124results about How to "Excellent supercapacitor performance" patented technology

The invention discloses an oxidized grapheme / polyaniline super capacitor composite electrode material and the preparation method and the application thereof. The preparation method comprise the following steps: firstly, adding oxidized graphite to water for ultrasonic dispersion so as to form an oxidized grapheme solution with uniformly dispersed single pieces; at room temperature, dropping aniline to the obtained oxidized grapheme solution for continuous ultrasonic dispersion to from a mixed solution; at a low temperature condition, adding hydrogen peroxide, ferric trichloride and a hydrochloric acid solution dropwise to the mixed solution, and stirring the solution for polymerization; and after the reaction is finished, centrifugating, washing and roasting the obtained mixed solution in vacuum to obtain the oxidized grapheme / polyaniline super capacitor composite electrode material which is used as the electrode material of an electricity storage system of a super capacitor and a battery. The oxidized grapheme / polyaniline super capacitor composite electrode material with good electrochemistry performance is obtained by the method, and the specific capacity of the oxidized grapheme and the polyaniline is greatly improved. In addition, the addition of the oxidized grapheme improves the charge and discharge service life of the polyaniline.

The invention belongs to the field of material science and energy storage and discloses a biomass-based porous carbon material, a preparation method thereof, and an application thereof in a supercapacitor. The method includes the steps of: 1) drying and crushing rice straws; 2) non-carbonizing or pre-carbonizing the crushed rice straws, uniformly mixing the rice straws with an activator water solution and drying the mixture, or non-carbonizing or pre-carbonizing the crushed rice straws and directly mixing the rice straws with a solid activator uniformly to produce a mixed product; and 3) placing the mixed product in a tube furnace to perform carbonizing activation in an inert gas atmosphere at high temperature; 4) washing the carbonized product in an acid solution and an alkali solution, and washing the carbonized product with deionized water to neutral, and drying the washed product to prepare the biomass-based porous carbon material. The porous carbon material has excellent supercapacitor performance and is simple in preparation method.

The invention discloses a biomass-based grading porous carbon and a preparation method thereof. The method comprises the following steps of shearing and sieving the biomass raw materials to 20 to 80 meshes; adding the materials into a double-salt system water solution; performing stirring; performing low-temperature hydro-thermal method pre-carbonization treatment for 5 to 20h at 180 to 300 DEG C;performing washing and filtering to obtain a pre-carbonization product; then raising the temperature to 600 to 1000 DEG C in inert atmosphere; performing carbonization activation treatment for 0.5 to8h; performing acid washing, alkali washing or ultrasonic treatment on the obtained product; then washing the materials by water to the neutral state; performing drying to obtain the biomass-based grading porous carbon. The hydrothermal carbonization is performed during the pre-carbonization; the double-salt system is used as a salt template and a pre-hole-forming agent; the adverse conditions are provided for the subsequent carbonization activation for preparing the porous carbon; the obtained porous carbon has high specific surface area and the loose three-dimensional connection pore passage structures; high electrical conductivity and good capacitive characters are realized; the biomass-based grading porous carbon can be applied to supercapacitors as carbon electrodes.

The invention discloses a film for a graphene / porous nickel oxide composite super capacitor. The invention is characterized in that the film is of a disordered nano porous structure, the aperture range is 10 to 350nm, the thickness of the film is 1 to 5 mu m, and the weight ratio of graphene to nickel oxide is (0.5:100) to (2:100). The method for preparing the film comprises the following steps: dissolving graphite oxide sheets and magnesium nitrate into an isopropanol solution so as to form a positively-charged graphite oxide sheet sol, then carrying out electrophoretic deposition on the obtained sol so as to obtain a graphene film; and through taking the graphene film as a deposition carrier, preparing a three-dimensional porous film for the graphene / porous nickel oxide composite super capacitor by using a chemical bath film-coating method. The porous composite thin film prepared by the method has the advantages of good mechanical capacity and super-capacitance property, high-discharge specific capacitance, high-ratio charge-discharge properties, high cycle life and the like, and has wide application prospects in the fields such as electric automobiles, communication, consumer electronics, signal control and the like.

