PL221360B1 - Electrochemical capacitor working in dihydroxybenzene and an alkali metal iodide solutions - Google Patents

Description

Description of the invention

The subject of the invention is an electrochemical capacitor working in solutions of dihydroxybenzenes and alkali metal iodides, 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-dihydroxybenzene, respectively) in the amount of 0.38 mol L ^-1 and an alkali metal iodide solution. 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 basic energy source 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 their appropriate modifications, as described in the paper: Elżbieta Frąckowiak, Franęois Beguin "Carbon materials 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, Cr3O3, 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

The electrodes showed 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), the application potential of each of these systems seemed to be unused.

-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.

(2)

1,4-dihydroxybenzene θ cyclohexane-2,5-dieno-1,4-dione

(3)

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

1,3-dihydroxybenzene θ 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, comprising positive and negative electrodes disposed in the electrolyte, positive electrode and negative are made of WĘGLO ₂ ester with a surface area of at least 200 m ² / g located in the electrolyte, characterized in that the positive electrode it is situated in the electrolyte which is the containing solution

-1 -1 -1 iodide ions with a concentration of 0.05 mol L ^- - 5 mol L ^- , preferably 1 mol L ^- , whose solvent is water, while the negative electrode (3) is located in the electrolyte, which is a mixture of two

-1 -1 -1 solutions: 0.01 mol L ^-1 - 0.5 mol L ^-1 , preferably 0.38 mol L ^-1 1,4-dihydroxybenzene or 1,2-di-1 -1 -1 hydroxybenzene and 0.01 mol L ^-1 - 5 mol L ^-1 , preferably 1 mol L ^-1 H 2 SO 4, of which water is the solvent.

PL 221 360 B1

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

Due to the high electrochemical activity of the above-mentioned redox pairs, electrochemical studies have also shown that the coupling of redox pairs containing dihydroxybenzenes and solutions of other elements or compounds such as iodine in the following configurations is beneficial:

- the positive electrode 4 is situated in the electrolyte 1, which is a mixture of two solutions -1 -1 -1: an aqueous solution containing iodide ions with a concentration of 0.05 mol L ^-1 - 5 mol L ^-1 , preferably 1 mol L ^-1 , while the negative electrode 3 is situated in the electrolyte 2, which is a mixture of two solutions -1 -1 -1 -1 equal to: 0.01 mol L ^-1 - 0.5 mol L ^-1 , preferably 0.38 mol L ^-1 - 1,4-dihydroxybenzene and 0.01 mol L ^-1 -1 -1 mol L ^-1 , preferably 1 mol L ^-1 H2SO4 - positive electrode 4 is located in electrolyte 1, which is a mixture of two solutions: an aqueous solution containing ions iodide with a concentration of 0.05 mol

-1 -1 -1

L ^-1 - 5 mol L ^-1 , preferably 1 mol L ^-1 , while the negative electrode 3 is situated in the electrolyte 2, -1 -1 -1 which is a mixture of two solutions: 0.01 mol L ^-1 - 0.5 mol L ^-1 , preferably 0.38 mol L ^-1 1,2-di -1 -1 -1 hydroxybenzene and 0.01 mol L ^-1 - 5 mol L ^-1 , preferably 1 mol L ^-1 H 2 SO 4.

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

> The capacity of a capacitor working with redox coupled pairs as electrolyte has increased compared to a capacitor working only with sulfuric acid as electrolyte, even with a current regime of 10A 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 it decreases to approx. 1 Wh kg ^-1 with a simultaneous power density of approx. 1000 W kg ^-1 .

> In the case of a capacitor operating in a solution of sulfuric acid with the addition of 1,4-dihydroxybenzene as the electrolyte, using the cyclic voltammetry method in a three-electrode system, it was shown that the electrode with a much larger capacity was the negative electrode.

-1 -1

As a result, the electrolyte with a concentration of 1 mol L ^-1 H2SO4 + 0.38 mol L ^-1 1,4-dihydroxybenzene can be used as the negative electrode electrolyte in coupled redox pairs; the electrolyte of the positive electrode should be an alkali metal iodide solution.

> In the case of sulfuric acid with the addition of 1,2-dihydroxybenzene as the electrolyte, using the cyclic voltammetry method in a three-electrode system, it was shown that the electrode with a much larger capacity is the positive electrode. As a result, the solution of H2SO4 + 1,2-dihydroxybenzene can be used as the electrolyte of the negative electrode in a coupled redox pair, in which the electrolyte of the positive electrode is an alkali metal iodide solution.

The invention is illustrated in Fig. 1 which is a schematic diagram of a capacitor.

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 and an alkali metal iodide. 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 1

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. 0.7 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 were transferred to vials containing electrolyte solutions. The positive electrode was placed in a 1 mol L ^-1 aqueous solution of potassium iodide, while the negative electrode 3 was placed

-1 -1 remained in electrolyte 2, which is a mixture of two solutions: 1 mol L ^-1 H2SO4 and 0.38 mol L ^-1 1,2-dihydroxybenzene. The vials were closed 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.

-1 -1

The capacitance value was 184 F g ^-1 for a discharge current density of 1 A g ^-1 .

Claims (1)

Patent claims 1. An electrochemical capacitor working solutions dihydroksybenzenów and alkali metal iodides consisting of positive and negative electrodes made of carbon material of a size ₂ vignette surface area of at least 200 m ² / g located in the electrolyte, characterized in that the positive electrode (4) is arranged it is in the electrolyte (1), which is a solution containing iodide ions -1 -1 -1 with a concentration of 0.05 mol L ^- - 5 mol L ^- , preferably 1 mol L ^- , the solvent of which is water, while the negative electrode (3) it is situated in the electrolyte (2), which is a mixture of two solutions -1 -1 -1 equal: 0.01 mol L ^-1 - 0.5 mol L ^-1 , preferably 0.38 mol L ^-1 1,4-dihydroxybenzene or 1,2-dihydroxy-1 -1 -1 benzene and 0.01 mol L ^-1 - 5 mol L ^-1 , preferably 1 mol L ^-1 H 2 SO 4, whose solvent is water. 2. The electrochemical capacitor according to claim 1 A method as claimed in claim 1, characterized in that the electrolytes (1) and (2) are separated by separators (5) and a membrane (6).