Lower Electronegativity Research Articles

Tailoring MXene Thickness and Functionalization for Enhanced Room-Temperature Trace NO2 Sensing

HighlightsGas-phase functionalization of X-MXene (X = –F, –OH, –O, –Br, –I) films crafted from sub-100 nm thin MXene flakes for highly sensitive NO2 sensors.I-MXene-based senor exhibited significant sensing performances toward trace NO2 at room temperature.The hydrophobicity, larger atomic size, lower electronegativity, and reduced shielding of -I contribute to the excellent sensing enhancement of I-MXene.

Constructing FeTe2 nanoparticles embedded in N-doped carbon nanofiber composites as a long-life and high-rate anode material for sodium-ion batteries

Tellurium metal exhibits notably high electrical conductivity along with low electronegativity.

The formation energy, phase transition, and negative thermal expansion of Fe2-xScxW3O12.

Tungstates with a molecular formula A2W3O12 exhibits a wider negative thermal expansion (NTE) temperature range than molybdates but are challenging to synthesize, especially when A = Fe or Cr with metastable structures. To enhance the structural stability of Fe2W3O12, Sc with lower electronegativity is adopted to substitute Fe according to Fe2-xScxW3O12, considering the thermodynamic stability of Sc2W3O12. It is shown that the solid solutions can be easily synthesized and the phase transition temperature (PTT) can be tuned to well below room temperature (RT). Theoretical calculations and experimental results show that the formation energy decreases and the W-O bond in Fe-O-W gradually strengthens as the substitution of Sc in Fe2-xScxW3O12 increases, indicating an increase in structural stability. NTE is enhanced after phase transition with an increase in the Sc content. The reduction in PTT and the enhancement in NTE properties of Fe2W3O12 could result in a decrease in the effective electronegativity of the Fe-site elements, resulting in a low formation energy and strengthened W-O bond in Fe-O-W, which corresponds to a more stable structure.

IR spectrum of SiH3OH2+SiH4: cationic OH⋯HSi dihydrogen bond versus charge-inverted SiH⋯Si hydrogen bond.

The low electronegativity of Si gives rise to a variety of nonconventional intermolecular interactions in clusters of silanes and their derivatives, which have not been well characterized yet. Herein, we characterize the structures of various isomers of bare and Ar-tagged SiH3OH2+SiH4 dimers composed of protonated silanol and silane by infrared photodissociation (IRPD) of mass-selected ions and dispersion-corrected density functional calculations (B3LYP-D3/aug-cc-pVTZ). The analysis of the IRPD spectra recorded in the OH stretch range reveals the competition between two types of nonconventional hydrogen bonds (H-bonds). The first one represents a OH⋯HSi ionic dihydrogen bond (DHB), in which SiH4 interacts with the H2O moiety of SiH3OH2+. The second one represents a charge-inverted SiH⋯Si ionic H-bond (CIHB), in which the SiH4 ligand interacts with the SiH3 moiety of SiH3OH2+. The latter may also be considered as a weak three-centre two-electron (3c-2e) bond. Although both types of H-bonds are computed to have comparable interaction strengths for SiH3OH2+SiH4 (D0 ≈ 35-40 kJ mol-1), DHB isomers dominate the population in the supersonic plasma expansion, while the abundance of CIHB isomers is roughly one order of magnitude lower, probably as a result of entropic factors.

FeS2 Nanoparticles in S-Doped Carbon: Ageing Effects on Performance as a Supercapacitor Electrode

Although transition metal sulfides have prodigious potential for use as electrode materials because of their low electronegativities, their large volume changes inhibit broad application. Moreover, there is only limited knowledge of the ageing processes of these materials at the nanoscale. Herein, nano-C/FeS2 materials were prepared via one-pot syntheses from green biodegradable carbon precursors, followed by activation and sulfidation. The increased activation/sulfidation time led to an increase in the size of the nanoparticles (7 to 17 nm) and their aggregation, as well as in an increase in the specific surface area. The materials were then used as electrodes in 2-electrode symmetric supercapacitors with 2 M KOH. The activation process resulted in improved capacitance (60 F g−1 at 0.1 A g−1) and rate capability (36%) depending on the composite porosity, conductivity, and size of the FeS2 particles. The ageing of the FeS2 nanoparticles was investigated under air, and a progressive transformation of the nano-FeS2 into hydrated iron hydroxy sulfate with a significant morphological modification was observed, resulting in drastic decreases in the capacitance (70%) and retention. In contrast, the ageing of nano-FeS2 during cycling led to the formation of a supplementary iron oxyhydroxide phase, which contributed to the enhanced capacitance (57%) and long-term cycling (132% up to 10,000 cycles) of the device.

