Electronic Structure Engineering Research Articles

Spaced-confined heterostructure engineering enables rapid ion transport in MoS2–Co9S8@C yolk-shell polyhedron for efficient lithium storage

The out-of-plane van der Waals interaction between stack molybdenum sulfide layers is not conducive to ion transport in Li-ion capacitors, resulting in the decreasing cycling and rate performance. To improve the ion transfer ability, it is an effective strategy to optimize interatomic forces by using refined architectures to construct interface atomic structure. Herein, a space confined molybdenum sulfide-cobalt sulfide heterostructure embed in carbon (MoS2–Co9S8@C) with yolk-shell polyheron morphology is reported via a sequential ion exchanging strategy. The refined heterostructure facilitates to build strong built-in electric field, enabling high ion transport efficiency in MoS2–Co9S8@C polyhedron anode. The space confined yolk-shell structure contributes to buffer the volume expansion effect. Benefitting from the structural confinement engineering and electronic structural engineering, MoS2–Co9S8@C yolk-shell heterostructure shows the excellent pseudocapacitance performance. In this case, a full cell of MoS2–Co9S8@C//porous carbon lithium-ion capacitor shows a high working voltage of ∼4 V, and the maximum energy and power densities of ∼172 Wh kg−1 and 22, 500 W kg−1, respectively.

Tackling Disorder in γ-Ga2 O3.

Ga2 O3 and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga2 O3 offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ-Ga2 O3 presents a particular challenge across synthesis, characterization, and theory due to its inherent disorder and resulting complex structure-electronic-structure relationship. Here, density functional theory is used in combination with a machine-learning approach to screen nearly one million potential structures, thereby developing a robust atomistic model of the γ-phase. Theoretical results are compared with surface and bulk sensitive soft and hard X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, spectroscopic ellipsometry, and photoluminescence excitation spectroscopy experiments representative of the occupied and unoccupied states of γ-Ga2 O3 . The first onset of strong absorption at room temperature is found at 5.1eV from spectroscopic ellipsometry, which agrees well with the excitation maximum at 5.17eV obtained by photoluminescence excitation spectroscopy, where the latter shifts to 5.33eV at 5K. This work presents a leap forward in the treatment of complex, disordered oxides and is a crucial step toward exploring how their electronic structure can be understood in terms of local coordination and overall structure.

Electronically engineering microstructural design for developing advanced steels: An exploration of high Si bainitic steel

Microstructure engineering is essential for developing advanced steels and is often carried out by thermomechanical processing. Here we report the engineering of microstructures of a high Si bainitic steel by tuning its electronic structure. It is experimentally found that the bainitic steel with Si addition processed with laser melting has a complex multiphase microstructure consisting of α-Fe, γ-Fe, ε-martensite, and nano-scale twin boundaries with significantly improved hardness. Furthermore, calculations based on density functional theory show that the observed microstructure is strongly correlated with changes in the electronic structures of Fe atoms around the Si impurities. In particular, electron localization around the Si impurities significantly alters the stacking fault energy, which promotes the formation of ε-martensite and nanoscale twin boundaries, while the Jahn-Teller splitting caused by Si dopants results in a FCC-to-BCC phase transition with a misorientation angle of 8° between the (200)γ and(1¯1¯0)α. This work suggests that controlling the microstructures by electronic structure engineering has great potential for designing new structural materials with excellent mechanical properties.

Enhanced oxygen evolution reaction by stacking single-crystalline freestanding SrRuO3

Single-crystalline transition metal oxide thin film has been employed to perceive the fundamental functions of electronic structure and charge transfer processes in water splitting processes. However, the surface area enlargement and strain tunability in a single-crystalline transition metal oxide are restricted in conventional epitaxy. In this study, we report the oxygen evolution reaction (OER) enhancement by a stack of multilayer SrRuO3 featured single-crystallinity, flexibility, and stackability. The controllable stack of multiple cylindrical SrRuO3 for surface enlargement in a magnitude of order and the emergent electronic structure transition, from t2g(3↑, 1↓) to t2g(3↑)eg(1↑), of Ru efficiently enhances the OER performance, the overpotential can be reduced by ~74 % and ~78 % in KOH and HClO4 respectively at 5 mA/cm2. Our study provides an approach for fine manipulation of single-crystalline freestanding oxide morphologically, and an efficient strategy aiming at the extreme enhancement of the electrochemically active surface area and the electronic structure engineering by strain.

