WO2013191578A1

WO2013191578A1 - Economic electrochemical cell

Info

Publication number: WO2013191578A1
Application number: PCT/RU2012/000628
Authority: WO
Inventors: Игорь Витальевич БУЗМАКОВ
Original assignee: Buzmakov Igor Vitalyevich
Priority date: 2012-06-18
Filing date: 2012-08-01
Publication date: 2013-12-27
Also published as: RU2012125242A

Abstract

The invention relates to the electrical engineering industry and can be used for the electrolysis of electrolytes and/or for producing electrical energy. The invention comprises an electrochemical cell, which is capable of using the Donnan potential and/or the internal Volta potential of the constituent parts of said electrochemical cell for increasing operational efficiency in electrolyser and current source modes. The Donnan potential of the electrolytes and the internal Volta potential of the conductors of the first order are sufficiently low, and therefore a substantial increase in the efficiency of the cell can be expected, for example, with a reduction in the productivity of said cell by means of a reduction in the voltage supplied to the cell from an external power supply source in the electrolyser mode and by decreasing the standard electrode potential difference of the electrodes in the current source mode.

Description

ECONOMIC ELECTROCHEMICAL ELEMENT

DESCRIPTION OF THE INVENTION

Technical field

The invention relates to the electrical industry and can be used for the electrolysis of electrolytes and / or for generating electricity.

An electrochemical cell is a device for producing electric current due to electrochemical reactions. Electric current may flow as a result of the circuit of an electrochemical cell formed by electrodes and an electrolyte, or under the influence of an applied external potential difference, in the latter case, electrochemical reactions result from the flow of electrical current through the electrochemical cell. /I. I. Gerasimov "The course of physical chemistry." Tutorial: For universities. In 2 t. ETC. - 2nd ed., Rev., the publishing house "Chemistry" Moscow 1973. - 624 s, p. 488 - 489, 573 /

The level of technology

Electrochemical cells are known, the main characteristic of which is an electromotive force equal to the difference in electrode potentials, depending in general on the nature of the substances used, their activities, temperature and pressure. /TO. Fetter "Electrochemical Kinetics", translated from German with the author's additions for the Russian edition edited by Corr. USSR Academy of Sciences prof. Kolotyrkina Ya.M., Chemistry Publishing House Moscow 1967. - 856 p., Pp. 32 - 44 /

During the operation of an electrochemical cell as a current source, the amount of transmitted energy depends on the electromotive force. energy load, and when working as a cell - the amount of energy expended by an external source. In all known electrochemical cells, such physical phenomena as the Donnan potential and the internal contact potential difference of conductors of the first kind are not used as sources of additional electromotive force.

DISCLOSURE OF INVENTION

The invention is an electrochemical cell (hereinafter referred to as Element), using Donnan potential and / or internal contact potential difference (hereinafter CRP) as sources of additional electromotive force (hereinafter emf) to increase the efficiency of electrolysis processes, when voltage is applied from an external of the power supply to the Element electrodes, and in the load connected to the Element electrodes, the net electricity generated by electrochemical reactions on the surfaces of the electrodes, in the absence of eshnego power.

The technical result of the invention is to increase the efficiency of the processes of electrolysis and the production of electricity, i.e. increase of the coefficient of performance (hereinafter the efficiency) of the Element

This result is achieved by the fact that the Element uses the Donnan potential and / or internal PKK of parts of electrodes for obtaining additional emf. in a chain and, as a result, increase in efficiency. The Donnan potential of electrolytes and the internal КРП of conductors of the first kind are rather small, therefore a significant increase in the efficiency of the Element can be expected, for example, when its performance decreases by reducing the voltage supplied to the element from an external power source, during its operation as electrolyzer, and reduce the difference of standard electrode potentials (ie, the voltage on the electrodes), when it works as a current source. It is permissible to reduce these voltages to the minimum level at which electrochemical reactions can take place at the electrodes, since for any electrochemical cell, the rule is always fulfilled that direct current can flow through it only if its external circuit is closed, and electrochemical reactions take place on the surface of its electrodes.

Below are the definitions of some of the terms used in the description of the invention, which are the most significant for understanding the essence of the invention.

The internal contact potential difference is equal to the Fermi energy difference of the contacting conductors, referred to the electron charge value. The internal КРП is a potential difference caused by the diffusion of electrons from a conductor with their greater concentration (and, accordingly, with a higher Fermi energy) into a conductor with a lower concentration (and, accordingly, with a lower Fermi energy). / Sivukhin D.V. General course of physics. Tutorial: For universities. In 5 t. T.III. Electricity. - 4th ed., Stereo. - M .: FIZMATLIT; MIPT Publishing House, 2004. - 656 p. - ISBN 5-9221-0227-3; 5-89155-086-5., P. 451 - 452 /

The electromotive force is the integral of the field strength of external forces in the area containing the current source (in other words, it is the work of external forces in moving a single charge). The external forces in the galvanic cells act on the boundaries between the electrolytes and the electrodes. They also act on the boundary between two dissimilar metals and determine the contact potential difference between them. / Sivukhin D.V. General course of physics. Tutorial: For universities. In 5 t. T. III. Electricity. - 4th ed., Stereo. - M .: FIZMATLIT; MIPT Publishing House, 2004. - 656 p. - ISBN 5 9221-0227-3; 5-89155-086-5., Pp. 189 - 193 /

