Porous carbonaceous materials have gained importance due to their multiple uses in energy storage applications. A cost-effective and promising way to synthesize these materials can be achieved through the KOH activation of carbons from agricultural by-products, by carefully controlling certain characteristics, such as yield and specific surface area. This work explores the synthesis and characterization of activated carbons (ACs) derived from brewery waste production and their potential use as cathode material in lithium-sulfur batteries. The study examines key parameters of the activation process, including pyrolysis temperature, soaking activation time, washing procedures, and mixing methods, to maximize the surface area and porosity of the resulting ACs. Different characterization techniques, such as scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption isotherms, were employed to evaluate the structural and chemical properties of the obtained ACs. As a result, biocarbons with highly competitive surface areas up to 1792 m2/g were achieved and tested as hosts for sulfur impregnation for its application in lithium-sulfur cells.

Lithium-oxygen batteries have gained prominence in recent years due to their potential advantages over conventional lithium-ion batteries, including higher energy density, cost-effectiveness and environmental sustainability. To fully exploit these advantages, it is essential to understand the interplay between porous carbon electrode materials and electrolytes in these devices. This study presents a nuclear magnetic resonance investigation of the confined LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) - TEGDME (tetraethylene glycol dimethyl ether) electrolyte within carbonaceous materials with different pore sizes. Three carbon materials (microporous, mesoporous, and hierarchical) were synthesized from the same precursor to ensure equivalent surface chemistry, which was verified by X-ray photoelectron spectroscopy. The dynamics and distribution of solvent and Li ions in the different pores were studied by 1 ${^1 }$ H and 7 ${^7 }$ Li, 1D and 2D exchange, NMR spectroscopy. It was found that the accessibility of Li + ${^+ }$ within the pores of the carbonaceous material depends not only on their size but also on their size distribution. The knowledge gained from this study can contribute to the design of the appropriate pore size distribution, which could optimize the electrolyte utilization and consequently increase the energy density of lithium-oxygen batteries.

The demand for more efficient energy storage devices has become increasingly important in order to face the ongoing energy transition. In this regard, it is equally important to attain the production of these devices with the lowest possible environmental impact. In light of this, the use of waste materials and low‐polluting methods has become a strategic priority. In this study, brewers’ spent grains were utilized as raw material to produce anodic electrodes for lithium‐ion batteries (LIBs). The synthesis process involves only two pyrolysis steps at low temperatures without any chemical treatment, reducing energy investment and waste generation. The result is a porous biocarbon structure—with mixed graphitic and amorphous characteristics—decorated with silica nanoparticles. The presence of silica greatly enhances storage capacity. The obtained biocarbon based electrodes exhibites a capacity of 455 mAh g−1 after 100 cycles, surpassing the standard anode material commonly used in commercial LIBs.

A sustainable cow hair-based biocarbon/sulfur composite was prepared via a melt-diffusion process and used as cathode for lithium-sulfur (Li-S) batteries, exhibiting high capacity, good rate capability, and excellent cyclability. The effect of the activation process during the formation of the biocarbon was deeply analyzed by thermogravimetry, N-2 adsorption, X-ray photoelectron spectroscopy, scanning and transmission electron microcopy, among others. A correlation between the composition and the surface area with the electrochemical performance was found. The best results were obtained using an activated sample and composite electrode containing 73 wt % sulfur, which present an initial discharge capacity of around 1200 mAh/g and 799 mAh/g after 100 cycles at a current density of 0.1 A/g. Moreover, a specific capacity of similar to 701 mAh/g was measured at 1 C. The great electrochemical performance of this electrode in Li-S batteries is attributed to the porous carbon structure. Taking into account that hair is one of the major waste produced in the leather sector, this work presents a promising approach to reuse this material by giving it added value through the preparation of carbon/sulfur composites for high-performance Li-S batteries.