Side‐Group‐Mediated Small Molecular Interlayer to Achieve Superior Passivation Strength and Enhanced Carrier Dynamics for Efficient and Stable Perovskite Solar Cells

AbstractConsidering the high surface defects of polycrystalline perovskite, chemical passivation is effective in reducing defects‐associated carrier losses. However, challenges remain in promoting passivation effects without compromising the carrier‐extraction yield at the perovskite interfaces. In this work, interlayer molecules functionalized with different side groups are rationally designed to investigate the correlation between defect‐passivation strength and interfacial carrier dynamics. It is revealed that Cl‐grafted molecules impose destructive effects on the perovskite structure due to its lower electronegativity and mismatched spatial configuration. The introduction of cyanide (CN) as a side group in molecules also leads to perovskite deformation and unfavorable hole collection. After the molecular optimization, the incorporation of carbonyl (C═O) as the side group (TPA─O) simultaneously promotes the carrier‐collection yield as well as sufficient defect passivation. As a consequence, the devices based on TPA─O yield a champion PCE of 23.25%, along with remarkable stability by remaining above 88.5% of initial performance after 2544 h storage in the air. Furthermore, this interlayer based on TAP─O enables flexible devices to achieve a high efficiency of 21.81% and promising mechanical stability. This work paves the way for further improving the performance of perovskite solar cells.

Modification of separators with neodymium oxide/graphene composite to enhance lithium-sulfur battery performance

Lithium-sulfur (Li–S) batteries have generated significant attention due to their high theoretical specific capacity and energy density among a host of energy storage power devices. Nevertheless, the lithium polysulfide dissolution shuttle that occurs within Li–S batteries will lead to capacity deterioration and inadequate cycling stability. In the paper, we proposed a measure to deal with the above problems by modifying the separator with Nd2O3/graphene composite in Li–S batteries. Graphene's special chemical properties and structural qualities make it an excellent choice for Li–S batteries. Meanwhile, Nd2O3 has a strong binding affinity with lithium polysulfide due to its low electronegativity, which exhibits Lewis's acidity and forms strong interactions with lithium polysulfide, which is strongly Lewis basic. By utilizing these advantageous properties, Li–S batteries assembling Nd2O3-decorated reduced graphite oxide modified polypropylene separators (Nd2O3/RGO/PP) demonstrate outstanding electrochemical performance, including a mere 0.0525% capacity attenuation rate under 2C during 1000 cycles and with exceptional rate performance of 614 mAh/g even at 3C. This study presents valuable knowledge for effectively modifying separators using rare earth oxides to incorporate graphene, ultimately promoting the practical application of Li–S batteries.

Molecular engineering of Mn-based cathode for enhanced intrinsic conductivity towards high mass-loading aqueous zinc-ion batteries

Manganese dioxide (MnO2) is a promising cathode for aqueous zinc-ion batteries (ZIBs) because of its low cost, high energy density and environmental friendliness. However, the intrinsic poor electrical conductivity and sluggish reaction kinetics lead to inferior rate capability, especially under high mass loading, which hinders its commercialization. Herein, we report a molecular engineering strategy that can enhance the intrinsic electrical/ionic conductivity of MnO2 and accelerate reaction kinetics. Electrochemical analysis reveals that boron-modified MnO2 (B-MnO2) delivers improved reaction kinetics since the tailored boron atoms with lower electronegativity can abate the strong electrostatic interactions between the cations and cathode. Theoretical calculations demonstrate that B-MnO2 possesses a smaller bandgap than MnO2, which can enhance its electrical conductivity. As a result, the developed Zn/B-MnO2 batteries display a high specific capacity (325.3 mAh/g at 200 mA g−1) and remarkable rate capability (99.4 mAh/g at 10 A/g). More importantly, at high mass loadings of 25 and 30 mg cm−2, the B-MnO2 cathodes can still deliver high specific capacity of 197.2 and 176.5 mAh/g, respectively. This work will pave a way toward the commercial applications of Mn-based cathodes.

