Solvothermal-induced construction of ultra-tiny Fe_(2)O_(3) nanoparticles/graphene hydrogels as binder-free high-capacitance anode for supercapacitors

Three-dimensional(3D) ultra-tiny Fe_(2)O_(3) nanoparticles/graphene hydrogels were prepared using a facile and efficient solvothermal reaction, by which the phase of iron oxide, particle size and the morphology of hydrogels can be precisely controlled by simply adjusting the solvothermal reaction time. Accordingly, the effect of the microstructures of hydrogels on electrochemical performance was systematically studied. It was found that Fe_(2)O_(3)/r GO-50 hydrogels(with a solvothermal reaction time of 50 min) possessed a desirable crystallinity, suitable particle size, decent porous structure, large specific surface area and high electrical conductivity, thus exhibiting a superior electrochemical performance as binder-free anode of supercapacitors: a large potential range of 1.15 V, an ultrahigh specific capacitance of 1090 F·g^(-1) at a current density of 2A·g^(-1) and excellent rate capability (531 F·g^(-1) at 10 A·g^(-1)). The rational design and systematic research of electrode materials will provide new lights for the preparation of advanced electrochemical energy storage devices.

Three Dimensional Sulfur-doped Graphene Hydrogels with Tetrathiafulvalene for High Performance Supercapacitors

By using tetrathiafulvalene as reducing and doping agents, three-dimensional （3D） sulfur-doped graphene hydrogels （SGHs） were facilely prepared in mixed solvents of dimethyl formamide and water. Several investigations reveal that TTF plays a critical role in the formation of such unique 3D architecture, as it not only reduces GO to self-assembly into 3D structures, but also can be transformed to TTF^·＋ and TTF^2＋ as doping agents in the reduction process. The morphology, crystal structure, chemical bonding, elemental composition and porosity of the as-prepared SGHs have been studied. Benefiting from well-defined and cross-linked 3D porous network architectures, the supercapacitors based on the SGHs in KOH 212.5 F·g^-1 at 0.3 A·g^-1. Furthermore, this capacitance also degree of reversibility in the repetitive charge/discharge cycling electrolyte exhibited a high specific capacitance of showed good electrochemical stability and a high test.

Flexible Three-Dimensional Graphene Hydrogels with Superior Conductivity and Excellent Electrochemical Performance for Supercapacitor Electrodes

Three-dimensional porous graphene hydrogels have been prepared by a green and facile but very efficient ap- proach using glucose as an assistant. Based on a one-step hydrothermal reaction with optimal experimental condi- tions such as the reaction time and temperature, the graphene hydrogels exhibit a superior electrical conductivity （95.3 S/m） and can be used as supercapacitor electrode without any binder or conducting additives but showing a high specific capacitance of 384.6 F/g at a current density of 1 A/g. The results show that addition of glucose can not only greatly decrease the reaction temperature but also shorten the reaction time. The superior performance of the three-dimensional porous graphene hydrogels as electrode for supercapacitor suggests its promising potentials in the field of energy storage devices.

Nano-/Micro-confined Water in Graphene Hydrogel as Superadsorbents for Water Purification

Confined water has been proven to be of great importance due to its pervasiveness and contribution to life and many fields of scientific research.However,the control and characterization of confined water are a challenge.Herein,a confined space is constructed by flexibly changing the pH of a graphene oxide dispersion under the self-assembly process of a graphene hydrogel(GH),and the confined space is adjusted with variation from 10.04 to 3.52 nm.Confined water content in GH increases when the pore diameter of the confined space decreases;the corresponding adsorption capacity increases from 243.04 to 442.91 mg g−1.Moreover,attenuated total reflectance Fourier transform infrared spectroscopy and Raman spectroscopy are utilized to analyze the hydrogen bonding structure qualitatively and quantitatively,and correlation analysis reveals that the improvement in the adsorption capacity is caused by incomplete hydrogen bonding in the confined water.Further,confined water is assembled into four typical porous commercial adsorbents,and a remarkable enhancement of the adsorption capacity is achieved.This research demonstrates the application potential for the extraordinary properties of confined water and has implications for the development of highly effective confined water-modified adsorbents.

Nanocellulose/nitrogen and fluorine co-doped graphene composite hydrogels for high-performance supercapacitors

Three-dimensional graphene materials have been studied as typical supercapacitors electrode materials by virtue of their ultrahigh specific surface area and good ion transport capacity.However,improvement of the poor volumetric electrochemical performance of these graphene materials has been required although they have high gravimetric energy density.In this work,nanocellulose/nitrogen and fluorine co-doped graphene composite hydrogels(NC-NFGHs)were prepared through a convenient hydrothermal approach utilizing ammonium fluoride as the heteroatom source.Nanocellulose(NC)and high concentration of graphene oxide(GO)were utilized to adjust the structure of NC-NFGHs and increase their packing density.Subsequently,the aqueous symmetric supercapacitor based on NC-NFGH-80 exhibits remarkable gravimetric(286.6 F·g^(-1))and volumetric(421.3 F·cm^(-3))specific capacitance at 0.3 A·g^(-1),good rate performance,and remarkable cycle stability up to 10,000 cycles.Besides,the all-solid-state flexible symmetric supercapacitors(ASSC)fabricated by NC-NFGH-80 also delivered a large specific capacitance of 117.1 F·g^(-1)at 0.3 A·g^(-1)and long service life over 10,000 cycles at 10 A·g^(-1).This compact porous structure and heteroatom co-doped graphene material supply a favorable strategy for high-performance supercapacitors.

