Well-defined Electronic Structure Research Articles

Faradically Dominant Pseudocapacitive Graphitic Carbon Nitride Nanosheets Decorated with Strontium Tungstate Nanospheres for Supercapattery Device and Hydrogen Evaluation Reaction

Transition metal oxides are promising for hydrogen evolution reaction (HER) and hybrid energy storage due to their excellent redox properties, inherent electrochemical activity, and abundant electroactive sites. A significant challenge limiting their broader application is their intrinsic low electrical conductivity and reduced electrochemical stability. For hybrid energy storage devices and HER, a highly electrochemical active material is designed from 2D graphitic carbon nitride nanosheet (g-C3N4) networks anchored with strontium tungstate nanospheres (SrWO4/g-C3N4). The excellent performance observed can be attributed to several factors: multiple electro-active sites, well-defined electronic structures, and interaction between SrWO4 nanosphere on the surface of g-C3N4 nanosheets surface. The supercapattery device exhibited superior energy density (65.4 W h/kg) and power density (1240.5 W/kg) in comparison. In addition, the theoretical technique was utilized to provide a detailed analysis of the experimental findings. In addition, the SrWO4/g-C3N4 material demonstrates a low overpotential of 129 mV at -10 mA/cm2, along with Tafel slope values of 67 mV/dec for the HER, and it exhibits excellent cyclic stability. This study presents an advanced method for designing SrWO4/g-C3N4-based supercapacitors and HER platforms with nanoscale structures and optimized interface arrangements.

Localization of hot carriers in Au144(SCH3)60 clusters doped with copper

Hot carriers (HCs) generated by visible light in metal nanostructures present significant potential for various applications. Nevertheless, comprehending HCs at a microscopic level has been a formidable challenge. This research delves into the spatial distribution of HCs within thiolate-protected Au144(SCH3)60 cluster doped with copper through real-time time-dependent density functional theory (rt-TDDFT). By accurately adjusting a Gaussian laser pulse to correspond to the dominant photoabsorption frequencies, we reveal the formation of hot electrons and hot holes. Throughout all the examined configurations, it was noted that copper doping creates a more pronounced influence on the distribution of hot holes compared to hot electrons, indicating the potential for precise control over HC generation in nanoscale systems with well-defined electronic structures.

Cu/CdCO3 catalysts for efficient electrochemical CO2 reduction over the wide potential window

High efficiency and low-cost catalyst-driven electrocatalytic CO2 reduction to CO production are of great significance for energy storage and development. The severe competitive hydrogen evolution reaction occurs at large negative potential window limits the achievement of the target product from CO2 at high efficiency. Here, we successfully prepared Cux/CdCO3 composite catalyst rich in interfaces, in which achieved high CO Faraday efficiency exceeded 90% in a wide potential window of 700 mV and highest value up to 97.9% at −0.90 V vs. RHE. The excellent performance can be ascribed to the positive contribution of Cux/CdCO3, which maintains a suitable high local pH value during electrochemical reduction, thus inhibiting the competitive hydrogen evolution reaction. Moreover, the compact structure between Cu and CdCO3 ensures fast electron transfer both inside catalysts and interface, thus speeding up the reaction kinetics of CO2 to CO conversion. Theoretically calculations further prove that the combination of Cu and CdCO3 provides the well-defined electronic structure for intermediates adsorption, significantly reducing the reaction barrier for the formation of CO. This work provides new insights into the design of efficient electrochemical CO2 reduction catalysts for inhibiting hydrogen evolution by adjusting the local pH effect.

3-D molecular stars with covalent axial bonding.

In designing three-dimensional (3-D) molecular stars, it is very difficult to enhance the molecular rigidity through forming the covalent bonds between the axial and equatorial groups because corresponding axial groups will generally break the delocalized π bond over equatorial frameworks and thus break their star-like arrangement. In this work, exemplified by designing the 3-D stars Be2 ©Be5 E5 + (E=Au, Cl, Br, I) with three delocalized σ bonds and delocalized π bond over the central Be2 ©Be5 moiety, we propose that the desired covalent bonding can be achieved by forming the delocalized σ bond(s) and delocalized π bond(s) simultaneously between the axial groups and equatorial framework. The covalency and rigidity of axial bonding can be demonstrated by the total Wiberg bond indices of 1.46-1.65 for axial Be atoms and ultrashort Be-Be distances of 1.834-1.841 Å, respectively. Beneficial also from the σ and π double aromaticity, these mono-cationic 3-D molecular stars are dynamically viable global energy minima with well-defined electronic structures, as reflected by wide HOMO-LUMO gaps (4.68-5.06 eV) and low electron affinities (4.70-4.82 eV), so they are the promising targets in the gas phase generation, mass-separation, and spectroscopic characterization.

