Excellent Electrode Material For Supercapacitors Research Articles

Optimizing phosphorene nanosheets for high performance all-solid asymmetric supercapacitors: A theoretical and experimental insight

This study probably for the first-time introduced a phase and morphology-tuned scalable, cost-effective method for large-scale production of Black Phosphorous/Phosphorene (BP), and investigated their in-depth electrochemical properties. Utilizing a one-pot mild wet chemical-assisted hydrothermal route in ethylenediamine, high-quality BP nanosheets were synthesized from amorphous red phosphorus (RP) with nearly 100 % conversion efficiency, yielding 7.1352 g for one batch at 130–170 °C. The resulting phosphorene nanosheets exhibited a small crystalline size (2.708 nm), hierarchically porous morphology, a 1.64 eV direct optical bandgap aligned with theoretically calculated bandgap using LDA approximation, and various structural defects, along with large specific surface area (50 m2g−1) and reduced number of layers (4–5) compared to prior literatures, suggesting electrochemical superiority. CV and GCD measurements in the potential window of −0.7 V to 0.1 V revealed its highest pseudo-capacitance response (84.91 %), reaching a maximum specific capacitance value of 759.748 Fg−1 at current density 2 Ag−1, surpassing all previous records. Moreover, BP displayed excellent cyclic stability of 89.8 % after 10,000 cycles, making it an excellent electrode material for supercapacitors. A solid-state asymmetric supercapacitor device (HASD), using BP, successfully lighted up 6 red LEDs for 10 s, achieving maximum specific energy density at 73.43 Wkg−1 at a power density of 1500 Wkg−1.

Restricted and epitaxial growth of MnO2-x nano-flowers in/out carbon nanofibers for long-term cycling stability supercapacitor electrodes

Carbon nanofibers (CFs) have been widely applied as electrodes for energy storage devices owing to the features of increased contact area between electrodes and electrolyte, and shortened transmission route of electrons. However, the poor electrochemical activity and severe waste of space hinder their further application as supercapacitors electrodes. In this work, MnO2−x nanoflowers restricted and epitaxial growth in/out carbon nanofibers (MnO2/MnO@CF) were prepared as excellent electrode materials for supercapacitors. With the synergistic effect of uniquely designed structure and the introduction of MnO and MnO2 nanoflowers, the prepared interconnected MnO2/MnO@CF electrodes demonstrated satisfactory electrochemical performance. Furthermore, the MnO2/MnO@CF//activated carbon (AC) asymmetric supercapacitor offered an outstanding long-term cycle stability. Besides, kinetic analysis of MnO2/MnO@CF-90 was conducted and the diffusion-dominated storage mechanism was well-revealed. This concept of “internal and external simultaneous decoration” with different valence states of manganese oxides was proven to improve the electrochemical performance of carbon nanofibers, which could be generalized to the preparation and performance improvement of other fiber-based electrodes.

Chemical vapor deposition-based synthesis of binder-free nanostructure α-MoO3 electrode material for PES devices

Molybdenum-based metal oxides have succeeded in incredible consideration for supercapacitor applications due to their outstanding structural, morphological and electrochemical properties. Herein, a highly porous orthorhombic MoO3 (α-MoO3) nanobenzene like nanosheets are synthesized on nickel foam (Ni–F) via a simple and cost-effective chemical vapor deposition (CVD) technique. The x-ray diffraction (XRD) analysis confirmed the synthesis of nanostructured α-MoO3 having multi oriented diffraction planes. The surface morphology (SEM) analysis indicated that the entwined nanobenzene through nano-rods/particles is beneficial for good electrical conductivity hence the high electrochemical performance of synthesized α-MoO3. The electrochemical properties of synthesized α-MoO3 electrode material like cyclic voltammetry (CV), galvanostatic charging–discharging (GCD) and electrochemical impedance spectroscopy (EIS) are analyzed using a three-electrode electrochemical workstation in 2 M KOH electrolyte solution. The synthesized α-MoO3 pseudocapacitor presented a maximum specific capacitance of 3206 F g−1 at a current density of 1 A/g. Moreover, α-MoO3 exhibits a cyclic stability of about 99.95% after 3000 cycles, high energy density (111 Wh kg−1), power density (2500 W kg−1) and negligible charge transfer resistance (0.6 ohms), indicating that it can serve as an excellent electrode material for supercapacitors. The Power law and Dunn’s model simulations also confirmed that the excellent electrochemical performance of synthesized α-MoO3 electrode material is contributed by capacitive as well as diffusion-controlled behavior.

