Tunable Electronic Structure Research Articles

Tunable electronic band structure, luminescence properties and thermostability of (Gd1–xLax)2Si2O7:Ce scintillator by adjusting La/Gd ratio

Mixed crystal strategy is an effective approach of improving the luminescence properties of optical materials and has been adopted widely in many systems. In this paper, the La-mixed Gd2Si2O7:Ce polycrystalline samples were successfully synthesized by a sol-gel method. The crystal structure and luminescence properties were confirmed and discussed by XRD, UV-Vis luminescence spectra, and XEL, respectively. The vacuum ultraviolet excitation spectra and thermoluminescence glow curves were also systematically investigated and discussed at varied temperature. A combination of the first-principles calculations and optical characterization experiments was employed to study the electronic band structure of host material, revealing that the band gap is narrowed and the 5d1 level of Ce3+ shifts to higher energy as the La content increases. The luminescence thermo-stability and activation energy were also measured and calculated. It indicates that thermo-stability is strongly dependent on the La concentration. An effective approach is developed to tune the electronic band structure, luminescence properties and thermostability of (Gd1–xLax)2Si2O7:Ce scintillator by adjusting La/Gd ratio.

In situ tuning of electronic structure of catalysts using controllable hydrogen spillover for enhanced selectivity

In situ tuning of the electronic structure of active sites is a long-standing challenge. Herein, we propose a strategy by controlling the hydrogen spillover distance to in situ tune the electronic structure. The strategy is demonstrated to be feasible with the assistance of CoOx/Al2O3/Pt catalysts prepared by atomic layer deposition in which CoOx and Pt nanoparticles are separated by hollow Al2O3 nanotubes. The strength of hydrogen spillover from Pt to CoOx can be precisely tailored by varying the Al2O3 thickness. Using CoOx/Al2O3 catalyzed styrene epoxidation as an example, the CoOx/Al2O3/Pt with 7 nm Al2O3 layer exhibits greatly enhanced selectivity (from 74.3% to 94.8%) when H2 is added. The enhanced selectivity is attributed to the introduction of controllable hydrogen spillover, resulting in the reduction of CoOx during the reaction. Our method is also effective for the epoxidation of styrene derivatives. We anticipate this method is a general strategy for other reactions.

Electronic structure tuning of FeCo nanoparticles embedded in multi-dimensional carbon matrix for enhanced bifunctional oxygen electrocatalysis

It is highly desirable to develop efficient, affordable and durable electrocatalysts to accelerate sluggish kinetics of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for expanding the applications of Zn-air batteries (ZABs). Here, Fe1Co2 alloy nanoparticles (NPs) embedded in N-doped carbon nanotubes/carbon nanosheets (CNTs/CNSs) (denoted as Fe1Co2-NC) were synthesized in situ by pyrolyzing Fe-chitosan, Co-chitosan chelates and urea. It is demonstrated that the interaction of Fe and Co can effectively modulate electronic structure of Fe and Co, in which ionic state cobalt and iron were partially oxidized, contributing to the enhanced intrinsic catalytic activity. Meanwhile, CNTs/CNSs multi-dimensional porous carbon frameworks facilitated adequate exposure of active sites and mass/electron smooth transport. Accordingly, the resulting Fe1Co2-NC catalyst exhibited a high half-wave potential of 0.88 V (vs. RHE) for ORR and a small over potential (0.356 V) for OER, rendering it with an ultralow potential difference (0.706 V) that can rival that of Pt/C + RuO2 (0.69 V). Impressively, the assembled ZABs with Fe1Co2-NC as a cathode catalyst achieved a high open circuit voltage (1.501 V), maximum power density (203.4 mW cm−2), energy density (820.30 W h kg−1) and robust durability with a slightly increased voltage gap (0.058 V) after 209 h charge-discharge test, shedding light on the great application potential.

A new family of carbonaceous cathodes for rechargeable batteries through electronic structure tuning engineering.

