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[Display omitted] Self-supporting tree skeleton and densely stackable phenolic resin are cleverly coupled together by a "rebar-concrete" structure. The thick electrode as a master of space utilization has extremely high areal and volumetric energy density. This work confirms the effective coupling of the self-supporting skeleton and powder materials, providing novel ideas for the preparation of thick electrodes with high mass loading. • A "rebar-concrete" structure is proposed to facilitate the high space utilization of thick electrodes. • The areal capacitance of the thick electrode reaches an astonishing 11F cm−2. • The assembled SSC device delivers competitive areal energy density of 0.63 mWh cm−2. The thick electrode design with high packing density of active materials can increase the capacity in a limited space. However, the key challenge is still to develop a system with high space utilization and ensure electron/ion transport in thick electrode. This work proposes an interesting "rebar-concrete" structure, which successfully prepared wood/phenolic resin-derived thick electrode with high space utilization by in-situ polymerization of phenolic resin (concrete) in the wood (rebar) channel. The electrode exhibits an excellent three-dimensional interconnected hierarchical pore structure due to the uniform activation of in-situ anchored KOH particles. The mass loading (35 mg cm−2) and areal capacitance (11F cm−2) of the obtained composite electrode are increased to 446 % and 1257 % of the original balsa wood, respectively. The assembled symmetric supercapacitor (SSC) exhibits a high energy density of 0.63 mWh cm−2 (3.91 mWh cm−3) and an excellent cycle stability (95 % retention after 50 000 cycles), showing good practicability in lighting LEDs or driving a fan. This strategy achieves effective coupling of self-supporting skeleton and powder materials, providing more insights and possibilities for the preparation of high energy density thick electrodes. [ABSTRACT FROM AUTHOR]

Flax fibers, with abundant resources and a low cost, are an excellent precursor of carbon fibers for supercapacitors. At present, they are very attractive for designing electrodes with high electrochemical performance via a simple and green way. Hence, we systemically control the specific surface area and pore structure of flax-based carbon fibers by impregnating them with zinc chloride (ZnCl2) solution. The results show that the dehydration and expansion effects of ZnCl2 affect the microstructure, which is directly related to the specific capacitance. After activation, the optimized electrode exhibited the highest specific capacitance of 105 F g−1 at a current density of 1 A g−1, which has been improved by more than 10 times compared to that of pure-flax based carbon fibers. Moreover, they also show an excellent cycling stability of 98.7% after 10 000 cycles, even at a high current density of 10 A g−1. These results further demonstrate that flax-based electrodes have potential to be applied to some relevant energy storage applications in the future. [ABSTRACT FROM AUTHOR]

Achieving a simple and mild preparation method to obtain high performance carbon-based flax fiber electrode for supercapacitor has become particularly important but still challenges. Hence, the excellent electrochemical performance of electrode was constructed by impregnation-heat treatment with ethylenediamine tetraacetic acid disodium zinc (EDTANa 2 Zn) and zinc nitrate (ZnNO 3) as activators. The results show that the decomposed zinc oxide (ZnO) of EDTANa 2 Zn leads to the prominently hierarchical porous structure and abundant nitrogen-doping, which provides more active storage sites for electrolyte. Likewise, the as-prepared electrode by EDTANa 2 Zn treatment exhibits the specific capacitance of 292 F g−1 at the current density of 0.5 A g−1, and keeps up with the capacitance retention of 102 % even after a 10, 000 long-cycles at the high current density of 10 A g−1. Significantly, the suitable zinc salt assisted preparation of high performance flax fiber carbon-based electrode provides a novel idea for future electrochemical energy storage. [Display omitted] • The obtained electrode was constructed by EDTANa 2 Zn and zinc nitrate. • The 950-EA electrode exhibits the specific capacitance of 292 F g−1–0.5 A g−1 • The 950-EA electrode keeps up with the capacitance retention of 102 % after 10,000 cycles. [ABSTRACT FROM AUTHOR]