Reinforced electrochemical energy storage through controlled construction of hierarchical hollow β-Ni(OH)2 microspheres enriched with oxygen vacancies induced by functionalized MWCNTs

As promising electrode materials, hollow-structured metallic oxides/hydroxides have attracted extensive attention for their significantly enhanced catalyst and electrochemical performances. In practice, however, it is still challenging to construct well-dispersed hollow structures using facile and versatile template-free methods. And, as a result of the weak conductivity of most metallic oxides/hydroxides, it is a particularly effective means to integrate metallic oxides/hydroxides with carbon-based conductive substrates or introduce oxygen vacancies for further promoting reaction kinetics and achieving boosted electrochemical performance. Herein, a novel composite material consisting of oxygen-rich vacancy β-Ni(OH)2 coupled with oxidized multi-wall carbon nanotubes (Ov-Nβ/Cm) was synthesized using a one-step hydrothermal technique without the need for templates. The hierarchical hollow microsphere structure was achieved by utilizing oxidized multi-wall carbon nanotubes (MWCNTs) as an alternative to conventional surfactants or templates. The uniform distribution of multistage pores in the newly designed Ov-Nβ/Cm composite facilitates the transportation of electrolyte ions, thereby endowing it with outstanding electrochemical performance. A straightforward technique for producing high-quality Ni(OH)2-based electrode materials is presented in this investigation, along with fresh perspectives on the formation mechanism of hollow-structured composites. Developing MWCNT-based hollow nanostructured composites with oxygen vacancies-enriched will offer an essential novel avenue to exploit excellent electrode materials for supercapacitors and other energy storage systems.

Heterostructures of NiFe-MOF/PBAs with high-performance supercapacitors obtained by compounding Prussian blue analogues on bimetallic organic frames

Metal organic framework (MOF) is considered as an excellent electrode material for supercapacitors due to its low cost and homogeneous nanostructure, but the drawbacks of single MOF, such as low specific capacity and stability, limit its development, so the design of bimetallic MOF structural composites is a challenging but favourable strategy for the development of supercapacitors. In this paper, NiFe-MOF/PBAs heterostructure, a bimetallic MOF material with a granular rod-like structure, is successfully prepared by using bimetallic MOF as a precursor and introducing [Co(CN)6]3− ions to further convert it into PBAs (Prussian blue analogs). Due to the special macroporous structure of PBAs, the composite combines the advantages of the two MOF materials, and the specific capacity is as high as 4270.19 C g−1 at 1 A g−1. The composite still has excellent electrochemical properties when assembled into devices. The specific capacity is 1996.01 C g−1 at 1 A g−1, the energy density reached 749.99 W h kg−1 at a power density of 415.85 W kg−1, and the decay rate is only 1.14 % after 20,000 cycles at 10 A g−1. These results indicate that the designed dual MOFs composite electrodes have good application prospects in the field of electrochemical energy storage.

