الفهرس 
Introduction and Literature surveyيوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Platinum-based catalysts are the most effective electrocatalysts for the anodic oxidation reaction of fuel cells. Additionally, the high expense of the Pt-based catalyst, approximately 54% of the total cost of fuel cells is another trouble for commercial fuel cells. For that, several Pd-based catalysts have been proposed as alternatives to Pt and replace the use of precious group metals (PGMs) by using non-precious group metals such as Ni, Fe, and Co. Nickel (Ni) is a highly versatile element that finds widespread use in both heterogeneous catalysis and electrocatalysis. One of its key advantages is its low cost and high abundance, combined with excellent corrosion stability in alkaline media. Ni tends to undergo oxidation, resulting in the formation of a thin surface oxide layer, approximately 1-2 nm in thickness, consisting of nickel oxide and nickel hydroxide. The presence of these oxides on the Ni surface can significantly impact its catalytic properties, particularly in low-temperature electrocatalysis. Project one: A comparative study of α-Ni(OH)2 and Ni nanoparticles supported ZIF-8@reduced graphene oxide-derived nitrogen-doped carbon for electrocatalytic ethanol oxidation. This study reported the development of a new electrocatalyst for ethanol oxidation in fuel cells based on nickel hydroxide/N-dopped zinc oxide@reduced graphene oxide (α-Ni(OH)2/ZNC@rGO). This nanocomposite was used as an electrocatalyst which exhibited a high efficiency toward ethanol oxidation. Reduced graphene oxide (rGO) was used as a support and conductive material in addition to increasing the stability of the electrocatalyst. It was loaded with a non-precious group metal like Ni in the form of nickel nanoparticles and nickel hydroxide. GO was prepared by the modified Hummer’s method and ZNC@rGO was prepared via a pyrolysis of ZIF-8@rGO at 700°C under nitrogen. The α-Ni(OH)2/ZNC@rGO was prepared via the reflux at 100 °C using ammonium hydroxide, while the Ni/ZNC@rGO was prepared via the hydrothermal method. The as-prepared samples were characterized by FT-IR, UV-vis, XRD and TEM measurements. FT-IR spectrum of GO shows various oxygen configurations in the structure including the hydroxyl groups (C-OH) from COOH and H2O at 3650- 3150 cm-1. Besides, the characteristic peaks at 2919.8, 1734, 1401, 1220, and 957 cm-1 correspond to the C-H, ketonic species (C=O), the O-H deformation, stretching vibration of the C-O group, and peroxide group, respectively. ZIF@rGO spectrum showed both the characteristic peaks of GO and ZIF-8 with very low intensities of the peaks at 3650- 3150 cm-1 related to the complete GO reduction to rGO. Compared to the peaks of ZIF-8, the disappearance of the Zn-N stretch band (420 cm-1) in the ZNC@rGO spectrum with a new observed peak at 459 cm-1 due to the Zn-O vibration confirmed the pyrolysis of the pristine MOF. For the Ni(OH)2/ZNC@rGO spectrum, there are three sharp peaks at 3390, 1615, and 626 cm-1 corresponding to the O-H stretching in Ni(OH)2 and H2O, the bending mode of O-H group in the interlayer H2O, and the stretching mode of Ni-O-H bond, respectively. XRD spectrum displayed the characteristic peak observed at 2 θ = 7.2 (110),10.4 (200), 12.7 (211), 14.6 (220), 16.5 (310), 18.0 (222), 24.5 (233), and 26.6° (134) indicating the high crystallinity of the as-synthesized ZIF-8 particles. The pattern of the ZNC@rGO shows various peaks at 2θ of 31.6 (100), 34.5 (0 0 2), 36.2 (101), 47.7 (102), 56.5 (110), 62.6 (103), and 68.2° (112) indicating that the derived ZnO nanoparticles Moreover, the XRD pattern of Ni/ZNC@rGO shows identical diffraction peaks of the pure ZNC@rGO with high crystallinity and a small shift to higher two theta value due to the incorporation of the Ni nanoparticles on the ZnO lattice. The pattern of Ni(OH)2/ZNC@rGO displays the characteristic peaks of the α-Ni(OH)2 nanoparticles at 9.9, 19.5, 33.6, 39.0, 52.7, and 60.0° attributing to the (001), (100), (110), (111), (103) and (201) reflections, respectively. Some of the characteristic peaks of ZNC and rGO are not as clear as those of pure ZNC@rGO due to the sharp peaks of alpha nickel hydroxide. Moreover, SEM and TEM analyses were performed to understand the morphological structures of the fabricated catalysts. The conducted SEM and TEM images of Ni(OH)2/ZNC@rGO show the growth of a thin layered spongy flake-like porous structure on the surface of the ZNC@rGO. The catalytic