Using sublattice symmetry breaking to tune the electronic structure and chemical stability of Si-substituted carbon-based 2D materials

This critical review provides an overview of current research on carbon-based nanostructured materials and their composites for use as supercapacitor electrodes. Particular emphasis has been directed towards basic principles of supercapacitors and various factors affecting their performance. The focus of the review is the detailed discussion regarding the performance and stability of carbon-based materials and their composites. Pseudo-active species, such as, conducting polymer/metal oxide have been found to exhibit pseudo-capacitive behavior and carbon-based materials demonstrate electrical double layer capacitance. Carbon-based materials, such as, graphene, carbon nanotubes, and carbon nanofibers, provide high surface area for the deposition of conducting polymer/metal oxide that facilitates the efficient ion diffusion phenomenon and contribute towards higher specific capacitance of the carbon based composite materials with excellent cyclic stability. However, further scope of research still exists from the view point of developing high energy supercapacitor devices in a cost effective and simple way. This review will be of value to researchers and emerging scientists dealing with or interested in carbon chemistry.

11 - Chemical methods for Xenes

The electronic structure and energetic stability of A2BX6 halide compounds with the cubic and tetragonal variants of the perovskite-derived K2PtCl6 prototype structure are investigated computationally within the frameworks of density-functional-theory (DFT) and hybrid (HSE06) functionals. The HSE06 calculations are undertaken for seven known A2BX6 compounds with A = K, Rb, and Cs; and B = Sn, Pd, Pt, Te, and X = I. Trends in band gaps and energetic stability are identified, which are explored further employing DFT calculations over a larger range of chemistries, characterized by A = K, Rb, Cs, B = Si, Ge, Sn, Pb, Ni, Pd, Pt, Se, and Te; and X = Cl, Br, I. For the systems investigated in this work, the band gap increases from iodide to bromide to chloride. Further, variations in the A site cation influences the band gap as well as the preferred degree of tetragonal distortion. Smaller A site cations such as K and Rb favor tetragonal structural distortions, resulting in a slightly larger band gap. For variations in the B site in the (Ni, Pd, Pt) group and the (Se, Te) group, the band gap increases with increasing cation size. However, no observed chemical trend with respect to cation size for band gap was found for the (Si, Sn, Ge, Pb) group. The findings in this work provide guidelines for the design of halide A2BX6 compounds for potential photovoltaic applications.

Effective reinforcement on the structural stability and electrochemical performances of ultra-high nickel cobalt free cathode material by co-doping

Environmental pollution poses a pressing global challenge, demanding innovative solutions for effective pollutant removal. Photocatalysts, particularly titanium dioxide (TiO2), are renowned for their catalytic prowess; however, they often require ultraviolet light for activation. Researchers had turned to doping with metals and non-metals to extend their utility into the visible spectrum. While this approach shows promise, it also presents challenges such as material stability and dopant leaching. Co-doping, involving both metals and non-metals, has emerged as a viable strategy to mitigate these limitations. Inthe fieldof adsorbents, carbon-based materials doped with nitrogen are gaining attention for their improved adsorption capabilities and CO2/N2 selectivity. Nitrogen doping enhances surface area and fosters interactions between acidic CO2 molecules and basic nitrogen functionalities. The optimal combination of an ultramicroporous surface area and specific nitrogen functional groups is key to achievehigh CO2 uptake values and selectivity. The integration of photocatalysis and adsorption processes in doped materials has shown synergistic pollutant removal efficiency. Various synthesis methods, including sol–gel, co-precipitation, and hydrothermal approaches had been employed to create hybrid units of doped photocatalysts and adsorbents. While progress has been made in enhancing the performance of doped materials at the laboratory scale, challenges persist in transitioning these technologies to large-scale industrial applications. Rigorous studies are needed to investigate the impact of doping on material structure and stability, optimize process parameters, and assess performance in real-world industrial reactors. These advancements are promising foraddressing environmental pollution challenges, promoting sustainability, and paving the way for a cleaner and healthier future. This manuscript provides a comprehensive overview of recent developments in doping strategies for photocatalysts and adsorbents, offering insights into the potential of these materials to revolutionize environmental remediation technologies.