Graphene-supported Cu2O-CoO heterojunctions for high performance supercapacitors

Transition metal oxides are excellent electrode materials for supercapacitors because of their high theoretical capacitance, good stability, environmental friendliness, and tunable structure. In this study, Cu2O-CoO heterojunction materials loaded on graphene oxide (Cu2O-CoO/GO) are prepared via the precipitation, hydrothermal, and heat treatment processes. Through the adsorption of transition metal ions by the oxygen-containing functional groups of GO, followed by alkali titration as well as hydrothermal reaction of Cu2+ and Co2+ ions, the hydroxides of metals are adsorbed on GO. Meanwhile, the reduced GO completes the self-assembly, and the GO with good spatial structure supports the formation of Cu2O-CoO heterojunction structure. The Cu2O-CoO/GO electrode material combines the high conductivity of GO with the excellent internal conductivity of Cu2O-CoO, and its abundant active sites and specific surface area, thereby ensuring good electrochemical performance. Thus, it enables reversible ion adsorption and desorption, exhibits the pseudocapacitance of copper oxide and cobalt oxide, and has higher capacitance performance than Cu2O/GO and CoO/GO electrodes. The specific capacitance of Cu2O-CoO/GO at 1 A g−1 is 723 F g−1. Cu2O-CoO/GO/ASC exhibits an energy density of 44.1 Wh kg−1 at 794 W kg−1 and capacitance retention rate of 89.3 % after 10,000 cycles. This indicates that the material has significant potential for a wide range of supercapacitor applications.

A rational preparation strategy of phase tuned MoO3 nanostructures for high-performance all-solid asymmetric supercapacitor

In this work, phase and morphology-tuned MoO3 nanostructures are synthesized through a novel modified co-precipitation method, and their electrochemical properties are investigated. For the first time, such a simple surfactant-assisted synthesis process aided by minor temperature variations is reported which results in phase transition of the nanoparticles from h-MoO3 nano-rods to α-MoO3 nano-flakes. The nanostructures thus developed are highly porous and crystalline with significantly large specific surface area as compared to previous literature. The theoretical bandgap energy of the optimized sample calculated using Perdew-Zunger local density approximation (LDA) is in good agreement with the experimental findings. An overall structural, morphological, and surface-behavioural analysis predicts the electrochemical superiority in 2D α-MoO3. The cyclic voltammetry and galvano-potentiometry measurements of 2D α-MoO3 in the potential window of −0.6 V to +0.2 V present the highest pseudo-supercapacitive response with a maximum specific capacitance of 829 F g−1 at 2 A g−1 as compared to h-MoO3 (452 F g−1) and h@α-MoO3(783 F g−1). Thus, the MoO3 2D nanostructures synthesized through our novel synthesis technique display excellent specific capacitance as compared to previous reported data. Additionally, α-MoO3 exhibits a galvanostatic charging-discharging cyclic stability of about 91% after 2000 cycles, indicating that it can serve as an excellent electrode material for supercapacitors. A solid-state asymmetric supercapacitor device is successfully constructed using α-MoO3 which can light up 4 red LEDs for 10 s. The specific energy density of the device reaches a maximum value of 36.3 W h kg−1 at the power density of 50 W kg−1.

Construction of Well-Defined Two-Dimensional Architectures of Trimetallic Metal-Organic Frameworks for High-Performance Symmetric Supercapacitors.

The high surface-to-volume ratio and extraordinarily large-surface area of two-dimensional (2D) metal-organic framework (MOF) architectures have drawn particular interest for use in supercapacitors. To achieve an excellent electrode material for supercapacitors, well-defined 2D nanostructures of novel trimetallic MOFs were developed for supercapacitor applications. Multivariate MOFs (terephthalate and trimesate MOF) with distinctive nanobrick and nanoplate-like structures were successfully synthesized using a straightforward one-step reflux condensation method by combining Ni, Co, and Zn metal species in equimolar ratios with two different ligands. Furthermore, the effects of the tricarboxylic and dicarboxylic ligands on cyclic voltammetry, charge-discharge cycling, and electrochemical impedance spectroscopy were studied. The derived terephthalate and trimesate MOFs are supported with stainless-steel mesh and provide a suitable electrolyte environment for rapid faradaic reactions with an elevated specific capacity, excellent rate capability, and exceptional cycling stability. It shows a specific capacitance of 582.8 F g-1, a good energy density of 40.47 W h kg-1, and a power density of 687.5 W kg-1 at 5 mA cm-2 with an excellent cyclic stability of 92.44% for 3000 charge-discharge cycles. A symmetric BDC-MOF//BDC-MOF supercapacitor device shows a specific capacitance of 95.22 F g-1 with low capacitance decay, high energy, and power densities which is used for electronic applications. These brand-new trimetallic MOFs display outstanding electrochemical performance and provide a novel strategy for systematically developing high-efficiency energy storage systems.