Cathodic Pd1-XNiX Nanocatalyst Development for Alkaline Fuel Cell Applications

Alkaline fuel cells are a versatile, low-emission alternative energy source for use in transportation, as well as for portable and stationary power applications. These systems use chemical energy from the electrochemical conversion of hydrogen and oxygen gas to produce electrical energy, with only water and heat as by-products. They operate through two interdependent redox reactions within the cell consisting of oxidation of hydrogen fuel at the anode and reduction of oxygen at the cathode. One of the most significant barriers that fuel cells face is the sluggish nature of the oxygen reduction reaction (ORR) and its dependence on platinum (Pt), a rare and costly metal, as a catalyst for the reaction. Through the development and optimization of the structures and materials, the amount of precious metal catalyst can be decreased without sacrificing performance and enabling an increase in the commercial viability of the device.An alternative cathode material is palladium (Pd), which possesses similar chemical properties to Pt but is more stable in alkaline media and available in a greater abundance. Additionally, the catalytic ability of Pd is comparable to that of Pt, but due to the electronic structure of Pd, it bonds oxygen to a stronger extent, leading to a reduced activity. Theoretical analyses of the Pd electronic structure have shown that tuning the metal d-band decreases the oxygen-metal adsorption strength and increases the catalytic ability.1 Tuning of the metal d-band can be achieved experimentally through the addition of ancillary metals, thus altering the electronic structure of the catalyst. Furthermore, volcano trends of metal alloys in acidic media have shown a significant increase in activity when plotted against the oxygen adsorption strength.2 The increase in activity is particularly evident when Pt, for example, is alloyed with ancillary nickel (Ni). Due to the decreased stability of Pt in alkaline media, this study aims to assess the variations in activity of Pd through the addition of varying amounts of Ni. The incorporation of Ni increases the Pd utilization and incorporates a more cost-effective and abundant transition metal, enabling a decrease in the amount of precious metal required for the catalyst. Furthermore, the use of nanoparticles as the basis for the cathode catalyst creates a high surface area on which the ORR can occur. Nanoparticles allow for a more efficient use of the catalyst materials and, consequently, decrease the amount of metal required and the overall cost of the catalyst.This study assesses the viability of palladium-nickel nanocatalysts synthesized using a water-in-oil microemulsion3 method. The synthetic method was optimized to produce small, well-dispersed nanoparticles with a narrow size distribution ideal for the ORR. Furthermore, the synthesis was tuned to produce the desired ratios of Pd to Ni to determine an optimal composition for increased catalytic performance. The analysis of these nanocatalysts includes assessing the relationship between their composition, structure, and function using a combination of electrochemical and microscopy techniques. The results demonstrate a promising catalytic activity, indicating a comparable performance for all compositions. The consistent performance allows for a significant decrease in the precious metal content through the replacement with a more abundant and cost-effective metal. Further studies are being carried out to better understand the stability of these materials in alkaline media under a range of operating conditions relevant to the ORR. These studies aim to enhance the durability and to increase the overall viability of the catalyst. B. Hammer, J.K. Nørskov, Theoretical surface science and catalysis - calculations and concepts, Adv. Catal. 45 (2000) 71-129.A. Holewinski, H. Xin, E. Nikolla, S. Linic, Identifying optimal active sites for heterogeneous catalysis by metal alloys based on molecular descriptors and electronic structure engineering, Curr. Opin. Chem. Eng. 2 (2013) 312-319.S. Lankiang, M. Chiwata, S. Baranton, H. Uchida, C. Coutanceau, Oxygen Reduction Reaction at Binary and Ternary Nanocatalysts Based on Pt, Pd and Au. Electrochim. Acta. 182 (2015) 131–142.

