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Articles by Riaz AHMED
Total Records ( 3 ) for Riaz AHMED
  Muhammad ARSHAD , Saeed- ur-REHMAN , Ammad Hussain QURESHI , Khalid MASUD , Muhammad ARIF , Aamer SAEED and Riaz AHMED
  The nitrate complexes of transition metals with 1,2-diimidazoloethane (DIE) of the general formula M(DIE)(NO3)2, where M = Co(II), Cu(II), Zn(II), and Cd(II), were synthesized. The compositions of metal complexes and ligand were investigated by elemental analysis in order to ensure their purity and the structure elucidations were based on conductivity measurements, room temperature magnetic moment studies, proton NMR, and electronic and IR spectra. The thermal behavior of these complexes possessing distorted tetrahedral geometry and their ligand was studied by means of thermoanalytical techniques in static air atmosphere in order to determine their mode of decomposition and thermal stability. All these complexes and ligand show 2-step weight loss upon heating to 740 °C, with simultaneous loss of inorganic and organic fragments exhibiting almost the same mode of decomposition pattern. The residue after heating above 640 °C corresponded to metal oxide. There was no residue in the case of ligand. The composition of intermediates and end products formed during degradation was confirmed by microanalysis and IR spectroscopy. It follows from the results that the thermal stability of the complexes increases in the following sequence:
Co(II) < Cu(II) < Zn(II) < Cd(II)
  Abdul Sattar Ali KHAN , Riaz AHMED and Muhammad Latif MIRZA
  The catalytic activities of an equal amount of 3 different carbon supported catalysts containing 10% Pt, 20% Pt + 10% Ru, and 30% Pt were evaluated in neutral and basic media for methanol oxidation by cyclic voltammetry. The prominent oxidation peak for methanol appeared in the forward anodic sweep at around 1.0 V in neutral medium, while in basic medium it appeared at significantly lower potential close to 0.2 V. The peak current for methanol oxidation was higher on a catalyst containing higher Pt loading. The comparison of polarization behavior of 20% Pt + 10% Ru and 30% Pt catalysts showed that the presence of Ru increases the catalytic activity at the lower polarization region. The enhancement of catalytic activity by Ru was more obvious in basic medium as compared with neutral medium. The heterogeneous rate constants were evaluated from peak current data. At room temperature, the heterogeneous rate constant for methanol oxidation on a given catalyst was higher in basic medium as compared with neutral medium. The effect of temperature on peak current was investigated. At lower temperature, the catalytic activities were lower in neutral medium but approached near that in basic medium at higher temperature owing to the higher apparent enthalpy of activation “Δ H*” for methanol oxidation in neutral medium. The Δ H* values were calculated from the analysis of peak current data and found to be in the range 24 to 27 kJ mol-1 in neutral medium and 15 to 17 kJ mol-1 in basic medium.
  Abdul Sattar Ali Khan , Riaz Ahmed and Muhammad Latif Mirza
  Platinum-based catalysts are considered the most efficient catalysts for triggering electrochemical reactions in proton exchange membrane (PEM) fuel cells. In the present study, commercial catalysts containing 10% and 30% Pt supported on Vulcan XC-72 carbon were studied to assess their performance in PEM fuel cells. Both catalysts consisted of Pt particles of almost the same size. The utility of these catalysts in PEM fuel cells was studied by finding the real surface area and rate of electro-oxidation of methanol in 0.5 M H2SO4 by using cyclic voltammetry. The methanol oxidation reaction was used for characterization of catalysts of PEM fuel cells due to the liquid nature of methanol and the close resemblance of basic electrochemical features of direct methanol fuel cells and PEM fuel cells. Comparison of the data of real surface area and rate of electro-oxidation of methanol showed that 30% Pt catalyst having higher Pt loading is more suitable for PEM fuel cells as compared with 10% Pt catalyst. The PEM fuel cell components were designed and fabricated for testing of membrane electrode assemblies (MEAs). The importance of an additional gas diffusion layer in the form of carbon paper was also emphasized for improving gas diffusion and electrical contact of electrodes of MEAs with the flow field area of monopolar/bipolar plates of PEM fuel cells. The MEAs prepared from 10% and 30% Pt catalysts with Pt loading of 0.5 mg cm-2 gave the maximum power density of 119 and 185 mW cm-2, respectively. It was concluded that nanosize carbon supported Pt catalysts having higher Pt loading are more suitable catalysts for preparing high performance MEAs of PEM fuel cells and the cyclic voltammetric data of real surface area and rate of methanol oxidation may be utilized to assess the performance of a given catalyst prior to its use in the preparation of MEAs of PEM fuel cells.
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