A dual-template strategy assisted synthesis of porous coal-based carbon nanofibers for supercapacitors

The electrospun carbon nanofibers (ECNFs) with the advantages of facile preparation method, excellent electrical conductivity and ease compounding are expected to be excellent electrode materials for supercapacitors. However, the tiny specific surface area and low specific capacitance prevent the further development of carbon nanofibers. In this work, the porous coal-based carbon nanofibers (PCCNFs-2) are fabricated via a facile dual-template method, which can be directly employed as a flexible electrode material for supercapacitors without the addition of any conductive agents and binders. As a result, the flexible self-supporting electrode (PCCNFs-2) achieves a specific capacitance of 262.0 F g−1 at a current density of 1 A g−1, excellent rate performance (81.0 % capacitance retention at a current density of 20 A g−1) and excellent cycling stability (after 10,000 cycles, 124 % capacity retention at 2 A g−1). Furthermore, the aqueous symmetrical supercapacitors (SCs) assembled with melamine foam as the storage electrolyte at an operating voltage of 1.2 V achieved an energy density of 18.5 Wh kg−1 at a power density of 150.5 W kg−1. The effective construction of this porous carbon nanofiber assures the structural integrity and achieves excellent electrochemical performance of the electrode material, which develops a new strategy for efficient utilization of porous coal-based carbon nanofibers in supercapacitors.

Activated carbon nanofibers derived from polyimides containing aryl imidazole and hydroxyl groups for high-performance supercapacitors

In this work, the carbon nanofibers (CNFs) are first prepared by electrospinning the poly(amic acid) (PAA) solution containing aryl imidazole and hydroxyl groups, followed by thermal imidization, rearrangement and carbonization. Then, the CNFs are further treated with KOH to obtain activated CNFs. The effects of the PAA concentration, rearrangement time, carbonation temperature and mass ratio of CNFs/KOH on the electrochemical properties are investigated. The results show that the sample HPI-CNF-20-2-800 displays the best electrochemical performance. After activation, the A-HPI–CNF–1/3 exhibits a maximum specific surface area of 1762 m2 g−1 and pore volume of 0.92 cm3 g−1, leading to a high specific capacitance of 325.0 F g−1 at 0.5 A g−1. Moreover, the specific capacitance can reach 234.6 F g−1 when the current density is 20 A g−1. Furthermore, the symmetric supercapacitor fabricated by A-HPI–CNF–1/3 shows a maximum energy density of 29.17 Wh kg−1, coupled with a power density of 500.0 W kg−1. The capacitance retention rate of the supercapacitor maintains about 99.95% after 20,000 charge-discharge cycles at 1 A g−1. Therefore, this work provides a novel rearrangeable precursor for the preparation of activated CNFs with a considerable electrochemical performance, which will be considered as excellent electrode materials for supercapacitors.