RuO2 electronic structure and lattice strain dual engineering for enhanced acidic oxygen evolution reaction performance

Developing highly active and durable electrocatalysts for acidic oxygen evolution reaction remains a great challenge due to the sluggish kinetics of the four-electron transfer reaction and severe catalyst dissolution. Here we report an electrochemical lithium intercalation method to improve both the activity and stability of RuO2 for acidic oxygen evolution reaction. The lithium intercalates into the lattice interstices of RuO2, donates electrons and distorts the local structure. Therefore, the Ru valence state is lowered with formation of stable Li-O-Ru local structure, and the Ru–O covalency is weakened, which suppresses the dissolution of Ru, resulting in greatly enhanced durability. Meanwhile, the inherent lattice strain results in the surface structural distortion of LixRuO2 and activates the dangling O atom near the Ru active site as a proton acceptor, which stabilizes the OOH* and dramatically enhances the activity. This work provides an effective strategy to develop highly efficient catalyst towards water splitting.

Sb-etching-doping engineering TiSe2@C core–shell with low polarization effect enabling enhanced lithium storage performance

The critical challenge of TiSe2 anode for lithium-ion battery (LIB) lies in the severe polarization due to the accumulation of excessive lithium ions and Li3TiSe2 phase during charge/discharge process, resulting in reduced active sites and sluggish interfacial transport kinetics. To solve the issues, Sb doped TiSe2@C core–shell is synthesized via a combined ion etching-doping route. During the process, the introduced Sb element in MIL-125 triggers a synergistic etching-ion exchanging reaction, leading to a structure change of TiSe2 from bulk to core–shell as well as homogeneous Sb-doping in TiSe2. The unique structure demonstrates nano-crystallization of bulk TiSe2 and the formation of local built-in electric field, providing enough achievable active sites and enhancing interfacial charge/ion transfer kinetics. Benefitting from the synergistic effect of structural engineering and electronic structural engineering, polarization effect is weakened and pseudocapacitance storage ability is improved, leading to the high specific capacity and cycle stability of 502 mAh g−1 after 100 cycles at 0.1 A g−1. Therefore, the synthetic route of Sb doped TiSe2@C core–shell anode can be extended to related nanostructured systems for high performance energy storage device application.

Co-Fe-P Nanosheet Arrays as a Highly Synergistic and Efficient Electrocatalyst for Oxygen Evolution Reaction.

The rational design and synthesis of highly efficient electrocatalysts for oxygen evolution reaction (OER) is of critical importance to the large-scale production of hydrogen by water electrolysis. Here, we develop a bimetallic, synergistic, and highly efficient Co-Fe-P electrocatalyst for OER, by selecting a two-dimensional metal-organic framework (MOF) of Co-ZIF-L as the precursor. The Co-Fe-P electrocatalyst features pronounced synergistic effects induced by notable electron transfer from Co to Fe, and a large electrochemical active surface area achieved by organizing the synergistic Co-Fe-P into hierarchical nanosheet arrays with disordered grain boundaries. Such features facilitate the generation of abundant and efficiently exposed Co3+ sites for electrocatalytic OER and thus enable Co-Fe-P to deliver excellent activity (overpotential and Tafel slope as low as 240 mV and 36 mV dec-1, respectively, at a current density of 10 mA cm-2 in 1.0 M KOH solution). The Co-Fe-P electrocatalyst also shows great durability by steadily working for up to 24 h. Our work thus provides new insight into the development of highly efficient electrocatalysts based on nanoscale and/or electronic structure engineering.

