Anionic Electrons Research Articles

Boosting Photoredox Catalysis Using a Two-Dimensional Electride as a Persistent Electron Donor.

Electrides, which have excess anionic electrons, are solid-state sources of solvated electrons that can be used as powerful reducing agents for organic syntheses. However, the abrupt decomposition of electrides in organic solvents makes controlling the transfer inefficient, thereby limiting the utilization of their superior electron-donating ability. Here, we demonstrate the efficient reductive transformation strategy which combines the stable two-dimensional [Gd2C]2+·2e- electride electron donor and cyclometalated Pt(II) complex photocatalysts. Strongly localized anionic electrons at the interlayer space in the [Gd2C]2+·2e- electride are released via moderate alcoholysis in 2,2,2-trifluoroethanol, enabling persistent electron donation. The Pt(II) complexes are adsorbed onto the surface of the [Gd2C]2+·2e- electride and rapidly capture the released electrons at a rate of 107 s-1 upon photoexcitation. The one-electron-reduced Pt complex is electrochemically stable enough to deliver the electron to substrates in the bulk, which completes the photoredox cycle. The key benefit of this system is the suppression of undesirable charge recombination because back electron transfer is prohibited due to the irreversible disruption of the electride after the electron transfer. These desirable properties collectively serve as the photoredox catalysis principle for the reductive generation of the benzyl radical from benzyl halide, which is the key intermediate for dehalogenated or homocoupled products.

Enhanced Activation of CO2 on h-BN Nanosheets via Forming a Donor–Acceptor Heterostructure with 2D M2X Electrenes

The activation of CO2 is the first crucial step in the CO2 reduction reaction (CO2RR), but it faces the challenge of the ultrahigh chemical stability of the CO2 molecule. Two-dimensional (2D) hexagonal boron nitride (h-BN) has been considered as a promising electrocatalytic interface material due to its high specific surface area, N- and B-active sites, and adjustable chemical reactivity through interactions with other materials. Here we report a donor–acceptor heterostructure (DAH) containing 2D h-BN and M2N (M = Ca, Sr, and Ba) or Y2C electrene, single-layer electride materials, toward the activation of the CO2 molecule on the basis of first-principles calculations. Our results demonstrate that a considerable number of electrons (0.1 e per BN unit) transfer from M2X electrene to the h-BN sheet due to the strong electrostatic interaction between the cation boron in the h-BN sheet and the anion electron gas in M2X electrides, which significantly enhances the CO2 activation activity of the h-BN monolayer. The adsorption of CO2 on h-BN is exothermic, with a negligible energy barrier down to 0.013 eV. Meanwhile, the overpotential of the hydrogenation of CO2 to HCOOH is as low as 0.17 V on the h-BN/Y2C DAH, implying superior performance for the CO2 reduction on the h-BN/M2X DAH. This work provides a strategy for activating CO2 on the h-BN monolayer by building a DAH with 2D electride materials.

Correlating inhomogeneity in anionic electron density with hydrogen incorporation in Y5Si3 electrides

Correlating inhomogeneity in anionic electron density with hydrogen incorporation in Y₅Si₃ electrides

First-principles calculations to investigate electronic, elastic, and optical properties of one dimensional electride Y5Si3

Y5Si3 is an air- and water- stable electride in which part of electrons are confined in one-dimensional channels composed of Y atoms. Y5Si3 has a promoting effect on ammonia synthesis at ambient pressure due to the unique properties of these electrons at interstitial cavities (anionic electrons). Here we carry out a detailed study of electronic structure, optical and elastic properties of Y5Si3. It is found that the anionic electrons form a valence band near the Fermi energy level and it is mainly contributed by the Y-4d orbital. The calculated results of optical and mechanical properties indicated that Y5Si3 is a brittle metal and exhibits weak anisotropy. Our present work provides a comprehensive understanding on physical properties of Y5Si3.

