Carbon nano-onions (CNOs) were successfully synthesized by employing the flame pyrolysis (FP) method, using flaxseed oil as a carbon source. The alcohol reduction method was used to prepare Pd/CNOs and Pd-Sn/CNOs electro-catalysts, with ethylene glycol as the solvent and reduction agent. The metal-nanoparticles were supported on the CNO surface without adjusting the pH of the solution. High-resolution transmission electron microscopy (HRTEM) images reveal CNOs with concentric graphite ring morphology, and also PdSn nanoparticles supported on the CNOs. X-ray diffractometry (XRD) patterns confirm that CNOs are amorphous and show the characteristic diffraction peaks of Pd. There is a shifting of Pd diffraction peaks to lower angles upon the addition of Sn compared to Pd/CNOs. X-ray photoelectron spectroscopy (XPS) results also confirm the doping of Pd with Sn to form a PdSn alloy. Fourier transform infrared spectroscopy (FTIR) displays oxygen, hydroxyl, carboxyl, and carbonyl, which facilitates the dispersion of Pd and Sn nanoparticles. Raman spectrum displays two prominent peaks of carbonaceous materials which correspond to the D and G bands. The Pd-Sn/CNOs electro-catalyst demonstrates improved electro-oxidation of methanol and ethanol performance compared to Pd/CNOs and commercial Pd/C electro-catalysts under alkaline conditions.
Abstract A series of Pd nanoparticles supported on V 2 O 5 immobilized on functionalized carbon, % Pd (1, 3, and 5) and % V 2 O 5 (10, 20, and 30), were prepared by sodium borohydride‐assisted microwave polyol synthesis for glycerol oxidation reaction (GlyOR) in an alkaline medium. Electrocatalysts loading, temperature, V 2 O 5 immobilization, and their synergistic effect on the electrocatalytic performance are systematically studied. The electrocatalysts′ morphology and electronic properties were investigated using X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Transmission electron microscopy, and X‐ray photoelectron spectroscopy. A significantly improved GlyOR is observed with increased V 2 O 5 content and Pd percentage. The 5 %Pd/30 %V 2 O 5 ‐fAC showed the highest mass activity of 2157.3 mA . mg Pd −1 , a more negative onset potential of 0.62 V RHE , versus the commercial equivalent, and possessed high stability and durability. The increase in electrocatalytic activity is attributed to the effective immobilization of V 2 O 5 on fAC efficient synergism between Pd and V 2 O 5 , strong metal support interaction (SMSI), and great exposure of the electroactive sites. The results herein contribute significantly to the understanding of the physicochemical and electrochemical effects of metal oxide immobilization, microwave irradiation, % Pd/% Metal oxide optimization, and SMSI on metal oxide‐carbon hybrid electrocatalysts for GlyOR, opening new avenues for fabricating high‐performance direct alkaline glycerol fuel cells.
Mn-doped spinel oxides MnxNi1−xCo2O4 (x = 0, 0.3, 0.5, 0.7, and 1) were synthesized using the citric acid-assisted sol–gel method. The Mn0.5Ni0.5Co2O4 (x = 0.5) supported on carbon nanosheets, Mn0.5Ni0.5Co2O4/C, was also prepared using the same method employing NaCl and glucose as a template and carbon source, respectively, followed by pyrolysis under an inert atmosphere. The electrocatalytic oxygen reduction reaction (ORR) activity was performed in alkaline media. Cyclic voltammetry (CV) was used to investigate the oxygen reduction performance of MnxNi1−xCo2O4 (x = 0, 0.3, 0.5, 0.7, and 1), and Mn0.5Ni0.5Co2O4 was found to be the best-performing electrocatalyst. Upon supporting the Mn0.5Ni0.5Co2O4 on a carbon sheet, the electrocatalytic activity was significantly enhanced owing to its large surface area and the improved charge transfer brought about by the carbon support. Rotating disk electrode studies show that the ORR electrocatalytic activity of Mn0.5Ni0.5Co2O4/C proceeds via a four-electron pathway. Mn0.5Ni0.5Co2O4/C was found to possess E1/2(V) = 0.856, a current density of 5.54 mA cm−2, and a current loss of approximately 0.11% after 405 voltammetric scan cycles. This study suggests that the interesting electrocatalytic performance of multimetallic transition metal oxides can be further enhanced by supporting them on conductive carbon materials, which improve charge transfer and provide a more active surface area.
Abstract The Pt‐Sn/CNDs electrocatalyst was synthesized by the alcohol reduction method with the aim to reduce platinum loading and improve electroactivity. XPS results showed that the nanoparticles were present in the form of Pt‐Sn metallic alloy with a significant amount of SnO‐ species which facilitate the rapid oxidation of CO intermediates. The lattice parameter of Pt in Pt‐Sn/CNDs electrocatalyst was calculated to be 0.3926 nm; this value is higher than 0.3921 nm, the lattice parameter of Pt in Pt/CNDs electrocatalyst. XRD results proved that incorporating tin (Sn) into the Pt/CNDs electrocatalyst modifies the face centred cubic shape of platinum to a crystalline structure which improves the alcohol electro‐oxidation reactions. The electrochemical tests proved that the Pt‐Sn/CNDs electrocatalyst exhibited high current densities and lower poisoning rates compared to the Pt/CNDs and Pt/C electrocatalysts. The Pt‐Sn/CNDs electrocatalyst showed the greatest electroactivity for both methanol and ethanol electro‐oxidation reactions.
Carbon nanofibers (CNFs) supported by Pd and Pd-Sn electro-catalysts were prepared by the chemical reduction method using ethylene glycol as the reducing agent. Their physicochemical characteristics were studied using high resolution-transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Bruanaer-Emmett-Teller (BET) analysis. FTIR revealed that oxygen, hydroxyl, carboxylic and carbonyl functional groups facilitated the dispersion of Pd and Sn nanoparticles. The doping of Pd with Sn to generate PdSn alloy was also confirmed by XPS data. The amorphous nature of CNFs was confirmed by XRD patterns which exhibited the Pd diffraction peaks. When Sn was added to Pd/CNFs, the diffraction peaks moved to lower angles. HRTEM images revealed that the CNFs with cylindrical shape-like morphology and also Pd-Sn nanoparticles dispersed on carbon support. The catalytic activity and stability towards alcohol electro-oxidation in alkaline medium at room temperature was evaluated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The obtained Pd-Sn/CNFs electro-catalyst exhibited a better electro-catalytic activity than Pd/CNFs and Pd/C electro-catalysts for both methanol and ethanol oxidation. The improvement of the electrochemical performance was associated with the synergistic effect via the addition of Sn which modified the Pd atom arrangement, thereby promoting oxidation through a dehydrogenation pathway. Furthermore, SnO2 generates abundant OH species which helps with increasing the rate of the oxidative removal of carbon monoxide (CO) intermediates from Pd sites.
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