RuSe2-CoTe Heterogeneous Surfaces Coated with NC Layer for Excellent HER Performance under Alkaline Condition.

Electrocatalytic hydrogen production has been a promising high-purity hydrogen production technology, attracting a large number of researchers' research interest. Ru has a hydrogen binding capacity similar to Pt, but its price is far lower than Pt, making it a promising alternative to Pt. However, a single Se electronic structure modulation is not sufficient to enable RuSe2 to be used for practical applications on a large scale due to the lack of electrons. Therefore, choosing a suitable way to electronically modulate the Ru atoms in RuSe2 can effectively improve the activity of the catalyst. Cobalt telluride (CoTe) can significantly enhance electrocatalytic performance due to tellurium's low electronegativity and excellent metal properties. In this work, the NC layer possesses excellent electrical conductivity and CoTe acts as an electron donor to optimize the electronic structure locally and trigger electron transfer efficiently. The RuSe2-CoTe/NC electrode requires an overpotential of only 25.4 mV (10 mA cm-2), which is superior to that of RuSe2/NF (65 mV) and CoTe/NC (115 mV). Meanwhile, the Tafel slope of RuSe2-CoTe/NC (67.8 mV dec-1) was better than that of RuSe2/NF (113.6 mV dec-1) and CoTe/NC (209.5 mV dec-1), showing that the build-up of the superior heterojunction makes the RuSe2-CoTe/NC with better hydrogen evolution reaction (HER) reaction kinetics. In addition, after 30 h of long-term stability testing, no significant decrease in catalytic activity was observed, proving the good stability of the RuSe2-CoTe/NC catalyst.

Lateral layered heterostructure bimetallic selenides Bi2Se3-FeSe2 @C for ultra-sensitive electrochemical sensing platform

Selenides possess more electroactive unsaturated edge sites and superior redox activity, due to larger ionic radius together with low electronegativity of Se in comparation with sulfur and oxygen. However, mono-metallic selenides still suffer from the intrinsic limitations of low conductivity and electrochemical activity, which hinders their application in electrochemical sensor. Benefiting from the synergistic effects, bimetallic selenides exhibit relatively high electrical conductivity and electrochemical property. Moreover, heterostructure engineering is identified as an ingenious technology to endow materials with desired functions for developing high performance devices. Herein, a carbon-encapsulated bimetallic selenides (Bi2Se3-FeSe2 @C) composite with lateral layered heterostructure was synthesized and employed as electrode material for electrochemical biosensing. The formed few-layered Bi2Se3-FeSe2 @C lateral heterostructure with a large surface area possesses superb electrochemical properties and abundant immobilized sites toward acetylcholinesterase (AChE). The robust AChE-NF/Bi2Se3-FeSe2 @C/GCE biosensor exhibited promising monocrotophos detection performance along with high sensitivity, a wide linear range (10−5 ∼10 µg mL−1) and low limit of detection (1.51 ×10−13 M).

Computational Insights into Excited State Intramolecular Double Proton Transfer Behavior Associated with Atomic Electronegativity for Bis(2'-benzothiazolyl)hydroquinone.

Inspired by the distinguished regulated photochemical and photophysical properties of 2-(2'-hydroxyphenyl)benzazole derivatives, in this work, the novel bis(2'-benzothiazolyl)hydroquinone (BBTHQ) fluorophore is explored, looking at its photo-induced behaviors associated with different substituted atomic electronegativities, i.e., BBTHQ-SO, BBTHQ-SS and BBTHQ-Se compounds. From the structural changes, infrared (IR) vibrational variations and simulated core-valence bifurcation (CVB) indexes for the dual hydrogen bonds for the three BBTHQ derivatives, we see that low atomic electronegativity could be conducive to enhancing hydrogen bonding effects in the S1 state. Particularly, the O4-H5⋯N6 of BBTHQ-SO and the O1-H2⋯N3 of BBTHQ-SSe could be strengthened to be more intensive in the S1 state, respectively. Looking into the charge recombination induced by photoexcitation, we confirm a favorable ESDPT trend deriving from the charge reorganization of the dual hydrogen bonding regions. By constructing the potential energy surfaces (PESs) along with the ESDPT paths for the BBTHQ-SO, BBTHQ-SS and BBTHQ-Se compounds, we not only unveil stepwise ESDPT behaviors, but also present an atomic electronegativity-regulated ESDPT mechanism.

