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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]

Progress in sustainable energy development often relies upon the idea of making use of green materials and agents to fabricate the components of high‐performance energy storage devices. Herein, we show that a relatively high energy density of 11.9 Wh kg−1 at a 0.1 A g−1 current density in a 1 M H2SO4 solution and a stable capacitance performance for up to 10000 cycles can be achieved in a symmetric supercapacitor (SC) made of two identical hierarchical porous carbon (HPC) electrodes derived from bean curd and 10 wt.% potassium carbonate (K2CO3); both of which are non‐toxic, edible materials. Such HPC, defined as HPC‐10, which was made through a one‐pot activation process followed by carbonization at 750 °C, exhibits high specific surface area of 2514 m2 g−1, hierarchical porous framework (i. e., simultaneous presence of abundant micropores, mesopores, and macropores), and contains N and O dopant components. In a three‐electrode system, HPC‐10 showed specific capacitances of 486 F g−1 in a 1 M H2SO4 and 404 F g−1 in a 6 M KOH, both obtained at a 0.1 A g−1 current density. This work also evaluates systematically the porous structure and electrochemical performance of HPC as a function of K2CO3 concentration from 0 wt.% to 15 wt.%. [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]

Abstract: Nickel nanoparticles are prepared successfully through reducing nickel chloride by hydrazine hydrate and are tested as supercapacitor electrode material for the first time. The as-prepared nickel nanoparticles are characterized intensively by a variety of means such as SEM, TEM, XRD and XPS. TEM observations and XRD analysis demonstrated that the size of nickel nanoparticles is about 12nm. XPS analyses indicate that the surface nickel atoms can react easily with O2 and water in the atmosphere to form nickel oxide/hydroxide species. As evidenced by electrochemical measurements, these surface nickel oxide/hydroxide species can generate substantial pseudocapacitance, reaching up to 416.6Fg−1 for nickel nanoparticles, which is higher than most carbon electrode materials reported in the literatures. This kind of surface metal oxides/hydroxides that generate pseudocapacitance may also occur on other metal nanoparticles except nickel nanoparticles, which provides a new approach to searching for electrode materials with even higher capacitance. [Copyright &y& Elsevier]

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]

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]

Abstract: In the past decades, nickel and cobalt oxide/hydroxide materials have been investigated intensively for supercapacitor applications. Some works report very high specific capacitance values, up to 3152Fg−1, for these materials. By contrast, some other works report quite modest capacitance values, up to 380Fg−1 for the same materials prepared using same strategy. It is found that most works reporting very high capacitance value applied nickel foam as current collector. In this paper, surface chemistry and electrochemical properties of nickel foam are investigated by XPS analysis, cyclic voltammetry and galvanostatic charge–discharge measurement. The results show that using nickel foam as current collector can bring about substantial errors to the specific capacitance values of electrode materials, especially when small amount of electrode active material is used in the measurement. It is suggested that an electrochemically inert current collector such as Ti or Pt film should be used for testing electrochemical properties of nickel and cobalt oxide/hydroxide positive electrode materials. [Copyright &y& Elsevier]

[Display omitted] • F content and porous structure are tuned by heating and chemical reduction of FG. • Semi-ionic C-F species enhance the supercapacitive properties in KI electrolyte. • The introduction of KI promotes the specific capacitance up to 583 from 17 F/g. To investigate the effect of structural properties of fluorinated graphene (FG) on the supercapacitive properties in KI additive electrolyte, the porous structure and surface F element content of FG were adjusted via chemical reduction by hydrazine and heating treatment. Systematically electrochemical measurements show that there is a dramatical increase of specific capacitance (583 F/g) in KI-additive electrolyte due to the pseudocapacitance brought by KI compared with that (17 F/g) in pure H 2 SO 4 electrolyte. Investigation on the relationship between F content and areal capacitance show that small amount of F content, especially for semi-ionic C-F species with better electronic conductivity compared with covalent C-F species, can effectively promote the areal capacitance. With moderate F content and relatively high specific surface area, the assembled symmetric supercapacitor can deliver an energy density of 8.89 Wh kg−1 and exhibits a long cyclic stability. [ABSTRACT FROM AUTHOR]

Abstract: N-doped carbon replicas of zeolite Y are prepared, and the effect of cation nature of zeolite (H+ or Na+) on the carbon replicas is studied. The morphology, structure and surface properties of the carbon materials are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The pore regularity, pore parameter and surface chemical properties of the carbons may strongly depend on the cation nature of the zeolite Y. The carbon replicas of zeolite HY (H-form of zeolite Y) possesses higher pore regularity and much larger surface area than those of zeolite NaY (Na-form of zeolite Y), while the latter carbons seem to possess higher carbonization degrees. Electrochemical measurements show a large faradaic capacitance related to the N- or O-containing groups for the prepared carbons. Owing to the large specific surface area, high pore regularity and heteroatom-doping, the HYC800 sample derived from zeolite HY presents very high gravimetric capacitance, up to 312.4Fg−1 in H2SO4 electrolyte, and this carbon can operate at 1.2V with good retention ratio in the range of 0.25 to 10Ag−1. [Copyright &y& Elsevier]

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]