Nitrogen-doped graphene hydrogel-supported NiPt-CeOx nanocomposites and their superior catalysis for hydrogen generation from hydrazine at room temperature

The safe and efficient storage and release of hydrogen is one of the key technological challenges for the fuel cell-based hydrogen economy. Hydrazine monohydrate has attracted considerable attention as a safe and convent chemical hydrogen-storage material. Herein, we report the facile synthesis of NiPt-CeOx nanocomposites supported by three-dimensional nitrogen-doped graphene hydrogels （NGHs） via a simple one-step co-reduction synthesis method. These catalysts were composition-dependent for hydrogen generation from an alkaline solution of hydrazine. （NisPt5）I-（CeOx）0.B/NGH exhibited the highest catalytic activity, with 100% hydrogen selectivity and turnover frequencies of 408 h^-1 at 298 K and 3,064 h^-1 at 323 K. These superior catalytic performances are attributed to the electronic structure of the NiPt centers, which was modified by the electron interaction between NiPt and CeOx and the strong metal-support interaction between NiPt-CeOx and the NGH.

Capacitive Performances of Reduced Graphene Oxide Hydrogel Prepared by Using Sodium Hypophosphite as Reducer

The hydrogels of reduced graphene oxide （rGOHGs） have been synthesized through treating GO with various concentrations of sodium hypophosphite （NaH2PO2） under hydrothermal condition. The results reveal that the structure of rGOHGs changes along with the increase of the concentration of NaH2PO2. The rGO sheets prepared with low concentration of NaH2PO2 exhibit more crimples and larger specific surface area than those prepared with high concentration of NaH2PO2. The measurements of the capacitive performances of rGOHGs reveal that the rGOHGs prepared with low concentration of NaH2PO2 possess larger specific capacitance （Cs） than that prepared with high concentration of NaH2PO2 at low cyclic voltammetry scan rates. However, the rGOHGs prepared with high concentration of NaH2PO2 possess larger Cs at high scan rates, more stability and better high-rate capability than those prepared at low concentration. It is believed that the structures and properties of rGOHGs can be adjusted by controlling the concentration of NaH2PO2 according to the requirement.

Holey graphene hydrogel with in-plane pores for high- performance capacitive desalination

Capacitive deionization is an attractive approach to water desalination and treatment. To achieve efficient capacitative desalination, rationally designed electrodes with high specific capacitances, conductivities, and stabilities are necessary. Here we report the construction of a three-dimensional （3D） holey graphene hydrogel （HGH）. This material contains abundant in-plane pores, offering efficient ion transport pathways. Furthermore, it forms a highly interconnected network of graphene sheets, providing efficient electron transport pathways, and its 3D hierarchical porous structure can provide a large specific surface area for the adsorption and storage of ions. Consequently, HGH serves as a binder-free electrode material with excellent electrical conductivity. Cyclic voltammetry （CV） measurements indicate that the optimized HGH can achieve specific capacitances of 358.4 F.g 1 in 6 M KOH solution and 148 F.g-1 in 0.5 M NaCl solution. Because of these high capacitances, HGH has a desalination capadty as high as 26.8 mg.g-1 （applied potential： 1.2 V; initial NaCI concentration： -5,000 mg.L-l）.

One-step synthesis of monodispersed Pt nanoparticles anchored on 3D graphene foams and its application for electrocatalytic hydrogen evolution

Although platinum-based materials are regarded as the state-of-the-art electro-catalysts for hydrogen evolution reaction(HER),high cost and quantity scarcity hamper their scale-up utilization in industrial deployment.Herein,a one-step strategy was developed to synthesize multi-walled carbon nanotubes and reduced graphene oxide supported Pt nanoparticle hydrogel(PtNP/rGO-MWCNT),in which only ascorbic acid was used as the reductant for one-pot reduction of both GO and chloroplatinic acid.The hydrogel can be directly used as a flexible binder-free catalytic electrode to achieve high performance of HER.Compared to conventional strategies,the current strategy not only significantly reduces the Pt loading to 3.48 wt%,simplifies the synthesis process,but also eliminates the use of any polymer binders,thus decreasing the series resistance and improving catalytic activity.An overpotential of only 11 mV was achieved on as-prepared PtNP/rGO-MWCNT to drive a geometrical current density of 10 mA/cm2 in0.5 mol/L H2 SO4,with its catalytic activity being kept over 15 h.In acidic medium,the HER activity of the PtNP/rGO-MWCNT catalyst exceeds most of the reported Pt-based electro-catalysts and is 3-fold higher than that obtained on commercial Pt/C electrode.

