Materials For Electrochemical Energy Storage Research Articles

Negative Thermal Expansion Behavior Enabling Good Electrochemical-Energy-Storage Performance at Low Temperatures.

Metal-ion batteries (such as lithium-ion batteries) are very popular energy-storage devices nowadays. However, low temperatures cause their poor electrochemical kinetics and performance, significantly limiting their wide applications in cold environments. Here, we propose that electrochemical energy-storage materials with negative-thermal-expansion (NTE) behavior can enable good low-temperature electrochemical performance, which becomes a new strategy to tackle the low-temperature issues of metal-ion batteries. LiTi2(PO4)3 (LTP) with an a-direction thermal expansion coefficient of -1.1 × 10-7 K-1 is used as a model material. As the temperature decreases, the transverse vibration of O atoms not only increases the transverse distances among O atoms connected to Li/Ti atoms, but also widens the Li+-transport channels and enlarges Li+-insertion sites along the [12 -1] direction, which are mainly controlled by the lattice parameter a. Consequently, carbon-coated LTP (C-LTP) retains good electrochemical performance at -10 °C, including fast Li+ diffusivity (84% of that at 25 °C), large capacity (96% of the theoretical capacity), and superior rate capability (83% capacity retention at 5C vs. 0.5C). Moreover, the more open crystal structure of LTP at the lower temperature allows smaller maximum unit-cell-volume expansion, resulting in better cycling stability of C-LTP at -10 °C (96.8% capacity retention over 1000 cycles at 2C).

Plasma‐assisted fabrication of multiscale materials for electrochemical energy conversion and storage

AbstractPlasma, the fourth state of matter, is characterized by the presence of charged particles, including ions and electrons. It has been shown to induce unique physical and chemical reactions. Recently, there have been increased applications of plasma technology in the field of multiscale functional materials' preparation, with a number of interesting results. This review will begin by introducing the basic knowledge of plasma, including the definition, typical parameters, and classification of plasma setups. Following this, we will provide a comprehensive review and summary of the applications (phase conversion, doping, deposition, etching, exfoliation, and surface treatment) of plasma in common energy conversion and storage systems, such as electrocatalytic conversion of small molecules, batteries, fuel cells, and supercapacitors. This article summarizes the structure–performance relationships of electrochemical energy conversion and storage materials (ECSMs) that have been prepared or modified by plasma. It also provides an overview of the challenges and perspectives of plasma technology, which could lead to a new approach for designing and modifying electrode materials in ECSMs.

Skeletal Nitrogen Functionalization of Isostructural 2D Conjugated MOFs for Enhancement of the Dual-Ion Storage Capacity.

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are emerging as promising electrode materials for electrochemical energy storage. However, a viable path to realize superior dual-ion storage in 2D c-MOFs has remained elusive. Here, we report the synthesis of Cu2(Nx-OHPTP) 2D c-MOFs (x=0,1,2; OHPTP=octahydroxyphenanthrotriphenylene) with precise aromatic carbon-nitrogen arrangements, based on the π-conjugated OHPTP ligand incorporated with one or two nitrogen atoms. The skeletal nitrogen modification in Cu2(Nx-OHPTP) allows the synergistic introduction of additional redox sites, and thus substantially favors the unique dual-ion adsorption capacity. Consequently, the Cu2(N2-OHPTP) cathode exhibits a largely enhanced electrochemical performance for dual-ion storage (i.e., Li+ and Cl-) with a high specific capacity of 53.8 mAh g-1, which is twice that of Cu2(N0-OHPTP) and 1.3 times that of Cu2(N1-OHPTP). Furthermore, the Cu2(N2-OHPTP) electrode displays a favorable rate performance of 52% and good cycling stability of 96% after 1000 cycles. We identify N-centered redox sites as additional Li+ adsorption sites. In addition, calculations underline the synergistic enhancement of the Cl- adsorption energy by about 1.0 eV at the more electron-poor CuO4 linkages after N-incorporation. This work paves the way for the precise design of 2D c-MOFs with superior electrochemical properties, advancing their application in dual-ion storage applications.

