Extreme ultraviolet (EUV)-induced radiation exposure chemistry in organotin–oxo systems, represented by the archetypal (R–Sn)12O14(OH)6(A)2 cage, has been investigated with density functional ...theory. Upholding existing experimental evidence of Sn–C cleavage-dominant chemistry, computations have revealed that either electron attachment or ionization can single-handedly trigger tin–carbon bond cleavage, partially explaining the current EUV sensitivity advantage of metal oxide systems. We have revealed that tin atoms at different parts of the molecule react differently to ionization and electron attachment and have identified such selectivity as a result of local coordination chemistry instead of the macro geometry of the molecule. An ionization–deprotonation pathway has also been identified to explain the observed evolution of an anion conjugate acid upon exposure and anion mass dependence in resist sensitivity.
Electrochemistry is necessarily a science of interfacial processes, and understanding electrode/electrolyte interfaces is essential to controlling electrochemical performance and stability. ...Undesirable interfacial interactions hinder discovery and development of rational materials combinations. By example, we examine an electrolyte, magnesium(II) bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) dissolved in diglyme, next to the Mg metal anode, which is purported to have a wide window of electrochemical stability. However, even in the absence of any bias, using in situ tender X-ray photoelectron spectroscopy, we discovered an intrinsic interfacial chemical instability of both the solvent and salt, further explained using first-principles calculations as driven by Mg2+ dication chelation and nucleophilic attack by hydroxide ions. The proposed mechanism appears general to the chemistry near or on metal surfaces in hygroscopic environments with chelation of hard cations and indicates possible synthetic strategies to overcome chemical instability within this class of electrolytes.
Across the life course, new forms of community, ways of keeping in contact, and practices for engaging in work, healthcare, retail, learning and leisure are evolving rapidly. Breaking new ground in ...the study of technology and aging, this book examines how developments in smart phones, the internet, cloud computing, and online social networking are redefining experiences and expectations around growing older in the twenty-first century. Drawing on contributions from leading commentators and researchers across the world, this book explores key themes such as caregiving, the use of social media, robotics, chronic disease and dementia management, gaming, migration, and data inheritance, to name a few.
The rapid insertion and extraction of Li ions from a cathode material is imperative for the functioning of a Li-ion battery. In many cathode materials such as LiCoO2, lithiation proceeds through ...solid-solution formation, whereas in other materials such as LiFePO4 lithiation/delithiation is accompanied by a phase transition between Li-rich and Li-poor phases. We demonstrate using scanning transmission X-ray microscopy (STXM) that in individual nanowires of layered V2O5, lithiation gradients observed on Li-ion intercalation arise from electron localization and local structural polarization. Electrons localized on the V2O5 framework couple to local structural distortions, giving rise to small polarons that serves as a bottleneck for further Li-ion insertion. The stabilization of this polaron impedes equilibration of charge density across the nanowire and gives rise to distinctive domains. The enhancement in charge/discharge rates for this material on nanostructuring can be attributed to circumventing challenges with charge transport from polaron formation.
Abstract
An overarching challenge of the electrochemical carbon dioxide reduction reaction (eCO
2
RR) is finding an earth-abundant, highly active catalyst that selectively produces hydrocarbons at ...relatively low overpotentials. Here, we report the eCO
2
RR performance of two-dimensional transition metal carbide class of materials. Our results indicate a maximum methane (CH
4
) current density of −421.63 mA/cm
2
and a CH
4
faradic efficiency of 82.7% ± 2% for di-tungsten carbide (W
2
C) nanoflakes in a hybrid electrolyte of 3 M potassium hydroxide and 2 M choline-chloride. Powered by a triple junction photovoltaic cell, we demonstrate a flow electrolyzer that uses humidified CO
2
to produce CH
4
in a 700-h process under one sun illumination with a CO
2
RR energy efficiency of about 62.3% and a solar-to-fuel efficiency of 20.7%. Density functional theory calculations reveal that dissociation of water, chemisorption of CO
2
and cleavage of the C-O bond—the most energy consuming elementary steps in other catalysts such as copper—become nearly spontaneous at the W
2
C surface. This results in instantaneous formation of adsorbed CO—an important reaction intermediate—and an unlimited source of protons near the tungsten surface sites that are the main reasons for the observed superior activity, selectivity, and small potential.