The invention provides an electrode material in a hollow tubular structure, and the electrode material is in the hollow tubular structure which consists of a composite hydroxide / copper hydroxide / copper-contained metal substrate. The chemical formulation of the composite hydroxide is MxM'y(OH)2, wherein M is Ni2+ or Co2+, M' is Co2+, Al3+, or Fe3+. According to the invention, a method of solution dipping and constant potential deposition, and a copper hydroxide nanowire array grows on the copper-contained metal substrate in an in-situ manner. The composite hydroxide is deposited on a copper hydroxide nanorod in electrolyte containing mixed metal salt solution in a manner of electro-deposition through employing the method of constant potential deposition. Meanwhile, electrochemical corrosion enables the copper hydroxide nanorod to be dissolved in a process of electro-deposition, thereby obtaining the hollow tubular structure of the composite hydroxide / copper hydroxide / copper-contained metal substrate. The electrode material is good in super-capacitance performance, and can be used for a super-capacitor.

The invention discloses a 3D nitrogen-doped graphene / molybdenum disulfide compound and a preparation method thereof. A 3D nitrogen-doped graphene / molybdenum disulfide composite material (3D G-N / MoS2) is formed via synthesis under the alkaline condition in a homogeneous precipitation method by taking CaC2O4 as a pore forming agent and using a bifunctional reagent thioacetamide to provide a nitrogen source and a sulfur source. CaC2O4 in laminations is removed by ultrasonic dissolution under the acidic condition to form the 3D porous nitrogen-doped graphene / molybdenum disulfide composite material. The preparation method is simple and environment-friendly, MoS2 nano-sheets are uniformly distributed in the surface of graphene, the contact area with graphene is larger, the catalysis performance is high, and the method can be widely applied in the fields including electrocatalysis, photocatalysis and hydrogen evolution catalysis.

The invention discloses a preparation method for a composite electrode material composed of graphite and manganese dioxide. The preparation method comprises the following steps of: firstly, preparing a colloidal solution of a graphite oxide-manganese dioxide composite material by taking the graphite as a carrier, potassium permanganate as a manganese source and citric acid as a reducing agent; secondly, reducing the prepared graphite oxide-manganese dioxide composite material by taking hydrazine hydrate as the reducing agent; and thus obtaining a graphite-manganese dioxide composite material. The material has good performance of a super capacitor, and can be used as the electrode material of the super capacitor.

The present invention discloses a method for preparing an electrode material molybdate for a super capacitor and the application thereof. The method comprises the steps of dissolving cobalt salt or nickel salt and sodium molybdate in a solution formed by water and oleylamine, carrying out hydrothermal reaction, carrying out centrifugation, washing and drying processing, carrying out calcinations under an inert atmosphere, and carrying out grinding to obtain powder to obtain a carbon-coated molybdate super capacitor electrode material. The carbon-coated cobalt molybdate or nickel molybdate electrode material prepared by the preparation method is applied to the super capacitor, and the method has the advantages of simple synthesis process, good repeated performance and mass production.

The invention discloses a method for preparing composite of grapheme with different oxidation degrees and manganese dioxide. The method comprises the processes of: respectively carrying out low-temperature, intermediate-temperature and high-temperature subsection reactions on original graphite, and concentrated sulfuric acid with a mass concentration of 98% and potassium permanganate so as to obtain graphite oxide; dispersing the graphite oxide in de-ionized water, and reducing the prepared graphite oxide with hydrazine hydrate so as to obtain the grapheme oxide with different oxidation degrees by controlling reduction time; and mixing the grapheme oxide with MnCl2*4H2O in an isopropyl alcohol solution, and adding a water solution of the potassium permanganate to prepare the composite of the grapheme with the different oxidation degrees and the manganese dioxide through oxidation reduction. The method provided by the invention has the advantages as follows: materials used in the method are rich in storage amount and low in cost, so that the method is good in commercialization; an dispersing agent, a stabilizer and the like do not need to be added, and a pure chemical technology is used, so that simple operation, no pollution and low energy consumption can be realized; and the prepared composite material of the grapheme and the manganese dioxide has high purity and good stability.