Modulation the reaction paths of oxygen removal by electronic effects for Fe5C2(100) surfaces

This study employed spin-polarized density functional theory and investigated the removal of surface oxygen on Fe5C2(100) surfaces substituted with first-row transition metals. It was observed that the substituted metals with lower electronegativity, such as Cr and Mn, could hinder the removal of surface oxygen. Conversely, substituted metals with higher electronegativity, such as Co, Ni, and Cu, facilitates the removal of surface oxygen. The results revealed a clear correlation between the energy barrier for oxygen removal and the electronegativity of substituted metals, which provides a straightforward and efficient approach to estimate the energy barrier for oxygen removal on iron carbide surfaces. Furthermore, the study demonstrated that the oxygen removal pathway is dependent on the electronegativity of substituted metals. For Cr and Mn substituted surfaces (low electronegativity), the oxygen removal via CO2 pathway is preferable both in thermodynamics and kinetics, while for Cu substituted surfaces (high electronegativity), the hydrogenation of O to H2O is more favorable. These findings reveal the significance of electronic promoters in catalyst design.

Alkali metal and alkaline earth metal perovskites for oxidative coupling of methane and oxidative dehydrogenation of ethane

In this study, alkali metal and alkaline earth metal perovskites have been synthesized using simple preparation methods for catalyzing the oxidative coupling of methane (OCM) and oxidative dehydrogenation of ethane (ODHE). The influence of their structural parameters (such as tolerance factor t, unit cell free volume (Vf), electronegativity of A- and B-site elements, average metal-oxygen energy, and crystalline phase transition) on basic sites and reaction performance is also systematically investigated. The results show that these two perovskites have similar active sites for OCM and ODHE reactions, with the moderate and strong basic sites favoring the OCM reaction and the moderate basic site facilitating the ODHE reaction. The surface basicity of these perovskites reflects the electron-donating ability of lattice oxygen, which in turn affects the production of reactive oxygen species (O2−, O22−, and O−). Moderate basic sites are abundant and closely related to oxygen vacancies, with high oxygen vacancy concentrations generating abundant reactive oxygen species. Meanwhile, Vf values of perovskites govern the CH4, C2H6, and O2 conversions, the electronegativity of elements affects the catalyst basicity, and the average metal-oxygen energy and crystalline phase transition alter the moderate basic sites. Overall, it concludes that perovskites should meet the following conditions to achieve excellent catalytic performance for OCM and ODHE: moderate Vf, low electronegativity of A- and B-site elements, low average metal oxygen energy, and a crystalline structure that changes with temperature.

InZnTiON Channel Layer for Highly Stable Thin-Film Transistors and Light-Emitting Transistors.

In this study, we incorporated TiN as a carrier suppressor into an amorphous InZnO channel to achieve stable channels for thin-film transistors (TFTs) and light-emitting transistors (LETs). The low electronegativity and standard electrode potential of the Ti dopant led to a reduction in the number of oxygen vacancies in the InZnO channel. Moreover, the substitution of nitrogen into the oxygen sites of InZnO effectively decreased the excess electrons. As a result, the cosputtering of the TiN dopant resulted in a decrease in the carrier concentration of the InZnO channel, serving as an effective carrier suppressor. Due to the distinct structures of TiN and InZnO, the TiN-doped InZnO channel exhibited a completely amorphous structure and a featureless surface morphology. The presence of oxygen vacancies in the InZnO channel creates trap states for electrons and holes. Consequently, the TFT with the InZnTiON channel demonstrated an improved subthreshold swing and enhanced stability during the gate bias stress test. Furthermore, the threshold voltage shift (ΔVth) changed from 3.29 to 0.86 V in the positive bias stress test and from -0.92 to -0.09 V in the negative bias stress test. Additionally, we employed an InZnTiON channel in LETs as a substitute for organic semiconductors. The reduction in the number of oxygen vacancies effectively prevented exciton quenching caused by hole traps within the vacancies. Consequently, appropriate TiN doping in the InZnO channel enhanced the intensity of the LET devices.

