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    A COMPARATIVE STUDY FOR SODIUM BOROHYDRIDE DEHYDROGENATION AND ELECTROOXIDATION ON CERIUM AND COBALT CATALYSTS
    (Health & Environment Assoc, 2020) Hansu, Tulin Avci; Caglar, Aykut; Sahin, Omer; Kivrak, Hilal
    In the present study, Co/CNT and Ce/CNT catalysts are prepared via sodium borohydride (NaBH4) reduction method. Co/CNT and Ce/CNT catalysts are examined to the dehydrogenation and electrooxidation of NaBH4. NaBH4 dehydrogenation activities of these Co/CNT and Ce/CNT catalysts are performed in alkaline environment. 5% Co/CNT catalyst exhibits superior hydrogen evolution compared with other catalysts. Activation energy is calculated using Arrhenius equation. Initial rate for this catalyst is found as 1700 ml H-2 g(cat)(-1) min(-1). As a result of the kinetic calculations, the activation energy of the catalyst is calculated as 44,68775 kj/mol. The degree of reaction (n) is found to be 0.5 by trial and error. In conclusion, 5% Co/CNT catalyst is a promising catalyst for hydrogen production from NaBH4. Cyclic voltammetry (CV) analysis is utilized to examine the electrochemical activity of the catalysts for NaBH4 electrooxidation. 0.1% Co/CNT catalyst has 0.38 mA cm(-2) (3181 mA mg(-1) Co) specific activity.
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    A remarkable Mo doped Ru catalyst for hydrogen generation from sodium borohydride: the effect of Mo addition and estimation of kinetic parameters
    (Springer, 2020) Hansu, Tulin Avci; Sahin, Omer; Caglar, Aykut; Kivrak, Hilal
    At present, carbon nanotube supported monometallic Ru at 3 wt% Ru loading (3% Ru/CNT) per gram support and bimetallic RuMo at 3 wt% Ru loading per gram support (3% Ru-Mo/CNT) at varying Ru:Mo atomic ratios are synthesized via sodium borohydride (NaBH4) reduction method to investigate their performance towards NaBH4 hydrolysis. These monometallic Ru/CNT and bimetallic Ru:Mo/CNT catalysts prepared at varying Ru:Mo atomic ratios are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), and transmission electron microscopy (TEM). Characterization results reveal that Mo addition to Ru alters the electronic state of the catalysts. The NaOH concentration, the amount of catalyst, the NaBH4 concentration and the temperature parameters that affect the hydrolysis rate of this synthesized and developed catalyst were examined. The kinetic calculations of these parameters related to the order of the reaction were determined. Under optimum conditions catalyst hydrogen production rate was found to be 82,758.43 ml H-2 g(cat)(-1) min(-1). The reaction order (n) and activation energy (E-a) are determined as 0.42 and 35.11 kJ mol(-1). Ru:Mo/CNT catalyst is a novel and promising catalyst for hydrogen generation from NaBH4.
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    Enhanced Photocatalytic Hydrogen Production on Cd-, Te-, Se-, and S-Doped Titanium Dioxide Catalysts
    (Springer, 2023) Kaya, Sefika; Saka, Ceren; Caglar, Aykut; Kaya, Mustafa; Kivrak, Hilal
    Herein, cadmium (Cd)-, tellurium (Te)-, selenium (Se)-, and sulfur (S)-doped titanium dioxide (TiO2) support material catalysts are prepared via incipient wetness impregnation. Hydrogen generation performances of the prepared catalysts from sodium borohydride (NaBH4) by methanolysis are investigated. Experimental studies are carried out under ultraviolet (UV) illumination and in the dark. The highest initial hydrogen generation rate is reached on 0.1% Cd/TiO2 catalyst under UV illumination. The optimum catalyst, sodium borohydride, and methanol amounts and temperature parameters affecting the initial hydrogen generation rate are investigated and obtained as 0.025 g, 0.150 g, 2 mL, and 60 degrees C, respectively. The initial hydrogen generation rate of 0.1% Cd/TiO2 catalyst is 16130.64 mL/min.gcat in optimum conditions. The activation energy of the reaction with the 0.1% Cd/TiO2 catalyst is calculated by carrying out kinetic studies. The activation energy is 22.48 kJ/mol. X-ray diffraction (XRD), electron microscopy with energy-dispersive x-ray spectroscopy (SEM-EDX), inductively coupled plasma mass spectrometry (ICP-MS), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) analytical techniques are performed to characterize the catalysts. The results show that TiO2 catalysts doped with Cd, Te, Se, and S, which are cheaper than noble metals, are promising for the production of hydrogen from NaBH4 by methanolysis under UV illumination.