Prediction of the two-dimensional Janus ferrovalley material LaBrI

Two-dimensional (2D) ferrovalley materials, displaying coexistence of spontaneous spin and valley polarizations, have recently attracted significant attention due to their potential for applications in the fields of spintronics and valleytronics. However, unfortunately, to date only a few 2D ferrovalley materials exist. Here, first-principles calculations predict a 2D Janus ferrovalley material lanthanum bromiodide (LaBrI). It is found that LaBrI is a stable ferromagnetic electride, whose magnetic moment originates mainly from the interstitial anionic electrons. The magnetic transition temperature of LaBrI monolayers is estimated to be far beyond room temperature, and a sizable magnetic anisotropy with easy in-plane magnetization is also present. Most importantly, LaBrI monolayers exhibit a large valley polarization due to the concurrent broken space- and time-reversal symmetries, with the calculated valley polarization reaching up to 59 meV. This value is comparable to that of the ferrovalley materials reported to date. Intriguingly, the inequivalent Berry curvature at the two valleys takes opposite values, giving rise to an anomalous valley Hall effect, where a valley current with an accompanying net charge Hall current may be induced.

Designing of benzodithiophene (BDT) based non-fullerene small molecules with favorable optoelectronic properties for proficient organic solar cells

To extinguish the thirst of extraordinary tailback in the stock of energy and to jack up the operational effectiveness of organic solar cells, 5 new donor molecules namely BDTM1, BDTM2, BDTM3, BDTM4, BDTM5 have been designed by the structural tailoring of the already experimentally synthesized POBDT-4Cl. POBDT-4Cl is taken as a reference designated as BDTR. All the designed chromophores constitute benzodithiophene as donor and thiophene bridged end-capped (3-methyl-5-methylene-2-thioxothiazolidin-4-one) BDTM1, (2-methylenemalononitrile) BDTM2, (methyl 2-cyanoacrylate) BDTM3, (2-(3-methyl-5-methylene-4-oxothiazolidin-2-ylidene)malononitrile) BDTM4, (4-(5-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazole) BDTM5 acceptor groups. Influence of different terminal acceptor moieties on the molecular orbitals, density of states (DOS), maximum absorption (λmax), energy required for the generation of electron and hole carrier, transition density matrix (TDM), dipole moment, reorganization energy (RE), and open-circuit voltage (VOC) has been inquired via density-functional theory (DFT) and time-dependent density functional theory (TDDFT) methodology using B3LYP/6-31G (d,p) and these afore-mentioned features of newly devised molecules have been compared with the reference (BDTR). Among all newly designed molecules (BDTM1-BDTM5), BDTM1 exhibited the highest λmax value of 725 nm. BDTM3, BDTM4, and BDTM5 have displayed the highest dipole moment than the reference (BDTR). Cation (hole) transport rate of BDTM5 (0.00578 eV) and BDTM2 (0.00632 eV) has been explored lower than BDTR (0.00662 eV). Similarly, BDTM5 has displayed lower anion (electron) transport rate (0.00578 eV) relative to BDTR (0.00603 eV). Among all designed molecules, BDTM5 has expressed formidable and unique results accompanied by the lowest band gap (1.90 eV), comparable λmax (720 nm), and VOC. All newly constructed molecules have exposed enhanced VOC. Briefly, the thiophene bridged end-capped acceptor modification approach has been demonstrated compelling in providing the door to plan profoundly effective photovoltaic materials accompanied by exquisite optoelectronic parameters.

Strong electronic correlations in interstitial magnetic centers of zero-dimensional electride β−Yb5Sb3

Using dynamical mean-field theory, we investigate the correlated nature of quantum-confined electrons localized in the crystal voids of the zero-dimensional electride $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Yb}}_{5}{\mathrm{Sb}}_{3}$. In this work, maximally localized Wannier functions were used to obtain an analytical description of the half-filled electride electronic states and to establish a high degree of their localization, with the magnetic moment of $1{\ensuremath{\mu}}_{\mathrm{B}}$ per anionic cavity. We reproduced the Mott metal-insulator transition, obtained the experimentally observed energy gap, and demonstrated the decrease of resistivity with increasing temperature, typical for semiconductors. The Curie-type temperature dependence of the compound's magnetic susceptibility was calculated and found to be in close agreement with experiment. These results obtained prove that the Coulomb correlations between the localized anionic electrons are the source of the observed electronic and magnetic properties of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Yb}}_{5}{\mathrm{Sb}}_{3}$.

Electron attachment to tetrazoles: The influence of molecular structure on ring opening reactivity.