Skeletal Nitrogen Functionalization of Isostructural 2D Conjugated MOFs for Enhancement of the Dual‐Ion Storage Capacity

Two‐dimensional conjugated metal‐organic frameworks (2D c‐MOFs) are emerging as promising electrode materials for electrochemical energy storage. However, a viable path to realize superior dual‐ion storage in 2D c‐MOFs has remained elusive. Here, we report the synthesis of Cu2(Nx‐OHPTP) 2D c‐MOFs (x=0,1,2; OHPTP=octahydroxyphenanthrotriphenylene) with precise aromatic carbon‐nitrogen arrangements, based on the π‐conjugated OHPTP ligand incorporated with one or two nitrogen atoms. The skeletal nitrogen modification in Cu2(Nx‐OHPTP) allows the synergistic introduction of additional redox sites, and thus substantially favors the unique dual‐ion adsorption capacity. Consequently, the Cu2(N2‐OHPTP) cathode exhibits a largely enhanced electrochemical performance for dual‐ion storage (i.e., Li+ and Cl‐) with a high specific capacity of 53.8 mAh g−1, which is twice that of Cu2(N0‐OHPTP) and 1.3 times that of Cu2(N1‐OHPTP). Furthermore, the Cu2(N2‐OHPTP) electrode displays a favorable rate performance of 52% and good cycling stability of 96% after 1000 cycles. We identify N‐centered redox sites as additional Li+ adsorption sites. In addition, calculations underline the synergistic enhancement of the Cl− adsorption energy by about 1.0 eV at the more electron‐poor CuO4 linkages after N‐incorporation. This work paves the way for the precise design of 2D c‐MOFs with superior electrochemical properties, advancing their application in dual‐ion storage applications.

How Do the Four Core Factors of High Entropy Affect the Electrochemical Properties of Energy-Storage Materials?

High-entropy materials (HEMs) are extremely popular for electrochemical energy storage nowadays. However, the detailed effects of four core factors of high entropy on the electrochemical properties of HEMs are still unclear. Here, a high-entropy La1/4Ce1/4Pr1/4Nd1/4Nb3O9 (HE-LaNb3O9) oxide is prepared through multiple rare-metal-ion substitution in LaNb3O9, and uses HE-LaNb3O9 as a model material to systematically study the effects of the four core factors of high entropy on electrochemical energy-storage materials. The high-entropy effect lowers the calcination temperature for obtaining pure HE-LaNb3O9. The lattice distortion in HE-LaNb3O9 leads to its decreased unit-cell-volume variations, which benefits its cyclability. Based on the restrained diffusion arising from the lattice distortion, the Li+ diffusivity of HE-LaNb3O9 at room temperature (25°C) is limited, which causes its lowered rate capability. However, the Li+ diffusivity of HE-LaNb3O9 at high temperature (60°C) becomes faster than that of LaNb3O9, which is attributed to the alleviated lattice distortion at the high-temperature, resulting in higher rate capability. The cocktail effects in HE-LaNb3O9 enable its larger electronic conductivity, better electrochemical activity, more intensive Nb5+ ↔ Nb3+ redox reaction, and larger reversible capacity. The insight gained here can provide a guide for the rational design of new HEMs with good energy-storage properties.

Zinc cobalt sulfide with carbon (graphene oxide and CNT) based nanocomposite as positive electrode for asymmetric coin cell supercapacitors