Electric vehicles(EVs) and grid storage for renewable energies will require batteries in tens of millions of tons, and thus they need to be sustainable. EVs call also for batteries with higher energy density than currently available, and this value is intrinsically limited by the properties of the transition metal oxide(TMO) cathodes [1]. There are two possible strategies to overcome these limitations: i) increase the operating voltage in the >4.4 V range; and ii) attempt to use more than one electron per transition metal [2]. The first strategy faces problems of electrolyte stability limit and oxygen evolution, and thus safety hazards. The second is limited to vanadium and nickel, but using only1.3 electrons for the former,

Bi‐based photocatalysts for light‐driven environmental and energy applications: Structural tuning, reaction mechanisms, and challenges

AbstractEnvironmental pollution and energy crisis have become major challenges to sustainable development of human society. Solar‐driven photocatalytic technology is regarded as an extremely attractive solution to environmental remediation and energy conversion. Unfortunately, practical applications of traditional photocatalysts are restricted owing to the poor absorption of visible light, insufficient charge separation and undefined reaction mechanism. Therefore, developing novel visible light photocatalysts and exploring their modification strategies are significant in the area of photocatalysis. Bi‐based photocatalysts have attracted wide attention due to unique geometric structures, tunable electronic structure and decent photocatalytic activity under visible light. At present, Bi‐based photocatalysts can be mainly classified as bismuth metal, binary oxides, bismuth oxyhalogen, multicomponent oxides and binary sulfides, and so forth. Although they can be used as independent photocatalysts for environmental purification and energy development, their efficiency is not ideal. Therefore, many efforts have been made to enhance their photocatalytic performance in the past few decades. Significant progresses in determining the fundamental properties of photocatalysts, improving the photocatalytic performance and understanding the photocatalytic mechanism in important reactions have been made benefited from the various new developed concepts and approaches. This review introduces the structural properties of Bi‐based photocatalysts in detail and summarizes the design and modification strategy for improving the photocatalytic performance, including metal/nonmetal doping, construction of heterojunctions, regulation of crystal facet exposure, and structural defects. Furthermore, we discuss the catalysis mechanisms of Bi‐based materials in terms of semiconductor photocatalysis and plasmonic photocatalysis. Finally, the applications, challenges and prospects of Bi‐based photocatalysts are proposed to guide the future work.image

Electronic Structure Tuning of 2D Metal (Hydr)oxides Nanosheets for Electrocatalysis.

2D metal (hydr)oxide nanosheets have captured increasing interest in electrocatalytic applications aroused by their high specific surface areas, enriched chemically active sites, tunable physiochemical properties, etc. In particular, the electrocatalytic reactivities of materials greatly rely on their surface electronic structures. Generally speaking, the electronic structures of catalysts can be well adjusted via controlling their morphologies, defects, and heterostructures. In this Review, the latest advances in 2D metal (hydr)oxide nanosheets are first reviewed, including the applications in electrocatalysis for the hydrogen evolution reaction, oxygen reduction reaction, and oxygen evolution reaction. Then, the electronic structure-property relationships of 2D metal (hydr)oxide nanosheets are discussed to draw a picture of enhancing the electrocatalysis performances through a series of electronic structure tuning strategies. Finally, perspectives on the current challenges and the trends for the future design of 2D metal (hydr)oxide electrocatalysts with prominent catalytic activity are outlined. It is expected that this Review can shed some light on the design of next generation electrocatalysts.

Predictive screening and validation on chemical looping oxygen carrier activation by tuning electronic structures via transition metal dopants

Owing to its high fuel conversion efficiency and in-situ CO2 capture capability, chemical looping is a promising and versatile platform for fossil fuel utilization. Through the circulation of oxygen carriers (OCs), which are usually metal oxides, the carbonaceous fuels are oxidized into power/heat and/or value-added chemicals by lattice oxygen of OC in the fuel reactor. The reactivity of OC towards the carbonaceous fuels is crucial to the success of chemical looping processes. Incorporating low-percentage dopants into OC is a promising strategy to improve their reactivity while maintaining the recyclability. Consequently, a systematic screening strategy in dopant selection with a solid physical foundation is highly desired. Using hematite (α-Fe2O3) as the model OC material, density functional theory calculations were conducted herein to exemplify the impact of transition metal dopants on the surface reactivity with CO and CH4, the two most common C1 reducing agents in fossil fuels. We found that the amount of electrons accumulated on the lattice oxygen that bound with dopants is a key descriptor to evaluating the surface reactivity in the Mars-van Krevelen type reactions, which can be tailored by dopants with different electronegativities. Cu and Ni were predicted to be the most effective dopants, and such theoretical predictions were validated in temperature-programmed reduction and cyclic redox experiments, where a significant reactivity enhancement was observed using only 1% atomic ratio of effective dopants. The proposed screening strategy is expected to facilitate new OC designs and modifications in an energy and cost effective manner, thus significantly expedites the development of chemical looping technologies.

