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Morphological control of metal-organic frameworks (MOFs) at the micro/nanoscopic scale is critical for optimizing the electrochemical properties of them and their derivatives. In this study, manganese organic phosphate (Mn-MOP) with three distinct two-dimensional (2D) morphologies was synthesized by varying the molar ratio of Mn2+ to phenyl phosphonic acid, and one of the morphologies is a unique palm leaf shape. In addition, a series of 2D Mn-MOP derivatives were obtained by calcination in air at different temperatures. Electrochemical studies showed that 2D Mn-MOP derivative calcined at 550 °C and exhibited a superior specific capacitance of 230.9 F g−1 at 0.5 A g−1 in 3 M KOH electrolyte. The aqueous asymmetric supercapacitor and the constructed flexible solid-state device demonstrated excellent rate performance. This performance reveals the promising application of 2D Mn-MOP materials for energy storage. [ABSTRACT FROM AUTHOR]

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 (Ti3C2TX/Cu‐BTC, Ti3C2TX/Fe,Co‐PBA, Ti3C2TX/ZIF‐8, and Ti3C2TX/ZIF‐67) that combine the advantages of MOFs and MXenes to enhance stability and improve conductivity. Subsequently, 3D hollow Ti3C2TX/ZIF‐67/CoV2O6 composites with excellent electron‐ and ion‐transport properties derived from Ti3C2TX/ZIF‐67 were synthesized. The specific capacitance of the Ti3C2TX/ZIF‐67/CoV2O6 electrode was 285.5 F g−1, which is much higher than that of the ZIF‐67 and Ti3C2TX/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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, the porous CoCCHH-CoSe heterogeneous-tube @PEDOT:PSS foam architecture with abundant surface defects and vacancies is prepared. The porous structure provides a large number of channels for ion transport, and the surface defects and vacancies provide abundant active sites for adsorption and oxidation reactions. [Display omitted] It is still challenging to construct stable 3D energy storage materials at the nanoscale by precise pore structure control and reasonable surface modification. Herein, a novel interwoven porous Co(CO 3) 0.35 Cl 0.20 (OH) 1.10 (CoCCHH)-CoSe heterogeneous-tube @PEDOT:PSS 3D foam with abundant active sites is presented as supercapacitor electrodes. The electrochemical results indicated that the pore structure provides ample space for redox reaction, and increases the number of ion transport channels. Besides, rational surface modification brings about sufficient active sites for redox reaction. The stable, porous PEDOT:PSS foam with a 3D elastic frame exhibited excellent electrical conductivity. Thus, the CoCCHH-CoSe@PEDOT:PSS foam possessed excellent specific capacitance and energy density, due to the synergistic effect of the unique 3D structure and surface defects. The home-made supercapacitor with CoCCHH-CoSe@PEDOT:PSS foam as cathode materials showed high specific capacitance (440.6F g−1 at 1 A g−1) and excellent energy density (137.7 Wh kg−1). This work provides a valuable strategy to develop potential materials for electrochemical energy storage. [ABSTRACT FROM AUTHOR]

In this paper, the water-soluble PEDOT:PSS film not only increases the toughness of the rGO/CoFe 2 O 4 /PEDOT:PSS paper but also increases the wettability. The device can be charged in both positive and negative directions, and when change charging direction, the electrochemical performance of the device is also excellent. [Display omitted] • The water-soluble PEDOT:PSS film not only increases the toughness of the rGO/CoFe 2 O 4 /PEDOT:PSS paper but also increases the wettability. • The rGO/CoFe 2 O 4 /PEDOT:PSS paper as electrodes of supercapacitor has high specific capacitance of 229.6 mF cm−2 at current density 1 mA cm−2. • The symmetric supercapacitor shows the energy density of 25.9 Wh kg−1 at power density of 135.3 W kg−1. • The device can be charged in both positive and negative directions, and when change charging direction, the electrochemical performance of the device is also excellent. Nowadays, safe, toughness, flexible and wearable energy storage devices have become a research hotspot. However, the safety and stability of flexible devices are still challenging because traditional wearable energy storage devices are difficult to overcome the problems of leakage, toxic and fragile electrolyte and so on. In this study, we successfully designed and constructed a continuous porous conductive polymer PEDOT:PSS film coated graphene (rGO) and CoFe 2 O 4 nanospheres composite paper electrode material. rGO paper has the advantages of good electrical conductivity and large surface area, but the graphene sheet without oxygen group has very weak adhesion between sheets, and the surface is completely hydrophobic. The water-soluble conductive polymer PEDOT:PSS film successfully increased the toughness and wettability of the graphene composite paper, and the kinetic fitting verified that the polymer improved the rate performance and electrochemical activity of the graphene composite paper. The area specific capacitance, energy density and power density of the symmetric supercapacitor made of rGO/CoFe 2 O 4 /PEDOT:PSS paper are 229.6 mF cm−2, 25.9 Wh kg−1 and 135.3 W kg−1. More importantly, the device can be charged in both positive and negative directions, and when change charging direction, the electrochemical performance of the device is also excellent. This solves the safety problem caused by the wrong connection between positive and negative poles of the supercapacitor, and also makes a contribution to the safety development of flexible supercapacitors. [ABSTRACT FROM AUTHOR]