The electron-induced reactivity of 5-(4-chlorophenyl)-1H-tetrazole and 5-chloro-1-phenyl-1H-tetrazole was studied using a trochoidal electron monochromator quadrupole mass spectrometer experimental setup. 5-(4-chlorophenyl)-1H-tetrazole underwent dissociative electron attachment to form Cl-, [M-HCl]-, and [M-H]-. 5-chloro-1-phenyl-1H-tetrazole underwent associative electron attachment to form the parent anion and dissociative electron attachment to form Cl-, CN2Cl-, [M-N2-Cl]-, and [M-HCl]-. For each anion product, the ion yield was measured as a function of incident electron energy. Density functional theory calculations were performed to support the experimental results with estimates of the energetic thresholds for the different reaction pathways. While the tetrazole group is susceptible to electron-induced ring opening in both molecules, this process was only observed for 5-chloro-1-phenyl-1H-tetrazole, indicating that this process is influenced by the structure of the molecule.

2D Electrides: MXene Phase with C3 Structure Unit: A Family of 2D Electrides (Adv. Funct. Mater. 24/2021)

In article number 2100009, Gustavo M. Dalpian, Hannes Raebiger, and co-workers report the discovery of a family of 2D electride materials with composition M2CO2, where M = Sc, Y, La, Lu, Tm, and Ho. The electride behavior emerges in a new structural phase for MXenes, where the hexagonal carbon layer is broken up into C3 trimers, and anionic electrons get trapped in the voids between the C3 units.

Theoretical prediction of room-temperature two-dimensional ferromagnetism in an yttrium iodide electride

Through a global structure search combined with density functional theory calculations, we predict a two-dimensional (2D) electride ferromagnet, yttrium iodide (YI). The ground-state YI structure has YI layers bound by relatively weak van der Waals interactions; the interlayer binding energy is only $--0.016\phantom{\rule{0.16em}{0ex}}\mathrm{eV}/{\AA{}}^{2}$. Each YI layer has strongly localized anionic electrons in interstitial spaces, which is a crucial characteristic of electrides. The hybridization of these interstitial $s$-band lone-pair electrons and the $d$-band electrons of Y gives rise to a Stoner-type instability, resulting in 2D ferromagnetic orders with magnetic moments of $1.28\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ per unit cell. Our Monte Carlo simulations further demonstrate that the Curie temperatures of bulk and monolayer YI are as high as 380 and 383 K, respectively. Phonon dispersion calculations and ab initio molecular dynamics simulations also show that the YI layers are dynamically and thermodynamically stable at room temperature. These findings suggest that monolayer YI is a promising candidate for a room-temperature 2D ferromagnet.

Two-Dimensional Magnetic Anionic Electrons in Electrides: Generation and Manipulation

Introducing magnetism to anionic electrons (AE) of electrides, especially for those confined in two-dimensional (2D) interlayer spaces, could provide a promising way to generate 2D spin-polarized free electron gas. However, the realization of this is challenging. Here, we propose a strategy for generating 2D magnetic AE, which requires two fundamental criteria, i.e., coexistence of localized AE (LAE) and delocalized AE (DAE) and a nearly half-filled LAE. Applying this to Y2C, the magnetism of 2D AE is tunable or sensitive to external strain, hole doping, and layer thickness, depending on the competition between atomic-orbital electrons, DAE, and LAE. Remarkably, a reversible on/off switching of magnetism can be achieved in bilayer Y2C by an electric field. Furthermore, the 2D magnetic AE in Y2C thin films are more robust against oxidation due to spatially selective hole doping effects. The manipulation of spin-polarized 2D AE gas paves a new way for designing spintronic devices with van der Waals magnets.

Electronic structure of graphene/Y2C heterostructure and related doping effect

Until now, many attempts have been made to dope graphene in various ways, but each method turned out to have pros and cons. In this study, to overcome the limitations of doping methods, yttrium hypocarbide (Y2C) is investigated as one prospective material to dope graphene, using density functional theory calculations. In monolayer Y2C, the anionic electrons localized away from Y atomic layers are confirmed to contribute to occupied states near the Fermi level. Next, we investigate the electronic structure of graphene in heterojunction with Y2C. Anionic electrons of Y2C occupy the empty states of graphene in graphene/Y2C heterostructure, which makes the Dirac cone of graphene located at about 1.7 eV below the Fermi level. Such charge transfer of anionic electrons to graphene and the flatness of electric cloud of anionic electrons leads to evenly n-doped graphene in graphene/Y2C heterostructure. This suggests that Y2C is a good candidate to dope graphene.