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    Fabrication of novel palladium-platinum based graphene/ITO electrodes and third metal addition effect through the glucose electrooxidation
    (Elsevier Science Sa, 2022) Caglar, Aykut; Hansu, Tulin Avci; Sahin, Ozlem; Kivrak, Hilal
    Graphene was coated on Cu foil by chemical vapor deposition (CVD) method. The graphene on the Cu foil was modified by doping N. Then, N-doped graphene (G) was coated on several layers of indium tin oxide (ITO) electrodes. In addition, Pd, Pt, and M (Ag, V, Ni, Zn) metals were electroprecipitated on the graphene/indium tin oxide electrode by electrochemical technique. In this way, the glucose (C6H12O6) electrooxidation activities of these electrodes obtained from PdMPt-N doped graphane/indium tin oxide were investigated by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. The obtained materials were characterized by SEM-EDX. Results revealed that the network of Pd, Pt, Ag, V, Ni, Zn and graphene was clearly visible from the SEM results. As a consequence, PdZnPt-N doped G/ITO showed the most effective C6H12O6 electrooxidation activity with a specific activity of 14.5 mA cm(-2), considerably above the literature's published values. In all electrochemical measurements, PdZnPt-N doped G/ITO exhibited the best electrocatalytic activity, stability, and resistance. PdZnPt-N doped G/ITO electrode is promising electrode for glucose electrooxidation.
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    Hydrolysis and electrooxidation of sodium borohydride on novel CNT supported CoBi fuel cell catalyst
    (Elsevier Science Sa, 2020) Hansu, Tulin Avci; Caglar, Aykut; Sahin, Omer; Kivrak, Hilal
    At present, Co, Bi, CoBi, and CoBi/CNT catalysts are prepared via co-precipitation method and sodium borohydride (NaBH4) reduction method for NaBH4 electrooxidation and hydrolysis. These Co, Bi, and CoBi catalysts are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), N-2 adsorption-desorption, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and Temperature Programmed Reduction (TPA). These catalysts are employed for NaBH4 hydrolysis and further measurements are performed to investigate their NaBH4 electrooxidation activity. For NaBH4 hydrolysis, NaOH concentration, reaction temperature, NaBH4 concentration, and catalyst amount are optimized for CoBi and CoBi/CNT catalysts. Furthermore, the rate constants (k) are found between 20 and 50 degrees C and the activation energy is calculated from the Arrhenius equation. The hydrogen generation rates on CoBi (95-5) and % 10 CoBi (95-5)/CNT catalysts are found as 2605.6ml H-2 g(-1)cat min(-1) and 12996 ml H-2 g(-1)cat min(-1), respectively. NaBH4 electrooxidation is investigated with cyclic voltammetry (CV), chronoampemmetry (CA), and electrochemical impedance spectroscopy (EIS) measurements. Maximum mass activities are obtained as 5.86 mA mg(-1) Co for CoBi and 25.7 mA mg(-1) Co for CoBi/CNT catalysts. EIS and CA results are also in a good agreement with CV results in terms of stability and electrocatalytic activity of CoBi/CNT catalyst. The CoBi/CNT catalyst is believed to be a promising anode catalyst for the direct borohydride fuel cell (DBFC).
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    The characterization and sodium borohydride electrooxidation of novel carbon nanotube supported copromoted Pd as anode catalyst for fuel cell
    (Wiley, 2022) Caglar, Aykut; Hansu, Tulin A.; Sahin, Omer; Kivrak, Hilal
    In the present study, the effect of Co addition on Pd is investigated. Pd/CNT and PdCo/CNT catalysts are prepared via the sodium borohydride (SBH, NaBH4) reduction method. The X-ray diffraction, transmission electron microscope, and inductively coupled plasma-mass spectrometry analyses are performed to characterize the PdCo(70-30)/CNT catalyst. These characterization results reveal that Pd/CNT and PdCo/CNT catalysts are prepared successfully. NaBH4 electrooxidation activities of PdCo/CNT catalysts are examined with electrochemical methods such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. PdCo(70-30)/CNT catalyst has 11.52 mA/cm(2) specific activity, 477.18 m(2)/g electrochemical active surface area, and the best electrochemical stability. Pd is a promising catalyst for NaBH4 electrooxidation reaction.