الفهرس 
Title : Electrochemical Conversion Reactions of Some Chemical Compounds over Modified Surfaces
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Abstract
Electrochemical treatment is an efficient approach for urea-decontamination from aqueous media. Reliable electro-catalysts are therefore crucial for water decontamination applications. We introduce in this work a newly developed composite by modifying a nickel substrate with nickel oxide nanoparticles (NiO), multiwalled carbon nanotubes (CNTs) and ionic liquid crystals (ILCs). The composite modifier (Ni/NiO+CNTs) exhibit an outstanding specific catalytic current for 0.33 M urea electro-oxidation in 1M KOH of 1303 A•g-1•cm-2. The optimum regime of the catalyst administration to the substrate surface is a layer of ILCs followed by a mixture of CNTs and NiO with a ratio of 1:1 by mass (Ni/ILCs/NiO+CNTs (1:1)). The presence of nickel oxide (NiO) is anticipating increasing the catalytic efficiency for UOR. CNTs beside their unique electronic properties they, allow better distribution of the catalyst exposure. The inclusions of ILCs assist the ionic exchange of the electrode surface and increase substantially the performance of the catalyst. In presence of ionic liquids, the interactions between ions at the electrode surface are controlled by Coulombic interactions with double-layer reconstruction. The change in the carbon-based component of the catalyst affects the electro-catalytic current; reduced graphene oxide (RGO) exhibit relatively lower value compared to CNTs. The Tafel slope, the exchange current density, charge transfer coefficient, diffusion coefficient, and heterogeneous rate constant in 0.33 M urea/1.0 M KOH for the optimized electrode (Ni/ILCs/NiO+CNTs (1:1)) are: 33.0 mV•dec-1, 2.89 × 10-5 A•cm-2, 0.389, 1.70 × 10-3 cm2•s-1, 1.51 × 105 mol-1•L•s-1, respectively. The calculated activation energy of the electrochemical conversion of urea is 5.28 kJ•mol-1. The electrode shows high stability when used for extended time to constant applied potential of about +0.5 V for urea electro-oxidation. The conversion efficiency increased in the order Ni/ILCs/NiO+CNTs > Ni/NiO+CNTs > Ni/NiO compared to the Ni surface. The novelty in the catalyst used for urea conversion is the employment of less toxic materials, namely CNTs and ILCs, with the minimum amount of NiO. The synergistic effect of all catalyst’s components employed proved effective in the catalytic conversion process. In the second part,numerous studies on TM-based electrocatalysts have recently been published, showing their effective potential to catalyze the hydrazine-assisted HER. The strong catalytic efficacy of the Ni-based electrocatalysts for HER and HzOR resulted in a considerable reduction in the cell voltage needed for water splitting.In absence of Hyz a relatively small shift in potential of 0.03 V takes place when the onset of HER is recorded at -1.15 V with specific current density of -6.77 A.cm-2.g-1. Hyz oxidation (HyzOR) assists the oxygen evolution reaction (OER). Inspection of the OER takes place at an onset potential of +0.0524 V in presence of Hyz with a driven specific current of 94.8 A.cm-2.g-1 and a difference in potential of 0.85 V is observed in absence of Hyz. The onset potential in absence of Hyz is +0.902 V with a driven specific current of 27.1 A.cm-2.g-1. These results prove that Hyz is easily electro-oxidized compared to water. The resulting improvement in the overall water splitting is due to the participation of each of the surface modifiers to the electrocatalytic process.The stability of the Ni/ILC/NiO+CNTs electrode is examined by subjecting the electrode to an extended exhaustive electrolysis using chronoamperometry in 0.5 M Hyz/1.0 M KOH for two hours in which the current decreases by 11% from the 10th minute to the end of experiment time (120 min). This reflects that the modified electrode is relatively stable for exhaustive electrolysis applications. The calculated value of the activation energy is 3.91 kJ.mol-1.The relative low value ofEaascertains the ease of HyzOR-OER at the Ni/ILCs/NiO + CNTs electrode. Relatively higher activation energy values were reported in the literature for other electrochemical conversion processes.