A ceramic-powder polymer composite, making use of a relaxor ferroelectric polymer that has a high room-temperature dielectric constant as the matrix, is developed. The experimental data show that the dielectric constant of the composites with Pb(Mg1/3Nb2/3)O3–PbTiO3 powders can reach more than 250 with weak temperature dependence. In addition, the composites under a proper preparation procedure exhibit a high breakdown field strength (>120 MV/m), leading to a maximum energy storage density of more than 15 J/cm3. Experimental results also indicate that the high electron irradiation does not have much effect on the dielectric behavior of Pb(Mg1/3Nb2/3)O3–PbTiO3 powders, possibly due to the relaxor nature of the ceramic.
2D MXene materials are of considerable interest for future energy storage. A MXene film could be used as an effective flexible supercapacitor electrode due to its flexibility and, more importantly, its high specific capacitance. However, although it has excellent electronic conductivity, sluggish ionic kinetics within the MXene film becomes a fundamental limitation to the electrochemical performance. To compensate for the relative deficiency, MXene films are frequently reduced to several micrometer dimensions with low mass loading (<1 mg cm−2), to the point of detriment of areal performance and commercial value. Herein, for the first time, the design of a 3D porous MXene/bacterial cellulose (BC) self‐supporting film is reported for ultrahigh capacitance performance (416 F g−1, 2084 mF cm−2) with outstanding mechanical properties and high flexibility, even when the MXene loading reaches 5 mg cm−2. The highly interconnected MXene/BC network enables both excellent electron and ion transport channel. Additionally, a maximum energy density of 252 µWh cm−2 is achieved in an asymmetric supercapacitor, higher than that of all ever‐reported MXene‐based supercapacitors. This work exploits a simple route for assembling 2D MXene materials into 3D porous films as state‐of‐the‐art electrodes for high performance energy storage devices.
MXenes have attracted great interests as supercapacitors due to their metallic conductivity, high density, and hydrophilic nature. Herein we report Ti3C2‐Cu/Co hybrids via molten salt etching in which the existence of metal atoms and their interactions with MXene via surficial O atoms were elucidated by XAFS for the first time. The electrochemical investigation of Ti3C2‐Cu electrode demonstrated the pseudocapacitive contribution of Cu and a splendid specific capacitance of 885.0 F g−1 at 0.5 A g−1 in 1.0 M H2SO4. Symmetric supercapacitor Ti3C2‐Cu//Ti3C2‐Cu was demonstrated with operating voltage of 1.6 V, areal capacitance of 290.5 mF cm−2 at 1 mA cm−2, and stability over 10 000 cycles. It delivered an areal energy density of 103.3 μWh cm−2 at power density of 0.8 mW cm−2, based on which a supercapacitor pouch was fabricated. It provides deeper insights into the molten salt mechanism and strategies for designing MXene‐based materials for electrochemical energy storage.
In this study, we propose a versatile method for synthesizing uniform three-dimensional (3D) metal carbides, nitrides, and carbonitrides (MXenes)/metal-organic frameworks (MOFs) composites (Ti 3 C 2 T X /Cu-BTC, Ti 3 C 2 T X / Fe,Co-PBA, Ti 3 C 2 T X /ZIF-8, and Ti 3 C 2 T X /ZIF-67) that combine the advantages of MOFs and MXenes to enhance stability and improve conductivity. Subsequently, 3D hollow Ti 3 C 2 T X /ZIF-67/CoV 2 O 6 composites with excellent electronand ion-transport properties derived from Ti 3 C 2 T X /ZIF-67 were synthesized. The specific capacitance of the Ti 3 C 2 T X / ZIF-67/CoV 2 O 6 electrode was 285.5 F g À 1 , which is much higher than that of the ZIF-67 and Ti 3 C 2 T X /ZIF-67 electrode. This study opens a new avenue for the design and synthesis of MXene/MOF composites and complex hollow structures with tailorable structures and compositions for various applications.