Discovering the ultralow thermal conductive A2B2O7-type high-entropy oxides through the hybrid knowledge-assisted data-driven machine learning

Lattice engineering and distortion have been considered one kind of effective strategies for discovering advanced materials. The instinct chemical flexibility of high-entropy oxides (HEOs) motivates/accelerates to tailor the target properties through phase transformations and lattice distortion. Here, a hybrid knowledge-assisted data-driven machine learning (ML) strategy is utilized to discover the A2B2O7-type HEOs with low thermal conductivity (κ) through 17 rare-earth (RE = Sc, Y, La–Lu) solutes optimized A-site. A designing routine integrating the ML and high throughput first principles has been proposed to predict the key physical parameter (KPPs) correlated to the targeted κ of advanced HEOs. Among the smart-designed 6188 (5RE0.2)2Zr2O7 HEOs, the best candidates are addressed and validated by the principles of severe lattice distortion and local phase transformation, which effectively reduce κ by the strong multi-phonon scattering and weak interatomic interactions. Particularly, (Sc0.2Y0.2La0.2Ce0.2Pr0.2)2Zr2O7 with predicted κ below 1.59 Wm−1 K−1 is selected to be verified, which matches well with the experimental κ = 1.69 Wm−1 K−1 at 300 K and could be further decreased to 0.14 Wm−1 K−1 at 1473 K. Moreover, the coupling effects of lattice vibrations and charges on heat transfer are revealed by the cross-validations of various models, indicating that the weak bonds with low electronegativity and few bonding charge density and the lattice distortion (r*) identified by cation radius ratio (rA/rB) should be the KPPs to decrease κ efficiently. This work supports an intelligent designing strategy with limited atomic and electronic KPPs to accelerate the development of advanced multi-component HEOs with properties/performance at multi-scales.

Resonant electron confinement and sheath expansion heating in magnetized capacitive oxygen discharges

In weakly magnetized capacitive radio frequency (RF) plasmas electrons accelerated into the plasma bulk by the expanding RF boundary sheath at one electrode can be returned to this electrode due to their gyromotion around an externally applied magnetic field oriented parallel to the electrodes. If the driving frequency and magnetic field are chosen so that the electron cyclotron frequency, ω ce, equals half of the driving RF, ω rf, such energetic beam electrons will be returned to the sheath during its expansion phase and, thus, will be confined and heated resonantly. This magnetized RF sheath resonance (MRSR) effect is studied based on kinetic particle-in-cell simulations in weakly magnetized capacitively coupled oxygen plasmas. In comparison with electropositive argon plasmas, this resonance mechanism is found to be affected strongly by the electronegativity of oxygen discharges. In the unmagnetized case, low-pressure capacitive oxygen discharges operate in an electropositive mode, where nonlinear high-frequency sheath oscillations play an important role similar to previous observations in electropositive discharges with low electron densities. If the resonance condition is fulfilled (), the discharge efficiency is enhanced due to the MRSR effects, resulting in an increase in plasma density. Our numerical results demonstrate that this resonance effect is particularly efficient at low pressure and low electronegativity. However, in strongly electronegative discharges, the time it takes a typical resonant electron to return to the expanding sheath edge is found to be affected by drift and ambipolar electric fields in the plasma bulk, which cause a deviation from the resonance condition, resulting in a reduction of this type of resonance effect.

Promotion effects of alkali metals on iron molybdate catalysts for CO2 catalytic hydrogenation

CO2 hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes, as well as to produce valuable chemicals from renewable and abundant resources. Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons. Iron-molybdenum catalysts have found numerous applications in catalysis, but have been never evaluated in the CO2 hydrogenation. In this work, the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal (Li, Na, K, Rb, or Cs) were characterized using X-ray diffraction, hydrogen temperature-programmed reduction, CO2 temperature-programmed desorption, in-situ 57Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy. Their catalytic performance was evaluated in the CO2 hydrogenation. During the reaction conditions, the catalysts undergo the formation of an iron (II) molybdate structure, accompanied by a partial reduction of molybdenum and carbidization of iron. The rate of CO2 conversion and product selectivity strongly depend on the promoting alkali metals, and electronegativity was identified as an important factor affecting the catalytic performance. Higher CO2 conversion rates were observed with the promoters having higher electronegativity, while low electronegativity of alkali metals favors higher light olefin selectivity.