The invention relates to preparation methods of porous carbon from towel gourd vegetable sponge and a composite material of the porous carbon and application of the porous carbon and the composite material in supercapacitor electrode materials. The method for preparing the porous carbon comprises the following steps: (1) washing the towel gourd vegetable sponge, and performing carbonization heat treatment in an atmosphere containing NH3 at a proper temperature; (2) mixing the carbonized product and KOH in a proper proportion, and activating in N2 at the temperature of 750 DEG C. The inner diameter of pore passages of the prepared porous carbon is between 1mu m and 15mu m, the pore wall thickness is between 0.3mu m and 1mu m, and the activated specific surface area can be 1510m<2> / g. The method for preparing the composite material comprises the following steps: reacting the porous carbon with a KMnO4 solution, and growing MnO2 nanosheets, thereby obtaining a porous carbon / MnO2 composite material; or reacting the porous carbon with aniline to obtain a porous carbon / aniline composite material. When serving as the supercapacitor electrode materials, the prepared porous carbon and the composite material thereof have more excellent performance and favorable application prospect compared with a conventional carbon material.

The invention belongs to the technical field of material science and energy chemical engineering, and discloses a biomass-based nitrogen self-doped porous carbon material and a preparation method and application thereof. The preparation method includes the steps that chitin or chitosan is treated in high-temperature water at 180-300 DEG C for 2-24 hours, and a pre-carbonized product is obtained; the pre-carbonized product is mixed evenly with an activating agent aqueous solution, then the mixture is dried and heated to 600-1000 DEG C in an inert atmosphere for carbonization and activation for 0.2-10 hours, and the carbonized product is washed with an acid solution, then washed with water to be neutral and dried to obtain the biomass-based nitrogen self-doped porous carbon material. The high-temperature water treatment is conducted on chitin or chitosan, a favorable condition is thus provided for subsequent carbonization and activation for the preparation of the porous carbon material, and the nitrogen self-doped porous carbon material is excellent in super capacitor performance and CO2 adsorption property.

The invention relates to a manganese dioxide / ferric oxide nanometer composite material as well as a preparation method and application thereof, and belongs to a preparation technology and application field of inorganic matter composite materials. The structure of the composite material is characterized by utilizing a manganese dioxide nanometer bar as main body and covering nanometer ferric oxide granules on the surface of the manganese dioxide nanometer bar, wherein the composite material is prepared by utilizing potassium ferrocyanide and potassium permanganate as raw materials, and performing hydro-thermal synthesis, solid-liquid separation and drying steps on the raw materials, and the prepared inorganic nanometer composite material has excellent supercapacitor property. The preparation method of manganese dioxide / ferric oxide nanometer composite material provided by the invention is simple in structure and low in cost, and no dispersing agent or template is added; furthermore, the obtained manganese dioxide / ferric oxide nanometer composite material has the advantages of strong controllability, excellent supercapacitor property, and the like, so that the manganese dioxide / ferric oxide nanometer composite material has brilliant industrial application prospect.

The invention discloses a three-dimensional porous compound film of a super-capacitor and a preparation method thereof. The preparation method comprises the following steps of: reacting for 60-180 seconds by the cathodic electro-deposition method to generate a three-dimensional porous nano nickel film; reacting for 100-400 seconds to deposit by using the three-dimensional porous nano nickel film as the carrier and the cathodic electro-deposition method, compounding a cobalt hydroxide nano sheet layer on the three-dimensional porous nano nickel film and preparing the three-dimensional porous nano nickel / cobalt hydroxide nano sheet compounded film for the super-capacitor, wherein the aperture of the three-dimensional porous nano nickel layer is 5-10 microns; the distance between the sheets of the cobalt hydroxide nano sheet layers is 10-300 nm; the thickness of the compound film is 30-200 microns; and the weight ratio of the cobalt hydroxide nano sheet to the three-dimensional porous nono nickel film is 5:100 to 20:100. The compound film disclosed by the invention has high capacitance, high power, high energy density and high cycle life and has wide application prospect in the fields such as electric automobiles, communication and signal control and the like.

The invention belongs to a metal-organic framework material, and discloses a composite nanometer metal-organic framework material which has a spherical three-dimensional nanoflower structure and whichis formed by self-assembling of metal ions and an organic component, and application of the material in super-capacitor performance. A one-step synthesis technique is adopted, and self-assembling ofa terephthalic acid organic ligand, cobalt chloride and nickel chloride in a mixture solution consisting of N,N-dimethyl formamide, ethanol and water is utilized to obtain the metal-organic frameworkspherical nanoflower structure with uniform distribution dimension and size and with a diameter of 7-12 [mu]m. Similar nanometer materials can be synthesized by the method. In addition, the metal-organic framework material has a high number of active sites and has good electrical conductivity, so that the metal-organic framework material has good super-capacitor performance.

