Browsing by Author "Ali, S."

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Open Access
Development of CuAg/Cu2O nanoparticles on carbon nitride surface for methanol oxidation and selective conversion of carbon dioxide into formate
(Elsevier, 2020) Nazir, Roshan; Kumar, A.; Saad, M. A. S.; Ali, S.
Herein we report a catalyst consisting of CuAg/Cu2O nanoparticles (NPs), synthesized on the two-dimensional carbon nitride (Csingle bondN) surface via galvanic exchange route for electrocatalytic methanol oxidation and carbon dioxide reduction. The lower reduction potential of copper ([Cu+(aq) + e− → Cu(s)], + 0.52 eV) compared to Ag ([Ag+(aq) + e− → Ag(s)], +0.80 eV) makes Cu(0) easily exchangeable by Ag+ ions via galvanic exchange without applying any external bias. In a two-step process, the Cu NPs are synthesized first on Csingle bondN surface by adsorbing Cu2+ precursors and reducing them by NaBH4. Due to unstable nature of Cu2+ in aqueous medium some Cu2O NPs (a mixed phase of Cu/CuO) were also formed. Thereafter in the second step, Ag+ precursors are brought in contact with the already synthesized Cu and Cu2O nanoparticles (NPs). The Cu and Cu2O NPs present on the surface of Csingle bondN are partially exchanged by Ag atoms to generate bimetallic CuAg/Cu2O NPs. Two atoms of Ag are expected to be deposited for every Cu atom replaced. As galvanic replacement occurs on the solid surface of carbon nitride, there is only a partial replacement of Cu and Cu2O atoms. The catalysts Csingle bondN/Cu/Cu2O and Csingle bondN/CuAg/Cu2O were evaluated for their performance towards methanol oxidation and carbon dioxide reduction. Csingle bondN/CuAg/Cu2O showed twice the current density for methanol oxidation than Csingle bondN/Cu/Cu2O in a 0.5 M methanol solution. Probably the reason for high activity of Ag than Cu is related to the weak bond of oxygen on silver substrate for oxidation reactions and strong binding affinity on copper substrate. In case of carbon dioxide reduction (CO2 reduction) the product was identified to be formate by oxidizing the product (formate) on a Pt ring electrode. The results revealed Csingle bondN/CuAg/Cu2O shows a better selectivity towards formic acid formation than Csingle bondN/Cu/Cu2O using the rotating ring disc electrode (RRDE). A probable reason may be the strain induced by alloy formation which could favor a reduced coverage of adsorbed hydrogen and a decrease in oxophilicity of the compressively strained copper.
Open Access
Electrochemical properties of single-crystalline Mn3O4 nanostructures and their capacitive performance in basic electrolyte
(Electrochemical Science Group, 2016) Shah, H. U.; Wang, F.; Toufiq, A. M.; Khattak, A. M.; Iqbal, A.; Ghazi, Z. A.; Ali, S.; Li, X.; Wang, Z.
Single-crystalline Mn3O4 square-shaped nanostructures have been successfully synthesized by hydrothermal method without using any surfactant. The as-prepared products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and High Resolution transmission electron microscopy (HRTEM). To assess the potential properties of nanostructures, galvanostatic charging-discharging and cyclic voltammetry measurements were performed for their use in supercapacitors. The Mn3O4 nanoarchitectures used as supercapacitor electrode in 1mol L-1 KOH electrolyte have a specific capacitance value of 355.5 F g-1 at a low current density of 0.35 A.g-1. The device still retain 85.08% of its initial capacitance afterwards 2000 cycles at a current density of 5 A.g-1. The as-synthesized Mn3O4 nanostructures exhibited a good rate capability and stability for electrochemical properties. These results indicate their potential application as electrode material for high performance supercapacitor in basic medium.
Open Access
Nanosheet synthesis of mixed Co3O4/CuO via combustion method for methanol oxidation and carbon dioxide reduction
(American Chemical Society, 2020) Nazir, Roshan; Khalfani, A.; Abdelfattah, O.; Kumar, A.; Saad, M. A. S.; Ali, S.
This paper represents a study of mixed Co3O4/CuO nanosheet (NS) synthesis via solution combustion synthesis for oxidation of methanol and carbon dioxide (CO2) conversion. The mixed oxide NS of Co3O4/CuO is a hybrid structure of Co3O4 and CuO NSs. We applied this mixed oxide NS of Co3O4/CuO for methanol oxidation and carbon dioxide (CO2) conversion, and the results revealed that the activity of the mixed oxide NS surpassed the activity of the corresponding individual Co3O4 and CuO metal oxide NSs, both in methanol oxidation and in CO2 conversion. The mass activity of the mixed Co3O4/CuO NS produced at 0.627 V versus Ag/AgCl during methanol oxidation (0.5 M) was 12 mA g–1, which is 2.4 times better than that of Co3O4, whose mass activity is 5 mA g–1, and 4 times better than that of the CuO NS, whose mass activity is 3 mA g–1. The methanol oxidation peak at 0.62 V versus Ag/AgCl was also more intense than individual oxides. The trend in performance of methanol oxidation follows the order: Co3O4/CuO > Co3O4 > CuO. In the case of CO2 reduction, we experienced that our product was formate, and this was proved by formate oxidation (formate is formed as a product during the reduction of CO2) on the surface of the Pt ring of a rotating ring-disc electrode. Similar to methanol oxidation, Co3O4/CuO also showed superior activity in carbon dioxide reduction. It was experienced that at −1.5 V, the current density rises to −24 mA/cm2 for the Co3O4/CuO NS, that is, 0.6 times that of the CuO NS, which is −15 mA/cm2, and 3 times more than that of the Co3O4 NS, which is 8 mA/cm2. The trend in performance of CO2 reduction follows the order: Co3O4/CuO > CuO > Co3O4.
Open Access
Novel predistortion algorithm for OFDMA
(IEEE, 2009) Ali, S.; Markarian, G.; Arıkan, Erdal
The RF amplifier in a wireless communication system is usually non-linear in nature. If such an amplifier is used in OFDMA based systems, it will cause serious degradation. This degradation will be both in terms of the reduction in BER and the generation of out of band noise. In this paper we have worked on the linearization method of the amplifier. This work is on a hybrid methodology, in which estimation of the model is performed in frequency domain and compensation is performed in time domain. The downlink preamble of the IEEE802.16e system is used here for the estimation purpose. The results for the suppression of spectra are shown at the end.