The Role of the Height Fluctuation Effect in the Tunable Interfacial Electronic Structure of the Vertically Stacked BP/MoS2 Heterojunction

Two-dimensional (2D) van der Waals (vdw) heterojunction devices exploiting unique physical properties are the backbone of new electrical, magnetic, and optical sensing technologies, a key advantage...

Evolution of antiferromagnetism in Zn-doped heavy-fermion compound CeRh(In1−xZnx)5

We report the dependence of antiferromagnetism on Zn-doping concentration in the newly synthesized $\mathrm{CeRh}{(\mathrm{I}{\mathrm{n}}_{1\text{\ensuremath{-}}x}\mathrm{Z}{\mathrm{n}}_{x})}_{5}$ single crystal with $x\ensuremath{\le}0.023$. X-ray-diffraction measurements showed a smooth decrease of lattice parameters with an increasing Zn concentration, indicating a positive chemical pressure effect. The electrical resistivity, specific heat, and magnetic susceptibility measurements revealed that the antiferromagnetic transition temperature ${T}_{\mathrm{N}}$ initially decreases from 3.8 K for pure $\mathrm{CeRhI}{\mathrm{n}}_{5}$ to 3.1 K at $x=0.012$; then, it becomes flat, remaining at approximately 3.1 K between Zn concentrations of 0.012 and 0.017, and finally, it increases to 3.3 K at 0.023 Zn concentration. These results suggest that the change in the electronic structure induced by Zn doping is more important than the chemical pressure effects with regard to tuning the magnetic order. A study on the electronic structure and pressure tuning of the newly synthesized heavy-fermion compound $\mathrm{CeRh}{(\mathrm{I}{\mathrm{n}}_{1\text{\ensuremath{-}}x}\mathrm{Z}{\mathrm{n}}_{x})}_{5}$, which does not include a toxic element, is expected to further enhance our understanding of the competing ground states emerging in heavy-fermion systems.

Electronic structure engineering of SrTiO3 via rhodium doping: A DFT study

SrTiO3, with a highly tunable electronic structure has been recently studied for its thermoelectric (TE) properties. Although originally believed to be a poor TE material, doped SrTiO3 has shown considerable improvement in its TE properties. Herein, we study the electronic structure modifications in Rh doped SrTiO3 by varying the dopant site by using first principles density functional theory calculations. Rh acts as a resonant dopant in SrTiO3 by distorting the density of states near the Fermi level. Transport property calculations predict Rh doped SrTiO3 to be a potential TE material. The results reveal both p- and n-type TE material could be developed by devising synthetic technique to direct Rh towards Ti or Sr site, respectively.

Controlling magnetic order, magnetic anisotropy, and band topology in the semimetals Sr(Mn0.9Cu0.1)Sb2 and Sr(Mn0.9Zn0.1)Sb2