activity of the electrocatalyst toward the ethanol oxidation was examined by cyclic voltammetry and linear scan voltammetry in an alkaline solution (KOH) at a potential window ranging from -0.2 to 0.6 V vs Ag/AgCl with a scan rate of 50 mV s-1 in the presence and absence of ethanol. The Ni(OH)2/ZNC@rGO catalyst shows a remarkable increase in the current density due to the presence of high conductive rGO, the electron donation to α-Ni(OH)2 from ZnO, and the redox activity of the heteroatoms (N- atom). Furthermore, the Ni(OH)2/ZNC@rGO composite exhibited excellent stability and durability. The CV technique was performed for consecutive hour-long periods over the potential for 900 cycles at a potential of -0.2- 0.6 V in 1 M KOH containing 1M EtOH. It is observed that the Ni(OH)2/ZNC@rGO catalyst can maintain a stable potential with a continuous increase in the current density of the EOR highlighting the remarkable activity and catalytic stability due to the increase of the redox species Ni2+/3+ on the surface. Moreover, the chronoamperometric responses of the Ni(OH)2/ZNC@rGO were recorded for 3000 s at a constant potential (0.6 V) in an alkaline solution containing ethanol. The current density of EOR at the Ni(OH)2/ZNC@rGO remained at 92% after 3000 s compared with the original value which is higher than that of the commercial 20 wt.% Pt/C (64%) indicating the high stability of the prepared electrode. This might be owing to the high conductivity, and huge surface area of the supporting material (rGO and N-doped carbon) as well as the high activity of α-Ni(OH)2 and ZnO nanoparticles. The EIS approach is used to assess the kinetics on the surface, The Ni(OH)2/ZNC@rGO electrode has a smaller semicircle diameter than the other electrocatalysts and demonstrates the reduced resistance of the charge transfer for EOR and higher kinetics on the surface. Moreover, the catalyst exhibits faster electron transfer during the EOR which is confirmed by the smaller value of the charge transfer resistance (Rct) achieving the best electron conductivity and ions transport compared to the other prepared electrocatalysts. Finally, this work commences a new avenue of synthesizing cost-effective electrocatalysts based on metal double hydroxides. Project Two: Enhanced electrocatalytic activity and stability of PdNi alloy supported TiO2@nitrogen doped carbon derived MOFs for ethanol oxidation in alkaline media. This study reported the development of an electrocatalyst for ethanol oxidation in fuel based on PdNi alloy / N-dopped TiO2@reduced graphene oxide (PdNi/TNC@rGO). 2D layered alloy materials have attracted significant interest in this field due to their high efficiency toward ethanol oxidation interaction, abundant intermediate band states, and superior stability. The PdNi/TNC@rGO catalyst was prepared via the in-situ reductions of palladium and nickel salts using sodium borohydride (NaBH4). Different ratios of the Pd and Ni nanoparticles; Pd/TNC@rGO, Ni/TNC@rGO, Pd0.2Ni0.8/TNC@rGO, Pd0.8Ni0.2/TNC@rGO, and Pd0.6Ni0.4/TNC@rGO were prepared and tested for ethanol oxidation performance. The as-prepared catalysts were characterized by FT-IR, UV-vis, XRD and TEM measurements. Notably, all characteristic peaks of NH2-MIL-125 disappeared after the thermal treatment indicating the successful derivation of TiO2/NC from NH2-MIL-125. Moreover, the intensity of these peaks decreased by the doping of the nickel and palladium nanoparticles indicating the successful distribution of these nanoparticles on the surface of the TiO2/NC matrix. Obviously, several bands were observed in the FT-IR spectrum of the TNC@rGO sheet which is characteristic of different oxygen-containing functional groups of GO. The adsorption broadband of the intermolecular H-bonding of OH groups is observed from 3600 to 3000 cm-1, which disappeared in the spectra of nanocomposites due to the reduction of GO to rGO. Also, the characteristic peaks at 1728 and 1627 cm-1 were assigned to the stretching vibrations of the (-C=O) group of COOH groups. The peak identified at 1050 cm-1 was characteristic of the stretching vibrations of the (C-O-C) functional group. Compared with TNC@rGO, the peaks of PdNi composites have a slight shift because the doping of Pd and Ni nanoparticles can enhance the electron delocalization between the π electrons in graphene and electric charge in the nitrogen-doped carbon matrix. The results clearly prove a covalent connection between the PdNi nanoparticles and TNC@rGO. Moreover, The