated by cyclic voltammetry in 1 M potassium hydroxide solution. The results reveal that the electrode possesses higher conductivity and lower polarization loss compared to bare Ni foam, opening wider perspectives to design composites with improved electrochemical performance.
- 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.
- Tailored 3D foams decorated with nanostructured manganese oxide for asymmetric electrochemical capacitorsPublication . Siwek, K. I.; Eugenio, S.; Aldama, I.; Rojo, J. M.; Amarilla, J. M.; Da Costa Ribeiro, Ana Paula; Moura E Silva, Teresa; Montemor, M.F.Tailored 3D (Ni and NiCo) metallic foam architectures were produced by electrodeposition and decorated via electrochemical routes with manganese oxide (MnOx) to serve as positive electrodes for supercapacitors. For comparative purposes, an electrode made of commercial Ni foam was also prepared. The foam-based electrodes were paired with a carbon cloth electrode and used to assemble asymmetric electrochemical cells. The electrochemical response of these cells was studied by applying different electrochemical techniques. In addition, two different protocols (cycling and floating) were applied to assess cells durability and fade. Despite the significant differences in the decorated foams morphology and structure their electrochemical responses revealed similar trends. The electrodes made of tailored foams showed higher specific capacitance, better capacitance retention at high current load and enhanced cycling stability compared to the electrodes made of commercial foam. The asymmetric cells made with the tailored foams revealed higher (maximum) specific energy (11-14 Wh kg(-1)) and specific power (1.3-1.4 x 10(4 )W kg(-1)) compared to cells assembled with commercial foams (8.4 Wh kg(-1) and 6.3 x 10(3) W kg(-1)). The durability tests evidenced that corrosion of the NiCo electrodeposited foams and electrochemical dissolution of MnOx are possible causes of cells degradation.