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Reduced graphene oxide hydrogels (rGOHs) with tunable surface functionalities were prepared through a hydrothermal treatment. The self‐standing hydrogels were directly used as electrode materials without any binder or conducting agent in aqueous electrolyte. Electrochemical measurements show that the hydrogels can endure high potential up to 1.7 V in acid (H2SO4) and KI‐additive (H2SO4+KI) electrolyte. With the introduction of extra pseudocapacitance through KI, rGOH possesses a high specific capacitance of 539 F g−1, which is much larger than that (141 F g−1) in acid electrolyte. The energy density for rGOHs‐based supercapacitor with can reach up to 54 Wh kg−1 and the value can maintain at 28.8 Wh kg−1 even a high power density of 8500 W kg−1. Such a good supercapacitive performance can be attributed to the open porous and interconnected structure, together with surface functionalities. [ABSTRACT FROM AUTHOR]

Abstract: New nitrogen‐doped hierarchical porous carbons (HPCs) with large surface areas were prepared from bean curd through a one‐step impregnation activation method at 750 °C with CH3COOK as an activating agent. The porous carbons were characterized by a variety of techniques such as N2‐sorption analysis, scanning electron microscope (SEM), transmission electron microscope (TEM), and X‐ray photoelectron spectroscopy. The results show that there are numerous macropores with a pore size of ∼200 nm observed by SEM and TEM as well as micropores probed by N2‐sorption analysis, indicating a hierarchical porous structure for these carbon materials. The effect of activating agent dosage on the porous structure of carbon was carefully investigated. The Brunauer‐Emmett‐Teller specific surface area and nitrogen content for the optimized carbon are 2180 m2 g−1 and 2.62 at%, respectively. As evidenced by electrochemical measurements, the as‐prepared carbon has a good capacitive performance and the specific capacitance is calculated to be 284 F g−1 at a current density of 0.1 A g−1 in KOH electrolyte. More importantly, this carbon could deliver a high capacitance up to 118 F g−1 at a very high current density of 30 A g−1 due to its hierarchical porous structure, which will facilitate the ion transfer under high current density. Our research highlights the potential application of these HPCs as high‐performance electrode materials for electric double‐layer capacitors. [ABSTRACT FROM AUTHOR]

Phosphorus-doped hierarchically porous carbon (HPC) is prepared with the assistance of freeze-drying using colloid silica and phytic acid dipotassium salt as a hard template and phosphorus source, respectively. Intensive material characterizations show that the freeze-drying process can effectively promote the porosity of HPC. The specific surface area and P content for HPC can reach up to 892 m2 g−1 and 2.78 at%, respectively. Electrochemical measurements in aqueous KOH and H2SO4 electrolytes reveal that K+ of a smaller size can more easily penetrate the inner pores compared with SO42−, while the developed microporosity in HPC is conducive to the penetration of SO42−. Moreover, P-doping leads to a high operation potential of 1.5 V for an HPC-based symmetric supercapacitor, resulting in an enhanced energy density of 16.4 Wh kg−1. Our work provides a feasible strategy to prepare P-doped HPC with a low dosage of phosphorus source and a guide to construct a pore structure suitable for aqueous H2SO4 electrolyte. [ABSTRACT FROM AUTHOR]

The development of supercapacitors with high energy density and power density is an important research topic despite many challenging issues exist. In this work, porous carbon material was prepared from corn straw biochar and used as the active electrode material for electric double-layer capacitors (EDLCs). During the KOH activation process, the ratio of KOH/biochar significantly affects the microstructure of the resultant carbon, which further influences the capacitive performance. The optimized carbon material possesses typical hierarchical porosity composed of multi-leveled pores with high surface area and pore volume up to 2790.4 m 2 g −1 and 2.04 cm 3 g −1 , respectively. Such hierarchical micro-meso-macro porosity significantly improved the rate performance of the biochar-based carbons. The achieved maximum specific capacitance was 327 F g −1 and maintained a high value of 205 F g −1 at a ultrahigh current density of 100 A g −1 . Meanwhile, the prepared EDLCs present excellent cycle stability in alkaline electrolytes for 120 000 cycles at 5 A g −1 . Moreover, the biochar-based carbon could work at a high voltage of 1.6 V in neutral Na 2 SO 4 , and exhibit a high specific capacitance of 227 F g −1 , thus giving an outstanding energy density of 20.2 Wh kg −1 . [ABSTRACT FROM AUTHOR]