The wave reversal mode is a magnetization reversal mechanism that appears in ferromagnetic nanotubes of certain geometric parameters when an external magnetic field is applied perpendicular to their axes. The distinctive feature of this mode is that leads to well-defined S-shaped hysteresis curves. In order to gain insight into the stability of this latter effect, we have performed micromagnetic simulations for permalloy and nickel nanotubes obtaining a non-monotonic behavior for coercivity as well as for remanence as a function of nanotube diameter for both materials. Motivated on these latter intriguing results, we found that measuring the area that encloses the hysteresis curve is a novel and simple strategy to identify the appearance of the wave reversal mode. An additional contribution of this work is the proposal of a new magnetic phase diagram that allows determining the stability of this reversal mechanism as a function of the geometric and magnetic parameters of the tubes.

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This work contributes to the understanding of angular dependence of the magnetic properties of Permalloy nanowire arrays by means of a comparative analysis between experiment and micromagnetic simulations. On the one hand, Permalloy nanowires of 30 nm in diameter and 1 mu m in length were synthesized by AC electrodeposition inside mesoporous alumina templates. Magnetic experimental measurements show that both coercivity and remanence decrease monotonously as the angle, at which the external field is applied, increases. On the other hand, the comparison between the simulation of a nanowire array and that performed for one single nanowire reveals that the magnetostatic interactions between the nanowires strongly modifies not only the shape of the hysteresis curve but also the coercivity and remanence values. Besides, simulations also disclose that the nanowires reverse their magnetization through the nucleation and propagation of transverse domain walls. Moreover, the simulation of an array of nanowires also discloses that the hysteresis curve exhibits noticeable jumps in the magnetization that are proportional to the number of nanowires that reverse their magnetization in the array. This latter could provide an interesting hint to control the performance of magnetic nanodevices.

We have investigated the magnetic properties of 14 nm thick and 1 mu m long nickel and permalloy nanotubes with external diameters of 40 and 100 nm as a function of the angle theta at which the external magnetic field is applied. Our results show that the coercivity of 40 nm diameter nickel nanotubes follows a non-monotonic behavior from theta = 0 degrees up to theta = 60 degrees, while that corresponding to permalloy displays an increasing monotonic trend at the same angular range. At theta = 90 degrees, both materials evidence a sharp drop of the coercivity to zero, indicating that the reversal mechanism has changed to a pseudo-coherent rotation. On the other hand, nickel and permalloy nanotubes with 100 nm in diameter exhibit a similar angular dependence of the coercivity, reversing their magnetization through the nucleation and propagation of vortex domain walls for angles lower than 75 degrees. For theta = 90 degrees, a novel striking mechanism, the wave reversal mode (W), arises. This phenomenon leads to an unusual S-type shape in the hysteresis curves at those given parameters, which is until now an effect that has not been reported for these nanostructures.

Fil: Carraro, Paola Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Centro de Investigacion y Tecnologia Quimica. Universidad Tecnologica Nacional. Facultad Regional Cordoba. Centro de Investigacion y Tecnologia Quimica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Fisica Enrique Gaviola. Universidad Nacional de Cordoba. Instituto de Fisica Enrique Gaviola; Argentina

In this paper we have compared the angular dependence of the magnetic properties of permalloy (Ni80Fe20) and nickel nanowires by means of micromagnetic simulations. For each material we have chosen two diameters, 40 and 100 nm. Permalloy nanowires with smaller diameters (d = 40 nm) exhibit greater coercivity than nickel nanowires, regardless of the angle at which the external magnetic field is applied. In addition, both Py and Ni nanowires exhibit the same remanence values. However, the nanowires of larger diameters (d = 100 nm) exhibit a more complex behavior, noting that for small angles, nickel nanowires are those that now exhibit a greater coercivity in comparison to those of permalloy. The magnetization reversal modes vary as a function of the angle at which the external field is applied. When the field is applied parallel to the wire axis, it reverts through nucleation and propagation of domain walls, whereas when the field is applied perpendicular to the axis, it reverts by a pseudo-coherent rotation. These results may provide a guide to control the magnetic properties of nanowires for use in potential applications.