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Physchem, Volume 3, Issue 3 (September 2023) – 6 articles

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30 pages, 7783 KiB

Open AccessReview

Carbon-Based Materials for Energy Storage Devices: Types and Characterization Techniques

by Freddy Escobar-Teran, Hubert Perrot and Ozlem Sel

Physchem 2023, 3(3), 355-384; https://doi.org/10.3390/physchem3030025 - 13 Sep 2023

Cited by 9 | Viewed by 3547

Abstract

The urgent need for efficient energy storage devices (supercapacitors and batteries) has attracted ample interest from scientists and researchers in developing materials with excellent electrochemical properties. Electrode material based on carbon, transition metal oxides, and conducting polymers (CPs) has been used. Among these materials, carbon has gained wide attention in Electrochemical double-layer capacitors (EDLC) due to its variable morphology of pores and structural properties as well as its remarkable electrical and mechanical properties. In this context, the present review article summarizes the history of supercapacitors and the basic function of these devices, the type of carbon electrode materials, and the different strategies to improve the performance of these devices. In addition, we present different approaches to studying the charging mechanism of these devices through different electrochemical techniques existing in the literature, since a deeper understanding of the interfacial charge storage mechanisms is also crucial in the elaboration and performance of the electrode material. We make a comparison of the different techniques and present their advantages and challenges. Taking these advances into account, we consider that the coupling between two methods/techniques provides a better understanding of the charge storage mechanisms in energy storage devices. Full article

(This article belongs to the Special Issue Advances in Carbon and Nanomaterials)

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13 pages, 3156 KiB

Open AccessArticle

Capture and Reaction of CO₂ and H₂ Catalyzed by a Complex of Coronene: A Computational Study

by Luis G. Guillén, Lioudmila Fomina and Roberto Salcedo

Physchem 2023, 3(3), 342-354; https://doi.org/10.3390/physchem3030024 - 22 Aug 2023

Viewed by 1741

Abstract

An organometallic complex of coronene (Cor) and chromium (Cr) was designed and used as a catalyst in a simulated process in which a CO₂ molecule is captured, activated, and then reacts with a hydrogen molecule (H₂) to yield formic acid (HCOOH). The structural characteristics and local aromaticity are due to the similarity in the binding scheme with the bis(benzene)chromium (Cr-Bz₂). Such a molecular fragment, referred to here as a “Clar’s site”, involves a single chromium atom that binds to CO₂ by transferring electron density through backdonation. Therefore, the capture of CO₂ outside the Cr₃-Cor₂ complex allows for the carrying out of a hydrogenation process that involves the breaking of one of the C−O bonds, the double addition of hydrogen, the formation of HCOOH and its release, regenerating the structure of the Cr₃-Cor₂ complex. The thermodynamic and kinetic results of this reaction are analyzed, as well as the nature of the orbitals and the relevant interactions of this process. This work explores a new concept for the creation of single atom catalysts (SACs), taking advantage of the high electron density around the metallic center and the sandwich architecture, having shown that it can perform the catalytic reduction of CO₂. Full article

(This article belongs to the Section Theoretical and Computational Chemistry)

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10 pages, 1699 KiB

Open AccessFeature PaperReview

Electronically Excited States of Free Radicals

by Igor V. Khudyakov

Physchem 2023, 3(3), 332-341; https://doi.org/10.3390/physchem3030023 - 7 Aug 2023

Viewed by 2030

Abstract

Formation of the excited doublet (D) and quartet (Q) states of free radicals under their photoexcitation is discussed. The relative positions of the D and Q states are compared to the positions of the photoexcited states of organic molecules (Jablonsky diagram). A number of representative cases of the excited states of free radicals detected by their transient absorption or emission are presented. A special case of the population having the lowest Q state in some radicals is discussed. A spin–statistical factor in the reactions of Q and D is debated. Full article

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13 pages, 5746 KiB

Open AccessArticle

Examining the Hydration Behavior of Aqueous Calcium Chloride (CaCl₂) Solution via Atomistic Simulations

by Lida Yan and Ganesh Balasubramanian

Physchem 2023, 3(3), 319-331; https://doi.org/10.3390/physchem3030022 - 5 Aug 2023

