PL221361B1 - Electrochemical capacitor working in dihydroxybenzene solutions - Google Patents

Description

Description of the invention

The subject of the invention is an electrochemical capacitor working in dihydroxybenzene solutions, consisting of two porous carbon electrodes with a developed surface, working in an electrolyte solution with the addition of dihydroxybenzenes (1,2- or 1,4-1

-dihydroxybenzene) in an amount of 0.38 mol L ^-1 . This type of capacitor is used as an energy storage device.

Electrochemical capacitors (also called supercapacitors), unlike conventional energy sources, i.e. electrochemical cells, accumulate a charge in an electrical double layer. The charging of the electrical double layer consists in the separation of charges and then their accumulation in the pores of the electrode at the electrode / electrolyte interface. Therefore, it is necessary to use electrode materials with a developed specific surface (most often 2 -1 carbon materials with a surface area above 1000 m ² g ^-1 ) and appropriate porosity, which was described in the works:

Elżbieta Frąckowiak, Franęois Beguin "Electrochemical storage of energy in carbon nanotubes and nanostructured carbons" Carbon 40 (2002) 1775-1787 and Elżbieta Frąckowiak "Carbon materials for supercapacitor application" Physical Chemistry Chemical Physics 9 (2007) 1774-1785. Due to the electrostatic nature of the accumulation of charge, supercapacitors are characterized by very high power, which they are able to deliver in a very short time (on the order of a few milliseconds). Thanks to this, they have been used in various types of applications that require high power, such as: hybrid drives in vehicles (mainly in start / stop systems or energy recovery during braking), port cranes, safety systems in aircraft (landing gears) and electricity management. produced from renewable sources (wind turbines, solar cells). Electrochemical capacitors can also use Faraday reactions during energy storage. These types of chemical reactions, related to the change in the oxidation state of the reactants (redox reactions), are the main source of energy in conventional electrochemical cells. In the case of supercapacitors, they allow you to increase the capacity, the so-called pseudocapacity and energy density, therefore the electrochemical capacitor accumulating the charge as a result of charging and discharging the electrical double layer and from the redox reaction is called a pseudo-capacitor. Obtaining the pseudo-capacity effect in carbon materials can be obtained by appropriate modifications, as described in the work: Elżbieta Frąckowiak, Franęois Beguin "Carbon m aterials for the electrochemical storage of energy in capacitors" Carbon 39 (2001) 937-950, such as:

1) carbon oxidation aimed at increasing the oxygen content in the form of functional groups (e.g. by chemical treatment, electrochemical polarization),

2) formation of carbon / conductive polymer composites by electropolymerization of a monomer (aniline, pyrrole) on the surface of a carbon electrode or by chemical polymerization methods,

3) introducing electroactive particles of transition metal oxides such as RuO2, TiO2, Cr2O3, MnO2, Co2O3 into the carbon material.

An innovative solution is to use the phenomenon of pseudo-capacity, for which the electrolyte is responsible, not the electrode material. Different types of solutions, in which the abovementioned redox reactions occur under the influence of polarization, can be successfully used as a pseudo-capacity source, e.g. the invention application P-386352 "Carbon electrode of a supercapacitor in iodide solutions". So far, in scientific reports on this subject, there has been some information about capacitors using a mixture of sulfuric acid and hydroquinone as an electrolyte, e.g. in the work: Silvia Roldan, Marcos Granda, Rosa Menendez, Ricardo Santamaria, Clara Blanco "Mechanisms of energy storage in carbon -based supercapacitors modified with a quinoid redox-active electrolyte "The Journal of Physical Chemistry 115 (2011) 17606-17611] and Silvia Roldan, Clara Blanco, Marcos Granda, Rosa Menendez, Ricardo Santamaria" Towards a further generation of high-energy carbon -based capacitors by using redox-active electrolytes ”Angewandte Chemie 123 (2011) 1737-1739. Supercapacitors operating in an electrolyte containing different redox pairs are also the subject of patent applications: application P-392370 "Electrochemical capacitor" or WO 2010068929 (A2) Cambis Jose Farahmandi (Chula Vista, California, USA) "Active electrolyte electrochemical capacitor". In each case, the coupling of appropriately selected redox pairs was used, allowing to obtain high capacitance and energy values of the capacitor.

Electrochemical characteristics of capacitors working in acidic solutions (1 mol

L ^-1 H2SO4) with the addition of dihydroxybenzenes proved that for each of these systems only one

PL 221 361 B1 from the electrodes has a high capacity. In the case of the electrolyte H2SO4 + 1,4 dihydroxybenzene it was the negative electrode, while in the case of the electrolyte H2SO4 + 1,2-dihydroxybenzene it was the positive and / or negative electrode.

Since the total capacitance of the capacitor is the resultant of the capacitance of both electrodes, according to equation (1).

_ 1 1 ć - c ~ ⁺ ~ c ~ _ the application potential of each of these systems seemed untapped.

-1 -1

In the case of operation of a capacitor with a solution of 1 mol L ^-1 H2SO4 + 0.38 mol L ^-1 1,4-dihydroxybenzene as an electrolyte, a significant increase in the capacity of the system can be noticed only after the appropriate number of cycles that the system must run. This is due to a process called grafting. In this case, it consists in increasing the number of oxygen groups through specific electrosorption of 1,4-dihydroxybenzene on the surface of the carbon material, thanks to which the share of the quinone / hydroquinone redox reaction in subsequent cycles becomes greater. As a result, the capacity of such a system increases accordingly. This process is shown in Fig. 2.

