Vol 5 No 1 (2023)

• The Thermal Kinetics of Methanol Oxidation on Pt/MWCNT Electrocatalysts in Alkaline Media

  Haitao zheng, Mmalewane Modibedi

  In this study, the thermal electrooxidation of methanol on a Pt/MWCNT catalyst was examined in alkaline media across the temperature range of 298-363 K. The investigation utilized cyclic voltammetry (CV), quasi-state polarization, and electrochemical impedance spectroscopy (EIS) methods to explore the kinetics of the methanol electrooxidation reaction (MEOR). At elevated temperatures, the kinetics of methanol electro-oxidation on the Pt/MWCNT catalyst within an alkaline solution (1.0 mol/L KOH) were notably accelerated compared to room temperature. This acceleration can be attributed to the reduced methanol dehydrogenation reaction at relatively low temperatures. The Tafel slopes experienced changes as the temperature increased. These variations in Tafel slopes are likely linked to alterations in the rate-determining step of the MEOR as a function of temperature. The EIS outcomes revealed a decrease in charge-transfer resistance as temperature increased. This phenomenon is associated with the interplay between interfacial and diffusion impedances, as well as the surface roughness of the highly dispersed electrode surface.

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• A Review on Pseudocapacitors: Advances in Nb Oxide - Sodium-Ion Systems

  Edna Jerusa Pacheco Sampaio, Adilar Goncalves dos Santos Junior, Cristiano Campos Araujo, Celia de Fraga Malfatti

  Pseudocapacitive supercapacitors have emerged as an important alternative to storage electrochemical energy. Among the several possible configurations of material for electrodes and electrolyte composition, the combination of oxides containing niobium and electrolytes based on sodium-ion has been presented as a very promising set. This review summarizes the main advances in the development of supercapacitors that use the Nb oxide - sodium-ion system. The electrochemical energy storage mechanisms are described and the influence of the type of electrolyte (aqueous or non-aqueous) is discussed. It was possible to verify that non-aqueous electrolytes are widely more used to assemble the Nb oxide - sodium-ion arrangements. For these systems the energy storage is controlled by the mechanism of intercalation/deintercalation of sodium-ions in the oxide structure. Despite non-aqueous electrolytes exhibit the advantage of operating in a wider window potential, they have disadvantages such as low electrical conductivity and sluggish Na⁺ kinetics. To overcome these aspects, works in the field have generally focused on improving the properties of the oxides, especially concerning its conductivity through core@shell systems, composites or doping. On the other hand, few studies were found in the literature concerning the Nb oxide - sodium-ion systems that use aqueous electrolytes. Nevertheless, these works showed promising results such as an expansion of the potential window usually used in aqueous electrolytes or the possibility to apply the Nb oxide as cathode or anode.

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• The Effect of Ultrasonic Cavitation on Surficial Properties of Metals and Industrial Processes

  Haitao Zheng, Mkhulu Mathe

  Ultrasonic cavitation is a phenomenon that occurs when high-frequency sound waves are introduced into a liquid medium, causing the formation and collapse of small bubbles within the liquid. These bubbles generate high-energy shock waves that can change the surface of nearby materials, leading to various physical and chemical effects. In this review, we briefly summarized the influence of ultrasonic cavitation on the surficial properties of metals and some industrial processes, particularly focusing on the effects of surface roughness, surface cleaning, and surface activation/modification and surface corrosion.

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• Optical Properties of the Crystalline Silicon-black Silicon-perovskite Tandem Solar Cells

  Ferdinand Gasparyan

  The optical properties of a tandem three-layered structure of crystalline silicon-black silicon-perovskite have been theoretically studied for using it in solar energy conversion. The transfer matrix method is used for obtaining the analytical expressions for the reflection, transmission, and absorption coefficients. It is shown that the transfer matrix method can be successfully applied to the more complicated case of three layers with complex refractive indexes. Numerical calculations performed at an angle of incidence of radiation of 60^o showed that in the region of short wavelengths the reflection coefficient takes on low values (several percent), which gradually increase and become > 10% at wavelengths above 0.8 μm. The theoretically modeled results of the reflection coefficient are in good agreement with experimental data carried out for the structures crystalline silicon-black silicon-TiO₂-perovskite. The discrepancy between the experimental and model data slowly increases with increasing wavelength. The transmittance was extremely low and increased slowly with the increasing wavelength. It is found that cheaper and easier created tandem crystalline silicon-black silicon-perovskite structure may have the potential for solar energy conversion.

