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Transition metal nitrides (TMNs) are promising electrode materials for high-performance energy storage devices owing to their excellent conductivity, thermal stability, high theoretical capacity and excellent electrochemical activity. However, the structural instability present in the electrochemical reaction process significantly limits their widespread application. Herein, we present a V–Ni-based nitride heterojunction on carbon cloth (VN/Ni3N–Ni/CC) as an active electrode material for flexible supercapacitors. The VN/Ni3N–Ni/CC composite electrode was successfully fabricated through controllable nitridation of the corresponding vanadium–nickel oxide grown on carbon cloth (V–Ni–O/CC) precursors. The electrochemical results reveal that the areal capacitance of the VN/Ni3N–Ni/CC based supercapacitor with a nitriding temperature of 400 °C and a nitriding time of two hours can achieve a maximum areal capacitance of 845.63 mF cm−2 at a current density of 0.5 mA cm−2, and the electrode in the three-electrode system retains 86.1% of its initial capacitance value after 1500 cycles at a current density of 10 mA cm−2. In addition, the assembled flexible all-solid-state symmetric supercapacitor using the VN/Ni3N–Ni/CC electrode exhibits an areal capacitance ratio of 19.1 mF cm−2 at a current density of 0.4 mA cm−2 and excellent cycling stability. Moreover, it displays exceptional flexibility under different bending angles highlighting its potential for integration into flexible electronic devices. [ABSTRACT FROM AUTHOR]

Amorphous vanadyl phosphate/graphene nanohybrids is successfully synthesized by first exfoliating bulk layered vanadyl phosphate (VOPO 4 ·2H 2 O) into nanosheets, and then hydrothermal treatment with graphene oxide (GO). The electrochemical properties of the resulted materials are systematically investigated. It is found that a phase transformation from crystalline to amorphous is occurred to VOPO 4 ·2H 2 O. As supercapacitor electrode material, the amorphous VOPO 4 /graphene composite exhibits a high specific capacitance (508 F g −1 at 0.5 A g −1 ), an excellent rate capability (359 F g −1 at 10 A g −1 ), and a good cycling stability (retention 80% after 5000 cycles at 2 A g −1 ). Particularly, it simultaneously has a greatly enhanced energy density of 70.6 Wh·kg −1 with a power density of 250 W kg −1 . The outstanding energy storage performance mainly originates from the generation of amorphous VOPO 4 phase that facilitates ion transport by shortening ion diffusion paths and provides more reversible and fast faradic reaction sites, the hybridization with graphene that greatly improves the electric conductivity and structure stability, and the unique layer-on-sheet nanohybrid structure that effectively enhances the structure integrity. This work not only provides a facile method for the preparation of amorphous VOPO 4 /graphene composites, but also demonstrates the enhanced energy density and rate capability of amorphous VOPO 4 -based materials for potential application in supercapacitors. [ABSTRACT FROM AUTHOR]

Graphene/CoO nanocomposites with different morphologies were fabricated by hydrothermal method. The morphology of nanocomposites was characterized by scanning electron microscopy. These composites could be used as the electrode materials for supercapacitors. The eletrochemical behavior of the composite was tested by cyclic voltammetry and galvanostatic charge-discharge measurements in 1.0 mol/L KOH solution. The results showed that the graphene/CoO nanopetal composite exhibited excellent electrochemical performance. The specific capacitance value could reach up to 714 F/g at a scan rate of 2 mV/s. Besides, the capacitance of the graphene/CoO nanopetal composite was 841 F/g at a current density of 0.1 A/g. After galvanostatic charge-discharge 1000 laps at the current density of 0.4 A/g, the specific capacitance could keep 96.7% of original capacitive value, demonstrating its good cycling stability. Graphical Abstract: [ABSTRACT FROM AUTHOR]

A ternary nanocomposite of graphene/polyaniline (PANI)/porous silica MCM-41 (MCM-41) was prepared by a hydrothermal method. The amount of graphene oxide (GO) in the graphene/PANI/MCM-41 nanocomposite had a strong effect on the supercapacitor performance. The experimental results showed that the specific capacitance of the graphene/PANI/MCM-41 nanocomposite could reach the highest value when the GO content was 50%. The specific capacitance of the nanocomposite was 405 F g−1 at a current density of 0.8 A g−1. Furthermore, over 91.4% of the original capacitance was retained after repeating the galvanostatic charge–discharge for 1000 cycles. The performance of the prepared supercapacitor containing different amounts of GO were studied in detail. [ABSTRACT FROM AUTHOR]