Introduction Knowledge of the thermal stability of nanocrystalline materials is important for both technological and scientific reasons. From a technological point of view, the thermal stability is important for consolidation of nanocrystalline particulates without coarsening the microstructure. That is, many methods, as described in Chapter 2, for synthesis of nanocrystalline materials result in particulate products which must be consolidated into bulk form. Since most consolidation processes involve both heat and pressure, the thermal stability of the nanoscale microstructure is always at risk. The goal of particulate consolidation is to attain essentially 100% theoretical density and good particulate bonding while preventing or minimizing grain growth of the nanocrystalline grains. Understanding the scientific nature of stability, grain growth of nanocrystalline microstructures is a criterion for allowing strategies for minimizing grain growth to be developed. A basic scientific question with regard to nanocrystalline materials is whether their behavior involves “new physics” or is simply the expected grain-size-dependent behavior extrapolated to nanocrystalline grain sizes. Thermal stability is an important phenomenon to be addressed in this regard. The thermal stability in a broader sense involves not only the stability of the grain structure, that is the microstructure, but also the stability of the structure of the grain boundaries in nanocrystalline materials. A number of investigations on the thermal stability of nanocrystalline materials have been conducted. Grain growth in nanocrystalline materials has been reviewed by Suryanarayana (1995), Weissmuller (1996), and Malow and Koch (1996a,b).

When a solid is subjected to external pressure, it can undergo either structural transformation or remain stable in its parent structure. The sequence of structural transformations, when mapped for similar materials, viz., isostructural, isoelectronic and so on, can be used to create a map showing the evolution of structures under pressure for such materials. Such maps are useful in predicting high pressure phases. The structural transitions and the stability of materials as a function of pressure are intricately connected to their electronic structure. Many a times it is advantageous to know the stability of the material under pressure just by calculating its electronic structure. This can be accomplished only if several homologues materials are studied and the stability criteria arrived at by correlating their electronic structure with their structural stability under pressure. Further, as a function of pressure, the electronic structure changes can lead to enhancement in certain desired electronic, physical or mechanical properties. Several examples are known, wherein, pressure tuning of the band structure leads to improved properties. In this paper, we have discussed the above mentioned areas and presented a perspective of the above using the results of our own studies on f-electron based intermetallics (f-IMCs).

There is a high fundamental interest in the surface and bulk chemistry of quantum dot (QD) solids, as they have proven to be very promising materials in optoelectronic devices. The choice of surface ligands for quantum dots in solid devices determines many of the film properties, as the ligands influence for example the doping density, chemical stability and charge transport. Lead halide ligands have developed as the main ligand of choice for lead sulfide quantum dots, as they have been shown to passivate quantum dot surfaces and enhance the chemical stability. In this study, we successfully varied the ligand composition on the surface of PbS quantum dot films from pure lead iodide to pure lead bromide and investigated its influence on the chemical and electronic structure of the QD solids using hard X-ray photoelectron spectroscopy (HAXPES). Furthermore, we developed a surface treatment to prevent the surface oxidation of a bulk PbS reference sample. Through measurements of this sample and of lead halide reference samples, we were able to assign the contributions of different chemical bonding to the Pb 4f core level and of different atomic orbitals to the valence band spectral shape of the QD materials. Overall, we found that the valence band edge position was very similar for all different iodide:bromide ratios and that all investigated compositions were able to protect the quantum dot surfaces within solid films from oxidation. However, the ligand composition significantly influences the sample stability under X-rays. The iodide rich QD solids showed the highest stability with very little to no chemical changes over several hours of X-ray exposure, while the bromide rich QD solids changed already within the first hour of exposure.