Preparation of self-supporting NiCoP/graphene materials and their performance of supercapacitors

The NiCoP material directly grown on the nickel foam substrate was prepared by hydrothermal method and low temperature phosphating method, NiCoP was directly grown on the conductive current collector to make an adhesive-free electrode, and rGO was used as a conductive network to cover the surface of the active material to form a self-supporting structure composite electrode, denoted as NiCoP/rGO-NF. The results show that the NiCoP/rGO-NF electrode has a specific capacitance of 2137.8 F g−1 (at 1 A g−1 current density), while NiCoP/rGO-NF still maintains a specific capacitance of 86.5 % after 10,000 cycles at a current density of 5 A g−1. The assembled ASC device has an energy density of 54.25 W h kg−1 at a power density of 750 W kg−1. At a current density of 5 A g−1, NiCoP/rGO-NF//AC showed a capacity retention rate of 87.3 % after 10,000 cycles, indicating that the prepared NiCoP/rGO-NF greatly improved the electrical conductivity of the material and the conductivity in contact with the electrolyte area, has the potential as an excellent electrode material for supercapacitors.

A multi-layer-structured nickel-based electrode for high-performance binder-free asymmetric quasi-solid-state hybrid supercapacitors

A novel multi-layer-structured NiMn LDH/rGO/Ni(OH)2@Ni foam (LRN@NF) is synthesized by a method combining hydrothermal and dip-coating processes, acting as an excellent electrode material for supercapacitors. The specific multi-layer structure and synergism of all the components boosts the electrochemical performance. Microstructural characterization illustrates the successful formation of the multi-layer structure and also demonstrates the important role of the incorporated graphene layers for the growth of NiMn LDH. The NiMn LDH/rGO/Ni(OH)2@Ni foam shows a high specific capacity of 7.49C·cm−2 (specific capacitance of 14.40 F·cm−2) at 1 mA·cm−2. Furthermore, the asymmetric quasi-solid-state hybrid supercapacitor (LRN@NF//AC; AC represents activated carbon) exhibits a high specific energy density of 0.23 mWh·cm−2 at a specific power density of 0.91 mW·cm−2 with a voltage window of 1.6 V, and 0.12 mWh·cm−2 of energy density can be maintained even at 64.04 mW·cm−2. Therefore, the LRN@NF electrode is suggested to be a promising candidate for high-performance supercapacitors, and our research also demonstrates the feasibility and universality of the construction idea for excellent multi-layer-structured supercapacitor electrodes.

Design of hierarchical porous carbon nanofibrous membrane for better electrochemical performance in solid-state flexible supercapacitors

The pore structure dramatically influences the electrochemical behavior of carbon nanofibers. The electrochemical performance of flexible carbon nanofibers as electrode materials for supercapacitors can be controlled by changing the size and quantity of pores. Hollow porous carbon nanofibers (HPCNFs) are prepared by coaxial electrostatic spinning and high-temperature carbonization. According to the nitrogen adsorption/desorption curve, HPCNF has a large specific surface area and good pore size distribution. In addition, cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) are used to analyze the electrochemical performance of HPCNF. Results show that the specific capacitance of hollow porous carbon nanofibers is 168.8 F/g at the current density of 1 A/g. Moreover, the specific capacitance retention of HPCNF is 95.61 % after 2000 cycles of charge and discharge at the current density of 5 A/g, exhibiting a stable cycle performance. In addition, solid-state supercapacitors assembled without any adhesives or conductive agents also show good cycle stability and excellent flexibility. As a result, HPCNF with flexibility, high specific surface area, and excellent electrochemical performance has broad prospects as an excellent electrode material for supercapacitors. Therefore, HPCNF has the advantages of good flexibility, high specific surface area, and excellent electrochemical performance. This paper proposes reasonable methods and creates more possibilities for future research and the application of flexible electrode materials for supercapacitors and flexible wearable electronic devices. • Different levels of hierarchical porous carbon nanofibrous membranes are constructed. • The effect of pores in carbon nanofibers on electrochemical performance are deeply studied. • Symmetric solid-state supercapacitors exhibit excellent stability and flexibility. • The charge distribution in supercapacitor are simulated by finite element method.

