Transition Metal Chalcogenides Research Articles

Synthesis of Gadolinium-Doped Molybdenum Diselenide Nanospheres for Ultrasensitive Electrochemical Determination of Essential Amino Acid in Human Serum and Milk Samples

The electrocatalytic activity and electronic conductivity of 2D transition metal chalcogenides are usually enhanced by as follows the ideal strategy such as doping or substitution heterogeneous atoms. Here, a rare Earth metal ion of gadolinium (Gd3+) was doped with MoSe2 and synthesized through the hydrothermal method. The morphology and nanostructure of Gd3+ with MoSe2 spheres were analyzed under X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron, High-resolution transmission electron microscopy analysis, Field emission scanning electron microscopy, and energy-dispersive spectroscopy. Furthermore, the Gd3+ doped MoSe2 sphere modified glassy carbon electrode (Gd@MoSe2/GCE) was used for the sensing of tryptophan. The Gd@MoSe2 modified GCE shows remarkable sensing performance of tryptophan resulting in a linear range (20 nM–220 μM) with a low detection limit (6.7 nM). Under the optimal condition, the developed electrochemical sensor was successfully used to determine tryptophan (TRP) in blood serum and milk samples. The electrochemical biosensing results suggest that the doping of the Gd3+ doped MoSe2 sensor is a promising electrocatalyst in biological and food samples.

Nonlinear optical properties of PVD-grown Cr2Te3 film and its nonlinear switching application

Recently, two-dimensional (2D) nanomaterials have been investigated extensively in the field of nonlinear photonics. Cr2Te3, which is one of the 2D transition metal chalcogenides, has garnered attention in the field of spintronics and optoelectronics because of its fascinating magnetic and optical properties. Despite its potential in optoelectronics, Cr2Te3 has rarely been studied in the field of nonlinear photonics. This study investigates the nonlinear optical responses of nanoscale-layered Cr2Te3 films grown by physical vapor deposition at telecommunication wavelengths. A large nonlinear absorption coefficient of –(1.43 ± 0.06) × 105 cm/GW and a nonlinear refractive index of –1.22 ± 0.04 cm2/GW at 1560 nm obtained through Z-scan measurements indicate that the Cr2Te3 film shows saturable absorption and self-defocusing properties at telecommunication wavelengths. Density functional theory calculation show that Cr2Te3 is suitable for broadband optical device. The potential of the nanoscale-layered Cr2Te3 film as a base medium for a nonlinear optical switch was evaluated by fabricating a saturable absorption mirror (SAM). Stable Q-switched pulses with a maximum repetition rate of 33.35 kHz and minimum temporal width of 2.62 μs were readily achieved from a fiber laser cavity incorporating the SAM.

Triggering Mixed Cationic‐Anionic Redox in Cu2‐xSe Cathodes via Tailored Charge‐Carrier for High Energy Density Aqueous Zn Batteries

AbstractThe further application of promising transition‐metal chalcogenides (TMCs) cathodes in dilute neutral aqueous Zn batteries (AZBs) is mainly plagued by unsatisfactory working voltages (usually <1 V vs Zn2+/Zn) and their conventional cationic redox centers reaching theoretical capacity limit. Hence, to break the confinement, a novel Zn‐Cu2‐xSe battery is developed in dilute neutral‐aqueous electrolyte by introducing a tailored charge‐carrier, which not only alters the intercalation potential of ions embedded into Cu2‐xSe (vs Zn2+/Zn, working voltage from ≈0.4 to ≈1.2 V) but also activates the anionic redox centers of Cu2‐xSe (capacity release from 143.4 to 323.2 mAh g−1 at 0.4 A g−1). In situ synchrotron X‐ray diffraction (SXRD) and substantial ex situ characterizations reveal the multi‐step phase conversion undergone by cathode and triggered additional Se‐based anionic (Sen2−/Se2−) reversible redox reaction. A multi‐electron synergistic transfer process established on the cationic‐anionic redox centers circumvents the slow relaxation of single‐ion charge compensation achieving high‐capacity and enhanced ion diffusion kinetics. As a result, an extraordinary energy density of up to 406.2 Wh kg−1 at 240 W kg−1 is implemented (calculated based on the mass of Cu2‐xSe cathode), which is ≈8.4 times higher than that of conventional Zn‐Cu2‐xSe batteries, representing an advanced development toward energetic AZBs.