Three-dimensional nitrogen-doped graphene hydrogel supported Co-CeOx nanoclusters as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane

The development of highly active noble-metal-flee catalysts for catalytic hydrolysis of ammonia borane is mandatory for its application in hydrogen storage. Herein, Co-CeOx nanoclusters have been successfully anchored on a three-dimensional nitrogen-doped graphene hydrogel （NGH） by a simple coreduction method and further used as efficient catalysts to catalytic hydrolysis of ammonia borane at room temperature. Thanks to the strong synergistic electronic effect between Co and CeOx, as well as the strong metal-support interaction between Co-CeOx and 3D NGH, the as-synthesized Co-（CeOx）0.91/NGH catalyst exhibits superior catalytic activity toward hydrolysis of ammonia borane, with the turnover frequency （TOF） value of 79.5 min 1, which is almost 13 times higher than that of Co]NGH, and higher than most of the reported noble-metal-free catalysts.

Self-assembly of graphene oxide nanosheets in t-butanol/water medium under gamma-ray radiation

The research on the properties of graphene oxide（GO） in various media has become one of the hottest topics since GO is now the main raw material for graphene-based advanced materials. In this work, the g-ray radiation chemistry effect of GO nanosheets and their self-aggregation behavior in t-butanol/water medium were investigated. The results show that GO nanosheets are reduced and hydroxyalkylated simultaneously by the alcohol free radicals produced by the radiolysis of t-butanol/water solution under g-ray radiation. The radiation-modified GO nanosheets will self-assemble into a self-standing graphene hydrogel when the p H of the solution is lower than 2. A hydroxyl-functionalized free-standing graphene aerogel is further obtained simply by freeze-drying. This work provides not only a general self-assembly mechanism of GO nanosheets in strong acidic alcohol/water media under high energy radiation, but also a facile and economical preparation method for hydroxyalkylated graphene-based aerogel.

High Rate Performance of Aqueous Magnesium-iron-ion Batteries Based on Fe_(2)O_(3)@GH as the Anode

Aqueous Mg-ion batteries(MIBs)are safe,non-toxic and low-cost.Magnesium has a high theoretical specific capacity with its ion radius close to that of lithium.Therefore,aqueous magnesium ion batteries have great research advantages in green energy.To acquire the best electrode materials for aqueous magnesium ion batteries,it is necessary for the structural design in material.Fe_(2)O_(3)is an anode material commonly used in Li-ion battery.However,the nano-cube Fe_(2)O_(3)combined with graphene hydrogels(GH)can be successfully prepared and employed as an anode,which is seldom researched in the aqueous batteries system.The Fe_(2)O_(3)/GH is used as anode in the dual MgSO_(4)+FeSO_(4)aqueous electrolyte,avoiding the irreversible deintercalation of magnesium ions.In addition,the Fe element in anode material can form the Fe^(3+)/Fe^(2+)and Fe^(2+)/Fe^(3+)redox pairs in the MgSO_(4)+FeSO_(4)electrolyte.Thus,the reversible insertion/(de)insertion of magnesium and iron ions into/from the host anode material can be simultaneously achieved.After the initial charge,the anodic structure is changed to be more stable,avoiding the formation of MgO.The Fe_(2)O_(3)/GH demonstrates high rate properties and reversible capacities of 198,151,121,80,75 and 27 mAh g^(−1)at 50,100,200,300,500 and 1000 mA g^(−1)correspondingly.

Enhanced removal of organic pollutant by separable and recyclable rGH-PANI/BiOI photocatalyst via the synergism of adsorption and photocatalytic degradation under visible light

A novel three-dimension separable and recyclable r GH-PANI/BiOI photocatalyst with the synergism of adsorption-enrichment and photocatalytic-degradation was successfully prepared via a facile three-step hydrothermal method.The three-dimension reduced graphene oxide hydrogel(rGH)in with flower-like BiOI photocatalyst uniformly distributed not only possesses excellent adsorption and electron transport properties,but also is easy to be separated from water for recycling.In addition,polyphenylamine(PANI)provides superior hole transport ability due to its delocalizedл-лconjugate structure.The cooperation of rGH and PANI greatly enhances the separation efficiency of photogenerated carriers,and finally improves the photocatalytic degradation behaviors.The removal rates of Rhodamine B(RhB)by rGH-PANI/BiOI-70%composite under visible light respectively reach 100%and 50.13%in static and dynamic systems,which are 12.85 and 3.58 times of BiOI,respectively.The removal rate does not show decrease after 5 recycles indicating the excellent separable and recyclable property of rGH-PANI/BiOI photocatalyst.The work provides an essential reference for designing and constructing hydrogel-based ternary composite photocatalysts with excellent synergism of adsorption and photocatalysis,which shows great potential in the treatment of water pollution.