The invention relates to a preparation method of an electrode material of a silver / graphene thin film supercapacitor, which comprises the steps: (1) dispersing oxidized graphite into ultrapure water at room temperature, adding silver nitrate after performing ultrasound, agitating and mixing the mixture and then adding sodium borohydride, and continuously agitating the mixture to obtain a partially reduced silver / oxidized graphite dispersion, wherein the mass ratio of sodium borohydride to oxidized graphite is 2:1-1:1; and (2) adding sodium borohydride into the partially reduced silver / oxidized graphite dispersion, raising temperature to 70-85 DEG C under nitrogen atmosphere, maintaining temperature for 1-3h, and performing centrifugal washing to obtain a silver / graphene dispersion; filtering the silver / graphene dispersion to form a film-like product; and washing the product with ultrapure water to obtain the electrode material of the silver / graphene thin film supercapacitor. The preparation method is simple and the film forming process is free from a conducting additive and a bonder, so that the preparation method is appropriate for industrialized production. The electrode material of the silver / graphene thin film supercapacitor obtained by the invention has high specific capacitance and good conducting performance, higher flexibility and wide application prospect.

The invention discloses an electron beam irradiation method for the preparation of nitrogen-doped reducing graphene. The method comprises the steps of: a, preparing a urea solution, adding graphene oxide, placing in an ultrasonic oscillator, and mixing the solution uniformly; b, adding isopropanol, then adding aqueous ammonia solution, and stirring the mixed solution in a magnetic stirrer for thorough mixing; c, placing the mixed solution in a sealed container, and introducing nitrogen to saturate the nitrogen in the solution; d, subjecting the nitrogen saturated mixed solution to irradiation treatment under electron beam irradiation generated by an electron accelerator; e, washing the irradiation reaction product with ethanol, washing with distilled water, and separating in a high speed centrifuge to remove unreacted ions; and f, drying the products from separation in a vacuum oven to obtain a black nitrogen-doped reducing graphene material. The method has the advantages of simple process, mild conditions, cheap and easily available raw materials, no toxic solvent and environment-friendliness; and the produced nitrogen-doped graphene material has a super capacitor performance.

The invention relates to a nano-porous copper-loaded shape-controlled copper-based oxide composite as well as a preparation method and application thereof. The composite comprises an amorphous matrixat a core layer, nano-porous copper layers clamped at the two sides of the amorphous matrix and a copper-based oxide layer prepared through in situ oxidation, wherein the amorphous matrix is a TixCuyZrz alloy ingredient, x, y and z are atomic percents, x is more than or equal to 45 and less than or equal to 60, y is more than or equal to 40 and less than or equal to 50, z is more than or equal to1 and less than or equal to 5, and the sum of x, y and z is equal to 100; and the thickness of each nano-porous copper layer is 1.5-4[mu]m, ligament width is 32-55nm, and aperture size is 18-42nm. Theinvention simplifies preparation technology and avoids unnecessary energy waste, and copper-based oxides are generated through in situ oxidation on the surface of nano-porous copper and are firmly combined with a substrate, so that the composite can be taken as electrode slices of a supercapacitor independently.

The invention relates to the field of the synthesis of composite materials, and provides an in-situ preparation method of a three-dimensional conductive MOF@MXene composite electrode in order to solvethe problem of poor conductivity of MOFs, which comprises the following steps: adding MAX phase powder into an HF solution, etching for 5-24 hours, centrifugally washing with deionized water until the pH value of the upper solution is 6-7, and carrying out vacuum drying to obtain multilayer MXene powder; uniformly dispersing the powder in the deionized water, adding chloroacetic acid, stirring atroom temperature, adding a NaOH solution, carrying out stirring reaction for 1-12 hours, carrying out centrifugal washing, and carrying out vacuum drying to obtain MXene-COOH powder; dispersing the powder into the deionized water, adding a metal salt, a ligand and ammonia water in order, carrying out air-blowing stirring reaction at 50-70 DEG C, and finally, carrying out centrifugal washing and drying to obtain the three-dimensional conductive MOF@MXene composite powder. The method is efficient and stable in process and simple in process, the prepared composite powder can serve as a super-capacitor electrode material, and the stable and efficient energy storage is achieved.

