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In this work, Co(OH) 2 buds direct growth on Ni foam (Co(OH) 2 buds/Ni foam) is prepared via a hydrothermal method. Their structure and morphologies are characterized by using X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy. Result shows that the Co(OH) 2 buds are assembled by several nanorods and uniformly covered on the surface of Ni foam. Due to its unique structure, the Co(OH) 2 buds/Ni foam electrode shows high capacitive performance and long cycle life. The specific capacitance of Co(OH) 2 buds/Ni foam is as high as 2041 F g −1 at a current density of 3 mA cm −2 in 6 M KOH electrolyte, and 811 F g −1 even at a high current density of 60 mA cm −2 . The capacitance of the Co(OH) 2 buds/Ni foam electrode remained 72.4% after 1000 cycles at 18 mA cm −2 . An asymmetric supercapacitor was successfully assembled, in which Co(OH) 2 buds/Ni foam and AC used as positive and negative electrode, respectively. The energy density of the AC//Co(OH) 2 buds/Ni foam supercapacitor reaches to 20.3 W h kg −1 at a power density of 90.6 W kg −1 . Our result shows that the Co(OH) 2 materials are promising candidate for electrochemical energy applications. [ABSTRACT FROM AUTHOR]

K-ion batteries (KIBs) are widely considered as a promising alternative to Li-ion batteries (LIBs) due to the cost effective and earth abundant features of K. However, identifying a potential anode for KIBs showing good capacity and stability is still challenging. Because traditional graphite suffers from poor stability owing to the large volume expansion during the insertion/extraction of K ions. Non-graphite carbon is a good candidate because of the disordered nature. A facile high temperature pyrolysis method was adopted to obtain bio-derived carbon materials. Among different kinds of biomass precursors, the porous dandelion seed with nitrogen doping shows the best electrochemical performance with a specific capacity of 168 mAh g−1. The nitrogen-doped carbon presents good K ion adsorption capability and enhanced wettability, which is demonstrated in Fig.S1. Moreover, after introducing activation agent (KOH) in the carbonization process, the capacity in improved to 243 mAh g−1. Meanwhile, the as-prepared carbon material delivers good capacity retention of 91% after 100 cycles. Therefore, the hierarchically porous doped carbon derived from renewable biomass precursor shows great economical potential as KIBs anode. Unlabelled Image • The bio-derived carbon activated by KOH maintain maintain an integrated porous microstructure. • The heteroatoms-doped bio-derived carbon exhibits high specific capacity as K ions anode. • The abundant bio-mass precursor enables large scale preparation of the carbon materials. [ABSTRACT FROM AUTHOR]

MnO 2 is regarded as an ideal material of supercapacitor since its low-cost, environment friendly and high specific capacitance but hindered by its poor electrical conductivity. Developing a composite electrode that combines nano-structure MnO 2 with a conductive skeleton such as carbon materials could make up for the shortcomings. Here, porous activated carbon (PAC) is synthesized by using low-cost wheat bran as biomass carbon precursor and a mixture of NaCl/ZnCl 2 as combined solvent-porogen. The resultant PAC sample presents a hierarchical porous structure and large specific surface area up to 1058 m2 g−1. Afterwards, MnO 2 nanosheets decorated PAC (MnO 2 @PAC) is prepared via an in-situ hydrothermal deposition. It is a key finding that the ion/electron transfer kinetics of MnO 2 @PAC could be effectively improved by the addition of hierarchical porous carbon. Thus, the MnO 2 @PAC electrode displays a high specific capacitance (258 F g−1 at 1 A g−1) and superior rate performance (82.8% capacitance retention with the current density ranging from 1 A g−1 to 20 A g−1). Furthermore, an asymmetric supercapacitor is assembled by employing the MnO 2 @PAC as the positive electrode and PAC as negative electrode, which exhibits a high energy density of 32.6 Wh kg−1 and as well as 93.6% capacity retention at over 10,000 charge/discharge cycles. • Porous activated carbon (PAC) is synthesized by a controllable molten salt method. • MnO 2 nanosheets were deposited on the PAC through a simple hydrothermal reaction. • The MnO 2 @PAC displays high specific capacitance and outstanding stability. • The PAC//MnO 2 @PAC asymmetric supercapacitor exhibits energy density of 32.6 Wh kg−1. [ABSTRACT FROM AUTHOR]