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Low conductivity of metal oxide electrode and low specific capacitance of carbon electrode restrict the further commercial application of supercapacitors. Manganese oxides/carbon composites were prepared by a simple method using homemade porous carbon and KMnO 4 as raw materials. The composites have both high capacitance of metal oxides and high conductivity of carbon due to Mn-O-C interaction. The optimized composite electrode exhibited an incredible ultra-high specific capacitance of 550, 520, 481, 402, and 318 F/g at the current densities of 1, 2, 3, 5, and 10 A/g, respectively. Moreover, the assembled asymmetric supercapacitor (ASC) device obtains an astonishing energy density of 50.2 Wh/kg at a power density of 800 W/kg, while 90.5 % capacitance after 10,000 cycles is still maintained. Meanwhile, ASC devices show great potential applications in energy storage, such as lighting 35 lights and running an electronic stopwatch. This material will promote the development of manganese/carbon composite supercapacitors for its simple preparation methods, ultra-high performance, and is expected to be a promising candidate for commercially large-scale applications. [Display omitted] • Manganese oxides/carbon composite with splendid specific capacitance was prepared by a simple method. • The assembled asymmetric supercapacitor (ASC) device obtains an astonishing energy density of 50.2 Wh/kg (800 W/kg). • The ASC device shows excellent cycling stability with a capacitance remaining of 90.5 % after 10,000 cycles. [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]

Biomass resources are promising precursors for porous carbon materials attributing to their renewable, plentiful and low-cost characteristics. In this work, hierarchical porous carbon materials are synthesized by carbonizing the mixture of starch rich biomass precursor and potassium citrate. Potassium citrate is vital for the formation of hierarchical porous structure. The specific surface area of carbon material is greatly enhanced with the addition of potassium citrate and gradually increases with the rise of carbonization temperature. APCs-750 obtained from 750 °C displays the best capacitance performance attributing to a high specific surface area (1105.64 m2 g−1) and a high oxygen content (10.25 at.%). APCs-750 exhibits the highest specific capacitance of 242.5 F g−1 at 0.2 A g−1, good rate performance (119.0 F g−1 at 50 A g−1) and excellent stability (retaining 96.5 % after 20,000 cycles). In addition, the symmetric supercapacitor of APCs-750 shows a high energy density of 12.38 Wh kg−1 at the power density of 99.72 W kg−1 and keeps a capacitance retention of 91.3 % after 20,000 cycles. Hence, this work provides a facial strategy to synthesis high capacitance performance hierarchical porous carbon materials from starch rich precursor. [Display omitted] • Hierarchical porous carbon materials with 3D network structure are synthesized. • One-step carbonization and activation process is designed. • Potassium citrate is vital for the formation of hierarchical porous structure. • The effect of carbonization temperature is investigated. • The carbon materials display good rate performance and stability. [ABSTRACT FROM AUTHOR]

Renewable cellulose-based papers are considered as a good resource for energy storage devices owing to their interlaced microfibrillar structure and high electrolyte absorptivity. Herein, an all-cellulose-based solid-state high-rate supercapacitor assembled with cellulose paper-derived self-supporting porous carbon electrodes and filter paper separator is designed. Benefiting from ingenious surface chemistry and pore structure engineering, the electrodes possess interconnected network structure, hierarchical pores, and appropriate N/O doping levels. The electrode demonstrates high specific capacitance (222.2 F g−1 at 0.2 A g−1), prominent rate capability (120.1 F g−1 at 100 A g−1), and outstanding cyclic stability (98.7 % capacitance retention after 20,000 cycles at 80 A g−1), which surpass most of cellulose-based self-supporting carbon electrodes ever reported. By integrating the well-designed electrodes with a piece of filter paper separator, the assembled symmetric solid-state supercapacitor (1.2 V) achieves an encouraging specific capacitance of 115.0 F g−1 along with an impressive energy density of 22.9 Wh kg−1 and a maximum power density of 15.9 kW kg−1. Moreover, the symmetric supercapacitor with 1 M Et 4 NBF 4 organic electrolyte (3 V) delivered a maximum energy density and power density of 62.5 Wh kg−1 and 54.9 kW kg−1, respectively. This study proposes a design concept of all-cellulose-based solid-state supercapacitors, which presents a promising direction toward environmentally friendly and sustainable energy storage technology. [Display omitted] • A facile solvothermal reaction and carbonization/activation route was proposed to tailor pore and surface characteristics. • All-cellulose-based symmetric supercapacitor was designed by integrating N/O-CP-50 electrodes and filter paper separator. • Excellent comprehensive performance was achieved for N/O-CP-50-based symmetric supercapacitor. • The typical all-cellulose-based solid-state devices balance the cost and performance of portable electronic devices. [ABSTRACT FROM AUTHOR]

Heteroatoms-doped biomass-derived carbon materials (HBC), a new task and hotspot of the current energy research, especially supercapacitor, have featured with low cost and rich sources with enhanced physical, chemical and electrical properties compared with those of pure counterparts. Nevertheless, converting the biomass into high-performance carbon materials by green chemical activators and dopants is still imperatively needed. Herein, a simple and cost-effective one-step method was proposed, using different nitrogen-containing compounds (NH 4 Cl, (NH 4) 2 CO 3 and urea) as both activation agent and dopant, to prepare nitrogen-doped biomass-derived hierarchical porous carbon materials (HPCs). The effect of nitrogen-containing compounds on the electrochemical performance of HPCs was also studied. Among them, NH 4 Cl is proved to be the porogen with the minimum collapse of pollen grain and urea can be identified as the most effective N dopant. Furthermore, the prepared HPC-urea (HPC-U) electrode deliver the highest specific capacitance of 300 F g−1 at 1 A g−1 and rate performance of 50% from 1 to 50 A g−1 in three electrode system, while HPC-NH 4 Cl possesses the maximum capacitance retention rate of 95.2% after 10,000 cycles. In addition, HPC-U based SCs exhibits the highest energy density (14.3 Wh kg−1). Notably this work may provide a certain guideline for choosing N dopants and porogens to prepare biomass-derived carbon materials for the target application. [Display omitted] • An integrated carbonization, activation and doping process for hierarchical porous carbon. • Heteroatoms-rich camellia pollen is used as carbon precursor. • Three nitrogenous compounds is utilized as both activation agent and dopant. • NH 4 Cl is proved to be the porogen with minimum collapse of pollen grain. • Urea can be identified as the most effective N dopant. [ABSTRACT FROM AUTHOR]