The invention discloses a preparation method for an electroactive polypyrrole film. The preparation method comprises the following steps of: preparing an aqueous solution of single pyrrole, an electrolyte solution and a protonic acid solution; secondly, mixing the three solutions; and obtaining a polypyrrole film electrode material on a conducting substrate by using a unipolar pulse electric polymerization. According to the preparation method disclosed by the invention, the operation is simple; products are easily obtained; no oxidant is needed; and the secondary pollution caused by the oxidant is avoided. The polypyrrole film electrode material prepared by the method in a neural solution has higher discharging stability.

The invention relates to a manganese dioxide nanowire array electrode on a titanium substrate and a preparation method thereof. The electrode is formed by manganese dioxide nanowire arrays on the titanium substrate, the diameter of a single manganese dioxide nanowire is 50-500 nanometers, and the manganese dioxide nanowires are vertically, uniformly and tensely distributed on the surface of titanium and are in an array form. The preparation method of the electrode comprises the following steps of fully mixing potassium permanganate, deionized water, acetone and hydrochloric acid solution to obtain mixed solution; arranging a titanium sheet in the mixed solution, arranging the mixed solution into a reactor, sealing the reactor, heating the reactor to 200 DEG C, and keeping the temperature for nine hours to ten hours; taking the titanium sheet out after the mixed solution is naturally cooled down, and obtaining the manganese dioxide nanowire array electrode on the titanium substrate. The manganese dioxide nanowire array electrode is applied to a lithium ion battery to show good circulating performance and rate capability and applied to a supercapacitor to show excellent electrochemical performance.

The invention discloses graphene paper and a preparation method and application thereof. According to the preparation method disclosed by the invention, the preparation of the graphene paper is performed by taking conventional graphite paper as a basal body. The preparation method comprises the following specific steps: S1, performing oxidation stripping on the graphite paper by using a mixed oxidizing agent with strong oxidizing property, and then, cleaning and drying; S2, performing high-temperature calcination reduction on oxide graphene paper under an inert gas atmosphere to obtain the graphene paper. The preparation method is simple in process and low in cost, and suitable for large-scale volume industrial production. A paper form is kept by the prepared graphene paper, so that the graphene paper is very high in stripping degree, excellent in electrical conductivity and superhigh in specific surface area and very good in electrochemical capacitance performance. Compared with a traditional powder operation method, the preparation method is more convenient. The graphene paper product can be directly used as an electrode material of a supercapacitor, and is broad in application prospect in the energy storage aspect.

The invention relates to a preparation method of a graphene film for a supercapacitor. The method comprises the steps of (1), washing oxidized graphite with deionized water at a room temperature, mixing with the deionized water to a suspension with a concentration of 1-5mg / ml, conducting ultrasonic for 1-3h, removing sediment in the centrifuge washing process, rotationally evaporating at 40-45 DEG C until oxidized graphite collosol is formed, and (2), placing an oxidized graphite film with a mix proportion of 1:40-120cm<2> / mL into hydrazine hydrate, reacting for 4-15h at 90-120 DEG C, and washing with the deionized water. The preparation method is simple, no conductive agent or binding agent is required, an easy-to-industrialize blade-coating film forming method is adopted, and the obtained graphene film for the supercapacitor is high in specific capacitance, good in conductivity and higher in flexibility, and has wide applications in energy storage fields such as supercapacitors and lithium ion batteries.

The invention discloses a preparation method of a shape-controllable ordered layer porous chromium carbide skeleton carbon material for a supercapacitor. In a preparation process, a chromium carbide precursor with a special shape is synthesized through template control, a chromium atom is removed by using an etching agent in situ to obtain a micropore, then orderly arranged meso pores with regular pore passages are obtained by removing a mesopore template to form porous carbon hierarchically combined by meso pore and micropores, wherein the shape of the chromium carbide framework carbon can be controlled through a template process, the relative content of the micropores and the meso pores can be adjusted through controlling a synthesis reaction condition and a raw material ratio, and thus the ordered layer porous chromium carbide skeleton carbon the pore structure and the pore diameter distribution of which are accurate and adjustable in atom-scale level and controllable in shape is obtained. According to the preparation method, a shape-controlled porous electrode material for a novel supercapacitor, which is high in specific capacitance, small in ion diffusion and transfer impedance, better in rate capability, excellent in cycle performance and controllable in shape can be obtained.

