Ludwe Luther Sikeyi

The development of high-performance and durable electrode materials is crucial for next-generation energy storage devices. In this study, a novel MnO2@MoS2@rGO heterostructure was successfully synthesized via a facile hydrothermal method. Comprehensive structural and morphological analyses were performed using XRD, Raman spectroscopy, BET, XPS, SEM-EDS, and TEM techniques. Electrochemical evaluations in a 6 M KOH electrolyte revealed that the heterostructure achieved a remarkable specific capacitance of 571.8 F g-1 at 1 A g-1, significantly outperforming bare MnO2, which exhibited 205.98 F g-1 at the same current density. This superior performance is attributed to the synergistic effects of the conductive rGO network and the robust heterostructure, which facilitate rapid electron transport and ion diffusion. Furthermore, freestanding an asymmetric supercapacitor (ASC) device fabricated with a high mass loading of 10.8 mg cm−2 (MnO2@MoS2@rGO//AC) delivered a specific capacitance of 119.5 F g−1 at 1 A g−1. The device also exhibited an outstanding energy density of 37.18 Wh k g-1 at a power density of 752 W k g-1, exceptional cyclic stability of 95.8% over 10,000 cycles, and successfully powered an LED for 8 minutes. These results demonstrate the exceptional practical applicability of the MnO2@MoS2@Rgo heterostructure for high-performance energy storage devices.

Practical supercapacitor applications rely on the development of high-performance, cost-effective electrode materials that provide high energy density and reliable stability. In this study, we synthesized a ternary Fe2O3@Mn2O3@rGO nanocomposite using a simple co-precipitation method. Its composition and structure were confirmed through XRD, SEM, XPS, and BET analyses. Electrochemical evaluation in a three-electrode system demonstrated a high specific capacitance of 446 F g⁻¹ at 1 A g⁻¹, surpassing the performance of Fe2O3 and Mn2O3 electrodes individually. This enhanced performance is attributed to the synergistic effects of the ternary composite. An asymmetric supercapacitor (ASC) device was fabricated using the ternary composite as the positive electrode and activated carbon (AC) as the negative electrode in a 6 M KOH electrolyte, achieving a maximum cell voltage of 1.5 V. The ASC delivered a maximum specific capacitance of 112 F g-1 at 1 A g-1, a high energy density of 35.21 Wh kg-1, and a power density of 3150 W kg-1. Moreover, the device demonstrated excellent capacitance retention of 96.2% over 5000 cycles, underscoring its potential as a high-performance electrode material for advanced energy storage systems.

This study explores the synthesis and potential application of nickel (Ni) nanoparticles encapsulated within mesoporous hollow carbon spheres (Ni@MHCS) as a promising catalyst for Fischer–Tropsch synthesis (FTS). The encapsulation strategy aims to mitigate common issues in catalysis, such as nanoparticle sintering and agglomeration, thereby enhancing catalyst stability and performance under demanding reaction conditions typical for hydrocarbon synthesis. The Ni@MHCS materials were synthesized, and their structural and compositional integrity was confirmed using various characterization techniques including transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) analysis, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. TEM confirmed the successful encapsulation of Ni nanoparticles within the hollow carbon structures. PXRD affirmed the presence of crystalline Ni, while TGA provided insights into thermal stability and composition. BET analysis characterized the surface area and porosity, crucial for catalytic accessibility, and spectroscopic methods (Raman, FTIR) confirmed the carbonaceous nature of the spheres and successful template removal. The catalyst activity and selectivity were evaluated using the Fischer–Tropsch reaction. The findings highlight the potential of Ni@MHCS as a suitable catalyst system for converting syngas or other suitable feedstocks into various hydrocarbons, offering a novel approach to sustainable energy solutions.