Room-temperature antiferromagnetic CrSe monolayer with tunable metal–insulator transition in ferroelectric heterostructures

Recently, there has been a rapidly growing interest in two-dimensional (2D) transition metal chalcogenide monolayers (MLs) due to their unique magnetic and electronic properties. By using an evolutionary algorithm and first-principles calculations, we report the discovery of a previously unexplored, chemically, energetically, and thermodynamically stable 2D antiferromagnetic (AFM) CrSe ML with a Néel temperature higher than room temperature. Remarkably, we predict an electric field-controllable metal–insulator transition in a van der Waals heterostructure comprised of CrSe ML and ferroelectric Sc2CO2. This tunable transition in the CrSe/Sc2CO2 heterostructure is attributed to the change in the band alignment between CrSe and Sc2CO2 caused by the ferroelectric polarization reversal in Sc2CO2. Our findings suggest that 2D AFM CrSe ML has important potential applications in AFM spintronics, particularly in the gate voltage conducting channel.

The spontaneous symmetry breaking in Ta2NiSe5 is structural in nature

The excitonic insulator is an electronically driven phase of matter that emerges upon the spontaneous formation and Bose condensation of excitons. Detecting this exotic order in candidate materials is a subject of paramount importance, as the size of the excitonic gap in the band structure establishes the potential of this collective state for superfluid energy transport. However, the identification of this phase in real solids is hindered by the coexistence of a structural order parameter with the same symmetry as the excitonic order. Only a few materials are currently believed to host a dominant excitonic phase, Ta2NiSe5 being the most promising. Here, we test this scenario by using an ultrashort laser pulse to quench the broken-symmetry phase of this transition metal chalcogenide. Tracking the dynamics of the material's electronic and crystal structure after light excitation reveals spectroscopic fingerprints that are compatible only with a primary order parameter of phononic nature. We rationalize our findings through state-of-the-art calculations, confirming that the structural order accounts for most of the gap opening. Our results suggest that the spontaneous symmetry breaking in Ta2NiSe5 is mostly of structural character, hampering the possibility to realize quasi-dissipationless energy transport.

3D space-confined Co0.85Se architecture with effective interfacial stress relaxation as anode material reveals robust and highly loading potassium-ion batteries

Conversion-type transition metal chalcogenide anodes could bring relatively high specific capacity in potassium ion storage due to multiple electron transport reactions, but often accompanying huge volume changes and resulting in low cycle life and rapid capacity fading.While electrode materials are closely packed, the contact at the interface during potassiation/depotassiation is similar to point-to-point contact, generating strong stress to make self-aggregation occur. In this work, we constructed a 3D carbon framework to confine Co0.85Se nanocrystals in three-dimensional space, both fulfilling the requirements of the material's size in the nano-scale and providing the largest contact area for releasing stress. With this optimization, nitrogen-doped carbon confined Co0.85Se nanocrystals (Co0.85Se@NC) reach an ultra-stable cycle life over 4000 times with a specific capacity of 190.9 mA h g−1 at 500 mA g−1 and provide 155.6 mA h g−1 at 10 A g−1 in the rate capability test. It also renders the areal capacity up to 1.03 mA h cm−2 at 500 mA g−1 in the high-mass loading test. Furthermore, based on the finite element analysis, the 3D confinement strategy has the lowest interfacial stress, ensuring Co0.85Se nanocrystals with high structural integrity. This strategy can relieve the stress issue in the conversion-type anode and demonstrate superior electrochemical performance even at high-loading mass electrodes.

A Review of Transition Metal Sulfides as Counter Electrodes for Dye-Sensitized and Quantum Dot-Sensitized Solar Cells.