Cited by 2 | Viewed by 3475

Abstract

Equilibrium molecular dynamics simulations are performed to examine the hydration behavior of Ca²⁺ and Cl⁻ across a wide range of salt concentrations (from 1 wt.% to 60 wt.% CaCl₂) in an aqueous solution. The predicted radial distribution functions (RDFs) and coordination numbers (CNs) of Ca²⁺–water, Cl⁻–water, and Ca²⁺–Cl⁻ agree with the previous studies conducted at concentrations below the solubility limit at room temperature. The hydration limit of aqueous calcium chloride solution is identified at 10 wt.% CaCl₂ as the CNs remain constant below it. Beyond the bulk solubility limit ~44.7 wt.% CaCl₂, a noticeable decrease in the CN of Cl⁻ and water is recorded, implying the saturation of the solution. The solvating water molecules decrease with increasing salt concentration, which can be attributed to the growth in the number of ion pairs. Full article

(This article belongs to the Section Theoretical and Computational Chemistry)

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15 pages, 3387 KiB

Open AccessArticle

Association, Conformational Rearrangements and the Reverse Process of Aggregates Dissociation during Apomyoglobin Amyloid Formation

by Victor Marchenkov, Vitaly Balobanov, Mariya Majorina, Nelly Ilyina, Ivan Kashparov, Anatoly Glukhov, Natalya Ryabova and Natalya Katina

Physchem 2023, 3(3), 304-318; https://doi.org/10.3390/physchem3030021 - 24 Jul 2023

Viewed by 1307

Abstract

Amyloid formation is linked with serious human diseases that are currently incurable. Usually, in the study of amyloid aggregation, the description of the protein’s association is in focus. Whereas the mechanism of the cross-β-structure formation, and the presence of aggregation reversibility, remain insufficiently explored. In this work, the kinetics of amyloid aggregation of apomyoglobin (ApoMb) have been studied using thioflavin fluorescence, electron microscopy, and non-denaturing electrophoresis. An analysis of the concentration dependence of the aggregation rates allows the conclusion that ApoMb amyloid formation includes the stages of conformational rearrangements in the aggregates, followed by their association and the fibril formation. The study of the mutant variants aggregation kinetics showed that the association rate is determined by the amino acids’ hydrophobicity, while the rate of conformational rearrangements is affected by the localization of the substitution. An unexpected result was the discovery that ApoMb amyloid formation is reversible, and under native-like conditions, the amyloid can dissociate, producing monomers. A consequence of the reversibility of amyloid aggregation is the presence of the monomer after aggregation completion. Since the aggregation reversibility indicates the possibility of dissociation of already formed fibrils, presented data and approaches can be useful in finding ways for amyloid diseases treatment. Full article

(This article belongs to the Section Biophysical Chemistry)

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14 pages, 771 KiB

Open AccessArticle

Micromagnetic Approach to the Metastability of a Magnetite Nanoparticle and Specific Loss Power as Function of the Easy-Axis Orientation

by Nathaly Roa and Johans Restrepo

Physchem 2023, 3(3), 290-303; https://doi.org/10.3390/physchem3030020 - 10 Jul 2023

Cited by 2 | Viewed by 1648

Abstract

Magnetic nanoparticles (MNPs) have attracted a great interest in nanomedical research. MNPs exhibit many important properties. In particular, magnetic hyperthermia for selective killing of cancer cells is one of them. In hyperthermia treatment, MNPs act as nano-heaters when they are under the influence of an alternating magnetic field (AMF). In this work, micromagnetic simulations have been used to investigate the magnetization dynamics of a single-domain nanoparticle of magnetite in an external AMF. Special attention is paid to the circumstances dealing with a dynamic phase transition (DPT). Moreover, we focus on the influence of the orientation of the magnetic easy-axis of the MNP on the dynamic magnetic properties. For amplitudes of the external AMF above a certain critical value, the system is not able to follow the magnetic field and it is found in a dynamically ordered phase, whereas for larger amplitudes, the state corresponds to a dynamically disordered phase and the magnetization follows the external AMF. Our results suggest that the way the order-disorder DPT takes place and both the metastable lifetime as well as the specific loss power (SLP) are strongly dependent on the interplay between the orientation of the magnetic easy-axis and the amplitude of the external AMF. Full article

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