Neutron diffraction and magnetic susceptibility studies show that orthorhombic single-crystals of topological semimetals ${\rm Sr(Mn_{0.9}Cu_{0.1})Sb_2}$ and ${\rm Sr(Mn_{0.9}Zn_{0.1})Sb_2}$ undergo three dimensional C-type antiferromagnetic (AFM) ordering of the Mn$^{2+}$ moments at $T_N = 200\pm10$ and $210\pm12$ K, respectively, significantly lower than that of the parent SrMnSb$_2$ with $T_N=297 \pm 3$ K. Magnetization versus applied magnetic field (perpendicular to MnSb planes) below $T_N$ exhibits slightly modified de Haas van Alphen oscillations for the Zn-doped crystal as compared to that of the parent compound. By contrast, the Cu-doped system does not show de Haas van Alphen magnetic oscillations, suggesting that either Cu substitution for Mn changes the electronic structure of the parent compound substantially, or that the Cu sites are strong scatterers of carriers that significantly shorten their mean free path thus diminishing the oscillations. Density functional theory (DFT) calculations including spin-orbit coupling predict the C-type AFM state for the parent, Cu-, and Zn-doped systems and identify the $a$-axis (i.e., perpendicular to the Mn layer) as the easy magnetization direction in the parent and 12.5% of Cu or Zn substitutions. In contrast, 25% of Cu content changes the easy magnetization to the $b$-axis (i.e., within the Mn layer). We find that the incorporation of Cu and Zn in SrMnSb$_2$ tunes electronic bands near the Fermi level resulting in different band topology and semi-metallicity. The parent and Zn-doped systems have coexistence of electron and hole pockets with opened Dirac cone around the Y-point whereas the Cu-doped system has dominant hole pockets around the Fermi level with a distorted Dirac cone. The tunable electronic structure may point out possibilities of rationalizing the experimentally observed de Haas van Alphen magnetic oscillations.

Tuning the electronic structure of the earth-abundant electrocatalysts for oxygen evolution reaction (OER) to achieve efficient alkaline water splitting – A review

Abstract Tuning the electronic structure of the electrocatalysts for oxygen evolution reaction (OER) is a promising way to achieve efficient alkaline water splitting for clean energy production (H2). At first, this paper introduces the significance of the tuning of electronic structure, where modifying the electronic structure of the electrocatalysts could generate active sites having optimal adsorption energy with OER intermediates, and that could diminish the energy barrier for OER, and that could improve the activity for OER. Later, this paper reviews the tuning of electronic structure along with catalytic performances, synthetic methodologies, chemical properties, and DFT calculations on various nanostructured earth-abundant electrocatalysts for OER in alkaline environment. Further, this review discusses the tuning of the electronic structure of the several nanostructured earth-abundant electrocatalysts including oxide, (oxy)hydroxide, layered double hydroxide, alloy, metal phosphide/phosphate, nitride, sulfide, selenide, carbon containing materials, MOF, core–shell/hetero/hollow structured materials, and materials with vacancies/defects for OER in alkaline environment (including activity: overpotential (η) of ≤200 mV at 10 mA cm−2; stability: ≥100 h; durability: ≥5000 cycles). Then, this review discusses the robust stability of the electrocatalysts for OER towards practical application. Moreover, this review discusses the in situ formation of thin layer on the catalyst surface during OER. In addition, this review discusses the influence of the adsorption energy of the OER intermediates on OER performance of the catalysts. Finally, this review summarizes the various promising strategies for tuning the electronic structure of the electrocatalysts to achieve enhanced performance for OER in alkaline environment.

Tuning the electronic structure of AuNi homogeneous solid-solution alloy with positively charged Ni center for highly selective electrochemical CO2 reduction

Designing bimetallic electrocatalysts with homogenous element distribution and tunable electronic structure is attractive strategy to enhance the CO selectivity in electrochemical carbon dioxide reduction reaction (CO2RR). Herein, we report a concept of atom-polymer hybridization to synthesize AuNi homogeneous solid-solution alloy nanoparticles (NPs) with positively charged Ni center supported on electrospun carbon nanofibers (CNFs). The nanofibers host can strong restrict the separated growth of Au and Ni nanoclusters during the directly graphitization process, leading to the formation of homogeneous AuNi alloy. In-situ characterizations reveal the formation process and phase evolution of the AuNi alloy during the carbonization. The positively charged Ni when alloying with Au lead to the enhanced local electronic structure on AuNi homogeneous solid-solution alloy due to the electron-withdrawal effect of nearby Au atoms. The AuNi homogeneous solid-solution alloy exhibits a high CO selectivity with an optimal CO Faradaic efficiency (FECO) of 92% at −0.98 V (vs. RHE). Theoretical calculations indicate that the incorporation of Ni into Au can make the d-band center more positive and reduce the free energy barrier for the CO2 activation into *COOH and *CO desorption. Operando Raman spectroscopy provides the evidences that AuNi homogeneous solid-solution alloy can facilitate the activation of CO2 into *COOH and enhance the interaction between *COOH and AuNi (111) due to the change of electronic structure.

