الفهرس 
Chapter 1Only 14 pages are availabe for public view
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Abstract
The world’s growing energy demand, as well as environmental worries about air pollution and the greenhouse impact of fossil fuels, have sparked research into sustainable alternative energy sources. Hydrogen, among these options, has the potential to transform human life into a cleaner environment and provide sufficient power resources in the near future. The chemical energy stored in hydrogen can be converted into electricity via electrochemical cells such as fuel cells. There are different types of fuel cells that differ in their power density, used fuel, working temperature, and application. The proton exchange membrane (PEM) fuel cell is the most promising type, as it offers high power densities at temperatures below 100 oC.
Platinum (Pt) is currently used as an electrocatalyst in practically all low-temperature fuel cells. As a result, the manufacturing cost is rather expensive, limiting the range of applications. Therefore, the main objective of this research is to synthesize and characterize two different series of catalysts, namely (Ni-Co-Pt), and (Ni-Pd) with a small percentage of Pt and Pd, which were synthesized via electrospinning to generate fibers with diameters ranging from micrometer size down to the nanometer range by applying a high voltage. Electrospun fiber possesses a large specific area and high catalytic activity.
In this work, Ni-Co-Pt samples were prepared in different ratios for Ni11Co6Pt3/CNFs (S1), Ni14Co3Pt3/CNFs (S2), and Ni17Pt3/CNFs (S3). The metal and carbon ratios were set at 20% and 80%, respectively, using electrospinning and carbonization at 900 °C in an argon environment for 7 hours. Miscellaneous analysis tools were used to scrutinize the chemical composition, structural, morphological, and electrochemical properties. For samples with varying Co%, the carbonization process diminishes the fiber diameter of the obtained electrospun nanofibers from 140–580 nm to 120–300 nm. According to EDX mapping, Nickel, cobalt, and Platinum were completely and consistently integrated into the carbonized PVANFs. The manufactured Ni-Co-Pt/CNFs have a face-centered cubic (FCC) structure with lightly increased crystallite size as the Co% shrinks. The electrocatalytic characteristics of the samples were examined for ethanol, methanol, and urea electrooxidation. The catalytic performance and electrode stability were examined using cyclic voltammetry (CV) and chronoamperometry as a function of electrolyte content, scan rate, and reaction time. The activation energy required for the electrooxidation reaction lowers when Co is added to Ni, but electrode stability rises. In 1.5M methanol, the Ni11Co6Pt3/CNFs electrode exhibited the lowest onset potential and the maximum current density (30.6 A/g). This current density is diminished to 28.2 and 21.2 A/g for 1.5M ethanol and 0.33M urea, respectively. The electrooxidation of ethanol, methanol, and urea using the formed electrocatalysts is a combination of kinetic/diffusion control reactions. This study took a novel method to creating a high-efficiency Ni-Co-Pt-based electrooxidation catalyst for ethanol, methanol, and urea.
Nickel (II) acetate tetrahydrate (NiAc) and palladium (II) acetate tetrahydrate (PdAc) samples were synthesized by dissolving Ni14Pd6 (NP1), Ni16Pd4 (NP2), and Ni18Pd2 (NP3) in deionized water with PVA. The metal and carbon loadings were set at 20% and 80%, respectively. The final solution was stirred until clear, then followed by an electrospinning process and carbonization at 750 °C for 5 h in an argon atmosphere. The utilized characterization XRD technique confirmed the formation of carbon nanofibers decorated by discrete Ni, Pd nanoparticles, with crystallite sizes ranging from 4.48 to 9.12 nm. In the XRD patterns of Ni-Pd/CNFs, no extra peaks (hydroxide or oxide phases) were seen, confirming the maximum purity of the generated samples. The electrocatalytic characteristics of the samples were also studied for the electrooxidation of ethanol, and methanol. The catalytic performance and electrode stability were examined using cyclic voltammetry (CV) and chronoamperometry. The electrochemical measurements indicated that the introduced nanofibers of NP1 have good electrocatalytic activity toward methanol oxidation as the observed current density was 75 mA/cm2 and this proves that using Pd as an additive enhances the catalytic activity and stability of Ni. The CV measurement also demonstrated that NP2 is the best sample for ethanol electrooxidation because the current density is reduced by 8% compared to the initial current density.