Third-generation solar cells, including dye-sensitized solar cells (DSSCs) and quantum dot-sensitized solar cells (QDSSCs), have been associated with low-cost material requirements, simple fabrication processes, and mechanical robustness. Hence, counter electrodes (CEs) are a critical component for the functionality of these solar cells. Although platinum (Pt)-based CEs have been dominant in CE fabrication, they are costly and have limited market availability. Therefore, it is important to find alternative materials to overcome these issues. Transition metal chalcogenides (TMCs) and transition metal dichalcogenides (TMDs) have demonstrated capabilities as a more cost-effective alternative to Pt materials. This advantage has been attributed to their strong electrocatalytic activity, excellent thermal stability, tunability of bandgap energies, and variable crystalline morphologies. In this study, a comprehensive review of the major components and working principles of the DSSC and QDSSC are presented. In developing CEs for DSSCs and QDSSCs, various TMS materials synthesized through several techniques are thoroughly reviewed. The performance efficiencies of DSSCs and QDSSCs resulting from TMS-based CEs are subjected to in-depth comparative analysis with Pt-based CEs. Thus, the power conversion efficiency (PCE), fill factor (FF), short circuit current density (Jsc) and open circuit voltage (Voc) are investigated. Based on this review, the PCEs for DSSCs and QDSSCs are found to range from 5.37 to 9.80% (I-/I3- redox couple electrolyte) and 1.62 to 6.70% (S-2/Sx- electrolyte). This review seeks to navigate the future direction of TMS-based CEs towards the performance efficiency improvement of DSSCs and QDSSCs in the most cost-effective and environmentally friendly manner.

Iron Nickel Sulfide Nanorods for Oxygen and Hydrogen Evolution Reaction

AbstractThe electrochemical water splitting process needs fabrication of cost‐effective transition metal‐based materials for its commercialization process. Transition metal chalcogenides are good electrocatalysts for such processes in different media. Herein, we have synthesized Iron Nickel Sulfide (FeNiS2) nanorods by one step hydrothermal method. The synthesized material performed excellent bifunctional activity i. e. Hydrogen Evolution Reaction (HER) & Oxygen Evolution Reaction (OER) in basic environment. The nanorod shaped FeNiS2 deliver its OER activity at an overpotential of 250 mV to afford current density 10 mA cm−2. It shows low Tafel slope of 99 mV/dec along with 11 h stability. Further, we have tested HER activity and the as‐prepared material shows a good overpotential of 141 mV at 10 mA cm−2 and low Tafel slope of 104 mV/dec with durability of 9 h. The electrochemical characterization suggests that FeNiS2 nanorod could be an efficient, OER and HER electrocatalyst for water splitting reaction.

Metal-Organic Assembly Strategy for the Synthesis of Layered Metal Chalcogenide Anodes for Na+ /K+ -Ion Batteries.

Layered transition metal chalcogenides (MX, M=Mo, W, Sn, V; X=S, Se, Te) have large ion transport channels and high specific capacity, making them promising for large-sized Na+ /K+ energy-storage technologies. Nevertheless, slow reaction kinetics and huge volume expansion will induce an undesirable electrochemical performance. Numerous efforts have been devoted to designing MX anodes and enhancing their electrochemical performance. Based on the metal-organic assembly strategy, nanostructural engineering, combination with carbon materials, and component regulation can be easily realized, which effectively boost the performance of MX anodes. In this Review, we present a comprehensive overview on the synthesis of MX nanostructure using the metal-organic assembly strategy, which can realize the design of MX nanostructures, based on self-sacrificial templates, host@guest tailored templates, post-modified layer and derivative templates. The preparation routes and structure evolution are mainly discussed. Then, Mo-, W-, Sn-, V-based chalcogenides used for Na+ /K+ energy storage are reviewed, and the relationship between the structure and the electrochemical performance, as well as the energy storage mechanism are emphasized. In addition, existing challenges and future perspectives are also presented.

Applications of Transition Metal Oxides and Chalcogenides and their Composites in Water Treatment: a review

High population growth, industrialization, precipitous urban settlement, and poor government policies in some circles have increased resource consumption and various environmental activities that promote water pollution. Diverse materials such as nanomaterials, quantum dots, carbonaceous materials, and quaternary-metallic oxides have been very successful in removing benign pollutants from contaminated water bodies. Lately, transition metal oxides (TMOs) and transition metal chalcogenides (TMCs), and their composites have attracted favorable research interest in environmental applications due to their flexible elemental composition, manipulatable bandgaps, earth abundance, optoelectrical properties, visible light activity, and catalytic stability. This review explores the applications of these binary, ternary, quaternary, and heterostructure TMOs and TMCs for a broad range of biological, organic, and inorganic pollutants in water and wastewater treatment. The most popular water treatment strategies used include photocatalysis, adsorption, antimicrobial, persulfate/peroxymonosulfate activation, and the Fenton-like process. The mechanisms of catalysis for these processes were briefly highlighted. Lastly, the conclusion and prospects of the use of the TMOs and TMCs in water and wastewater treatment were discussed.

