High-entropy materials:Excellent energy-storage and conversion materials in the field of electrochemistry

High-entropy materials(HEMs),a new type of materials,have attracted significant attention in the field of electrocatalytic reactions,batteries and energy-storage materials over the past few years owing to their unique structure,controllable elementary composition,and adjustable properties.These excellent characteristics result from four major factors:high entropy,sluggish-diffusion,severe lattice distortion,and cocktail effect,and are used widely in energy-energy applications.This review aims to summarize the recent progress of HEMs in electrochemical energy-storage.We begin with the concept,structure,and four core effects of HEMs that provide the basic information on HEMs.Next,we discuss the major properties of HEMs and analyze the relationship between their structures and properties.Furthermore,we highlight the outstanding performance of HEMs in hydrogen storage,electrode materials of batteries,catalysis,and supercapacitors,and briefly explain the mechanisms of these materials that are crucial in energy storage and conversion.This review will assist in understanding the excellent energy-storage properties,intricacies of the phase structures,elemental interactions,and reaction mechanisms associated with HEMs.Moreover,challenges and future development prospects are summarized.This work will provide insight into the factors that are crucial for designing HEMs with energy storage properties.

Charge-transfer-regulated bimetal ferrocene-based organic frameworks for promoting electrocatalytic oxygen evolution

The ferrocene(Fc)-based metal-organic frameworks(MOFs)are regarded as compelling platforms for the construction of efficient and robust oxygen evolution reaction(OER)electrocatalysts due to their superior conductivity and flexible electronic structure.Herein,density functional theory simulations were addressed to predict the electronic structure regulations of CoFc-MOF by nickel doping,which demonstrated that the well-proposed CoNiFc-MOFs delivered a small energy barrier,promoted conductivity,and well-regulated d-band center.Inspired by these,a series of sea-urchin-like CoNiFc-MOFs were successfully synthesized via a facile solvothermal method.Moreover,the synchrotron X-ray and X-ray photoelectron spectroscopy measurements manifested that the introduction of nickel could tailor the electronic structure of the catalyst and induce the directional transfer of electrons,thus optimizing the rate-determining step of^(*)O→^(*)OOH during the OER process and yielding decent overpotentials of 209 and 252 mV at 10 and 200 mA cm^(−2),respectively,with a small Tafel slope of 39 mV dec^(−1).This work presents a new paradigm for developing highly efficient and durable MOF-based electrocatalysts for OER.

Metal-organic frameworks-derived metal phosphides for electrochemistry application

Metal-organic frameworks(MOFs)with high porosity and variable structure have attracted extensive attention in the field of electrochemistry,but their poor conductivity and stability have limited their development.Materials derived from MOFs can maintain the structural diversity and porosity characteristics of MOFs while improving their electrical conductivity and stability.Metal phosphides play an important role in electrochemistry because they possess rich active sites,unique physicochemical properties,and a porous structure.Published results show that MOF-derived metal-phosphides materials have great promise in the field of electrochemistry due to their controllable structure,high specific surface area,high stability and excellent electrical conductivity.MOF-derived metal-phosphides with significant electrochemical properties can be obtained by simply,economical and scalable synthetic methods.This work reviews the application of MOF-derived metal phosphides in electrochemistry.Specifically,the synthesis methodology and morphological characterization of MOFs derived metal-phosphides and their application in electrochemistry are described.Based on recent scientific advances,we discuss the challenges and opportunities for future research on MOF-derived metal-phosphides materials.

Synthesis and Utilization of MXene/MOF Hybrid Composite Materials

Metal-organic frameworks(MOFs)are crystalline porous architectures formed by the coordination of organic ligands with metal ions or clusters.MOFs are notable for their vast surface area,abundant active sites,high porosity,and tunable properties.However,their application in energy storage and catalysis is impeded by limited conductivity and chemical stability.A promising approach to mitigating these constraints is the integration of MOFs with other functional or conductive materials.MXenes,with their distinctive layered structure,exceptional electrical conductivity,and rich surface functional groups,provide numerous advantages when combined with MOFs.This review encapsulates the synthesis methodologies of MXene/MOF composites and explores their applications across various domains,including lithium-ion batteries,supercapacitors,lithium-sulfur batteries,zinc-ion batteries,electrocatalysts,and photocatalysts.