The controllable synthesis of metal-based nanoclusters for heterogeneous catalytic reactions has received considerable attention. Nevertheless, manufacturing these architectures, while avoiding aggregation and retaining surface activity, remains challenging. Herein, for the first time we designed NiCoFe-Prussian blue analogue (PBA) nanocages as a support for in situ dispersion and anchoring of polymetallic phosphide nanoparticles (pMP-NPs). Benefiting from the porous surfaces and the synergistic effects between pMP-NPs and the cyano groups in PBA, the NiCoFe-P-NP@NiCoFe-PBA nanocages exhibit a significantly enhanced catalytic activity for oxygen evolution reaction (OER) with an overpotential of 223 mV at 10 mA cm–2 and a Tafel slope of 78 mV dec–1, outperforming the NiCoFe-PBA nanocubes, NiCoFe-P nanocages, NiFe-P-NP@NiFe-PBA nanocubes, and CoFe-P-NP@CoFe-PBA nanoboxes. This work not only offers the synthesis strategy of in situ anchoring pMP-NPs on PBA nanocages but also provides a new insight into optimized Gibbs free energy of OER by regulating electron transfer from metallic phosphides to PBA substrate.
Oxygen-deficient bismuth oxide (r-Bi 2 O 3 )/graphene (GN) is designed, fabricated, and demonstrated via a facile solvothermal and subsequent solution reduction method. The ultrafine network bacterial cellulose (BC) as substrate for r-Bi 2 O 3 /GN exhibits high flexibility, remarkable tensile strength (55.1 MPa), and large mass loading of 9.8 mg cm −2 . The flexible r-Bi 2 O 3 /GN/ BC anode delivers appreciable areal capacitance (6675 mF cm −2 at 1 mA cm −2 ) coupled with good rate capability (3750 mF cm −2 at 50 mA cm −2 ). In addition, oxygen vacancies have great influence on the capacitive performance of Bi 2 O 3 , delivering significantly improved capacitive values than the untreated Bi 2 O 3 flexible electrode, and ultrahigh gravimetric capacitance of 1137 F g −1 (based on the mass of r-Bi 2 O 3 ) can be obtained, achieving 83% of the theoretical value (1370 F g −1 ). Flexible asymmetric supercapacitor is fabricated with r-Bi 2 O 3 /GN/BC and Co 3 O 4 /GN/BC paper as the negative and positive electrodes, respectively. The operation voltage is expanded to 1.6 V, revealing a maximum areal energy density of 0.449 mWh cm −2 (7.74 mWh cm −3 ) and an areal power density of 40 mW cm −2 (690 mW cm −3 ). Therefore, this flexible anode with excellent electrochemical performance and high mechanical properties shows great potential in the field of flexible energy storage devices.
based on connecting central metal atoms/ clusters and organic ligands, have attracted considerable attention.  MOFs can be rationally designed by modifying their constituting metal atoms/clusters and organic ligands, allowing a control of their shapes and sizes.  Shapes are typically controlled by introducing modulators (cosolvents or surfactants) that preferentially adsorb onto specific crystal planes, consequently hampering their growth. Furthermore, the size can be adjusted by changing the solvent ratio or reaction time. For these reasons, MOFs are endowed with outstanding properties and potential applications, such as in sensors,  electrocatalysis, [8,9] and energy-storage devices. [10,11] The porous structure of MOFs makes them promising host materials to anchor sulfur in Li-S batteries, and this has attracted considerable attention because of their high theoretical capacity (1675 mAh g −1 ). [12,13] The main obstacle to impede commercialization of Li-S batteries is the shuttle effect, leading to an irreversible loss of sulfur during the discharge process.  At present, a variety of carbonaceous materials have been adopted as host materials to enable uniform dispersion of sulfur.  However, the physical confinement of lithium polysulfides (LPS, chemical formula: Li 2 S x , 4 ≤ x ≤ 8) in nonpolar carbonaceous materials is not sufficient to prevent Metal-organic frameworks (MOFs) with controllable shapes and sizes show a great potential in Li-S batteries. However, neither the relationship between shape and specific capacity nor the influence of MOF particle size on cyclic stability have been fully established yet. Herein, MIL-96-Al with various shapes, forming hexagonal platelet crystals (HPC), hexagonal bipyramidal crystals (HBC), and hexagonal prismatic bipyramidal crystals (HPBC) are successfully prepared via cosolvent methods. Density functional theory (DFT) calculations demonstrate that the HBC shape with highly exposed (101) planes can effectively adsorb lithium polysulfides (LPS) during the charge/discharge process. By changing the relative proportion of the cosolvents, HBC samples with different particle sizes are prepared. When these MIL-96-Al crystals are used as sulfur host materials, it is found that those with a smaller size of the HBC shape deliver higher initial capacity. These investigations establish that different crystal planes have different adsorption abilities for LPS, and that the MOF particle size should be considered for a suitable sulfur host. More broadly, this work provides a strategy for designing sulfur hosts in Li-S batteries.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202107836.
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