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Here, a series of porous carbon based supercapacitor electrode materials have been synthesized by means of pyrolysis and hydrothermal methods combining with KOH activation using the biomass wastes mung bean husks as resources. The influence of synthesis process on the morphology, structure and supercapacitor performance of mung bean husks derived porous carbons has been investigated systematically. Especially, it is found that these oxygen-containing groups on the biochar play a crucial role in fabricating the three-dimensional (3D) hierarchical porous structure carbon. The original bio-structured porous carbon (PC 3-600 ), the 3D architecture porous carbon (HPC 2-700 ) and the porous carbon block (HPPC 2-700 ) have a high specific surface area, and the former mainly contains micropores and the latter two possess multistage pores. The specific capacitance of PC 3-600 , HPC 2-700 and HPPC 2-700 is respectively up to 390 F g -1 , 353 F g -1 , 304 F g -1 at 1 A g -1 , and still maintains as high as 287 F g -1 , 270 F g -1 and 235 F g -1 with corresponding retention ratio of 73.5%, 76.48%, 77.3% even at a high current density of 50 A g -1 . HPC 2-700 //HPC 2-700 symmetric supercapacitor achieves a high energy density of 20.4 Wh kg -1 at 872 W kg -1 in 1 M Na 2 SO 4 electrolyte., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The exploration of preparing hierarchically porous carbons with adjustable pore structure from renewable biomass has attracted increasing attention by researchers. In this paper, the hierarchically porous carbon with excellent electrochemical properties is synthesized using renewable sodium alginate as a carbon source by in-situ pyrolysis of 'egg-box' structure with the addition of thiourea. The type/concentration of template resources and the thiourea additive have an important influence on the regulation of pore structure and the content of heteroatom here. More importantly, the doping of graphitic-N is conducive to enhancing the cycle stability of the electrode material. The PCNS–Zn sample has the most outstanding electrochemical performance with the high specific capacitance of 350 F g−1 at 1 A g−1 and the good rate capability of 82% capacitance retention at 50 A g−1. In addition, PCNS–Zn electrode shows a prominent cycle life with the capacitance retention rate of 90.4% at 5 A g−1 after 5000 cycles. From the perspective of sustainability, low cost and easy operation, this scheme has a broad development prospect for preparing porous carbon with controllable pore structure. • Porous carbons have been prepared by assembling of alginate and divalent cationic. • The template sources have an influence on the pore structure and nitrogen species. • Thiourea could regulate the size of template nano particles. • The doping of graphitic-N is conducive to enhance the cycle stability. [ABSTRACT FROM AUTHOR]

• The 3D hierarchically porous carbon were synthesized via in-situ template and KOH activation from pectin. • The activation temperature and the addition of urea can adjust the content of heteroatoms and the pore structure. • The in-situ hard template can adjust the micropore/mesopores ratio. • The high specific surface area and its suitable micropore/mesopores ratio are helpful to promote charge storage and ion transfer. Pectin as a functional biopolymer has been successfully exploited to produce N/O co-doped 3D carbon architecture with hierarchical pores. A simple and novel in-situ template combining with KOH activation method is utilized to prepare porous carbon using calcium acetate as the template source and urea as a dopant. The in-situ CaCO 3 template, activation temperature and urea additive have a significant influence on the morphology, pore structure and performance of porous carbon. The high specific surface area of NHPC-700 (2928 m2 g −1) and its suitable micropore/mesopores ratio are helpful to promote specific capacitance and rate performance. The NHPC-700 possesses the high specific capacitance of 338 F g −1 at 1 A g −1 and the excellent capacitance retention of 83% from 1 A g −1 to 50 A g −1. Furthermore, the NHPC-700 symmetric supercapacitor shows an energy density of 22.4 Wh kg−1 at 880 W kg−1 in 1 M Na 2 SO 4. The efficient use of pectin to synthesize functionalized hierarchical porous carbon materials has a broad development prospect. Image, graphical abstract [ABSTRACT FROM AUTHOR]

[Display omitted] • N, S co-doped porous carbon/Sn composites are made by self-derived template method. • The synergistic effect of N, S co-doping is demonstrated by DFT calculations. • The Sn/NSPC anode yields a high discharge capacity of 712.6 mAh/g after 200 cycles. • Sn/NSPC full cell obtains a specific capacity of 572.6 mAh/g after 100 cycles. • The lithium storage mechanism is comprehensively revealed by in-situ XRD. Although single-heteroatom doped porous carbon/tin (Sn) composites have been extensively studied, an overall understanding of the effects of dual-heteroatoms doped porous carbon on the lithium storage properties of Sn is still insufficient. Herein, we provide a green self-derived templating strategy to synthesize the nitrogen, sulfur co-doped porous carbon/Sn composites (Sn/NSPC) with synergistic effect through one-step carbonization. The key to this approach is the self-generation of Na 2 CO 3 template, and it is apt to eliminate with water directly. The resultant NSPC can prevent the agglomeration of Sn particles. The synergistic effect is confirmed by density functional theoretical (DFT) calculations, revealing that N, S co-doped improves the electronic conductivity. The lithium storage mechanism and structural stability of Sn/NSPC electrode are researched via in-situ XRD and ex-situ XPS. The obtained electrode affords a discharge capacity (200 cycles, 712.6 mAh/g at 0.1 A/g) and long-life cyclability (2000 cycles, 330.1 mAh/g at 3 A/g). Additionally, the Sn/NSPC||LiCoO 2 full cell achieves excellent discharge capacity (572.6 mAh/g at 0.1 A/g) while remaining impressive cyclability (440.6 mAh/g at 1 A/g). This green and eco-friendly approach may be extended to the preparation of other heteroatom-doped carbon/Sn composites. [ABSTRACT FROM AUTHOR]