Abstract The world dependence on portable electronic devices has increased the demand for high-performance energy storage devices. The use of transition metal sulfides as faradaic electrode materials for electrochemical energy storage is rapidly increasing due to their high energy density. Herein Zinc Cobalt Sulfide (ZCS) with graphene oxide (GO) and carbon nanotubes (CNT) were used to create an interconnected ZCS composite network using a solvothermal technique. The materials were characterized by utilizing XRD, FT-Raman, TGA, FESEM/EDX, XPS, and BET. The electrochemical performance of the materials was examined using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The prepared electrodes exhibited both pseudocapacitor behavior and double-layer capacitor behavior, indicating the hybrid nature. Furthermore, All the electrode ZCS, ZCS/GO, ZCS/CNT, and ZCS/GO/CNT electrodes demonstrated higher capacitance behavior, with values of 420, 551, 585 and 811 F g−1 at 1 A/g. Among these ZCS/GO/CNT electrode exhibits outstanding electrochemical properties, with a notable retention of 81.08% at 10 Ag−1 because Combining ZCS nanoparticles with interconnected GO and CNT provides excellent electronic conductivity and stability. The assembled ZCS/GO/CNT//graphene oxide asymmetric coin cell (ACC) supercapacitor showed a high energy density of 33.3 Wh kg–1 at a power density of 624 W kg–1. The 3D nanostructure of ZCS/GO/CNT/Graphene oxide has great potential for developing foldable energy storage devices.

Ti3C2Tx-MXene based 2D/3D Ti3C2–TiO2–CuTiO3 heterostructure for enhanced pseudocapacitive performance

Ti3C2Tx MXene family is a promising electrode material for electrochemical energy storage, but it suffers from insufficient pseudocapacitive charge storage because of self-aggregation and oxidation degradation. To resolve the issue, this paper proposes a two-step process for synthesizing oxidation-controlled MXene-derived 2D/3D heterostructures that beneficially utilize oxidation and simultaneously improve conductivity. The first step generates in-situ 3D floral Ti3C2– TiO2 nanoribbons under partial oxidation of MXene. As the second step, further controlled oxidation with Cu ions transforms the 3D floral Ti3C2–TiO2 nanoribbons into 2D/3D Ti3C2–TiO2–CuTiO3 heterostructure. Leveraging the synergistic effects of MXene, TiO2, and CuTiO3, this 2D/3D heterostructure enhances the interlayered spacing, redox-active site concentration and alleviates low conductivity issue associated with TiO2 nanoribbons. At 2 mA/cm2, the proposed 2D/3D Ti3C2–TiO2–CuTiO3 heterostructure achieved a significantly higher capacitance of 599.2 mF/cm2, compared to MXene with a capacitance of 249.16 mF/cm2 and 3D floral Ti3C2–TiO2 nanoribbons with 498.5 mF/cm2. For practical evaluation, an asymmetric supercapacitor (ASC) device (Ti3C2–TiO2–CuTiO3//AC) was fabricated, which exhibited an energy density of 31.1 Wh/kg, power density of 1041.7 W/kg and capacitance retention of 83.7 % after 5000 continuous charging/discharging cycles. It opens new avenues for utilizing controlled oxidation to enhance pseudocapacitive properties.

Research Progress of Lignin-Derived Functional Materials for Electrochemical Energy Storage

Research Progress of Lignin-Derived Functional Materials for Electrochemical Energy Storage

A Novelly Hierarchical LDHs−Based Cathode with Reduced Deprotonation Barrier Toward High−Performance Alkaline Energy Storage

AbstractLayered double hydroxides (LDHs) are promising electrode materials for alkaline electrochemical energy storage (EES). However, their low capacity, sluggish rate performance, and limited cycle life significantly hinder practical applications. This study unlocks the direct deprotonation reaction pathway for LDH materials through theoretical calculations. Guided by this insight, a novelly hierarchical composite (LDH−TPA) with various dimensions and components is fabricated by introducing terephthalic acid (TPA), serving as a superior cathode material for alkaline EES devices. Experimental results and theoretical investigations reveal the transformation process for metal–organic framework quantum dots (MOF−QDs) and the enhanced mechanism of reaction kinetics in the LDH−TPA electrode. Benefiting from the reduced deprotonation barrier, optimized electronic structure, and fast electrons/ions transport rates, the LDH−TPA1 electrode demonstrates a high specific capacity of 267 mAh g−1 at 1 A g−1 and retains 167 mAh g−1 even at 20 A g−1, along with excellent cycling stability. Furthermore, an alkaline nickel−zinc battery (AZB) with LDH−TPA1 cathode is assembled, achieving a lifespan exceeding 3400 cycles, and a high energy density of 341.3 Wh kg−1 at a power density of 1640.9 W kg−1. This study is expected to provide new insight into the modification of LDHs and the advancement of alkaline energy systems.