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• Comparative Study of the Compressive Strength of Different Commercial Graphite Grades at Room and High Temperatures

  Michele Ballan, Stefano Corradetti, Lisa Centofante, Alberto Monetti, Mattia Manzolaro, Giovanni Meneghetti

  Graphite is often employed for several high temperature research and industrial applications, thanks to its refractoriness and its physical properties such as high thermal conductivity, low thermal expansion and excellent thermal shock resistance. However, its mechanical properties at high temperatures are often unknown and are strongly influenced by its microstructure and composition. This work is focused on a comparative analysis of the compressive strength up to 2000 ^oC of three different commercial graphite grades provided by TOYO TANSO. Two grades of the same kind but different density, IG-43 and IG-45, and a grade with finer grains, TTK-4, were considered. Such materials were selected as their nominal physical and chemical properties are suitable for withstanding the extreme working conditions typical of nuclear applications characterized by high temperature, high vacuum and radiation damage. For the performance of the compressive tests, a custom-built vacuum experimental equipment was used, capable of resistively heating conductive samples at a temperature level up to 2000 ^oC. Specimens with an hourglass shape were manufactured and tested in triplicate at room-temperature, 1000 ^oC and 2000 ^oC for each type of graphite. The dependence of the compressive strength on the graphite grade density and microstructure was highlighted, resulting in higher resistance for denser grades, in accordance with data reported by the supplier. Results collected for the room-temperature tests were consistent with the material datasheets, whereas at 2000 ^oC, an increase of approximately 30%-40% of the compressive strength was displayed compared to its room-temperature value.

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• Atomically Dispersed Co Atoms Stabilized by Nitrogen Species in Carbon Skeleton for Efficient Oxygen Reduction and Zn-air Batteries

  Rongrong Liu, Jizheng Feng, Tao Meng

  Atomically dispersed and nitrogen-coordinated single metal atom implanted into the carbon substrate holds great promise as Pt-liked catalysts for oxygen reduction reaction (ORR). However, the complicated synthetic procedures of single atomic catalysts heavily limit their widespread applications. Herein, the atomically dispersed Co stabilized by nitrogen species in carbon skeleton (Co-SAs/NC) is prepared by a controllable pyrolysis of the nano-confined Co-precursor, and further employed as alkaline ORR catalyst. The atomic configuration and electronic structure of Co-SAs/NC are systematic investigated by a wide range of advanced techniques, such as electron microscopic and X-ray absorption spectroscopy. As expected, Co-SAs/NC exhibites excellent ORR activity with a large onset and half-wave potentials, as well as good selectivity and favorable stability. More importantly, the outstanding ORR performances of Co-SAs/NC enable the assembled Zn-air battery to deliver a large specific capacity of 788.4 mAh•g_Zn^-1, a maximum power density of 233.6 mW•cm^-2, and a long cycle life.

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• Biomass-Derived Porous Carbon: Synthesis and Application for Energy Conversion and Storage

  Hong Liu, Shuai Liu, Lei Liu

  The conversion of biomass to carbonaceous materials have received wide attention these years. In particular, biomass-derived carbons demonstrate great potential as electrodes for different energy storage system due to their various architectures, low cost, and renewability. This review provided the recent progress in the synthesis and application of biomass-derived carbons and their hybrids as electrodes for energy storage. Various carbon structures including spheres, 1D fiber/tube, 2D sheets, 3D hierarchical porous carbon have been acquired from various biomass through different activation methods. Owing to their devise composition and morphology, the biomass-derived carbon materials are employed as electrodes for supercapacitors, metal-ion batteries and Li-S batteries. Finally, conclusions and outlook trends to the future development of biomass-derived carbons are proposed.

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