Engineering the morphology and electronic structure of atomic cobalt-nitrogen-carbon catalyst with highly accessible active sites for enhanced oxygen reduction

The stabilization of non-precious metals as isolated active sites with high loading density over nitrogen-doped carbon materials is essential for realizing the industrial application of single atom catalysts. However, achieving high loading of single cobalt active sites with greatly enhanced oxygen reduction reaction (ORR) activity and stability remains challenging. Here, an efficient approach was described to create a single atom cobalt electrocatalyst (Co SAs/NC) which possesses enhanced mesoporosity and specific surface area that greatly favor the mass transportation and exposure of accessible active sites. The electronic structure of the catalyst by the strong metal-support interaction has been elucidated through experimental characterizations and theoretical calculations. Due to dramatically enhanced mass transport and electron transfer endowed by morphology and electronic structure engineering, Co SAs/NC exhibits remarkable ORR performance with excellent activity (onset and half-wave potentials of 1.04 V (RHE) and 0.90 V (RHE), Tafel slope of 69.8 mV dec−1 and Jk of 18.8 mA cm−2 at 0.85 V) and stability (7 mV activity decay after 10,000 cycles). In addition, the catalyst demonstrates great promise as an alternative to traditional Pt/C catalyst in zinc-air batteries while maintaining high performance in terms of high specific capacity of (796.1 mAh/gZn), power density (175.4 mW/cm2), and long-term cycling stability (140 h). This study presents a facile approach to design SACs with highly accessible active sites for electrochemical transformations.

Rhombic TiO2 grown on g-C3N4 nanosheets towards fast charge transfer and enhanced Cr(VI) and NO removal

The strong band-to-band visible light absorption obtained by changing the bandgap of photocatalysts is desirable but challenging for TiO2. In this paper, a mechanochemical pre-reaction and subsequent heat-treatment process were used to create TiO2/g-C3N4 heterojunctions. Acid-treated H2Ti3O7 nanobelts and superior thin g-C3N4 nanosheets (CN) were ground evenly and further heat-treated to grow rhombic TiO2 in situ on the nanosheets. The heterojunctions exhibited a band gap with the absorption in visible light region. Heterojunction formation effective tunes the surface and electronic structures of the composite, resulting in significant decrease of bandgap. g-C3N4-based heterojunctions (5TCN) exhibited excellent H2 generation (4991 μmol/g/h) and NO removal. In contrast, a TiO2-based composite (95TCN) revealed efficient photo reduction of Cr(Ⅵ) which was 2 times of that of TiO2 sample and 22 times of that of CN. The photochemical reaction mechanism of TiO2 and g-C3N4-based composites was discussed with the ratio of TiO2 and g-C3N4. The excellent performance is ascribed to single crystal rhombic TiO2 nanoparticles grown in situ on g-C3N4 to form well-developed heterojunctions which accelerate the carrier transfer. These results inspire the electronic structure engineering of photocatalysts to improve visible light absorption and provide a magic strategy for excellent photochemical activities.

Strategies for boosting thermoelectric performance of PbSe: A review

• General physical properties of typical IV-VI compounds are summarized. • Phase diagram, crystal and electrical band structures of PbSe are presented. • Recent ways of adjusting charge and phonon transport processes in PbSe are updated. • Typical preparation methods for PbSe and their scalability are discussed. • Key challenges and future research directions of PbSe are discussed. Thermoelectric materials enable the direct conversion between waste heat and electric energy, playing an important role in alleviating energy crisis. Many excellent thermoelectrics developed so far contain expensive and scarce Te element, largely limiting their applications. Therefore, exploring Te-free compounds with extraordinary thermoelectric performance becomes a vital topic in thermoelectric community in recent years. PbSe is an ideal candidate that meets above criteria and has advanced rapidly in the last decade with reported peak ZT s close to 2.0. Herein we review the recent research progress of PbSe-based thermoelectric materials. This review article starts with a general introduction of the properties of IV-VI semiconductors as advanced thermoelectric materials by comparing their cost, crustal abundance, mechanical strength and chemical bonding. Following that, phase diagram, crystal and electronic band structures of PbSe are comprehensively summarized. Then we discuss how the frequently used dopants regulate its carrier concentrations. Subsequently, electronic band structure engineering (including resonant levels, band flattening, band convergence, band inversion, etc. ) and microstructural architecturing (including atomic arrangements, dislocation arrays, nanoscale precipitates, etc. ) approaches and their impacts on charge and phonon transport properties of PbSe are elaborated. Finally, we summarize the typical production processes of PbSe and comment on their scalability. The future directions for how to further improve the thermoelectric properties of PbSe and promote its applications are discussed at the end of this article.

