ABSTRACT
The study presents for the first time complex spinel NiFe2O4 nanoparticles supported on nitrogen and phosphorus co-doped carbon nanosheets (NPCNS) prepared using sol gel and the carbonization of graphitic carbon nitride with lecithin as a highly active and durable electrocatalyst for oxygen reduction reaction. The physicochemical properties of complex spinel NiFe2O4 on NPCNS and subsequent nanomaterials were investigated using techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The electrochemical activity of the electrocatalysts was evaluated using hydrodynamic linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The electrocatalytic performance of the NiFe2O4/NPCNS nanohybrid electrocatalyst is dominated by the 4e- transfer mechanism, with an onset potential of 0.92 V vs. RHE, which is closer to that of the Pt/C, and a current density of 7.81 mA/cm2 that far exceeds that of the Pt/C. The nanohybrid demonstrated the best stability after 14 400 s, outstanding durability after 521 cycles, and the best ability to oxidize methanol and remove CO from its active sites during CO tolerance studies. This improved catalytic activity can be attributed to small nanoparticle sizes of the unique complex spinel nickel ferrite structure, N-Fe/Ni coordination of nanocomposite, high dispersion, substantial ECSA of 47.03 mF/cm2, and synergy caused by strong metal-support and electronic coupling interactions.
ABSTRACT
Extensive investigations have been carried out on spinel mixed transition metal oxide-based materials for high-performance electrochemical energy storage applications. In this study, mesoporous Mn-substituted MnxZn1-xCo2O4 (ZMC) ternary oxide microspheres (x = 0, 0.3, 0.5, 0.7, and 1) were fabricated as electrode materials for supercapacitors through a facile coprecipitation method. Electron microscopy analysis revealed the formation of microspheres comprising interconnected aggregates of nanoparticles. Furthermore, the substitution of Mn into ZnCo2O4 significantly improved the surface area of the synthesized samples. The electrochemical test results demonstrate that the ZMC3 oxide microspheres with an optimal Mn substitution exhibited enhanced performance, displaying the largest specific capacitance of 589.9 F g-1 at 1 A g-1. Additionally, the ZMC3 electrode maintained a capacitance retention of 92.1% after 1000 cycles and exhibited a significant rate capability at a current density of 10 A g-1. This improved performance can be ascribed to the synergistic effects of multiple metals resulting from Mn substitution, along with an increase in the surface area, which tailors the redox behavior of ZnCo2O4 (ZC) and facilitates charge transfer. These findings indicate that the incorporation of Mn into mixed transition metal oxides holds promise as an effective strategy for designing high-performance electrodes for energy storage applications.
ABSTRACT
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.