The path to realizing low-cost, stable, and earth-abundant photoelectrodes can be enabled through a detailed understanding of the optoelectronic properties of these materials by combining theory and ...experimental techniques. Of the limited set of oxide photocathode materials currently available, CuFeO2 has emerged as a promising candidate warranting detailed attention. In this work, highly compact thin films of rhombohedral (3R) CuFeO2 were prepared via reactive co-sputtering. Despite its 1.43 eV indirect band gap, a cathodic photocurrent of 0.85 mA/cm2 was obtained at 0.4 V versus reversible hydrogen electrode in the presence of a sacrificial electron acceptor. This unexpected performance was related to inefficient bulk charge separation because of the ultrafast (<1 ps) self-trapping of photogenerated free carriers. The electronic structure of 3R-CuFeO2 was elucidated through a combination of optical and X-ray spectroscopic techniques and further complemented by first-principles computational methods including a many-body approach for computing the O K-edge X-ray absorption spectrum. Through resonant inelastic X-ray scattering spectroscopy, the visible absorption edges of CuFeO2 were found to correspond to Cu → Fe metal-to-metal charge transfer, which exhibits a high propensity toward self-trapping. Findings of the present work enable us to understand the performance bottlenecks of CuFeO2 photocathodes and suggest feasible strategies for improving material limitations.
Properties of soft crystalline materials such as synthetic polymers are governed by locations of constituent atoms. Determining atomic-scale structures in these materials is difficult because they ...degrade rapidly when studied by electron microscopy, and techniques such as X-ray scattering average over volumes much larger than coherent blocks of the unit cells. We obtained cryo-electron microscopy images of self-assembled nanosheets of a peptoid polymer, made by solid-phase synthesis, in which we see a variety of crystalline motifs. A combination of crystallographic and single-particle methods, developed for cryo-electron microscopy of biological macromolecules, was used to obtain high-resolution images of the crystals. Individual crystals contain grains that are mirror images of each other with concomitant grain boundaries. We have used molecular dynamic simulations to build an atomic model of the crystal structure to facilitate the interpretation of electron micrographs. Direct visualization of crystalline grains and grain boundaries on atomic length scales represents a new level of information for the polymer field.
The discharge mechanism in lithium sulfur batteries is still unknown and has been purported to involve significant concentrations of polysulfide radicals. Methods capable of quantifying these species ...in solution are therefore of paramount importance to revealing electrochemical pathways. Here we utilize DFT based X-ray Absorption Spectroscopy (XAS) simulations at the sulfur K-edge to obtain the spectra of polysulfide molecules in neutral, radical (−1) and dianionic (−2) charge states. Our calculations indicate that, contrary to recent propositions, the observed low energy, pre-edge feature in S K-edge XAS near 2470 eV is not exclusively due to radical species, but rather arises predominantly from core-excitations of terminal atoms, at the ends of linear polysulfides, to σ* orbitals, consistent with our previous results for the dianionic species. We do however find a spectral feature unique to radicals, lying 0.5-1 eV below the established pre-edge, that arises from 1s → π* transitions of the terminal atoms. Existing measurements on polysulfides show no evidence for such transitions. We predict that detection of linear radicals in polysulfide mixtures using XAS is limited to high mole fractions (>20%), due to the relatively weak XAS intensity of this π* feature.
Sulfur K-edge XAS of the trisulfur radical dissolved in TEGDME from first-principles calculations.
Abstract
Anion-tuning in metallic chalcogenides has been shown to have a significant impact on their electrocatalytic ability for overall water splitting. In this article, copper-based chalcogenides ...(Cu
2
X, X
= O, S, Se, and Te) have been systematically studied to examine the effect of decreasing anion electronegativity and increasing covalency on the electrocatalytic performance. Among the copper chalcogenides, Cu
2
Te has the highest oxygen evolution reaction (OER) activity and can sustain high current density of 10 and 50 mA cm
−2
for 12 h. The difference in intrinsic catalytic activity of these chalcogenide surfaces have been also probed through density functional theory calculations, which was used to estimate energy of the catalyst activation step. It was observed that the hydroxyl adsorption on the surface catalytic site is critically important for the onset and progress of OER activity. Consequently, it was also observed that the –OH adsorption energy can be used as a simple but accurate descriptor to explain the catalytic efficiency through volcano-like correlation plot. Such observation will have a significant impact on developing design principle for optimal catalytic surface exhibiting high performance as well as prolonged stability.
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