Reshaping the coordination and electronic structure of single atom sites on the right branch of ORR volcano plot

The coordination environment of atomic metal sites in single atom catalysts is of vital significance in tailoring the d-orbital states and thus the catalytic behavior towards oxygen reduction reaction (ORR), thereby offering great promise to boost activity via regulating the local chelation structure. Herein we designed a carbon coordination environment for the atomic M sites reside on the right leg of the volcano plot, to effectively counter balance the low adsorption energy of the metal center to oxygen species. Combining time-of-flight secondary ion mass spectrometry and density functional theory calculations, we unveiled the M-C coordination structure and the thus induced changes in electronic structure and ORR catalytic behavior. The reshape in coordination structure, i.e., the replacement of typical nitrogen coordination by low electronegativity carbon coordination, gives rise to exceptional intrinsic activity towards ORR. This work brings a new perspective to boost the activity of single atom catalysts on the weak bonding leg, with exceptional ORR activity being further expected through advancing the chelation structure.

Phosphorus Doping Strategy-Induced Synergistic Modification of Interlayer Structure and Chemical State in Ti3C2Tx toward Enhancing Capacitance

Heteroatom doping is considered an effective method to substantially improve the electrochemical performance of Ti3C2Tx MXene for supercapacitors. Herein, a facile and controllable strategy, which combines heat treatment with phosphorous (P) doping by using sodium phosphinate (NaH2PO2) as a phosphorus source, is used to modify Ti3C2Tx. The intercalated ions from NaH2PO2 act as “pillars” to expand the interlayer space of MXene, which is conducive to electrolyte ion diffusion. On the other hand, P doping tailors the surface electronic state of MXene, optimizing electronic conductivity and reducing the free energy of H+ diffusion on the MXene surface. Meanwhile, P sites with lower electronegativity owning good electron donor characteristics are easy to share electrons with H+, which is beneficial to charge storage. Moreover, the adopted heat treatment replaces –F terminations with O-containing groups, which enhances the hydrophilicity and provides sufficient active sites. The change in surface functional groups increases the content of high valence-stated Ti with a high electrochemical activity that can accommodate more electrons during discharge. Synergistic modification of interlayer structure and chemical state improves the possibility of Ti3C2Tx for accommodating more H+ ions. Consequently, the modified electrode delivers a specific capacitance of 510 F g−1 at 2 mV s−1, and a capacitance retention of 90.2% at 20 A g−1 after 10,000 cycles. The work provides a coordinated strategy for the rational design of high-capacitance Ti3C2Tx MXene electrodes.

Design and simple preparation of a novel 1D/2D/3D multi-structure composite for high-performance supercapacitors

In this paper, a novel NiCoCr-LDH/NiCoO2@NF (1D/2D/3D) composite are developed for supercapacitor. In the composite, one dimensional (1D) Cr-doped NiCoCr-LDH provided more active sites and facilitated redox reaction by modulating the valences of alloy elements. The enhanced cycle stability and conductivity were obtained due to the low electronegativity of two-dimensional (2D) NiCoO2 while high porosity and stability were achieved by the three-dimensional structure of (3D) Ni foam. Furthermore, heterointerface formed by LDH, metal oxides and Ni foam in the composite provided efficient methods to improve conductivity and stability of active electrode materials. Thanks to the above advantages, the NiCoCr-LDH/NiCoO2@NF composite exhibits remarkable performance as the anode of supercapacitor. The as-fabricated electrode using NiCoCr-LDH/NiCoO2@NF composites exhibits excellent area specific capacitance of 2.481 F cm−2 at 1 mA cm−2, which reaches about 3 times as much as traditional NiCo-LDH, and good capacitance retention of 67.3 % after 5000 cycles at 10 mA cm−2. Also, a NiCoCr-LDH/NiCoO2@NF//AC asymmetric supercapacitor has a high energy density of 0.214 mWh cm−2 at a power density of 0.774 mW cm−2, and showed good capacity retention of 54.39 % after 5000 cycles at 10 mA cm−2. This study reports a strategy to fabricate excellent battery-type electrode materials of supercapacitors via LDH composites design.