• The NiMn-MOFs-Ⅱ flexible electrodes have been prepared by one-step electrochemical deposition method. • The specific capacity of NiMn-MOFs-Ⅱ electrode is 2225.7 mF cm−2 at a current density of 2 mA cm−2. • The assembled flexible all-solid-state supercapacitor has obtained a high energy density of 0.76 mWh cm−2 at a power density of 75.7 mW cm−2. • The supercapacitor device prepared with the NiMn-MOFs-Ⅱ electrode exhibits outstanding cycling stability, with an initial capacitance retention of 81.9 % after 12,000 cycles at a current density of 2 mA cm−2. Metal-organic frameworks (MOFs) have significantly emerged as pioneering electrode materials in recent years for their exceptional properties, particularly in the field of supercapacitor applications. In this work, bimetallic NiMn-MOFs have been prepared onto carbon cloth (NiMn-MOFs/CC) via electrodeposition method. The obtained NiMn-MOFs are uniformly dispersed on the CC substrate, that can be served as an electrode material for flexible all-solid-state supercapacitors directly. The NiMn-MOFs/CC electrode indicates the greatest electrochemical performances when the molar ratio of Ni/Mn was 2:1. In a standard three-electrode system, the examined sample was subjected to a discharge current density of 15 mA cm−2, the area-specific capacitance of the NiMn-MOFs/CC electrode material was determined to be 2049.7 mF cm−2, with an impressive capacity retention of 87.38 % observed after 2000 cycles. Remarkably, the symmetric supercapacitor device constructed using NiMn-MOFs/CC, demonstrated outstanding flexibility, and remarkable long-term cycling stability. Even after 12,000 cycles, the initial specific capacitance of the device retained 81.9 %. Furthermore, the micro-device exhibited the capability to power a light-emitting diode (LED), demonstrating the practical energy storage applications of this electrode. [ABSTRACT FROM AUTHOR]

• TiO 2 /Ti 3 C 2 T x heterostructure was first synthesized through a facile and cost-effective aqueous self-assembly. • TiO 2 /Ti 3 C 2 T x heterostructure demonstrates enhanced specific capacity, outstanding rate capability and excellent cyclic stability. • TiO 2 /Ti 3 C 2 T x exhibits pseudocapacitive behavior which endows it with fast lithium storage kinetics. • TiO 2 /Ti 3 C 2 T x //CPC LIC obtains a wide operating voltage range and delivers an exceptionally high energy density (129.4 Wh·kg−1). Li ion capacitors (LICs) are such a kind of novel energy storage systems that possess the advantage of high energy density of batteries and high power density as well as long cycle life of capacitors. Here, TiO 2 /Ti 3 C 2 T x (MXene) heterostructure is prepared by a general ex situ route to the simple self-assembly of TiO 2 nanoparticles on Ti 3 C 2 T x nanosheets through van der Waals interactions. The obtained TiO 2 /Ti 3 C 2 T x heterostructure demonstrates enhanced specific capacity (304 mAh·g−1 at 100 mA·g−1), outstanding rate capability (∼120 mAh·g−1 at 2 A·g−1) and excellent cyclic stability due to the morphological and functional synergy of the two building blocks. Then, a novel LIC is successfully constructed utilizing TiO 2 /Ti 3 C 2 T x as anode and carrot-derived porous carbon (CPC) as cathode. The assembled TiO 2 /Ti 3 C 2 T x //CPC LIC owns a wide operating voltage window of 0–4.0 V, demonstrating an exceptionally high energy density (129.4 Wh·kg−1), a high power density (10 kW·kg−1), a rather good cycling stability with a capacitance retention of 77 % after 10,000 cycles at 1 A·g−1. This strategy can be applied to controllably prepare general transition metal oxide (TMO) nanostructures on the MXene nanosheets with a fast faradaic reaction. [ABSTRACT FROM AUTHOR]