Synthesized and characterization of Ce2(MoO4)2(Mo2O7)/MoO3 nanocomposites with Schiff-base ligand assistance as possible electrode materials for electrochemical energy storage

Transition metal oxides, which can deliver a cooperative impact through electrochemical processes, are now being investigated extensively as potential electrode materials for next-generation storage devices. Ce2(MoO4)2(Mo2O7)/MoO3 composites were created using hydrothermal technique aided by Schiff-base ligands in the low temperature and short time. Synthesis of composites in the presence of different ligands led to design different morphologies such as particles, plates, flower-shaped and spheres. The produced sample functions as an active component of the electrochemical energy storing arrangement, which is included of a KOH electrolyte and a three-electrode cell. Morphology affects both the durability of the compounds in the designed working electrode and the kinetics of the electrochemical process. Although, capacitance of Ce2(MoO4)2(Mo2O7)/MoO3 composites was considered at different morphologies for determining optimal performance. Results show ideal sample prepared in the presence of H2acacmda with microsphere morphology and surface area of 12.83 m2g−1 which demonstrates maximum capacity of 246 mAhg−1.

Advancements in Energy Storage and Conversion: The Role of High‐Energy Irradiation Technology

AbstractContemporary challenges have emerged concerning the capability and safety of secondary batteries in the energy storage field. Additionally, catalysts employed in the energy conversion confront issues including inadequate stability and elevated costs. In addition to its traditional use, high‐energy irradiation has found extended application in controlled manipulation of materials for electrochemical energy storage and conversion, due to its unique advantages of no secondary pollution, convenience, and efficiency. This review article shows the recent progress of the application of high‐energy irradiation technology in the field of energy storage and conversion for the first time. The mechanism of material modification via high‐energy irradiation was elaborated, and the application of high‐energy irradiation in tailoring materials for battery components and catalysts was discussed in detail. Finally, challenges for future research of high‐energy irradiation technology in the field of energy storage and conversion were proposed. This review article will provide important significance for subsequent research on high‐energy irradiation technology in the field of energy storage and conversion.

Antimony-mediated few-layer metallic MoSe2 with rich selenium vacancies for ultrafast sodium/potassium storage

Transition metal dichalcogenides with sandwich structure possess high theoretical capacity, while face the challenge of inferior inherent electronic conductivity and dramatic volume fluctuation during cycling, lessening their fascination for electrochemical energy storage material applications. Herein, we report a crystal phase modulation strategy to modulate the electronic structure by doping cation (Sb) into the few-layer 2H-phase MoSe2 lattice, thereby implants abundant selenium vacancies and expands the layer spacing, which transforms it into a 1T-phase (T-MoSe2/C-1). The few-layer 1T-MoSe2 nanosheets are confined within chlorella-derived N, P-doped bio-carbon, endowing T-MoSe2/C-1 with a rock-solid structure, rapid Na+/K+ transport kinetics, and high reversibility. Density functional theory calculations confirm that the antimony atoms in T-MoSe2/C-1 system significantly increase the electronic conductivity, decrease the Na+/K+ diffusion barrier and reinforce the adsorbed capability for Na+/K+. Consequently, the T-MoSe2/C-1 achieves a reversible capacity of 540 mAh/g at 0.5 A/g and delivers as high as 333 mAh/g even at a high rate of 25 A/g for SIBs. As the anode of PIBs, it maintains a stable capacity of 210 mAh/g after 1,000 cycles at 5 A/g. This study provides a new horizon on the phase regulation of transition metal dichalcogenides (TMDs) to improve sodium/potassium-ions storage.