Hydrothermally grown MnO2 composite nanospheres as an excellent electrode material for supercapacitors

Hydrothermally grown MnO2 composite nanospheres as an excellent electrode material for supercapacitors

Highly porous carbon material from polycyclodextrin for high-performance supercapacitor electrode

Using low-cost biomass to develop ultra-high specific surface area carbon electrode materials for supercapacitors is very important, but it is still challenging. In this paper, using the “bottom-up” idea and starting from the hydrolysate of starch, highly porous carbon material is fabricated by simple polymerization of β-cyclodextrin (CD) and chemical activation. The obtained material shows a maximum specific surface area (SSA) up to 3710 m2 g−1 and pore volume of 2.03 cm3 g−1. Thanks to the hierarchical porous structure and ultra-high specific surface area, the carbon based supercapacitors demonstrates high capacitance of 416 F g−1 at 0.5 A g−1 and excellent cycling stability of 100 % capacity retention after 10,000 cycles in 6.0 M KOH electrolyte system. Furthermore, an attractive energy density of 23.4 Wh kg−1 at a power density of 224.9 W kg−1 in 1.8 V Na2SO4 electrolyte system can be delivered. The polycyclic dextrin based porous carbon reported in this paper has better electrochemical performance than most carbon based electrode materials reported today, which provides a feasible synthetic method for the synthesis of excellent supercapacitor electrode materials.

Room-temperature solution-processed sharp-edged nanoshapes of molybdenum oxide for supercapacitor and electrocatalysis applications

We introduce a simple room-temperature (25–27 °C) solution process-inspired approach for obtaining sharp-edged nanoshapes like nanocubes, nanorods and nanoparticles of molybdenum oxide (MoO3) on a stainless-steel conducting substrate for supercapacitor and electrocatalysis applications. The nanoshape of MoO3 has strikingly been changed from nanocubes to nanopaticles dependig on HCl concentration. The MoO3 electrodes of different morphologies are systematically characterized by various characterization techniques for confirming phase, structure, and surface elementals. The electrochemical studies exhibit significant enhancement in specific capacitance and oxygen evolution reaction (OER) activity for MoO3 nanorod-based electrode. The specific capacitance of 2561.53 F g−1 for MoO3 nanorods is much higher than 608.20 F g−1 and 400.28 F g−1 for nanocubes and nanoparticles, respectively. Besides, with the 98.59% capacitance retention up to 2000 cycles, the electrode consisting nanorods is found to be highly stable. In the commercial point of view, the as-fabricated MoO3//MoO3 symmetric device adduces excellent energy/power density (69.06 Wh kg−1/1336.63 W Kg−1) at current density of 1 A g−1. The laboratory panel, Center for Nanomaterials & Energy Devices, containing nearly 42 LEDs has been ignited with full intensity using MoO3//MoO3 symmetric device as the practical demonstration of electrode material. From supercapacitor study, the MoO3 nanorod-based electrode endows excellent OER activity (overpotential of 246 mV; Tafel slope of 36 mV dec-1). In both cases, the MoO3 nanorod-based electrode produces excellent chemical and cyclic stability. Overall electrochemical results demonstrate that the MoO3 nanorod-based electrode would be excellent electrode material for supercapacitor as well as OER applications. The proposed room-temperature solution synthesis process is valuable and well effective in view of trouble-free, cost-effective, and scalability for commercial benefits.

All‐Solid‐State Flexible Symmetric Supercapacitor Based on Morphology Oriented Amorphous Cu−Co−B Alloy Nanosheets for Energy Storage

AbstractMetastable amorphous alloys having 2‐dimensional morphology are expected to be an excellent electrode materials for supercapacitors because of their defect rich nature, high degree of compositional as well as topological disorder and internal stresses. Herein, we investigated and demonstrated a new series of Cu−Co−B amorphous alloy nanosheets for energy storage. A clear and significant energy storage improvement by this Cu−Co−B nanosheets over the state‐of‐the‐art materials and flexible devices are manifested. Among the as‐synthesized materials, CuCo2B nanosheets exhibits an excellent specific capacity of 3503.6 F g−1 (389.2 mAh g−1) and a 99 % (at 50 A g−1) retention rate after 3000 cycles. An all‐solid state flexible symmetric Cu−Co−B|[EMIM][BF4] supercapacitor device (0–180° bending, 2.5 V) demonstrates a high energy density of 90.2 Wh kg−1, specific capacity (289.2 mAh g−1), power density (4623.6 W kg−1) and prolonged cycling stability (89 %) and Coulombic efficiency (104 %) over 10000 charge‐discharge cycles.