Three-Dimensional graphene (3D-G) material is regarded as an excellent carbon material, which reveals cross-linked porous structure, high specific surface area, strong mechanical strength and high conductivity inheriting from the graphene. In this work, we fabricate the novel 3D-G based materials by decoration of sodium citrate (SC) for supercapacitor and lithium ion batteries (LIBs) applications. SC with abundant functional groups and short carbon chain can ensure the interface between graphene sheets or between graphene and other composite materials, lead to shorter diffusion path for ions transportation. Owing to the large surface area and pore volume, 3D-G (SC) shows outstanding specific capacitance (301 F g −1 ) when it is applied in supercapacitors. Besides that, 3D-G (SC) compounds with Fe 3 O 4 particles and 3D-G@Fe 3 O 4 (SC) are applied in LIBs. The 3D-G@Fe 3 O 4 (SC) has a higher discharge capacity (1310.6 mAh g −1 ) than 3D-G@Fe 3 O 4 (1270 mAh g −1 ) at 0.1 C, and it even increase to an excellent capacity (1550 mAh g −1 ) after 100 cycles. Moreover, 3D-G@Fe 3 O 4 (SC) shows excellent cycling stability that specific capacity retains 1031 mAh g −1 after 1000 cycles. This work may extend a novel approach to prepare 3D-G electrode material for efficient storage devices. [ABSTRACT FROM AUTHOR]

A hierarchically porous carbon (HPC) is prepared via a facile hard-templating method using silica as a template, which is thoroughly removed by an in-situ polytetrafluoroethylene (PTFE) pyrolytic process without further post treatment. The Brunauer-Emmett-Teller specific surface area for HPC can reach up to 664 m2 g−1. The usage of PTFE and carbon precursor (glucosamine) lead to F, N co-doping on HPC. Electrochemical measurements show that HPC possesses a much higher specific capacitance (1161 F g−1) in a KI-additive electrolyte (H 2 SO 4 + KI) than that (183 F g−1) in H 2 SO 4 electrolyte due to the presence of oxidation states of I species such as IO 3 ˉ and I 3 ˉ, as confirmed by X-ray photoelectron spectroscopy (XPS), which can bring about superior pseudocapacitance by redox reaction. Furthermore, the operation voltage for the symmetric supercapacitor assembled by the as-prepared HPC can reach up to a much higher value of 1.7 V in KI-additive electrolyte compared with that in H 2 SO 4 electrolyte. Marrying high operation voltage and high specific capacitance, the assembled supercapacitor can deliver a high energy density of 78.8 Wh kg−1 under a high-power output of 680 W kg−1. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Engineering graphene with efficient ion and electron transport properties is vital for development of high performance, next generation energy storage devices. The protocols generally involve pore generation and doping of graphene with the heteroatoms. Herein we report the realization of pore generation, control, and N-doping of graphene in one single process using reduced metal salt as etching agent and environment friendly N 2 gas as doping agent. Furthermore, we found the porous structure (pore size and density), the dopant bonding configuration and doping amount can be controlled by change the metal salt and nitrogen source, which allows us to investigate the influence of pore and N-doping structure of porous graphene (PG) in their supercapacitor performance. Specifically, the N-doping, PG prepared by Ni salt (PG-Ni) shows the smaller pore size (average pore size of ~20–30 nm) and larger pore density. PG-Ni exhibits high specific capacitance of 575 F/g along with the energy density of 51.2 Wh/kg at 0.5 A/g current density and also shows good rate, cycling performances. Considering the excellent performance, ease of the process, and pore structure controllability, we believe the method provides a new route for developing graphene based high performance supercapacitors. Unlabelled Image • Pore generation, control, and N-doping of graphene in one single process • N atom doped by using N 2 as doping agent • N-doping configuration and porous structure can be controlled • Remarkable enhancement of supercapacitor permeance of N-doping porous graphene [ABSTRACT FROM AUTHOR]