Direct visualization of anionic electrons in an electride reveals inhomogeneities.

Electrides are an unusual family of materials that feature loosely bonded electrons that occupy special interstitial sites and serve as anions. They are attracting increasing attention because of their wide range of exotic physical and chemical properties. Despite the critical role of the anionic electrons in inducing these properties, their presence has not been directly observed experimentally. Here, we visualize the columnar anionic electron density within the prototype electride Y5Si3 with sub-angstrom spatial resolution using differential phase-contrast imaging in a scanning transmission electron microscope. The data further reveal an unexpected charge variation at different anionic sites. Density functional theory simulations show that the presence of trace H impurities is the cause of this inhomogeneity. The visualization and quantification of charge inhomogeneities in crystals will serve as valuable input in future theoretical predictions and experimental analysis of exotic properties in electrides and materials beyond.

MXene Phase with C3 Structure Unit: A Family of 2D Electrides

AbstractA new structural phase is discovered for M2CO2 MXenes with M = Sc, Y, La, Lu, Tm, and Ho. The hexagonal carbon layer sandwiched between M atoms, typical for MXenes, is transformed into C3 trimers with anionic electrons localized in quasi zero‐dimensional lattice spaces in‐between the C3 units, so the systems can be described as [M6 C3 O6]+II : 2e− electrides. The systems are readily ionized into [M6 C3 O6]+II with very low ionization energy via an anti‐doping mechanism. It is shown that this new structure of Sc2CO2 can bind multiple lithium atoms, with low migration barriers. The findings indicate that these M2CO2 MXenes with unusual carbon trimers are a new family of 2D electride insulators with the potential for charge storage applications, thermal field emission, and as anode material in lithium batteries.

Regulating Work Function of [Ca24Al28O64]4+:4e- Electrides Via Changing Solvated Electron Characters.

Since electrides behave as electron donors in catalytic reactions and device substrates due to the anionic electrons localized in periodic interstitial spaces, their work functions (Φ) could be used as key indicators in describing the high electron-donating power. Taking the [Ca24Al28O64]4+:4e- electride as an example, we here propose a new computational scheme of Φ and, further, characterize Φ of the bulk derivative structures of the electride for clarifying the relationship between structural characteristics and Φ. Results indicate that the external strain hardly affects Φ, but the interior heteroatom-doping and distortion bring about significant changes. All these unique variations of the bulk Φ are governed by the distribution and solvation character of anionic electrons in the cage conduction band states. The mechanism of regulating Φ revealed in this work may play a role in the rational design of electride-based catalysts and devices with a superior performance.

Investigation of electronic, elastic, and optical properties of topological electride Ca3Pb via first-principles calculations* *Project supported by the National Natural Science Foundation of China (Grant No. 12074013), the Research Innovation Fund for College Students of Beijing University of Posts and Telecommunications, the Fundamental Research Funds for the Central Universities, China, and the Research Funds of Renmin University of China (Grant

Electrides are unique materials with the anionic electrons confined to the interstitial sites, expecting important applications in various areas. In this work, the electronic structure and detailed physical properties of topological electride Ca3Pb are studied theoretically. By comparing the crystal structures and band structures of Ca3Pb and Ca3PbO, we find that after removing O2– ions from Ca3PbO, the remaining electrons are confined in the vacancies of the Ca6 octahedra centers, playing the role as anions and forming an additional energy band compared with that of Ca3Pb. These interstitial electrons partially result in the low work function of Ca3Pb. Moreover, the calculated mechanic properties imply that Ca3Pb has a strong brittleness. In addition, the dielectric functions and optical properties of Ca3Pb are also analyzed.