Highly active and stable Cu9S5-MoS2 heterostructures nanocages enabled by dual-functional Cu electrocatalyst with enhanced potassium storage

• Cu 9 S 5 /MoS 2 hollow nanocage heterostructure was studied as anode material for potassium-ion batteries. • Rational introduced Cu 0 intermediates effectively anchor K x S y polysulfides and facilitate rapid charge transfer. • Unique Cu 9 S 5 /MoS 2 nanocage showed superior conversion reaction reversibility in K-storage application. The intrinsic poor electrical conductivity, severe dissolution of K x S y intermediates, and inferior conversion reaction reversibility extremely impede the practical application of the transition-metal chalcogenides (TMDs) anode for potassium-ion batteries (PIBs). Herein, a rationally designed Cu 9 S 5 /MoS 2 /C heterostructure hollow nanocage was synthesized with assistance from metal-organic frameworks (MOFs) precursor. During the K-storage process, the homogeneously distributed the sulfiphilic nature of Cu 0 reaction product could act as a dual-functional catalyst, not only facilitating the rapid charge transfer but also effectively anchoring (K x S y ) polysulfides, thus boosting K-storage reactions reversibility during the conversion reaction process. When applied as an anode for PIBs, the as-prepared heterostructure exhibits excellent reversible capacity and long cycle lifespan (350.5 mAh g –1 at 0.1 A g –1 and 0.04% per cycle capacity decay at 1 A g –1 after 1000 cycles). Additionally, the potassium storage mechanism is distinctly revealed by in-situ characterizations. The nanoarchitecture designing strategy for the advanced electrode in this work could provide vital guidance for relevant energy storage materials. The hollow Cu9S5/MoS2/C nanocage has been rational designed and regarded as an anode material for potassium-ion batteries (PIBs). Due to the dual-functional catalytic effects of in-situ formed Cu0 nanograin during conversion reaction and homogeneously distributed heterointerfaces within Cu9S5/MoS2, the poor charge transfer, severe dissolution of KxSy polysulfides, and inferior phase transformation reaction reversibility can be significantly improved. It can not only strengthen the integral stability, but also enhance the K-storage properties with long-life and high-capacity.

External field regulation strategies for exciton dynamics in 2D TMDs

Two-dimensional (2D) transition metal chalcogenides (TMDs) are regarded as promising materials for micro-optoelectronic devices and next-generation logic devices due to their novel optoelectronic properties, such as strong excitonic effects, tunable direct bandgap from visible to near-infrared regions, valley pseudospin degree of freedom, and so on. Recently, triggered by the growing demand to optimize the performance of TMDs devices, external field regulation engineering has attracted great attention. The goal of this operation is to exploit the external fields to control exciton dynamics in 2D TMDs, including exciton formation and relaxation, and to finally achieve high-performance 2D TMDs devices. Although the regulation strategies of exciton dynamics in 2D TMDs have been well explored, the underlying mechanisms of different regulation strategies need to be further understood due to the complex many-body interactions in exciton dynamics. Here, we first give a brief summary of the fundamental processes of exciton dynamics in 2D TMDs and then summarize the main field-regulation strategies. Particular emphasis is placed on discussing the underlying mechanisms of how different field-regulation strategies control varied fundamental processes. A deep understanding of field regulation provides direct guidelines for the integrated design of 2D TMDs devices in the future.

A Facile Microwave-Assisted Nanoflower-to-Nanosphere Morphology Tuning of CuSe1–xTe1+x for Optoelectronic and Dielectric Applications

