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[Display omitted] • Self-O-doped Alpinia galanga stem-based carbon nanofiber succesfully synthesis. • The hierarchical porous carbon exhibit high specific surface area of 1065.58 m2/g. • The porous carbon was performed in solid-free binder form. • In 2-electrode system, supercapacitor possessed specific capacitance of 226F g−1. In this study, activated carbon with hierarchical pores and a nanofiber structure doped with oxygen was prepared using a pure biomass-based sustainable strategy involving integrated chemical impregnation and pyrolysis. Alpinia galangal stem was chosen as it functions as fast conductive network with abundant electrochemical active sites for high-grade electrode materials. The optimal precursor exhibited self-doping of oxygen ranging from 6.15 to 15.69 % with 1065.58 m2/g, which contributed to the redox reaction of the electrode material. When tested in a 2-electrode system, the porous carbon nanofibers showed a high specific capacitance of 226F g−1 at 1 A g−1 in 1 M H 2 SO 4 electrolyte, producing an energy density of 9.3483 Wh kg−1 with a coulombic efficiency of 89.01 %. The results showed that oxygen-doped hierarchical porous carbon nanofibers produced from Alpinia galangal stem biomass and designed to be solid-free of binders are highly promising as high-quality electrode materials that can improve sustainable supercapacitor performance. [ABSTRACT FROM AUTHOR]

• A facile method was reported by us to sustainably obtain 3D and defective nanocarbon from waste RS residue. • The key role of bacterial played in the formation of RS residue with unque structure and composition was revealed. • The underlying pyrolysis mechanism of RS residue is explored. • The obtained bio-char was demonstrated as a promising candidate for supercapacitor. Defective carbon nanomaterials with three-dimensional (3D) structure are showing great potential for advanced electrochemical storage and conversion devices, but its application is restricted by the synthesis, which is usually involved with complicate and energy-intensive processes. Herein, pyrolysis of rice straw (RS) residue, of which is collected from the bacterial assisted hydrolysis, is proposed by us here, and the obtained bio-char is defective with 3D structure and rich in oxygen-containing functional groups. Compared to the pristine one, specific surface area of the representative RS carbon (RSC2) was increased from 428.8 to 1131.7 m2 g−1. The assembled supercapacitor with RSC2 showed a high specific capacitance of 331F g−1 at a charge–discharge current density of 0.5 A g−1, and a capacity retention of 97.6% was maintained at 5 A g−1 even after 10,000 cycles. [ABSTRACT FROM AUTHOR]

• Series of Cu x NiCo 2−x O 4 synthesized by Microwave hydrothermal method. • The average grain size is in the range of 30–55 nm. • Highest Specific capacitance, C sp = 250.66 Fg−1 is observed for x = 0.06 sample. • Highest E = 22.22 Whkg−1 and P = 757.80 Wkg−1 were observed for x = 0.06 sample. A series of NiCu x Co 2-x O 4 with x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10 samples were synthesized using microwave hydrothermal method (MH). The structural, microstructural, and spectroscopic characterizations were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). All the samples are in Cubic phase with space group Fd3m. The samples x ≥ 0.08 shows some impurity phases. The average grain size for all the samples is in the range of 30–55 nm. The specific capacitance (C sp) 250.66 Fg−1, energy density (E) 22.22 Whkg−1 and power density (P) 757.80 Wkg−1 was observed for x = 0.06 with a mass loading of 7 mgcm−2 and in 2 M aqueous KOH electrolyte solution at a current density of 1 Ag−1. Therefore, the Cu doping with x = 0.06 shows good redox activities and hence can be used in electric batteries and supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu 0.95 Co 2.05 O 4 /Metal/NF exhibited relatively excellent performance. • The performance of Cu 0.95 Co 2.05 O 4 /Au/NF is good due to the close lattice spacing. • The metal buffer layer can effectively reduce the transfer resistance. The method of forming Cu or Au buffer layer on nickel foam (NF) by magnetron sputtering technology to enhance the energy storage capacity of following prepared supercapacitor anode material of Cu X Co 3-X O 4 was carried out in this paper, and the feasibility of surface treatment to improve the performance of supercapacitors was discussed. The buffer layer of Cu or Au can attenuate the lattice mismatch between NF and Cu X Co 3-X O 4 , and thus greatly reducing the transfer resistance and improving the electrochemical performance of the electrode material. The effect of Au is more obvious than Cu. The transfer resistance could be decreased effectively from 1.213 Ω to 0.012 Ω after Au sputtered, and the specific capacity increased spontaneously from 442.1C/g to 744.5C/g at a current density of 1A/g. The asymmetric supercapacitor (ASC) based on the modified anode material can achieve an energy density of 51.04Wh/kg when the power density is about 800 W/kg, and 93.9 % capacity retention rate after 4000 cycles. [ABSTRACT FROM AUTHOR]