crystalline characteristics and crystal size of the as-prepared catalysts were investigated by XRD pattern. For the Pd/TNC@rGO catalyst, a broad peak corresponding to graphitized carbon structures appears at 2θ of 26° in addition to the peaks of TiO2 at 25, 38, 48, 55, and 62° corresponding to 101, 110, 004, and 200 crystal planes, respectively. Besides, the characteristic peaks of Pd nanoparticles appear at 40.5, 46.8, and 68.4º, corresponding to the (111), (200), and (220) lattice planes, which can be well indexed to face-centred cubic (fcc) Pd according to the JCPDS card No. 05-0681. These peaks overlapped with the peaks of Ni nanoparticles in the Pd0.5Ni0.5/TNC@rGO catalyst giving higher intensity. The total survey of the XPS spectra for the Pd0.6Ni0.4/TNC@rGO(Ti) catalyst prepared shows the presence of C1s, O1s, N1s, Ti2p, Pd3d, and Ni2p which confirmed the successful synthesis of the catalyst. The SEM image shows the distribution of highly cohesive TiO2 nanoclusters and GO sheets on the surface of the nitrogen-doped carbon matrix. It was observed that the pyrolysis under the N2 atmosphere kept the morphology of the MOFs in the derived carbon matrix. The images show the good and uniform distribution of small particles of the Pd-Ni alloy on the surface of the derived nitrogen-doped carbon matrix. It was observed that the support prevents the agglomeration of the Pd-Ni alloy giving nanoparticles with small size which is suitable for high catalytic activity. HRSEM elemental mapping and EDX analysis were performed to validate and confirm the presence of the elemental composition of the Pd0.6Ni0.4/TNC@rGO electrode. The pyrolysis of the MOF gives a highly conductive carbon matrix which has more active sites owing to the presence of a heteroatom (nitrogen atom). Besides, the pyrolysis of MOF caused the formation of TiO2 nanoparticles on the surface of the support which enhances the oxidation of Pd and Ni bimetallic NP alloy to the active species (PdO) and NiO for EOR. For Pd0.6Ni0.4/TNC@rGO(Ti), the forward scan shows two anodic peaks at -0.38 V and -0.33 V attributed to the adsorption of OH- on the catalyst surface (Peak I) followed by the oxidation of Pd NPs to active species for PdO (Peak II). The cathodic peak in the reverse scan due to the reduction of PdO to PdNPs (Peak III) was observed at -0.32 V with a current density of 0.24 mA cm-2. The catalytic activity of the electrocatalyst toward the ethanol oxidation was examined by cyclic voltammetry and linear scan voltammetry in an alkaline solution (KOH) at a potential window ranging from -0.8 to 0.4 V vs Ag/AgCl with a scan rate of 50 mV s-1 in the presence and absence of ethanol. The Pd0.6Ni0.4/TNC@rGO(Ti) catalyst shows a remarkable increase in the current density due to the presence of high conductive rGO, the electron donation to α-PdNi alloy from the presence of a heteroatom (nitrogen atom) and TiO2 nanoparticles on the surface of the support due to the pyrolysis of MOF which enhances the oxidation of Pd NPs to the active species (PdO) for EOR. Furthermore, the Pd0.6Ni0.4/TNC@rGO(Ti) composite exhibited excellent stability and durability. The chronoamperometric responses of the Pd0.2Ni0.8/TNC@rGO, and commercial Pt/C (20 wt.%) electrodes were recorded for 500 s at a constant potential (-0.3 V) in an alkaline solution and continued for 3000 s with the addition of ethanol. The Pd0.6Ni0.4/TNC@rGO(Ti) exhibited high stability compared to other catalysts. This might be owing to the high conductivity, and huge surface area of the supporting material (rGO, N-doped carbon and TiO) as well as the alloy nanoparticles. The EIS approach is used to assess the kinetics on the surface. The Pd0.6Ni0.4/TNC@rGO electrode has a smaller semicircle diameter than the other electrocatalysts, demonstrating the reduced resistance of the charge transfer for EOR and higher kinetics on the surface. Moreover, the catalyst exhibits faster electron transfer during the EOR which is confirmed by the smaller value of the charge transfer resistance (Rct) achieving the best electron conductivity and ions transport compared to the other prepared electrocatalysts. These results are related to the high surface area of the rGO and the derived carbon. Besides, the rGO and N-doped carbon exhibit high conductivity which promotes the electron transfer process. Finally, this work commences a new avenue of synthesizing cost-effective electrocatalysts based on PdNi bimetallic NP alloy and nitrogen-doped carbon-derived MOFs.