Ternary alloy and metal oxides embedded in yolk–shell polyhedrons as bifunctional oxygen electrocatalyst

To improve the efficiency of oxygen electrolysis,exploiting bifunctional electrocatalysts with excellent activity and stability is extremely important due to the four-electron transfer dynamics of oxygen evolution reaction(OER)and oxygen reduction reaction(ORR).Herein,a series of yolk-shell hollow polyhedrons(YHPs)embedded with NiCoFe ternary alloy and metal oxides,which are named YHP-x(x=1,2,3,4),were reported.By controlled etching multi-layered zeolitic imidazolate frameworks and following pyrolytic integration,YHPs are endowed with mass transfer tunnels,accessible inner active sites,and good electrical conductivity.Due to the synergetic effect of the alloy,metal oxides and the yolk-shell structure,YHP-1 exhibits excellent ORR performance with a half-wave potential of 0.79 V and YHP-2 displays superior OER performance with a low overpotential of 257 mV at 10 mA cm−2.The strategy described in this work can be extended to a number of hollow/yolk-shell electrocatalysts for water splitting and metal–air batteries.

Electrochemical reconstruction: a new perspective on Sn metal-organic complex microbelts as robust anode for lithium storage

Tin-based materials with high theoretical capacity and suitable working voltage are ideal anode materials for lithium-ion batteries(LIBs). However, to overcome their shortcomings(volume expansion and inferior stability), the preparation processes are usually complicated and expensive. Herein, a tin-based metal-organic complex(tin 1,2-benzenedicarboxylic acid, Sn-BDC)with one-dimensional microbelt morphology is synthesized by a facile, rapid and low-cost co-precipitation method, and served as anode material for LIBs without any post-treatment. Sn-BDC exhibits a high reversible capacity with609/440 m Ah·g^(-1) at 50/2000 m A·g^(-1), and robust cycling stability of 856 m Ah·g^(-1) after 200 cycles at 200 m A·g^(-1),which are obviously superior to that of the Sn Ox/C counterparts. Moreover, an electrochemical reconstruction perspective on the lithium storage mechanism of Sn-BDC is proposed by systematic ex-situ characterizations. The reconstructed SnO_(2) replaces Sn-BDC and becomes the active material in the subsequent cycles. As the by-product of the lithiation reaction, the formed Li-based metal-organic complex(Li-BDC, wrapped around the reconstructed SnO_(2)) plays an important role in alleviating volume expansion and accelerating the charge transfer kinetics.This work is beneficial to design and construct the new electrode materials based on the electrochemical reconstruction for advanced LIBs.

Design and synthesis of nitrogen-doped hexagonal NiCoO nanoplates derived from Ni-Co-MOF for high-performance electrochemical energy storage

In order to further improve the potential application of nickel-cobalt oxide(NiCoO) in supercapacitors,we use controlled calcination of diffe rent Ni-Co-MOF([NiCo(HBTC)(4,4’-bipy)]) composites to obtain five kinds of nickel doped NiCoO(N-NiCoO) with different Ni/Co molar ratio.These N-NiCoO materials with unique hexagonal nanoplates structure,high specific surface area and high porosity indicate high and stable electrochemical activity.In particular,N-NiCoO-2 with a Ni/Co molar ratio of 2:1 exhibits the highest 945.79 F/g specific capacitance at 1 A/g and a high cycle stability of only 6.7% attenuation after 5000 cycles.Apart from the certain percentage of NiCoO with higher conductivity,nitrogen doping provides more reactive sites and the specific porous hexagonal nanoplates structure of the product itself accelerate electron transfer and promote electrolyte diffusion can more effectively enhance the electrochemical performance.Therefore,N-NiCoO synthesized via a simple method exhibit exciting potential and can be used as an electrode material for supercapacitors with good performance.

The stability of MOFs in aqueous solutions——research progress and prospects

Metal-organic frameworks(MOFs)are favored in the fields of adsorption,separation,catalysis,electrochemistry,and magnetism due to their advantages of large specific surface area,high porosity,controllable pore size adjustment,and dispersion of metal active sites.The application of MOFs involves multiple fields,which requires that MOFs have good water stability,as gaseous and liquid water inevitably exist in industrial processes.In this paper,the research status of the stability of MOFs in aqueous solutions was reviewed in recent years,including the design and synthesis,the influencing factors,and the applications of MOFs in water stability.