Switchable two-dimensional electrides: A first-principles study

Electrides, with excess anionic electrons confined in their empty space, are promising for uses in catalysis, nonlinear optics and spin-electronics. However, the application of electrides is limited by their high chemical reactivity with the environmental agents. In this work, we report the discovery of a group of two-dimensional (2D) moonolayer electrides with the presence of switchable nearly free electron (NFE) states in their electronic structures. Unlike conventional electrides, which are metals with floating electrons forming the partially occupied bands close to the Fermi level, the switchable electrides are chemically much less active semiconductors holding the NFE states that are 0.3-1.5 eV above the Fermi level. According to a high throughput search, we identified 12 2D candidates that possess such low-energy NFE states. Among them, 11 2D materials can likely be exfoliated from the known layered materials. Under external forces, such as a compressive strain, these NFE states stemming from the surface image potential will be pushed downward to cross the Fermi level. Remarkably, the critical semiconductor-metal transition can be achieved by a strain as low as 3% in 2D monolayer Na$_2$Pd$_3$O$_4$. As such, the switchable 2D electrides may provide an ideal platform for exploring novel quantum phenomena and modern electronic device applications.

Advances in Materials and Applications of Inorganic Electrides.

Electrides are materials in which electrons serve as anions. Here, the concept of inorganic electrides is extended in several respects: from ionic crystals to intermetallic compounds in host materials, from crystalline to amorphous solids, and from 0-dimensional to 1- and 2-dimensional materials in electron-confined spaces. In particular, 2D electrides, in which anionic electrons are sandwiched by cationic slabs, can form a bulk crystal of a 2-dimensional electron gas, thus exhibiting a large electron mobility and providing a platform for topological materials. Exploration of new electrides by computation and high pressure has advanced, revealing that an electride is a stable equilibrium phase of many elements and compounds under high pressure. This review describes the history and current status of electride research and next summarizes the chemical application of electrides and relevant materials. An emphasis is placed on catalysts for ammonia synthesis from N2 and H2 at mild conditions. This subject is accelerated by a demand for on-site ammonia synthesis using hydrogen produced by renewable energy sources. A wide applicability of electride for chemical reactions such selective hydrogenation and carbon-carbon coupling is shown by extending the concept of electrides. Finally, a view for the relationship between electrides and crystallographic voids and current issues are described.

Stability and bonding nature of clathrate H cages in a near-room-temperature superconductor LaH10

Lanthanum hydride (${\mathrm{LaH}}_{10}$) with a sodalitelike clathrate structure was experimentally synthesized to exhibit a near-room-temperature superconductivity under megabar pressures. Based on first-principles density-functional theory calculations, we reveal that the metal framework of La atoms has excess electrons at interstitial regions. Such anionic electrons are easily captured to form a stable clathrate structure of H cages. We thus propose that the charge transfer from La to H atoms is mostly driven by the electride property of the La framework. Furthermore, the interaction between La atom and H cage induces a delocalization of La $5p$ semicore states to hybridize with the H $1s$ state. Consequently, the bonding nature of ${\mathrm{LaH}}_{10}$ is characterized as a mixture of ionic and covalent bonding between La atom and H cage. Our findings demonstrate that anionic and semicore electrons play important roles in stabilizing clathrate H cages in ${\mathrm{LaH}}_{10}$, which can be broadly applicable to other compressed rare-earth hydrides with clathrate structures.

Layered Transition Metal Electride Hf2Se with Coexisting Two-Dimensional Anionic d-Electrons and Hf–Hf Metallic Bonds* *Supported by the National Natural Science Foundation of China (Grant No. 11774424), the Fundamental Research Funds for the Central Universities (Grant No. 2017RC20), the Research Funds of Renmin University of China (Grant No. 20XNH064), the CAS Interdisciplinary Innovation Team, the Beijing Natural Science Foundation (Grant No.

Electrides are unique materials, whose anionic electrons are confined to interstitial voids, and they have broad potential applications in various areas. In contrast to the majority of inorganic electrides, in which the anionic electrons primarily consist of s-electrons of metals, electrides with anionic d-electrons are very rare. Based on first-principles electronic structure calculations, we predict that the layered transition metal chalcogenide Hf2Se is a novel electride candidate with anionic d-electrons. Our results indicate that the anionic electrons confined in the Hf6 octahedra vacancy between [Hf2Se] layers mainly come from the Hf-5d orbitals. In addition, the anionic electrons coexist with the Hf–Hf multiple-center metallic bonds located in the center of neighboring Hf4 tetrahedra. The calculated work function (3.33 eV) for the (110) surface of Hf2Se is slightly smaller than that of Hf2S, which has recently been reported to exhibit good electrocatalytic performance. Our study of Hf2Se will enrich the electride family, and promote further research into the physical properties and applications of electrides.