Control of High-Harmonic Generation by Tuning the Electronic Structure and Carrier Injection.

High-harmonic generation (HHG), which is the generation of light with multiple optical harmonics, is an unconventional nonlinear optical phenomenon beyond the perturbation regime. HHG, which was initially observed in gaseous media, has recently been demonstrated in solid-state materials. Determining how to control such extreme nonlinear optical phenomena is a challenging subject. Here, we demonstrate the control of HHG through tuning the electronic structure and carrier injection using single-walled carbon nanotubes (SWCNTs). We reveal systematic changes in the high-harmonic spectra of SWCNTs with a series of electronic structures ranging from a metal structure to a semiconductor structure. We demonstrate enhancement or reduction of harmonic generation by more than 1 order of magnitude by tuning the electron and hole injection into the semiconductor SWCNTs through electrolyte gating. These results open a path toward the control of HHG in the context of field-effect transistor devices.

Ternary Pt–Au–FeOOH-decorated polyaniline nanocomposite for sensitive dopamine electrochemical detection

Abstract Electrochemical dopamine sensing is crucial for neurological diseases, but its practical application is challenged by sensitivity and anti-interference. Pt-decorated polymer electrode is desirable for dopamine sensing, but its unsatisfactory sensitivity, anti-poisoning capability, and stability limit its application. A new ternary Pt–Au–FeOOH-decorated polyaniline (PANI) nanocomposite (PANI/Pt–Au–FeOOH) modified electrode was successfully fabricated for dopamine (DA) detection. The electrochemical response of DA on PANI/Pt–Au–FeOOH-modified electrode obtained by differential pulse voltammetry (DPV) showed higher electrocatalytic activity than its contrastive unitary and binary Pt-decorated PANI nanocomposites. Analysis of DPV performance for PANI/Pt–Au–FeOOH-modified electrode showed a wide bilinear response of 10–200 and 0.001–10 μM, a low limit of detection (LOD) of 1 nM (0.001 μM), and outstanding anti-interference and stability. Human serum experiment revealed PANI/Pt–Au–FeOOH as a potential sensing electrode and indicated its high detection accuracy for DA. The PANI/Pt–Au–FeOOH also showed its advantage for UA detection. The remarkable advantages of its analytical performance for ternary Pt–Au–FeOOH may be ascribed to the tuning electronic structure and chemical properties of Pt by adjacent metal atoms. This work provides a new choice for the fabrication of advanced Pt-based nanocatalysts with enhanced electrochemical activity.

Structural Evolution and Optical Property Tunability by Halogen Substitution in [N(CH3)4]MX2 (M = Ga+, In+, X = Cl, Br): A Family of Organically Templated Metal Halides.

Structural transformation in hybrid halides is an attractive way to modulate and improve their optical properties. Following newly reported monovalent-metal-based organic-inorganic chlorides [N(CH3)4]MCl2 (M = Ga+, In+), their bromide analogues [N(CH3)4]MBr2 (M = Ga+, In+) were subsequently synthesized. Impressively, their structure transforms from noncentrosymmetric P4̅21m space group for chlorides to centrosymmetric P42/m space group for bromides. As the halogen changes, the (MBr2)- units are partially rotated along the c-axis, which can be attributed to the difference in the anion radius and H-bond interactions between host networks and guest molecules. In addition, the tunable electronic structure and optical anisotropy in this family are also presented. This work provides a typical example for exploring new asymmetric and symmetric organic-inorganic hybrid halides as appliable photoelectric functional materials.