CeO2 quantum dots doped Ni-Co hydroxide nanosheets for ultrahigh energy density asymmetric supercapacitors

By integrating the merits of lanthanide elements and quantum dots,we firstly design CeO2 quantum dots doped Ni-Co hydroxide nanosheet via a controllable synthetic strategy,which exhibits a large specific capacitance(1370.7 F/g at 1.0 A/g) and a good cyclic stability(90.6% retention after 4000 cycles).Moreover,we assemble an aqueous asymmetric supercapacitor with the obtained material,which has an extremely high energy density(108.9 Wh/kg at 378 W/kg) and outstanding cycle stability(retaining88.1% capacitance at 2.0 A/g after 4000 cycles).

Flexible sodium-ion capacitors boosted by high electrochemicallyreactive and structurally-stable Sb_(2)S_(3)nanowire/Ti_(3)C_(2)Tx MXene film anodes

The rapid development of portable,foldable,and wearable electronic devices requires flexible energy storage systems.Sodiumion capacitors(SICs)combining the high energy of batteries and the high power of supercapacitors are promising solutions.However,the lack of flexible and durable electrode materials that allow fast and reversible Na+storage hinders the development of flexible SICs.Herein,we report a high-capacity,free-standing and flexible Sb2S3/Ti_(3)C_(2)Tx composite film for fast and stable sodium storage.In this hybrid nano-architecture,the Sb_(2)S_(3)nanowires uniformly anchored between Ti_(3)C_(2)Tx nanosheets not only act as sodium storage reservoirs but also pillar the two-dimensional(2D)Ti_(3)C_(2)Tx to form three-dimensional(3D)channels benefiting for electrolyte penetration.Meanwhile,the highly conductive Ti_(3)C_(2)Tx nanosheets provide rapid electron transport pathways,confine the volume expansion of Sb_(2)S_(3)during sodiation,and restrain the dissolution of discharged sodium polysulfides through physical constraint and chemical absorption.Owing to the synergistic effects of the one-dimensional(1D)Sb_(2)S_(3)nanowires and 2D MXenes,the resultant composite anodes exhibit outstanding rate performance(553 mAh·g−1 at 2 A·g−1)and cycle stability in sodium-ion batteries.Moreover,the flexible SICs using Sb2S3/Ti_(3)C_(2)Tx anodes and active carbon/reduced graphene oxide(AC/rGO)paper cathodes deliver a superior energy and power density in comparison with previously reported devices,as well as an excellent cycling performance with a high capacity retention of 82.78%after 5,000 cycles.This work sheds light on the design of next-generation low-cost,flexible and fast-charging energy storage devices.

A controllable preparation of two-dimensional cobalt oxalate-based nanostructured sheets for electrochemical energy storage

Well-defined two-dimensional(2D)cobalt oxalate(CoC_(2)O_(4)·2H_(2)O)nanosheets exhibit more excellent property than common bulk cobalt oxalate due to high specific surface areas and high-efficient transport of ion and electron.However,the delicate control of the 2D morphology of CoC_(2)O_(4)·2H_(2)O during their synthesis remains challenging.Herein,2D CoC_(2)O_(4)·2H_(2)O nanosheets(M1),grown by straightforward chemical precipitation,can be tuned from three-dimensional(3D)structure during their synthesis with no templates or capping agents.This control is obtained by rationally changing the ratio of reactants with ethylene glycol as solvent.Moreover,Co_(3)O_(4)/CoC_(2)O_(4)composites(M1-250)have been fabricated through low-temperature thermal treatment of the M1 precursor in air,which possess porous surfaces with the 2D morphology maintained.Benefiting from the porous surfaces,more redox-active sites and better electrical conductivity of Co_(3)O_(4),the constructed M1-250//AC aqueous device manifest improved kinetics of the electrochemistry process with energy density of 27.9 Wh/kg at 550.7 W/kg and good cycling stability with sustaining 73.0 m Ah/g after 5000 cycles.

The introduction of cobalt element into nickel-organic framework for enhanced supercapacitive performance

Metal-organic frameworks(MOFs) as promising electrodes for supercapacitors are attracting increasing research interest. Herein, we report an effective strategy to improve the electrochemical performance of Ni-MOF for supercapacitor by introducing a secondary Co ion. The Co substitution of Ni in Ni-MOF can improve the intrinsic reactivity and stability. As a result, the bimetallic Co/Ni-MOF-1:15 with an optimal Co/Ni ratio delivers high specific capacitance(359 F/g at 0.5 A/g), good rate performance(81.5% retention at 5 A/g) and cycling stability(81% retention after 5000 cycles). These results demonstrate that the bimetallic synergistic strategy is an effective way to improve the pseudocapacitive performance of MOFs.