Enhancing Catalytic Activity of a Nickel Single Atom Enzyme by Polynary Heteroatom Doping for Ferroptosis-Based Tumor Therapy

As a rising generation of nanozymes, single atom enzymes show significant promise for cancer therapy, due to their maximum atom utilization efficiency and well-defined electronic structures. However, it remains a tremendous challenge to precisely produce a heteroatom-doped single atom enzyme with an expected coordination environment. Herein, we develop an anion exchange strategy for precisely controlled production of an edge-rich sulfur (S)- and nitrogen (N)-decorated nickel single atom enzyme (S-N/Ni PSAE). In particular, sulfurized S-N/Ni PSAE exhibits stronger peroxidase-like and glutathione oxidase-like activities than the nitrogen-monodoped nickel single atom enzyme, which is attributed to the vacancies and defective sites of sulfurized nitrogen atoms. Moreover, both in vitro and in vivo results demonstrate that, compared with nitrogen-monodoped N/Ni PSAE, sulfurized S-N/Ni PSAE more effectively triggers ferroptosis of tumor cells via inactivating glutathione peroxidase 4 and inducing lipid peroxidation. This study highlights the enhanced catalytic efficacy of a polynary heteroatom-doped single atom enzyme for ferroptosis-based cancer therapy.

Structure-Imposed Electronic Topology in Cove-Edged Graphene Nanoribbons.

In cove-edged zigzag graphene nanoribbons (ZGNR-Cs), one terminal CH group per length unit is removed on each zigzag edge, forming a regular pattern of coves that controls their electronic structure. Based on three structural parameters that unambiguously characterize the atomistic structure of ZGNR-Cs, we present a scheme that classifies their electronic state (i.e., if they are metallic, topological insulators, or trivial semiconductors) for all possible widths N, unit lengths a, and cove position offsets at both edges b, thus showing the direct structure-electronic structure relation. We further present an empirical formula to estimate the band gap of the semiconducting ribbons from N, a, and b. Finally, we identify all geometrically possible ribbon terminations and provide rules to construct ZGNR-Cs with a well-defined electronic structure.

Priority Occupation of C-Sites by N-Confining P-Implantation in Pyrrodic N-Sites in NCNT@P,N-Mo2C for Highly Efficient Electrocatalytic Hydrogen Evolution.

Optimizing the electronic configuration of Mo2C by activating heteroatom(s)-neighboring carbon atoms to enhance the activity of hydrogen evolution reaction (HER) has been demonstrated. However, the development of heteroatom-doped Mo2C to fabricate a water electrolyzer is still a challenge because of the limitation of a well-defined electronic structure of hybridization of Mo with heteroatom(s). Here, nitrogen (N) and phosphor (P) codoped Mo2C embedded carbon nanotubes (NCNT@P,N-Mo2C) with the priority occupation of C-sites by N, which well confines the P-implantation at the pyrrodic N-sites and brings out N-O bonding on the surface, which favorably modifies the electronic configuration of adjacent Mo, resulting in highly efficient pH-tolerant HER activity. This study not only presents a potential HER electrocatalyst candidate but also provides a strategy for the construction of a well-defined electronic structure of heteroatom(s)-neighboring carbon-based materials.

Be2H3L2− (L=CH3 and F–I): Hyperhalogen anions with ultrashort beryllium-beryllium distances

The superalkali cations and superhalogen anions commonly have different type of core moieties. Based on the previous reports that Be2H3L′2+ (L′=NH3 and noble gases Ne–Xe) are superalkali cations, in the present work, we designed the superhalogen anions Be2H3L2− (L=CH3 and halogens F–I), and both superalkali cations and superhalgen anions can be constructed using Be2H3 as the core moiety. The newly designed Be2H3L2− species are much more stable than their isoelectronic cationic counterparts Be2H3L′2+, as can be reflected by the highly exergonic substitution reaction of L′ ligand in Be2H3L′2+ with isoelectronic L− to give Be2H3L2−. These anionic species possess the well-defined electronic structure, which can be proven by their large HO-MO–LUMO gaps of 4.69 eV to 5.38 eV. It is remarkable that Be2H3L2− can be regarded as the hyperhalogen anions due to the extremely high vertical detachment energies (5.38 eV to 6.06 eV) and the Be–Be distances in these species (1.776 Å to 1.826 Å) are short in ultrashort metal-metal distances (defined as dM–M<1.900 Å) between main group metals. In the designed five small model species, three of them, i.e. Be2H3L2− (L=CH3, Cl, and Br), are kinetical viable global energy minima, which are the promising target for generation and characterization in anion photoelectron spectroscopy. The analogue molecule [t-Bu–Be2H3–t-Bu]− with bulky protecting tert-butyl (t-Bu) groups is designed as a possible target for synthesis and isolation in condensed states.

