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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]

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]