Reversible electrode reactions, the records of which are given below, are treated as a source of pseudocapacity.

1,2-dihydroxybenzene θ cyclohexane-3,5-diene-1,2-dione

1,3-dihydroxybenzene cyclohexane-1,3-dione

Reactions (2) and (3) are fast and reversible, while reaction (4) is most often irreversible and usually takes place only in the presence of additional strong oxidants. This is due to a thermodynamically unprecedented form of conjugated benzoquinones in cyclohexane-1,3-dione.

Each of these reactions takes place in a different potential region, which allows to use them as redox conjugated pairs, giving the effect of pseudo-capacity increasing the capacitance of the capacitor.

The invention relates to an electrochemical capacitor working solutions dihydroksybenzenów consisting of positive and negative electrodes made of carbonaceous material with a developed surface area of at ₂ least 200 m ² / g located in the electrolyte, characterized in that the positive electrode -1 is located in the electrolyte, which is a mixture of two solutions: 1 mol L ^-1 -1

H2SO4 and 0.38 mol L ^-1 1,2-dihydroxybenzene, the solvent of which is water, while the electro-1 da negative is located in the electrolyte, which is a mixture of two solutions: 1 mol L ^-1 H2SO4 -1 and 0.38 mol L ^-1 1,4-dihydroxybenzene in which the solvent is water.

It is advantageous if the electrolytes are separated by separators and a membrane.

Due to the use of the capacitor according to the claims of the invention, the following technical and operational effects were obtained:

The capacitance of a capacitor operating with coupled redox pairs as electrolyte has increased compared to a capacitor operating only with sulfuric acid as electrolyte, even with a current regime of 10 A g ^-1 .

-1 -1> Higher value of gravimetric power density (approx. 1000 W kg ^- ) and energy (approx. 4 Wh kg ^- ) compared to a capacitor operating only in 1 mol L ^-1 H2SO4, whose density value is -1 -1 energy decreases to approx. 1 Wh kg ^-1 with a simultaneous power density of approx. 1000 W kg ^-1 .

The invention has been shown in the drawings, where Fig. 1 shows a diagram of a capacitor, Fig. 2 dependence of capacitance on voltage (before and after cyclicity) for a capacitor with an electrolyte

-1 -1 mol L ^-1 H2SO4 + 0.38 mol L ^-1 1,4-dihydroxybenzene, Fig. 3 comparison of the capacitance of a condenser working only in sulfuric acid solution and working in a solution of 1 mol L ^-1 H2SO4 + 0.38 mol L ^-1 1,4-dihydroxybenzene, Fig. 4 dependence of the capacitance on the discharge current density, Fig. 5 shows the Ragone diagram for the abovementioned capacitor, i.e. the dependence of gravimetric energy on power.

The present invention is based on the use of the electrochemical activity of sulfuric acid solutions modified with the addition of a suitable organic compound, i.e. 1,2- or 1,4-dihydroxybenzene. This means that the electrodes 3 and 4 of the capacitor work in different electrolytes 1 and 2, separated from each other by separators 5 and membrane 6.

Since each of the electrodes in combination with the appropriate electrolyte constitutes an independent, electrochemically active redox system, it is possible to use them efficiently and achieve a high capacity value.

The invention is illustrated by the following example:

P r z k ł a d I

The electrodes of the electrochemical capacitor were made of active carbon, the real surface of which was 1470 m ² g ^-1 . Tablets with a diameter of 10 mm and a thickness of approx. 7 mm were obtained by pressing in a hydraulic press the mixture: 85% by weight. % carbon material, 10 wt. % binder (Kynar Flex 2801) and 5 wt. acetylene carbon black. Then, the electrodes prepared in this way together with separators (Whatman GF / F) were transferred to vials containing solutions of appropriate

-1 -1 of electrolytes with a sulfuric acid concentration of 1 mol L ^-1 and 0.38 mol L ^{-1 of} dihydroxybenzene and left for 24 hours. After this time, the separators (Whatman GF / F) were soaked with electrolytes and transferred together with the electrodes to the electrochemical vessel. Four types of electrolytes were tested.

mol L ^-1 H2SO4 mol L ^-1 H2SO4 + 1,2-dihydroxybenzene mol L ^-1 H2SO4 + 1,3-dihydroxybenzene (for comparison) mol L ^-1 H2SO4 + 1,4-dihydroxybenzene

Capacitors constructed in this way were subjected to electrochemical tests: cyclic voltammetry (1-20 mV / s), galvanostatic charge / discharge (200 mA / g-10 A / g).

The capacitance values were respectively: 135, 140, 120, 260 F g ^-1 for the discharge current density of 1 Ag ^-1 .

Claims (2)

Patent claims 1. An electrochemical capacitor working solutions dihydroksybenzenów consisting of positive and negative electrodes made of carbonaceous material with a developed surface competent _two inputs of at least 200 m ² / g located in the electrolyte, characterized in that the positive electrode 1 (4) is arranged in electrolyte (1), which is a mixture of two solutions: 1 mol L ^- H ₂ SO ₄ and 0.38 mol L ^-1 1,2-dihydroxybenzene, the solvent of which is water, while the negative electrode (3) is located in the electrolyte (2 ), which is a mixture of two solutions: 1 mol L ^- H ₂ SO ₄ and 0.38 mol L ^-1 1,4-dihydroxybenzene, the solvent of which is water. 2. The electrochemical capacitor according to claim 1 The method of claim 1, characterized in that the electrolytes (1) and (2) are separated by separators (5) and a membrane (6).