Electronic structure engineering of bimetallic Pd-Au alloy nanocatalysts for improving electrocatalytic hydrodechlorination performance

Regulating the electronic structure of Pd catalyst for promoting electrocatalytic hydrodechlorination is promising but still challenging. Herein, we propose an electronic structure engineering for accelerating the hydrodechlorination process by desigining bimetallic Pd-Au alloy nanoparticles (ANs) with electron-rich Pd as high-efficiency electrocatalysts. The Pd7Au3 ANs exhibits the highest electrocatalytic hydrodechlorination activity, the 4-chlorophenol hydrodechlorination efficiency reaches 98.35 % within 4 h, and the mass activity is 0.47 h−1 mgPd−1, which is 7.83 times as high as that of pure Pd nanoparticles. The experimental characterization and theoretical calculation reveal that Pd atoms “obtain” electrons and gold atoms “lose” electrons in Pd-Au ANs, resulting in the formation of electron-rich Pd, which promotes the desorption of the dechlorination product phenol and accelerates the renewal of active sites. This work provides an electronic structure engineering strategy of Pd-based electrocatalysts for electrocatalytic hydrodechlorination, which opens a new opportunity for rational design and construction of high-performance hydrodechlorination catalysts.

Tunable angle-dependent electrochemistry at twisted bilayer graphene with moiré flat bands.

Tailoring electron transfer dynamics across solid-liquid interfaces is fundamental to the interconversion of electrical and chemical energy. Stacking atomically thin layers with a small azimuthal misorientation to produce moiré superlattices enables the controlled engineering of electronic band structures and the formation of extremely flat electronic bands. Here, we report a strong twist-angle dependence of heterogeneous charge transfer kinetics at twisted bilayer graphene electrodes with the greatest enhancement observed near the 'magic angle' (~1.1°). This effect is driven by the angle-dependent tuning of moiré-derived flat bands that modulate electron transfer processes with the solution-phase redox couple. Combined experimental and computational analysis reveals that the variation in electrochemical activity with moiré angle is controlled by a structural relaxation of the moiré superlattice at twist angles of <2°, and 'topological defect' AA stacking regions, where flat bands are localized, produce a large anomalous local electrochemical enhancement that cannot be accounted for by the elevated local density of states alone.

Resonance states and hyperconvergence induced by tungsten doping in SnTe: Multiband transport leading to a propitious thermoelectric material

Discovery of dopants which can engineer the electronic structure of the thermoelectric materials beneficially to improve the figure of merit has been receiving a lot of attention. In this work, we study one such unique dopant, tungsten in SnTe by implementing first principles density functional theory approach. We predict that tungsten is a n-type resonant dopant which not only increases the band gap but causes convergence of valence sub-bands leading to increased Seebeck co-efficient due to increase in the effective mass and decrease in the bipolar conduction. We show for the first time, the introduction of hyperconvergence in the conduction sub-bands, a feature which was observed only in valence bands of SnTe and GeTe. In addition to the above features, it also introduces multiple electronic valleys near the Fermi level excluding the use of a co-dopant to exploit the benefits of the electronic structure engineering. A maximum ZT of ~1.61 theoretically achieved by tuning the chemical potential at 800 K makes this material worth being explored experimentally.

Electronic structure engineering of 2-D MoS2 sputtered thin films under ion beam irradiation: Induced by controlled defect generation