Machine-learning-assisted deciphering of microstructural effects on ionic transport in composite materials: A case study of Li7La3Zr2O12-LiCoO2

The effective diffusivity of ionic species in multiphase materials is critical for the design and function of composite materials for electrochemical energy storage. In practice, effective diffusivity depends sensitively not only on the intrinsic diffusivities of constituting materials but also on their topological arrangement; nevertheless, these coupled contributions are oversimplified in most analytical models. Here, we combine atomistically informed mesoscale modeling and machine learning (ML) analysis to unravel how such features affect effective diffusivity in two-phase composites. Using the Li7La3Zr2O12-LiCoO2 composite solid-state battery cathode as a model system, we compute effective diffusivity for 600 distinct dense polycrystalline microstructures with different topological configurations of grains, grain boundaries, and heterointerfaces. We verify that in addition to atomic-scale variabilities, microstructural feature diversity can significantly impact effective transport properties. Across the ensemble of test microstructures, this often results in bimodal distributions of effective diffusivity that encompass two qualitatively distinct operating mechanisms, which we identify via flux analysis. An ML approach reveals that the most critical determining factors for effective diffusivity are the connectivity of bulk phases and their heterointerfaces. The role of ionic mobility at the heterointerfaces is also discussed. These insights highlight the combined importance of microstructure and interface engineering in tuning the transport properties of ionic species in composite materials. Our framework can also be extended for understanding generic microstructure-property relationships in other complex multiphase materials.

Rational Construction of Heterostructures with n‐Type Anti‐Barrier Layer for Enhanced Electrochemical Energy Storage

AbstractAs a type of 2D materials, layered double hydroxides (LDHs) have emerged as potential candidates for electrochemical energy storage materials. To address their challenges of limited active sites and sluggish charge transfer kinetics, etc., this work presents an ingenious synchronous topochemical pathway (STP) method that enables the in situ anchoring of numerous nanosized Co9S8 on the rigid layers of LDHs. These n‐type anti‐barrier layers, generated by the ohmic contact between a quasi‐metal (Co9S8) and n‐type semiconductor (LDHs), alter the energy band structure and electron states near the Fermi level, optimizing the intrinsic conductivity and deprotonation reaction barriers of LDH materials. The prepared NiCoAl‐LDHs@Co9S8 (LCS) electrode exhibits remarkable electrochemical capacity (473.2 mAh g−¹ at 1 A g−¹) and operational stability (91.2% capacity retention after 20,000 cycles). Furthermore, an aqueous battery device constructed with LCS cathode and Fe‐Ni sulfide (FNS) anode demonstrates an impressive energy density of 118.5 Wh kg−¹ at a power density of 800 W kg−¹. This generalized structural design strategy achieves multiple enhancements in active sites, charge transfer efficiency, and structural stability of LDH materials, providing insights into the potential relationships between energy band and electrochemical performance in energy storage materials.

Microwave-assisted sol-gel synthesis of MFe2O4@SiO2 (M = Cu, Ni, Co) ceramic nanostructures using rice husk as a sustainable precursor for electrochemical energy storage

In this study, we report the synthesis of MFe2O4@SiO2 (M = Cu, Ni, Co) nanostructures by microwave-assisted sol-gel synthesis utilizing rice husk as a cost-effective silica precursor and polyethylene glycol (PEG) as a soft template. Structural and electrochemical properties were characterized using XRD, FTIR, FESEM, EDS, HRTEM, BET, and electrochemical techniques. The result revealed the formation of well-defined MFe2O4 spherical nanoparticles decorated mesoporous silica spheres. Electrochemical studies indicate that the CoFe2O4@SiO2 electrode performs better than the CuFe2O4@SiO2 and NiFe2O4@SiO2 electrodes in faradaic redox processes and supercapacitor performance, having a specific capacitance of 1263 F/g at 1 A. Asymmetric supercapacitor (ASC) with CoFe2O4@SiO2 as positive electrode exhibits high specific capacitance of 135.66 F/g at 1 A/g with good cycle stability retention (70.83 % at 10 A/g), high energy density (50.4 Wh/kg) and power density (891.522 W/kg). CoFe2O4@SiO2 performs better than CuFe2O4@SiO2 and NiFe2O4@SiO2 because cobalt ferrite (CoFe2O4) has higher electrical conductivity, superior redox activity, and better electrochemical stability. This study offers cost-effective potential electrode materials for electrochemical energy storage, combining environmental sustainability with superior electrochemical performance.