A novel 3D MnNi2O4@MnNi2S4 core-shell nano array for ultra-high capacity electrode material for supercapacitors

In this work, a novel 3D MnNi2O4@MnNi2S4 core-shell nano array was successfully grown on nickel foam (NF) via in-situ growth method, which omitted the addition of binder and conductive additive and the complicated electrode preparation process. The MnNi2O4@MnNi2S4 possesses a unique nanorod@nanosheet core-shell structure, which can provide abundant active sites near the electrode interface for rapid electrochemical reaction, so the MnNi2O4@MnNi2S4 electrode materials exhibit high specific capacitance and excellent electrochemical properties. It is worth noting that the specific capacitance of the MnNi2O4@MnNi2S4 reaches 3578.57 F g−1 at the current density of 1 A g−1, and 1009.52 F g−1 at the current density of 20 A g−1. When the current density is 15 A g−1, the specific capacitance retention rate reaches 93.1% after 5000 cycles, showing good cycling performance. Moreover, the MnNi2O4@MnNi2S4//AC asymmetric device also exihibits low leakage current and excellent self-discharge characteristics. So, the MnNi2O4@MnNi2S4 is an excellent electrode material for supercapacitors.

One‐Pot Green Process to Synthesize MXene with Controllable Surface Terminations using Molten Salts

AbstractSurface terminations of two‐dimensional MXene (Ti3C2Tx) considerably impact its physicochemical properties. Commonly used etching methods usually introduce ‐F surface terminations or metallic impurities in MXene. We present a new molten‐salt‐assisted electrochemical etching method to synthesize fluorine‐free Ti3C2Cl2. Using electrons as reaction agents, cathode reduction and anode etching can be spatially isolated; thus, no metallics are present in the Ti3C2Cl2 product. The surface terminations can be in situ modified from −Cl to −O and/or −S, which considerably shortens the modification steps and enriches the variety of surface terminations. The obtained −O‐terminated Ti3C2Tx are excellent electrode materials for supercapacitors, exhibiting capacitances of 225 F g−1 at 1.0 Ag−1, good rate performance (91.1 % at 10 Ag−1), and excellent capacitance retention (100 % after 10000 charge/discharge cycles at 10 Ag−1), which is superior to multi‐layered Ti3C2Tx prepared by other etching methods.

One-Pot Green Process to Synthesize MXene with Controllable Surface Terminations using Molten Salts.

Surface terminations of two-dimensional MXene (Ti3 C2 Tx ) considerably impact its physicochemical properties. Commonly used etching methods usually introduce -F surface terminations or metallic impurities in MXene. We present a new molten-salt-assisted electrochemical etching method to synthesize fluorine-free Ti3 C2 Cl2 . Using electrons as reaction agents, cathode reduction and anode etching can be spatially isolated; thus, no metallics are present in the Ti3 C2 Cl2 product. The surface terminations can be in situ modified from -Cl to -O and/or -S, which considerably shortens the modification steps and enriches the variety of surface terminations. The obtained -O-terminated Ti3 C2 Tx are excellent electrode materials for supercapacitors, exhibiting capacitances of 225 F g-1 at 1.0 Ag-1 , good rate performance (91.1 % at 10 Ag-1 ), and excellent capacitance retention (100 % after 10000 charge/discharge cycles at 10 Ag-1 ), which is superior to multi-layered Ti3 C2 Tx prepared by other etching methods.