Fan-like MnV_(2)O_(6) superstructure for rechargeable aqueous zinc ion batteries

In recent years,vanadate has attracted the attention of researchers for its application in electrode materials due to its high specific capacity and layered crystal structure.Herein,a typical manganese vanadium oxides (Mn V_(2)O_(6)) product is efficient synthesis via a simple one-step hydrothermal method at 200℃ for 16 h.The as-prepared Mn V_(2)O_(6) sample is found to be the unique one-dimensional fan-like superstructure consist of several nanorods.From a microcosmic point of view,VO6 octahedra sheets are connected by sharing edges which provides highly-open framework for rapid the intercalation and deintercalation of guest ions Therefore,stable Mn V_(2)O_(6) was prepared and used as a cathode material in aqueous zinc ion batteries,which displayed favorable specific discharge capacity,excellent coulombic efficiency and well cycling performance.

Photocatalytic uranium extraction boosted by dual effective active sites of porphyrin metal-organic frameworks

Porphyrinoid metal-organic frameworks(MOFs)with dual effective uranium uptake sites were synthesized through combined insitu and post-synthetic method.The MOF10@5 demonstrates the uptake amount of uranium reaches 1476 mg/g under visiblelight irradiation.The PN-MOF10@5 with dual uranyl uptake sites yields the amount of extracting uranyl of 1590 mg/g under visible-light irradiation.The density functional theory(DFT)calculations reveal strong interaction between uranyl and dual uranyl effective active sites.These MOFs demonstrate a powerful synthesis strategy for uranium extraction materials with dual effective active sites.

Hierarchically nanostructured transition metal oxides for supercapacitors

Highly efficient, clean, and sustainable electrochemical energy storage technologies have been investigated extensively to counter the shortage of fossil fuels and increasingly prominent environmental problems. Supercapacitors（SCs） have received wide attention as critical devices for electrochemical energy storage because of their rapid charging-discharging capability and long life cycle. Various transition metal oxides（TMOs）, such as MnO_2, NiO, Co_3O_4,and CuO, have been extensively studied as electrode materials for SCs. Compared with carbon and conducting polymers,TMO materials can achieve higher specific capacitance. For further improvement of electrochemical performance, hierarchically nano structured TMO materials have become a hot research area for electrode materials in SCs. The hierarchical nanostructure can not only offer abundant accessible electroactive sites for redox reactions but also shorten the ion diffusion pathway. In this review, we provide an overall summary and evaluation of the recent progress of hierarchically nano structured TMOs for SCs, including synthesis methods, compositions, structures, and electrochemical performances. Both single-phase TMOs and the composites based on TMOs are summarized. Furthermore, we also prospect the developing foreground of this field. In this view, the important directions mainly include： the nanocomposites of TMOs materials with conductive materials; the cobalt-based materials and the nickel-based materials; the improvement of the volume energy density, the asymmetric SCs, and the flexible all-solid-state SCs.

Thermo-induced nanocomposites with improved catalytic efficiency for oxygen evolution

Water electrolysis is a sustainable and environmentally benign process for energy conversion and production.The oxygen evolution reaction(OER),the anode reaction,is slower during water electrolysis than the hydrogen evolution reaction,the cathode reaction,because of the necessary four-electron transfer process.Therefore,exploring highly efficient OER catalysts is crucial for advancing the electrochemical water splitting reaction.

Improving the photocatalytic hydrogen evolution of UiO-67 by incorporating Ce4+-coordinated bipyridinedicarboxylate ligands

UiO-67 is a Zr-based metal–organic framework(MOF) containing an organic linker namely, the dianion of biphenyl-4,40-dicarboxylic acid(bpdc). Ce4+metal ions(0.02 Ce to Zr atom ratio) were incorporated into UiO-67 via partially replacing bpdc with the dianion of 2,20-bipyridine-5,50-dicarboxylic acid(bpydc);thus, the latter forms a bpydc-Ce complex. The resulting product(i.e., UiO-67-Ce) demonstrated a photocatalytic hydrogen evolution rate that was over 10 times higher than that of UiO-67. Through this modification, a new energy transfer channel is opened up. The energy transfer between the bpdc and bpydc-Ce ligands(i.e., from excited bpdc to bpydc-Ce) weakened the recombination of the charge carriers, which was confirmed by photoluminescence, emission lifetime, and transient absorption measurements. This study presents a new way to construct highly efficient MOF photocatalysts.