Untitled

Funder

Organizational Unit

Publications

Electrochemical performance of MnOx·center dot nH(2)O@Ni composite foam electrodes for energy storage in KOH media

Publication . Siwek, Katarzyna; Eugénio, S.; Moura E Silva, Teresa; MONTEMOR, FATIMA

Nanostructured porous MnO2, especially its hydrated amorphous and low crystalline form (MnO2·nH2O), has been one of the most promising material considered for charge storage applications, due to electrochemical similarities with RuO2 and its relative low cost. However, the intrinsic poor conductivity of MnO2 combined with the presence of structural water, which provides high ionic but low electronic conductivity, is a great hindrance for wider application. An effective approach to overcome this drawback involves the deposition of thin MnO2 layers on porous, high surface area metallic scaffolds. The present work addresses this route and provides novel insights thanks to the combination of MnOx·nH2O with custom-made Ni foams, fabricated via one-step electrodeposition using the dynamic hydrogen bubble template (DHBT). The porous Ni foams provide a scaffold with a 3D architecture with optimized pore size and surface. The composite electrode was fabricated by anodic deposition of MnOx·nH2O on the 3D Ni foams. The electrochemical behaviour was tested in 1 M KOH, since there are very few studies addressing the electrochemical behaviour of MnOx·nH2O in alkaline media for electrochemical supercapacitors applications. In addition, thermal treatment (150–250 °C) was performed to evaluate the effect of hydration on the material properties. The results revealed that the as-obtained composites are highly stable, displaying much higher specific capacitances with 73–90% (depending on the mass load) capacitance retention compared to their de-hydrated counterparts. The charge-discharge processes were found to be highly reversible throughout 5000 cycles, maintaining almost 100% columbic efficiency. In conclusion, the MnOx·nH2O@Ni composite electrodes showed a very stable pseudocapacitive behaviour and exceptional cycling performance in 1 M KOH, being therefore a promising alternative charge storage electrode for electrochemical supercapacitors.

2018-08-10Journal article

Restricted access

3D nickel foams with controlled morphologies for hydrogen evolution reaction in highly alkaline media

Publication . Siwek, K. I.; Eugénio, S.; Santos, Diogo; Moura E Silva, Teresa; MONTEMOR, FATIMA

Water 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.

2019-01-15Journal article

Restricted access

Pseudocapacitive response of hydrothermally grown MoS2 crumpled nanosheet on carbon fiber

Publication . Upadhyay, Kush; Nguyen, Tuyen; Moura E Silva, Teresa; Carmezim, Maria; MONTEMOR, FATIMA

Crumpled MoS2 nanosheets were synthesized directly on carbon fiber paper (CFP) through hydrothermal procedure. Molybdenum sulfide precursor was first produced in the solution and then introduced into the autoclave. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirmed the uniform growth of crumpled nanosheets on the CFP that were assigned to MoS2 according to X-ray photo electron spectroscopy (XPS) and Raman spectroscopy results. Electrochemical measurements of the as deposited MoS2 crumpled nanosheets performed in 1 M Na2SO4 evidenced a specific capacitance of 249 F g−1 at 2 A g−1 and the good rate capability by retaining 41.3% of initial capacitance at 10 A g−1. Electrochemical Impedance spectroscopy measurements showed very low charge transfer resistance and very short relaxation time accounting for the pseudocapacitive rectangular cyclic voltammetry (CV) and high rate capability.

2018-09-01Journal article

Open access