Effective improvement of lithium-ion battery anode performance of Ti3C2 by alkali metal ion treatment strategy

MXene has emerged as a promising electrochemical energy storage material due to modifiable layered structure and good electrical conductivity. However, its lamellar stacking has severely limited the electrochemical performance during charging and discharging. Herein, the Li-treated Ti3C2 and Na-treated Ti3C2 nanocomposites are prepared by hydrothermal treatment. Li-treated Ti3C2 exhibits the largest discharge specific capacity, with an initial capacity of 551.5 mA h/g at a rate of 0.1 A/g, which is 81.3 mA h/g higher than Na-treated Ti3C2. After 200 cycles, the Li-Ti3C2 possesses a final capacity of 321.1 mA h/g, better than Na-Ti3C2 (151.7 mA h/g) and Ti3C2 (119.3 mA h/g). The Li-Ti3C2 shows superior cycling performance at a high rate of 2 A/g and a capacity retention rate of 84 % after 1000 cycles. During hydrothermal treatment, the in situ generated TiO2 plays a crucial role in the targeted introduction of metal ions. Density functional theory (DFT) calculations verify that LiTiO2 phase in Li-treated Ti3C2 possesses low band gap and lowest Li migration barrier. The synergy of these factors leads to the improved electrochemical performance of Li-treated Ti3C2. This work provides novel design strategies for developing MXene materials as high performance lithium-ion batteries.

Energy storage chemistry: Atomic and electronic fundamental understanding insights for high-performance supercapacitors

The scarcity of fuels, high pollution levels, climate change, and other major environmental issues are critical challenges that modern societies are facing, mostly originating from fossil fuels-based economies. These challenges can be addressed by developing green, eco-friendly, inexpensive energy sources and energy storage devices. Electrochemical energy storage materials possess high capacitance and superior power density. To engineer highly efficient next-generation electrochemical energy storage devices, the mechanisms of electrochemical reactions and redox behavior must be probed in operational environments. They can be studied by investigating atomic and electronic structures using in situ x-ray absorption spectroscopy (XAS) analysis. Such a technique has attracted substantial research and development interest in the field of energy science for over a decade. The mechanisms of charge/discharge, carrier transport, and ion intercalation/deintercalation can be elucidated. Supercapacitors generally store energy by two specific mechanisms—pseudocapacitance and electrochemical double-layer capacitance. In situ XAS is a powerful tool for probing and understanding these mechanisms. In this Review, both soft and hard x rays are used for the in situ XAS analysis of various representative electrochemical energy storage systems. This Review also showcases some of the highly efficient energy and power density candidates. Furthermore, the importance of synchrotron-based x-ray spectroscopy characterization techniques is enlightened. The impact of the electronic structure, local atomic structure, and electronically active elements/sites of the typical electrochemical energy storage candidates in operational conditions is elucidated. Regarding electrochemical energy storage mechanisms in their respective working environments, the unknown valence states and reversible/irreversible nature of elements, local hybridization, delocalized d-electrons spin states, participation of coordination shells, disorder, and faradaic/non-faradaic behavior are thoroughly discussed. Finally, the future direction of in situ XAS analysis combined with spatial chemical mapping from operando scanning transmission x-ray microscopy and other emerging characterization techniques is presented and discussed.

Self-Exfoliating Benzotristriazine Macrocyclic Network: A New 2D Material for High-Performance Electrochemical Energy Storage.

