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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]

• 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]

A new strategy is proposed for the preparation of Fe 3 O 4 encapsulated in N-doped carbon (denoted as Fe 3 O 4 @NC) through a self-assembly of the colloidal FeOOH with polyaniline (PANI) and then a subsequent pyrolysis. Benefiting from the well-designed heterostructure, the resultant Fe 3 O 4 @NC shows an ultra-high gravimetric capacitance of 313 F g−1 at 1 A g−1 and still delivers 193 F g−1 at a high current density of 15 A g−1, demonstrating an excellent rate performance. In addition, it has an outstanding volumetric capacitance of 20.25 F cm−3 at 1 A g−1. The asymmetric supercapacitors (ASCs) are constructed by using Fe 3 O 4 @NC as anode and layered double hydroxides (LDHs) as cathode, respectively. Due to the enlarged voltage window and matched capacity and kinetics, the obtained CoMn-LDH//Fe 3 O 4 @NC ASC device shows a remarkable electrochemical performance with a large energy density up to 35 Wh·kg−1 at a power density of 900 W kg−1 and a high energy density of 24 Wh·kg−1 at a power density of 13.5 kW kg−1 as well as an excellent rate capability and a good cycling stability. The present work may provide an insight into the design of novel anode materials for high-performance ASCs. Image 1 • A two-step approach to prepare nitrogen-doped carbon encapsulated iron oxide. • Fe 3 O 4 @NC has high electronic conductivity and hierarchical porous structure. • Fe 3 O 4 @NC exhibits superior electrochemical performance as anode material. • CoMn-LDH//Fe 3 O 4 @NC ASC obtains a 1.8 V voltage window and high energy density. • The key to fabricate perfect ASCs is proper matching of capacity and kinetics. [ABSTRACT FROM AUTHOR]