Stable crystal structure prediction using machine learning-based formation energy and empirical potential function

SummaryAlthough it has been shown that configurational entropy can improve the structural stability in transition metal oxides (TMOs), little is known about the oxidation state of transition metals under random mixing of alloys. Such information is essential in understanding the chemical reactivity and properties of TMOs stabilized by configurational entropy. Herein, utilizing electron energy loss spectroscopy (EELS) technique in an aberration-corrected scanning transmission electron microscope (STEM), we systematically studied the oxidation state of binary (Mn, Fe)3O4, ternary (Mn, Fe, Ni)3O4, and quinary (Mn, Fe, Ni, Cu, Zn)3O4 solid solution polyelemental transition metal oxides (SSP-TMOs) nanoparticles. Our findings show that the random mixing of multiple elements in the form of solid solution phase not only promotes the entropy stabilization but also results in stable oxidation state in transition metals spanning from binary to quinary transition metal oxide nanoparticles.

Electronic structure and structural stability of LaAl2 and LaAl3—A comparative study

Electronic band structure calculation and structural stability of high pressure phases of selenium

A mineralogically-inspired silver–bismuth hybrid material: Structure, stability and application for catalytic benzyl alcohol dehydrogenations under continuous flow conditions

Maintaining structure and voltage stability of Li-rich cathode materials by green water-soluble binders containing Na+ ions

Lithium-ion batteries (LIBs) become an essential part of many portable devices and even electric vehicles than ever before. Among the various cathode materials, Ni rich layered cathode material has big attention because it has higher specific capacity and energy density. However, at a delithiated state, unstable Ni4+ leads to oxygen release and structural degradation and as a result, irreversible phase transition from R3m to electrochemical inactive Fm3m is observed. So, various strategy is applying to overcome this limitation like three-component system (NCM) or surface coating. However, NCM still cannot solve that problem perfectly and surface coating makes a problem like reducing specific capacity caused by insulating coating material (Al2O3, MnO2...etc) And also, this day, Co free structure of Ni rich cathode material has received more great attention as an alternative to NCM because of its hazardous toxicity and increasing price of Co. At this perspective, many studies have demonstrated Core-Shell or FCG (Full Concentration Gradient) structure can make better structural stability without Co metal than surface coating, which has insulated coating materials. In addition, core shell structure is easier to control the composition than FCG structure. However, in Core-Shell structure, interdiffusion of shell metal to core deteriorate the stability of Core-Shell material, so it needs very delicate heat treatment. And generally, to prevent interdiffusion from traditional core-shell structure, lower synthesis temperature or high valence metal dopant would be needed and that leads lower initial specific capacity or additional doped metal. So, we prevent the Mn interdiffusion by changing valence state of Mn in precursor through simple convection drying process not vacuum drying without decreasing synthesis temperature and additional dopant. Atomic interdiffusion in layered metal oxide structures follows the atomic migration through octahedral and tetrahedral sites. In case of various stated Mn, higher valence state Mn has higher energy barrier to migrate between each Oh and Td sites. Based on this theory, surface Mn rich shell can be oxidized easily under convection oven drying and highly oxidized Mn will be remained better than lower state Mn during high temperature calcination. These more remained Mn in shell can protect the particle surface from electrolyte attack and also higher valence state Mn makes slightly more Ni2+ due to thermodynamic stability and charge balance of Mn on the surface. And that Ni2+ in Li slab (Cation mixing) acts as a pillar to suppress irreversible phase transition of Ni rich materials. Through this surface passivation, phase transition (layered to rock salt ) propagation surface to bulk can be blocked. Furthermore, mechanical pulverization of secondary particle is also prevented because of less permeating electrolyte into bulk structure. Therefore, Li ion diffusion will not be sluggish after cycling as observed by GITT. In addition, more clear Ni rich core assure high specific capacity and faster electrochemical reaction kinetic without severe capacity fading. And also, in Full cell test (using graphite as anode), convection oven dried sample has better structure stability and that means our strategy for core-shell LiNi0.97Mn0.03O2 sample can be good candidate to alternate conventional cathode active material for Lithium ion battery practically. As prepared materials, atomic distribution was observed by EDS and XPS analysis. This study suggests useless of vacuum drying and more cost effective way to prepare Co free Core Shell LiNi0.97Mn0.03O2 cathode material for Lithium Ion Batteries.