The invention discloses a method for preparing a manganese dioxide nanosheet in a low-temperature hydrothermal mode. The method comprises the steps that potassium permanganate is used as a raw material, ethanediol is used as a reducing agent, SDS is used as a surfactant, and the manganese dioxide nanosheet is integrated in one step in the low-temperature hydrothermal mode. The manganese dioxide nanosheet is loose in layer, large in gap, large in specific area and good in electrical conductivity and super capacitive performance. The raw materials are easy to obtain, the cost is low, practicability is strong, environmental friendliness is achieved, and the method has the good application prospect in the aspect of supercapacitor electrode materials.

The present invention provides a carbon / manganese oxide composite material and a preparation method thereof. The carbon / manganese oxide composite material can be used as a supercapacitor electrode material. According to the carbon / manganese oxide composite material and the preparation method thereof of the invention, cheap, environmentally friendly, renewable and easily available wood flour is adopted as a raw material to prepare the carbon / manganese oxide composite material, the preparation method of the invention is advantageous in low cost compared with methods according to which excellent but expensive carbon materials such as ordered mesoporous carbon, graphene, carbon nanotubes and fullerenes are adopted; the carbon material in the composite material of the invention is an activated carbon material, and the activated carbon material itself can contribute high capacitance; and manganese oxide is loaded in situ on the surface of the activated carbon material through a high-temperature hydrothermal oxidation reaction, and therefore, the capacitance output capacity of the composite material can be improved.

Disclosed is a block supercapacitor, including two or more unit cells configured such that electrodes having a layered structure are disposed to face each other in an in-plane structure, wherein the two or more unit cells comprises an electrode arranged adjacent to each other respectively and the electrodes adjacent to each other are connected in series. As the unit cells are connected in series, a high-voltage supercapacitor can be provided.

The invention discloses a method for preparing a hierarchical pore carbonic oxide microsphere material. The method comprises the following steps: A, impregnating PU foam with a PAA solution, and drying for 6-20 hours at 50-90 DEG C in vacuum; B, heating the PU foam after impregnating and drying in an inert gas atmosphere, namely heating for 0.5-3 hours at 80-120 DEG C, increasing the temperature to 170-230 DEG C and heating for 0.5-3 hours, and increasing the temperature to 270-330 DEG C and heating for 0.5-3 hours; and C, roasting for 1-6 hours at 500-800 DEG C in the inert gas atmosphere after the heating treatment in the step B is completed, and cooling to room temperature. The method is simple, has low cost and short reaction time, and is suitable for industrial production; and the prepared carbonic oxide microsphere material has an ideal flower-like spherical shape, a micropore-mesopore-macropore hierarchical porous structure, a large specific surface area, high nitrogen content and excellent electrochemical performance, and has huge application prospects in the field of super-capacitors.

The present invention discloses composite with high energy storage capacity in energy storage devices comprising graphene, mesoporous graphitic carbon nitride (mc@g-C3N4) and to the process for preparation thereof. The present invention further discloses electrodes employing the said compositie and fabrication of high energy high power storage devices such as the Electric Double Layer Capacitor (EDLC) with these electrodes.

A composite material of an electrode unit includes: a porous electrode material being 50˜95 wt % of the composite material; an electret material being greater than O wt % and less than 15 wt % of the composite material; a dispersant material being 0˜15 wt % of the composite material; an adhesive material being 0˜15 wt % of the composite material; an electric conduction auxiliary agent being greater than O wt % and less than 30 wt % of the composite material. The porous electrode material includes porous particles and the electret material is distributed among the porous particles.

The invention discloses a high-performance nickel-cobalt oxide composite nanowire film for a super capacitor. Nickel salt and cobalt salt are used as raw materials, the nickel-cobalt composite nanowire film is generated on a metal titanium substrate, wherein the molar ratio of nickel salt and cobalt salt is 1-5:1-5. The film not only has the advantages of larger specific surface area, simplification in electrode preparation process, alkaline environment stability and the like, but also has excellent super capacitance performance, such as high quality specific capacity and favorable cycle performance, and is an excellent electrode material for the super capacitor in electrochemistry.