In this paper, we report a system of electrochemical polymerization to prepare a porous polymer nanolayer coated nanomaterial Co(CO 3) 0.5 (OH) (CoCHH)/PEDOT electrode with interwoven porous network structure. The PEDOT nanolayer has the advantages of controllable thickness, good electrical conductivity, porous and continuous. In addition, each unit of the special structure can be uniformly coated by nanolayer, and prevent the internal nanostructure from collapsing of the structure as electrolyte ions move in and out, and the conductivity and porosity of the composite electrode can be improved. [Display omitted] • The CC/CoCHH/PEDOT has unique interwoven porous network structure. • The PEDOT nanolayer has good electrical conductivity, porous and continuous. • The CC/CoCHH/PEDOT as cathode has specific capacitance of 1520 F g−1. • The asymmetric supercapacitor shows the energy density of 70.8 Wh kg−1. A common approach to research supercapacitors is to choose a special structure of nanomaterials combined with noble metal oxides to increase capacity. However, using precious metals as electrodes with special nanostructures is both expensive from a commercial point of view and detrimental to the commercialization of supercapacitors. Therefore, we report a system of electrochemical polymerization to prepare a porous polymer nanolayer coated nanomaterial Co(CO 3) 0.5 (OH) (CoCHH)/PEDOT electrode with interwoven porous network structure. The PEDOT nanolayer has the advantages of controllable thickness, good electrical conductivity, porous and continuous. In addition, each unit of the special structure can be uniformly coated by nanolayer, and prevent the internal nanostructure from collapsing of the structure as electrolyte ions move in and out, and the conductivity and porosity of the composite electrode can be improved. As a result, the positive electrode of the composite nanolayer system showed excellent stability, with capacitance retention of 92.7% after 2000 cycles. [ABSTRACT FROM AUTHOR]

In this paper, the electrochemical hydrolysis (ECH) system can be formed by using Co(OH) 2 /Co 3 S 4 nanorod and Co(OH) 2 /CoSe 2 heterostructure nanotube as electrocatalysts and as-prepared supercapacitors in series, and the water decomposition can be driven directly by the supercapacitor. The electrochemical hydrolysis effect is obvious, and significantly improves the performance of the electrochemical hydrolysis system. [Display omitted] • We synthesize Co(OH) 2 /Co 3 S 4 and Co(OH) 2 /CoSe 2 heterostructures. • Morphology, structure and performance of composites are controllable. • The Co(OH) 2 /CoSe 2 cathode has high specific capacity of 1238.3 C g−1. • The asymmetric supercapacitor shows the energy density of 68.9 Wh kg−1. A novel hierarchical porous Co(OH) 2 /CoSe 2 heterostructure composites are prepared by ion exchange method, and the precursor Co(CO 3) 0.5 (OH)∙0.11H 2 O (CoCHH) is synthesized by hydrothermal method. Because the precursor CoCHH has the advantages of mild preparation conditions and controllable morphology and structure, it is possible to prepare a complex hierarchical structure of Co(OH) 2 /CoSe 2. The porous Co(OH) 2 /CoSe 2 heterostructure nanosheet and Co(OH) 2 /CoSe 2 heterostructure nanotube have an excellent specific surface area of 90.5 m2 g−1 and 78.7 m2 g−1, which is significantly better than the precursor CoCHH nanosheet and CoCHH nanorod. The porous Co(OH) 2 /CoSe 2 heterostructure nanosheet as cathode of supercapacitor has high specific capacity of 1283.3 C g−1 at current density 1 A g−1 in 3 M KOH solution, and the Co(OH) 2 /CoSe 2 heterostructure nanotube only required 48 mV (vs. Reversible Hydrogen Electrode) to reach the 10 mA cm−2 for HER in 1 M KOH solution. In addition, with porous Co(OH) 2 /CoSe 2 heterostructure nanosheet as cathode and CNTs as anode, the as prepared asymmetric supercapacitor has satisfactory energy density (68.9 Wh kg−1 at power density of 189.7 W kg−1). Moreover, the electrochemical hydrolysis (ECH) system can be formed by using Co(OH) 2 /Co 3 S 4 nanorod and Co(OH) 2 /CoSe 2 heterostructure nanotube as electrocatalysts and as-prepared supercapacitors in series, and the water decomposition can be driven directly by the supercapacitor. The electrochemical hydrolysis effect is obvious, and significantly improves the performance of the electrochemical hydrolysis system. [ABSTRACT FROM AUTHOR]

Distinguishing key features is crucial to design supercapacitor materials upon transition-metal carbides and nitrides (MXenes). Herein, the machine learning strategy was adopted to explore the structure-property based on 600 MXenes, including M 2 XT 2 (T = bare, O, S) and their doped systems. To ensure the quality of the data set, all the MXenes data were calculated individually through density functional theory. The sure independence screening and sparsifying operator (SISSO) method was subsequently used to develop pseudocapacitance formulas according to the refined key features in terms of stability and electronic structures. It is found that, on the group-free surfaces, both ion adsorption strength and density of states 1.0 eV above Fermi level play crucial roles to regulate pseudocapacitance. For the surface-functionalized cases, the parameters electronegativity and specific heat are the keys to determine pseudocapacitance. Furthermore, statistical results show that the elements, leading to high pseudocapacitance, are located in the upper left, lower left and upper right regions of the periodic table for group-free, O-functionalized and S-functionalized MXenes, respectively. The structure-property relationship provides theoretical insights into the development of MXenes-based pseudocapacitive materials from a statistical point of view. [Display omitted] • High pseudocapacitive M 2 X MXenes are screened through first-principles calculations. • Important factors to determine pseudocapaitance are revealed by screening key features. • The pseudocapaitance formulas of MXenes are developed through machine learning. [ABSTRACT FROM AUTHOR]