TMDs (Transition-metal dichalcogenides) come out in contemporary years as a remarkable class of two-dimensional (2D) materials and have allured enormous consideration. In the class of TMD materials, Molybdenum disulfide (MoS 2 ) has unveiled encouraging applications in the domain of photonics, electronics, electrochemistry and energy. Specifically, the defects originated in MoS 2 play a significant role in modifying the magnetic, electronic, catalytic and optical peculiarities of MoS 2 , depicting an applicable way in modifying the efficiency of MoS 2 based devices. The course through which lattice defects influence the MoS 2 peculiarities are unresolved. In the present work, we present comprehensively how lattice defects impact the electronic structure of MoS 2. We have probed the prospect to employ swift heavy ion irradiation for nano-structuring of sputtered 2D MoS 2 thin films. Our extensive study of ion instigated structural, optical and morphological alterations in MoS 2 thin films manifests that resting on the parameters of irradiation profusion of defects can be established. Theoretically, the optical bandgap also has been determined using Density functional theory (DFT). We grow the thin films of MoS 2 by the sputtering method and induced the defect in MoS 2 thin films by ion irradiation. We evaluated how these defects impact the electronic structure of MoS 2 thin films by measurements taken from Raman, X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), UV–visible spectroscopy, Atomic force microscopy (AFM), X-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS).

MXene-Based Aerogel Anchored with Antimony Single Atoms and Quantum Dots for High-Performance Potassium-Ion Batteries.

Rationally electronic structure engineering of nanocomposite electrodes shows great promise for enhancing the electrochemical performance of rechargeable batteries. Herein, we report antimony single atoms and quantum dots (∼5 nm) codecorated Ti3C2Tx MXene-based aerogels (Sb SQ@MA) for high-performance potassium-ion batteries (PIBs). We found that the atomically dispersed Sb could modify the electronic structure of the Sb/Ti3C2Tx composite, improve the charge transfer kinetics, and enhance the potassium storage capability at the heterointerfaces. Additionally, the MXene-based aerogel with rich surface functional groups and defects provides abundant anchoring sites and endows the composite reinforced structural stability and highly efficient electron transfer. The high loading of Sb (∼60.3 wt %) with short ionic transport pathways is desired potassium reservoirs. These features synergistically enhance the rate and cycling performance of the Sb SQ@MA electrodes in PIBs. This work has demonstrated an enlightening technique to tailor the interface activity of heterostructured electrodes for electrochemical applications.

Surface Engineering of Morphology and Electronic Structure of Cop by Zn Doping for Enhanced Water Splitting Performance

Surface Engineering of Morphology and Electronic Structure of Cop by Zn Doping for Enhanced Water Splitting Performance

Strain engineering of electronic structure and mechanical switch device for edge modified Net-Y nanoribbons

Net-Y is a new two-dimensional carbon structure, which has attracted research interest recently. Here, we study the relevant AB-type ribbons with edge modification, focusing on their strain controlling effects on their electronic structure and device characteristics. Intrinsic ribbons are metallic, but hydrogen or oxygen termination can transform them into semiconductors. Applying strain can effectively control the band gap size, resulting in a transition from an indirect band gap to a smaller direct band gap under appropriate strain, favorably to light absorbing. Strain can also change the work function of ribbons, especially for compressive strains, the work function is lowered significantly, which is beneficial to the improving of the field emission behaviors of ribbons. The analysis demonstrates that the change in band gap size is closely related to the variation of bonding and non-bonding composition between atoms with strain, while the change of work function is due to the variation of the attraction force and repulsion force between atoms upon strain. More interestingly, the strain can significantly regulates the &lt;i&gt;I&lt;/i&gt;-&lt;i&gt;V&lt;/i&gt; characteristic of device based on related ribbons. Therefore, a strain-gated mechanical switch with a very high current switching ratio &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;on&lt;/sub&gt;/&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;off&lt;/sub&gt; can be obtained by making it reversibly work between the “on” and “off” states with stretching and compressing ribbons, which is of great significance in developing the logic circuits for flexible wearable electronic devices.

Syntheses and electronic structure engineering of transition metal nitrides for supercapacitor applications

This review summarizes recent advances in synthesis strategies, structural engineering, and unique properties of transition metal nitrides, along with the critical discussion on electrode designs for supercapacitors to meet commercial standards.

Bimetallic sites and coordination effects: electronic structure engineering of NiCo-based sulfide for 5-hydroxymethylfurfural electrooxidation

The electrocatalytic performance of 5-hydroxymethylfurfural (HMF) oxidation was improved by NiCo-based bimetallic-sites construction and S coordination species tuning.