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- Pseudocapacitive response of hydrothermally grown MoS2 crumpled nanosheet on carbon fiberPublication . Upadhyay, Kush; Nguyen, Tuyen; Moura E Silva, Teresa; Carmezim, Maria; MONTEMOR, FATIMACrumpled 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.
- Electrodeposited MoOx films as negative electrode materials for redox supercapacitorsPublication . Upadhyay, Kush; Nguyen, Tuyen; Moura E Silva, Teresa; Carmezim, Maria; MONTEMOR, FATIMAMoOx films composed of agglomerated nanoparticles were synthesized by potentiostatic electrodeposi-tion on stainless steel collectors for charge storage electrodes working in aqueous electrolyte (1 M H2SO4) and negative potential window. The agglomerated nanoparticles were amorphous in nature and possess mixed valance state. By optimizing the charge density applied during electrodeposition, the electrodes delivered maximum specific capacity of 228 C g_1 (507 F g_1) at 1 A g_1 for the sample electrodeposited at _0.3 C cm_2. This film showed very good rate capability and retained around 48% of specific capacity at 10 A g_1. The galvanostatic charge discharge cycling stability test showed 87% of initial capacity retained after 900 cycles, suggesting good stability behaviour. Electrochemical impedance spectroscopy (EIS) measurements evidenced lower equivalent series resistance for the sample electrodeposited at _0.3 C cm_2 among the tested samples, revealing its better electrochemical performance. Aging of the electrode with higher specific capacity was also investigated by performing EIS after different cycles; the results revealed an increment on the overall resistance, thus clarifying the capacity degradation.
- 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.