Origin of the enhanced oxygen evolution reaction activity and stability of a nitrogen and cerium co-doped CoS2 electrocatalyst

Nitrogen and cerium dopants in CoS2 contribute a well-defined electronic structure for improving electrochemical stability and activity.

Impact of chemical interface damping on surface plasmon dephasing.

The excellent light harvesting ability of plasmonic nanoparticles makes them promising materials for a variety of technologies that rely on the conversion of photons to energetic charge carriers. In such applications, including photovoltaics and photocatalysis, the excitation of surface plasmons must induce charge transfer across the metal-adsorbate or metal-semiconductor interface. However, there is currently a lack of molecular level understanding of how the presence of a chemical interface impacts surface plasmon dephasing pathways. Here, we report an approach to quantitatively measure the influence of molecular adsorption on the spectral shape and intensity of the extinction, scattering, and absorption cross-sections for nanostructured plasmonic surfaces. This is demonstrated for the case of thiophenol adsorption on lithographically patterned gold nanodisk arrays. The results show that the formation of a chemical interface between thiophenol and Au causes surface plasmons to decay more prominently through photon absorption rather than photon scattering, as compared to the bare metal. We propose that this effect is a result of the introduction of adsorbate-induced allowable electronic transitions at the interface, which facilitate surface plasmon dephasing via photon absorption. The results suggest that designed chemical interfaces with well-defined electronic structures may enable engineering of hot electron distributions, which could be important for understanding and controlling plasmon-mediated photocatalysis and, more generally, hot carrier transfer processes.

SFGP 2007 - Photosensitive Composite Disordered Nanostructures over Acceptor Supports: Selective Free Charge Carrier Generators for Environmental Applications

Amorphous and low-ordered photosensitive materials are not usually considered to be promising photocatalytic agents because of extremely short free charge carrier (FCC) lifetimes in their active components deprived of well-defined electronic structures. Using active supports favoring an efficient FCC separation in situ, it is possible to protect free charge carriers from the immediate recombination, so even the disordered photosensitive composites can be provided with important photocatalytic capacities. The examples of some environmental applications of this type of active materials, such as volatile organic compound (VOC) photocatalytic removal and bacteria sterilization, are presented in this paper.

Investigation of electronic structure of amorphous, metastable, and stable phases of Ge1Sb2Te4 film by high-resolution x-ray photoemission spectroscopy

The electronic structures of amorphous, metastable, and stable phases of Ge1Sb2Te4 film were investigated by high-resolution x-ray photoelectron spectroscopy. The Te 4d core level showed a negligible change in binding energy (BE). In the stable phase, the Ge 3d and Sb 4d core levels were, respectively, dominated by a spin-orbit-split feature at 0.1eV-lower BE and a well-defined component at 0.4eV-higher BE than those in the amorphous phase. The analysis suggests that the amorphous phase and the stable phase is respectively represented by a broad and a well-defined electronic structure and that the metastable phase is represented by two different kinds of local electronic structures. The valence-band structures showed a trend similar to that reported by Klein et al. [Phys. Rev. Lett. 100, 016402 (2008)] between the amorphous and metastable phases.

Measuring the electronic structure of disordered overlayers by electron momentum spectroscopy: the Cu/Si interface

The CuSi interface was studied by electron momentum spectroscopy. A thick disordered interface is formed if one material is deposited on the other. Electron momentum spectroscopy measures intensity as a function of binding energy and target electron momentum. Momentum resolution is demonstrated to be very helpful in interpreting the data, even for these disordered interfaces. The interface layer has a well-defined electronic structure, different from either Si or Cu, and consistent with silicide formation. Information is obtained about the total bandwidth of the interface compound, effective Brillouin zone size and Fermi radius. No clear differences are observed in the electronic structure of the interface layer for Si deposited on Cu or Cu deposited on Si. Copyright © 2006 John Wiley & Sons, Ltd.

Resonant electron scattering by molecules adsorbed on metal surfaces: angular aspects

The formation of a transient negative ion (AB −) is a very efficient way to transfer energy in a collision between an electron and an adsorbed molecule. It leads to the molecule excitation and fragmentation as well as to desorption processes. The AB − molecular ions correspond to well-defined electronic structures and this leads to well-defined electron angular distributions, characteristic of the ion symmetry. In the present work, we analyze in a classical approach how the electron-metal surface interaction (the polarization potential) influences the electron angular distributions. For certain symmetries, and adsorption geometries, the angular distribution is deeply modified by this interaction, which introduces a node in the distribution at 90° from the surface normal. This effect is discussed in relation with available experimental data.