Browsing by Author "Ulas, B."

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Direct Formic Acid and Formate Fuel Cells (Df
(Elsevier, 2020) Ulas, B.; Kivrak, H.D.
Among the direct liquid fuel cells, the direct methanol fuel cells (DMFCs) are the fuel cells closest to commercialization. However, direct formic acid fuel cells (DFAFCs) and direct formate fuel cells (DFFCs) are also promising energy conversion devices for portable applications. It is important to choose the appropriate anode catalyst, cathode catalyst and membrane to achieve high power density for these fuel cells. In particular, the mechanisms of reactions at the anode side are extensively studied by researchers. In this chapter, the mechanisms of the reactions taking place at the anode and cathode sides, and the reported anode catalysts for DFAFC and DFFC in recent years are presented. © 2021 Elsevier Inc. All rights reserved.
Introduction To Other Organic Fuel-Based Fuel Cells
(Elsevier, 2020) Ulas, B.; Kivrak, H.D.
Fuel cells are good alternative energy conversion systems that convert chemical energy directly into electrical energy to meet energy needs in the near future. Among the direct liquid fuel cells, direct alcohol fuel cells (DAFCs) are the widely studied organic-based fuel type; however, there are also other organic-based fuels that have a wide potential for use in fuel cells. Direct formic acid fuel cells (DFAFCs), direct dimethyl ether fuel cells (DDMEFCs), and direct formate fuel cells (DFFCs) are of interest to researchers because of their particular characteristics. These fuel cells have an important advantage in terms of storage and transportion compared to hydrogen-fed polymer electrolyte fuel cells (H2-PEMFC) similar to other DLFCs. While formic acid is preferred due to its high energy density, DME and formate attract attention with their low fuel crossover and high electrooxidation kinetics. This chapter gives an overview particularly of DFAFC, DFFC, and DDMEFC technology and stresses the barriers to commercialization of these types of fuel cells. © 2021 Elsevier Inc. All rights reserved.
Metal-Free Catalysts for Fuel Cell Applications
(Elsevier, 2022) Ulas, B.; Yagizatli, Y.; Demir-Kivrak, H.
Direct methanol fuel cells (DMFCs) are closer to commercialization than other fuel cells. These energy-conversion systems have extremely high potential, especially for portable devices. But the high cost of these fuel cells is the biggest obstacle to the commercialization of these devices. Many researchers have reported that anode and cathode catalysts account for the highest shares of fuel cell costs. These high costs are mainly driven by the costs of precious metals, which are used as anode and cathode catalysts for fuel cells for their high activity and stability. This chapter examines the preparation, characterization, and performances of platinum-free carbon-based and carbon-based metal-free anode and cathode catalysts for DMFCs. © 2022 Elsevier Inc. All rights reserved.
Optimization of Methyl Orange Decolorization by Bismuth(0)-Doped Hydroxyapatite/Reduced Graphene Oxide Composite Using Rsm-Ccd
(Springer, 2024) Ecer, U.; Yilmaz, S.; Ulas, B.; Koc, S.
In the current study, the catalyst for the decolorization of methyl orange (MO) was developed HAp-rGO by the aqueous precipitation approach. Then, bismuth(0) nanoparticles (Bi NPs), which expect to show high activity, were reduced on the surface of the support material (HAp-rGO). The obtained catalyst was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. The parameters that remarkably affect the decolorization process (such as time, initial dye concentration, NaBH4 amount, and catalyst amount) have been examined by response surface methodology (RSM), an optimization method that has acquired increasing significance in recent years. In the decolorization of MO, the optimum conditions were identified as 2.91 min, Co: 18.85 mg/L, NaBH4 amount: 18.35 mM, and Bi/HAp-rGO dosage: 2.12 mg/mL with MO decolorization efficiency of 99.60%. The decolorization process of MO with Bi/HAp-rGO was examined in detail kinetically and thermodynamically. Additionally, the possible decolorization mechanism was clarified. The present work provides a new insight into the use of the optimization process for both the effective usage of Bi/HAp-rGO and the catalytic reduction of dyes. © The Author(s) 2024.
Oxygen Reduction Reaction; Fuel Cells
(Springer Nature, 2024) Yagizatli, Y.; Acil, G.; Ulas, B.; Demir-Kivrak, H.
The principles of the oxygen reduction reaction (ORR), including elec-trocatalysts and kinetics, are covered in this chapter. Based on the literature, both experimental and theoretical methods are used to explore the ORR kinetics, including reaction processes catalyzed by various electrode materials and catalysts, such as Pt-based alloys, carbon materials, and transition metal macrocyclic complexes. It was emphasized that although there is a large literature on ORR, there is still a need to design materials that can compete with noble metal-containing catalysts for ORR. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Structural and Photon/Neutron Attenuation Features of Pbni/Cnt Nanocomposites: an Experimental Approach
(Pergamon-elsevier Science Ltd, 2023) Yorgun, N. Yildiz; Kavaz, E.; Ulas, B.; Yilmaz, Y.; Kivrak, H.
In this work, PbNi/CNT nanocomposites were prepared by sodium borohydride method at varying metallic molar ratios for determination of their structural and nuclear radiation shielding properties. As-prepared PbNi/CNTs were characterized by using transmission electron microscopy (TEM), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX), elemental mapping, and X-ray diffraction (XRD). Average particle sizes of Pb40Ni60/CNT, Pb60Ni40/CNT, Pb80Ni20/CNT, and Pb20Ni80/CNT materials were obtained as 5.6, 3.8, 4.2, and 4.2 nm, respectively. Radiation attenuation properties of the produced nanocomposites were investi-gated experimentally by irradiating the samples with gamma photons in the 34-383 keV energy range. The accuracy of the experimental results was checked with outcomes calculated with EpiXS software. Mass attenu-ation coefficient (MAC) was found in the range of 22.924-0.108 cm2/g, 5.473-0.129 cm2/g, 3.767-0.109 cm2/g, and 4.626-0.128 cm2/g for Pb20Ni80/CNT, Pb80Ni20/CNT, Pb40Ni60/CNT, and Pb60Ni40/CNT samples, respec-tively. Also, other photon shielding parameters (HVL, Zeff, EABF, and EBF) were calculated to make a comprehensive evaluation. The results show that 30% by weight Pb80Ni20 doped CNT has the lowest HVL and buildup factors values and the largest MAC, Zeff values. Finally, macroscopic cross-section values (sigma R) were obtained to estimate the ability of the nanocomposite samples to reduce the energy of fast neutrons. It was revealed that the sigma R values of the samples were in the range of 0.158-0.169 cm-1 and they had higher sigma R values than conventional neutron moderators.