Aza-fused aromatic π-conjugated networks are an important class of 2D graphitic analogs, which are generally constructed using aromatic precursors. Herein, the study describes a new synthetic approach and electrochemical properties of a self-exfoliating benzotristriazine 2D network (BTTN) constructed using aliphatic precursors, under relatively mild conditions. The obtained BTTN exhibits a nanodisc-like morphology, the self-exfoliation tendency of which is ascribed to the presence of structurally different macrocycles with high electronic repulsion between the layers. The benzotristriazine repeat units of BTTN is electroactive and holds higher carbon/nitrogen ratio when compared with the conventional graphitic aza-fused π-conjugated networks. The self-exfoliated BTTN nanodiscs show excellent electrochemical energy storage of 485 and 333 F g-1 at 1 A g-1 in three-electrode and two-electrode measurements, respectively. BTTN in a symmetric coin-cell architecture exhibits a high specific energy value of 46Wh kg-1 at a power density of 1kW kg-1 and shows excellent cyclic stability of 96% for 10000 and 90% for 30000 charge-discharge cycles at a higher current density of 5 A g-1, surpassing the device performance of most of the reported all-organic pseudocapacitive 2D networks.

Boosting supercapacitive performance of pristine covalent organic frameworks via phenolic hydroxyl groups: A two‐in‐one strategy

Two-dimensional covalent organic frameworks (COFs) are ideal electrode materials for electrochemical energy storage devices due to their unique structures and properties, and the accessibility and utilization efficiency of the redox-active sites within COFs are critical determinants of their pseudocapacitive performance. Via introducing meticulously designed phenolic hydroxyl (Ar-OH) groups with hydrogen-bond forming ability onto the imine COF skeletons, DHBD-Sb-COF exhibited improved hydrophilicity and crystallinity than the parent BD-Sb-COF, the redox-active sites (SbPh3 moieties) in COF electrodes could thus be highly accessed by aqueous electrolyte with a high active-site utilization of 93%. DHBD-Sb-COF//AC provided an excellent supercapacitive performance with an energy density of 78 Wh Kg−1 at the power density of 2553 W Kg−1 and super cycling stability, exceeding most of the previously reported pristine COF electrode-based supercapacitors. The “two-in-one” strategy of introducing hydroxyl groups onto imine COF skeletons to enhance both hydrophilicity and crystallinity provides a new avenue to improve the electrochemical performance of COF-based electrodes for high-performance supercapacitors.

(Invited) Two-Dimensional Layered Materials and Their Mixed-Dimensional Hybrids for Electrochemical Applications

Compared with their 3D counterparts, two-dimensional (2D) van der Waals (vdW) materials exhibit quantum confinement where charge carriers are spatially confined at the physical boundaries. Particularly, when mixing 2D materials with other low-dimensional (LD) materials, they exhibit enormous potential in electrochemical energy applications due to the unique properties arising from reduced dimensionality and, more importantly, material integration synergy.In this work, 2D transition metal dichalcogenides (MoS2) and their mixed low-dimensional hybrids (MLDHs) are introduced with an emphasis on the hybrid structure construction using the one-step solvothermal synthesis technique and their electrochemical applications. Fundamental insight into the synergistic effect of the MLDHs integration in terms of active site exposure, surface area enlargement, electrical conductivity improvement, and structural phase engineering for advancing the development of Li-ion batteries (LIBs) and electrocatalytic hydrogen evolution reaction (HER) will also be discussed. Specifically, in the case of LIBs, 2D-based binary hybrids (i.e., MoS2/MXene) deliver a Li-ion storage capacity of 540 mA h g−1 at 100 mA g−1 and a stable cycle performance up to 300 cycles. In sharp contrast, the 2D-based ternary MLDHs (i.e., MoS2/MXene/CNT) exhibit a higher Li-ion storage capacity (1500 mAh g−1 at 100 mA g−1), outstanding cycle stability (up to 300 cycles) and excellent rate capability (500 mAh g−1 at 4000 mA g−1) as an anode of LIBs. In the case of HER, the MLDH heterostructures show an overpotential of 169 mV with a low Tafel slope of 51 mV/dec and can be cycled to 1000 cycles. Leveraging the unique microreactor platform based on the 2D vdW platform, a mechanistic understanding of charge transport dynamics at the electrified electrode and current collector interface will be highlighted.The knowledge gained on how mixed-dimensional physics and chemistry will shed light on the design principle of the electrode materials for electrochemical energy storage and conversion and deepen the understanding of the process-structural-property-performance (PSPP) relationship of the vdW-based hybrid structures.