In direct alcohol fuel cells (DAFCs), energy conversion co‐occurs at the anode (alcohol oxidation reaction [AOR]) and cathode (oxygen reduction reaction [ORR]). The sluggishness of AOR and ORR needs highly electrocatalytically active and stable electrocatalysts that boost electrokinetics, which is central in electrocatalysts’ architectural design and modulation. This design entails enhanced engineering synthesis protocols, heteroatomic doping, metallic doping/alloying, and deliberate introduction of defective motifs within the electrocatalyst matrix. The electrocatalyst activity and behavior depend on the electrocatalysts’ nature, type, composition, and reaction media, acidic or alkaline. Alkaline media permits cheap nonplatinum group metals. This review elucidates the roles and electrocatalytic pathways on different AOR and ORR electrocatalysts and outlines the aspects distinguishing ORR in alkaline and acidic media. It gives up‐to‐date and ultramodern strategies, protocols, and underlying mechanisms pointing to the efficacy and efficiency of electrocatalysts. The focus centers on heteroatomic, metallic dopants, defects effects correlated to electrocatalytic properties and experimental and theoretical findings. For the advancement in the field, the present study discusses critical parameters for improving the performances of electrocatalysts for DAFCs and breakthroughs on the horizon. Conclusively, knowledge gaps and prospects of these materials for industrial viability and reigning futuristic research directions are presented.

Vegetable cooking oil is used in domestic and commercial kitchens owing to its ability to modify and enhance the taste of the food through the frying process. However, as the oil is used through several frying cycles, it changes colour to dark brown and acquires an unpleasant smell. At this point, the waste oil is usually discarded, thereby finding its way into freshwater streams due to poor disposal and thus becoming an environmental pollutant. To provide an alternative, ‘green’ route to waste oil disposal, herein we report on the metal-free synthesis of onion-like nanocarbons (OLNCs) made from waste cooking oil via flame pyrolysis. The OLNCs were then applied in the removal of hexavalent chromium ions from aqueous solutions. The as-synthesised OLNCs were found to have similar properties (size, quasi-spherical shape etc.) to those synthesised from pure cooking oils. The Fourier-transform infrared spectroscopy data showed that the OLNCs contained C-O-type moieties which were attributed to the oxygenation process that took place during the cooking process. The OLNCs from waste oil were applied as an adsorbent for Cr(VI) and showed optimal removal conditions at pH = 2, t = 360 min, Co = 10 mg/L and Q0max = 47.62 mg/g, superior to data obtained from OLNCs prepared from pristine cooking oil. The results showed that the OLNCs derived from the waste cooking oil were effective in the removal of hexavalent chromium. Overall, this study shows how to repurpose an environmental pollutant (waste cooking oil) as an effective adsorbent for pollutant (Cr(VI)) removal. Significance: Waste cooking oil outperformed olive oil as a starting material for the production of OLNCs for the removal of toxic Cr(VI) from water. The superior performance of the OLNCs from waste cooking oil was attributed to the higher oxygen content found on their surface and acquired through the cooking process. Not only are the OLNCs produced from waste cooking oil effective in the removal of Cr(VI), but they can be used multiple times before replacement, which makes them sustainable.

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.

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.

Pd/C, Pd/CNFs and Pd−Ru/CNFs nanocomposite materials were utilized as anode nanocatalysts in low‐temperature alkaline direct alcohol fuel cells. The palladium based nanocatalysts performance and stability were firmly relying upon the attributes of the carbon nanofibers (CNFs). CNFs were successfully synthesized employing a chemical vapour deposition method. The nanocatalysts were synthesized by dispersing Pd and Pd−Ru nanoparticles onto the CNFs surface using alcohol reduction method. The physical properties of the synthesized nanocatalysts were explored utilizing several techniques such as transmission electron microscope (TEM), scanning electron microscope‐Energy dispersive x‐ray (SEM‐EDX), X‐ray diffraction spectroscopy (XRD), X‐ray photoelectron spectroscopy (XPS) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP‐OES) and confirmed successful synthesis of Pd/C, Pd/CNFs and Pd−Ru/CNFs nanocomposite. TEM showed that Pd and Ru nanoparticles were uniformly dispersed on the CNFs support surface. ICP‐OES determined the palladium and ruthenium concentration in Pd/C, Pd/CNFs and Pd−Ru/CNFs nanocatalysts to be Pd (7.67 %), Pd (7.74 %), Pd (7.82 %) and Ru (3.22 %) respectively. The three prepared nanocatalysts were evaluated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) in the evaluation of ethanol and methanol oxidation reactions. CV, CA and EIS experiments of Pd−Ru/CNFs nanocatalyst displayed superior activity towards alcohol oxidation reaction in alkaline conditions than Pd/CNFs and commercial Pd/C nanocatalysts.