Transition metal chalcogenides have gained significant attention for their optoelectronic and electrical applications in various fields due to their elemental composition-dependent tunable properties. Here, a facile microwave-assisted approach was used to synthesize different CuSe1–xTe1+x-based nanomaterials. By varying the Se and Te concentrations, the morphology of CuSe1–xTe1+x was tuned from nanosheet-based flowers to nanospheres. With the increase in the value of the Te-to-Se content ratio, the material shows the transition from mixed nanosheets/nanospheres to pure nanospheres, where the average sheet thickness and sphere diameter are ∼25 and 80 nm, respectively. The as-synthesized material shows high crystallinity with mixed phases of hexagonal Cu2Te and CuSe. The chemical bonding of the material exhibits shifts of the spectra toward lower binding energies with the decrease in the Se-to-Te ratio. The material exhibits a change in the absorption edge with a blue shift of the optical bandgap for the increase of the Te content. The increment in the absorption makes them eligible for solar cell application. The photoluminescence spectra of different CuSeTe samples show broad emission in the 550–950 nm range with a peak at ∼700 nm. Such optical properties enable CuSeTe materials for possible applications in optoelectronic devices. The dielectric measurement of the sample exhibits an increase in the dielectric constant and loss with temperature, whereas a decrease in both the values is apparent for increase in the frequency. The dielectric study of the material reveals its potential application for energy storage. The photo-response study demonstrated that the material can be employed for photodetector application.

2D Layered Nanomaterials as Fillers in Polymer Composite Electrolytes for Lithium Batteries

AbstractPolymer composite electrolytes (PCEs), i.e., materials combining the disciplines of polymer chemistry, inorganic chemistry, and electrochemistry, have received tremendous attention within academia and industry for lithium‐based battery applications. While PCEs often comprise 3D micro‐ or nanoparticles, this review thoroughly summarizes the prospects of 2D layered inorganic, organic, and hybrid nanomaterials as active (ion conductive) or passive (nonion conductive) fillers in PCEs. The synthetic inorganic nanofillers covered here include graphene oxide, boron nitride, transition metal chalcogenides, phosphorene, and MXenes. Furthermore, the use of naturally occurring 2D layered clay minerals, such as layered double hydroxides and silicates, in PCEs is also thoroughly detailed considering their impact on battery cell performance. Despite the dominance of 2D layered inorganic materials, their organic and hybrid counterparts, such as 2D covalent organic frameworks and 2D metal–organic frameworks are also identified as tuneable nanofillers for use in PCE. Hence, this review gives an overview of the plethora of options available for the selective development of both the 2D layered nanofillers and resulting PCEs, which can revolutionize the field of polymer‐based solid‐state electrolytes and their implementation in lithium and post‐lithium batteries.

Synthesis of uniform two-dimensional non-layered α-MnSe by molecular sieves modified chemical vapor deposition

Large-area and uniform two-dimensional (2D) non-layered α-MnSe was successfully synthesized via the molecular sieve modified chemical vapor deposition (CVD). The molecular sieve serves both as a filter and a container to controllable release the Mn precursor in a stable and much lower concentration, leading to the uniform growth of 2D α-MnSe flakes. The thickness, crystalline quality and uniformity of the as-grown α-MnSe are further characterized. Our study validated the positive role of molecular sieve in the controllable growth of 2D α-MnSe, which is believed to be applicable to other non-layered transition metal chalcogenides (TMCs) and will be beneficial for their further applications in electronics, optoelectronics and spintronics.

Amorphous As2S3 Doped with Transition Metals: An Ab Initio Study of Electronic Structure and Magnetic Properties.

Crystalline transition-metal chalcogenides are the focus of solid state research. At the same time, very little is known about amorphous chalcogenides doped with transition metals. To close this gap, we have studied, using first principle simulations, the effect of doping the typical chalcogenide glass As2S3 with transition metals (Mo, W and V). While the undoped glass is a semiconductor with a density functional theory gap of about 1 eV, doping results in the formation of a finite density of states (semiconductor-to-metal transformation) at the Fermi level accompanied by an appearance of magnetic properties, the magnetic character depending on the nature of the dopant. Whilst the magnetic response is mainly associated with d-orbitals of the transition metal dopants, partial densities of spin-up and spin-down states associated with arsenic and sulphur also become slightly asymmetric. Our results demonstrate that chalcogenide glasses doped with transition metals may become a technologically important material.

Vapor-Phase Indium Intercalation in van der Waals Nanofibers of Atomically Thin W6Te6 Wires.