Electro-optical properties of monolayer and bilayer boron-doped [formula omitted]N: Tunable electronic structure via strain engineering and electric field

In this work, the structural, electronic and optical properties of monolayer and bilayer of boron doped C3N are investigated by means of density functional theory-based first-principles calculations. Our results show that with increasing the B dopant concentration from 3.1% to 12.5% in the hexagonal pattern, an indirect-to-direct band gap (0.8 eV) transition occurs. Furthermore, we study the effect of electric field and strain on the B doped C3N bilayer (B–C3N@2L). It is shown that by increasing E-field strength from 0.1 to 0.6V/Å, the band gap displays almost a linear decreasing trend, while for the > 0.6V/Å, we find dual narrow band gap with of 50 meV (in parallel E-field) and 0.4 eV (in antiparallel E-field). Our results reveal that in-plane and out-of-plane strains can modulate the band gap and band edge positions of the B–C3N@2L. Overall, we predict that B–C3N@2L is a new platform for the study of novel physical properties in layered two-dimensional materials (2DM) which may provide new opportunities to realize high-speed low-dissipation devices.

Electronic structure engineering on two-dimensional (2D) electrocatalytic materials for oxygen reduction, oxygen evolution, and hydrogen evolution reactions

Abstract Two-dimensional (2D) materials with the conservation of 2D configuration are excellent candidates for fundamental energy conversion and storage research and potential candidate for commercial applications. In this regard, this comprehensive review highlights the recent advances in the electronic structure tuning of 2D materials such as carbon/graphene, metal chalcogenides, metal oxides/hydroxides, MXenes, toward electrocatalytic energy conversions such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). First, this review offers a systematic summary of the classification, controllable synthesis, and formation mechanism of 2D nanomaterials. Later, the strategies for tuning the electronic structure of 2D nanomaterials, and further their impact on electrocatalytic properties are summarized, namely doping, defect engineering, temperature effect, composite and heterostructure formation. The recent development of electrocatalysts with novel nanosheets structures and compositions were discussed deeply. The understandings of the correlation between the electronic nature, activity and the shape, size, composition, and synthesis methods were summarized. Finally, some personal perspectives on future challenges of this research field will also be presented.

Bifunctional Heterostructured Transition Metal Phosphides for Efficient Electrochemical Water Splitting

AbstractReducing green hydrogen production costs is essential for developing a hydrogen economy. Developing cost‐effective electrocatalysts for water electrolysis is thus of great research interest. Among various material candidates, transition metal phosphides (TMP) have emerged as robust bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) due to their various phases and tunable electronic structure. Recently, heterostructured catalysts have exhibited significantly enhanced activities toward HER/OER. The enhancement can be attributed to the increased amount of accessible active sites, accelerated mass/charge transfer, and optimized adsorption of intermediates, which arise from the synergistic effects of the heterostructure. Herein, a comprehensive overview of the recent progress of bifunctional TMP‐based heterostructure is introduced to provide an insight into their preparation and corresponding reaction mechanisms. It starts with summarizing general fundamental aspects of HER/OER and the synergistic effect of heterostructures for enhanced catalytic activity. Next, the innovational strategies to design and construct bifunctional TMP‐based heterostructures with enhanced overall water splitting activity, as well as the related mechanisms, are discussed in detail. Finally, a summary and perspective for further opportunities and challenges are highlighted for the further development of bifunctional TMP‐based heterostructures from the points of practical application and mechanistic studies.

Twisted chromophore assist to tetrathiafulvalene-spiropyran hybrid driving four-state molecular switch

A series of novel molecular hybrids, in which tetrathiafulvalene (TTF) unit and spiropyran (SP) core are covalently linked to various typical π-conjugated bridges, has been designed based on auxiliary donors and acceptors model and twisted intramolecular charge transfer (TICT) strategy. And the second-order nonlinear optical (NLO) responses of these molecular hybrids have been investigated by using density functional theory (DFT) calculations. The results show that grafting of the TTF unit and SP core to the twisted chromophore (TC) can effectively enhances second-order NLO responses. The promoting effect of enhancing NLO response can be attributed to a strongly favorable charge transfer in TTF-TC-SP hybrid. More importantly, we have found that this TTF-TC-SP hybrid with donor-π-conjugated bridge-acceptor structure can efficiently switch the first hyperpolarizability across four states via redox and photochemical stimuli. Meanwhile, time-dependent (TD) DFT calculations were carried out to probe the origin of the second-order NLO response of TTF-TC-SP molecular hybrid. All these findings provide a clear and well understanding of the relationship between the tunable first hyperpolarizability and electronic structure. We hope these findings would be very useful to guide the search for potential polymorphic molecular switch.