It is an effective way to develop basswood (Tilia americana, hardwood)-derived thick carbon electrode for high energy density supercapacitors. The wood-derived anisotropic structural carbon electrodes have different transfer kinetics of the electrolyte, which will significantly affect the electrochemical performance especially at high current density. Therefore, the relationship between the sectional wood-derived electrodes and the electrochemical performance of supercapacitors were systematically studied. The results show that the high specific surface area (542 m2 g−1) of cross-sectional wood-derived carbon contributes to the excellent electrochemical performance (specific/area capacitance ~ 3040 mF cm−2/118 F g−1 at 1 mA cm−2, cycle stability ~ 82.2% after 10,000 cycles at 50 mA cm−2, and capacitive contribution of 76.64% at 5 mV s−1), which is attributed to the hierarchical porous structure and easily allows electrolytes to enter the interior even at high current density. This work provides a fundamental understanding of the dynamic behaviors of electrolyte at different wood sections, and it is expected to be extended to other wood species and wood-like structures for energy storage applications. [ABSTRACT FROM AUTHOR]

Hierarchical porous carbon-based electrodes, benefiting from their facilitated ion diffusion and electron conduction, have demonstrated enormous potential in supercapacitors. The preparation of hierarchical carbons with uniformity and appropriate porosity, however, still remains a grand challenge, which hinders their widespread applications. Herein, a hierarchical porous polyimide-derived carbon electrode (CPC-Fe/Zn) has been fabricated by employing bimetallic salts (Fe/Zn) as precursor and template to activate the cellulose/polyimide (PI) carbon (CPC). Originating from suitable distribution of mesopores and micropores, the obtained CPC-Fe/Zn delivers a high specific capacitance of 420 F/g at a current density of 1 A/g. Moreover, a symmetric supercapacitor device assembled with CPC-Fe/Zn exhibits delivers an energy density of 35.5 Wh/kg at a power density of 800 W/kg. Even at a larger current density of 20 A/g, the specific capacitance retention of such device still remains 92.5 % after 10,000 cycles, showing the rate performance and stability. This work has proposed a bimetallic salts template-assisted strategy to precisely modulate of the pore structure of carbon electrodes, which provides a promising platform to design superior electrodes for various electrochemical systems. [Display omitted] • The hierarchically porous structure of the material can be modulated precisely. • The symmetric supercapacitor exhibited a remarkable energy density of 35.5 Wh/kg @ 1000 W/kg. • The specific capacitance retention of symmetric supercapacitor reached 92.5 % after 10,000 cycles. [ABSTRACT FROM AUTHOR]

Although tremendous efforts have been devoted to manganous oxide (MnO)-based hybrid electrode materials, the rational design and facile preparation of high-performance MnO hybrid supercapacitors are still full of challenges, due to the inevitable agglomeration and limited stability of MnO within carbon matrixes. In this work, we developed a direct one-pot polymerization method to synthesize a series of Mn ion doped polylevodopa [P(L- DOPA)] synthetic melanin nanoparticles (Mn@SMNPs) for further transforming into small-sized hybrid carbon nanoparticles (MnO@CNPs, 20–80 nm) consisting of many stable Mn-related chemical bindings (C–N–Mn). The obtained MnO@CNPs electrode materials with physically spatial protection and well distribution of MnO could display high specific capacitance values (e.g., 545 F g−1 at 0.5 A g−1 in 6 M KOH electrolyte) within a wide operation voltage of 1.3 V. This work will continue to provide an inspiration towards the fabrication of the next-generation of high-performance synthetic melanin-based energy storage materials and devices. [Display omitted] ● MnO@CNPs were prepared through a facile one-pot fabrication strategy with small size and high MnO doping content. ● The obtained MnO@CNPs with physically protection showed a well distribution of MnO. ● The stable C–N–Mn chemical binding structure facilitates the stabilization of MnO during the charging and discharging. [ABSTRACT FROM AUTHOR]