One-dimensional (1D) conducting materials are of great interest as potential building blocks for integrated nanocircuits. Ternary 1D transition-metal chalcogenides, consisting of M6X6 wires with intercalated A atoms (M = Mo or W; X = S, Se, or Te; A = alkali or rare metals, etc.), have attracted much attention due to their 1D metallic behavior, superconductivity, and mechanical flexibility. However, the conventional solid-state reaction usually produces micrometer-scale bulk crystals, limiting their potential use as nanoscale conductors. Here we demonstrate a versatile method to fabricate indium (In)-intercalated W6Te6 (In-W6Te6) bundles with a nanoscale thickness. We first prepared micrometer-long, crystalline bundles of van der Waals W6Te6 wires using chemical vapor deposition and intercalated In into the crystal via a vapor-phase reaction. Atomic-resolution electron microscopy revealed that In atoms were surrounded by three adjacent W6Te6 wires. First-principles calculations suggested that their wire-by-wire stacking can transform through postgrowth intercalation. Individual In-W6Te6 bundles exhibited metallic behavior, as theoretically predicted. We further identified the vibrational modes by combining polarized Raman spectroscopy and nonresonant Raman calculations.

Low thermal expansion for self-compounded Fe1-xCoxS over a wide temperature range

Zero thermal expansion (ZTE) materials have great application prospects benefited by the inhibition of thermal shock and dimensional mismatch. Herein, a novel self-compounded Fe1-xCoxS composite was obtained by a simple low-temperature annealing method. The second non-stoichiometric phase with a few cation vacancies from the thermal annealing is key to optimizing the thermal expansion behavior. The negative thermal expansion (NTE) region of one phase overlaps the positive thermal expansion (PTE) region of another phase to achieve low expansion in the wide temperature zone. As a result, the obtained Fe0.94Co0.06S sample displays near ZTE covering a wide temperature range (αL = 1.9 ppm/K, ΔT = 176 K) by annealing. Furthermore, the synergistic effect from the self-compounded composite can effectively avoid thermal mismatch compared to the traditional composites with matrix and filler. This study provides a new strategy for regulating the thermal expansion of transition metal chalcogenide materials.

Electronic and surface modulation of 2D MoS2 nanosheets for an enhancement on flexible thermoelectric property

Two-dimensional materials have potential applications for flexible thermoelectric materials because of their excellent mechanical and unique electronic transport properties. Here we present a functionalization method by a Lewis acid-base reaction to modulate atomic structure and electronic properties at surface of the MoS2 nanosheets. By AlCl3 solution doping, the lone pair electronics from S atoms would enter into the empty orbitals of Al3+ ions, which made the Fermi level of the 1T phase MoS2 move towards valence band, achieving a 1.8-fold enhancement of the thermoelectric power factor. Meanwhile, benefiting from the chemical welding effect of Al3+ ions, the mechanical flexibility of the nanosheets restacking has been improved. We fabricate a wearable thermoelectric wristband based on this improved MoS2 nanosheets and achieved 5 mV voltage output when contacting with human body. We think this method makes most of the transition metal chalcogenides have great potential to harvest human body heat for supplying wearable electronic devices due to their similar molecular structure.

Facile synthesis of Ni3Se4/Ni0.6Zn0.4O/ZnO nanoparticle as high-performance electrode materials for electrochemical energy storage device

To enhance the performance of transition metal chalcogenide composite electrode material, a key point is a composite design and preparation based on the synergistic effect between the oxide and selenide materials. With a facile ‘one step template-annealing’ step, Ni3Se4, Ni0.6Zn0.4O and ZnO are simultaneously synthesized, by 500 °C annealing. With the increase of annealing temperature from 350 °C to 600 °C, nickel selenides change from NiSe2 to Ni3Se4 to NiSe. The charge storage capacity increases first and then decreases with the increase of annealing temperature, and the 500 °C annealing obtained three compound composite Ni3Se4/Ni0.6Zn0.4O/ZnO (NNZ-500) nanoparticle material displayed a high specific capacitance of 1089.2 F g−1 at 1 A g−1, and excellent cycle stability of 99.8% capacitance retention after 2000 cycles at 5 A g−1. Moreover, an asymmetric supercapacitor was assembled with NNZ-500 as the positive electrode material and activated carbon as the negative electrode material. This kind of asymmetric supercapacitor demonstrated a high energy density of 53.4 Wh kg−1 at 819.0 W kg−1, and cycle stability with 98.6% capacitance retention after 2000 cycles. This material preparation approach provides great potential for the future development of high performance transition metal composite electrode materials in energy storage applications.