The sum of the potential jumps on all the interfaces of the circuit is equal to the potential difference between the conductors located at the ends of the circuit, and is called the electromotive force of the conductor circuit ... Ed. a circuit consisting only of conductors of the first kind is equal to a potential jump between the first and last conductors with their direct contact (Volt's law). If the circuit is properly open, then the emf this circuit is zero. A correctly open conductor circuit, which includes at least one electrolyte, the Volta law is not applicable ... Obviously, only conductor circuits including at least one second-type conductor are electrochemical cells (or electrochemical circuits of cells). /I. I. Gerasimov "The course of physical chemistry." Tutorial: For universities. In 2 t. ETC. - 2nd ed., Rev., the publishing house "Chemistry" Moscow 1973. - 624 s, pp. 490 - 491 /

Hole conductivity is due to the presence of quantum states not occupied by electrons in the valence band. Such quantum states are called holes. In an electric field, the holes move in the same way as a positively charged particle with a certain mass would move under classical consideration. Due to the low concentration to the electrons in the conduction band and to the holes in the valence band, the classical Boltzmann statistics is applicable. / Sivukhin D.V. "General course of physics." Tutorial: For universities. In 5 t. ^" D.111." Electricity ". - 4th ed., Stereo. - M .:" FIZMATLIT "; MIPT Publishing House, 2004. - 656 p. - ISBN 5-9221-0227-3; 5 -89155-086-5., P. 431 - 434 /

Polyelectrolytes are polymers capable of dissociating in solution into ions, with a large number of periodically repeating charges arising in one macromolecule. Cross-linked polyelectrolytes (ion exchangers, ion exchange resins) do not dissolve, but only swell, while maintaining the ability to dissociate. / A.A. Tager, Physical Chemistry of Polymers, Chemistry Publishing House, Moscow 1968. - 536 p., Pp. 320 - 321 /

The Donnan potential is an equilibrium potential difference arising at the phase boundary between two electrolytes in the case that this boundary is not permeable for all ions. The impermeability of the boundary for some ions may be due, for example, to the presence of a membrane with very narrow pores, which are impassable for particles exceeding a certain size. Selective permeability of the interphase boundary occurs even if some ions are so firmly bound in one of the phases that they cannot leave it at all. This is how ionic, or ion-exchange groups, fixed by homeopolar bonds in a molecular lattice or matrix, behave in ion exchange resins. The solution inside such a matrix forms together with it a single phase; the solution outside it is the second. /TO. Fetter "Electrochemical Kinetics", translated from German with the author's additions for the Russian edition edited by Corr. USSR Academy of Sciences prof. Kolotyrkina Y.M., Chemistry Publishing House Moscow 1967. - 856 p., Pp. 76 - 79 / The electric double layer is a combination of two oppositely charged layers that appear at the interface between two layers located at some distance from each other. /TO. Fetter "Electrochemical Kinetics", translated from German with the author's additions for the Russian edition edited by Corr. USSR Academy of Sciences prof. Kolotyrkina Y.M., publishing house "KHIMIYA" Moscow 1967. - 856 s, p. 96 /

Intercalated carbon is crystalline carbon, in the interlayer space of the crystal lattice of which molecules of another substance, intercalate, are implanted. Such structures are also called intercalated graphite or graphite embedding compound (hereinafter referred to as CSG). CSAs are divided into two broad classes: donor and acceptor. The redistribution of the electron density between the intercalate molecules and carbon atoms in the acceptor-type GHGs leads to the appearance of an additional number of delocalized holes in the graphite layers. In donor compounds, the implanted substances donate their valence electrons, and conductivity is carried out by excess electrons in the carbon layers. Acceptor compounds are formed during the introduction of substances such as halogens, metal halides, acids. Donor compounds are formed when alkali or alkaline earth metals are embedded in a graphite matrix. / Link to the Internet information resource http://www.nanometer.ru/2008/12/21/grafit_54995.html, Nanometer nanotechnological community, publications / Brief Description of the Drawings

The drawing shows one of the possible options for the construction of the Element in section, the numbers denote its following components:

1 and 3 - two parts of the cathode, a composite positive electrode, on the surface of which electrochemical reactions of reduction of electrolyte cations take place;

1 - the external part of the electrode is a graphite rod, which is in electrical contact with the internal part and is intended, inter alia, to connect an external circuit;

3 - the inner part of the electrode is a compacted briquette of porous activated carbon intercalated with a donor impurity to increase the concentration of conduction electrons of the coal;

2 and 4 - two parts of the anode, a composite negative electrode, on the surface of which electrochemical oxidation reactions of electrolyte anions take place;

2 - the external part of the electrode is a graphite rod, which is in electrical contact with the internal part and is intended, inter alia, for connecting an external circuit;

4 - the inner part of the electrode is a compacted briquette of porous activated carbon intercalated with an acceptor impurity in order to reduce the concentration of conduction electrons and create hole conductivity of coal;

5 - waterproof vessel;

6 - membrane (diaphragm), impermeable to macromolecules of polyelectrolytes, but completely permeable to small ions and molecules, dividing vessel 5 into two parts. One part is the cathode. space, i.e. the space in which the cathode is located, and the second part is the anode space, i.e. the space in which the anode is located. When choosing the permeability of the membrane, the sizes of the solvate shells of ions and molecules in an aqueous solution are taken into account;

7 - an aqueous solution of anionic polyelectrolyte in water dissociating into negatively charged macroions and positively charged small K ⁺ counterions;

8 - an aqueous solution of cationic polyelectrolyte in water dissociating into positively charged macroions and negatively charged small counterions A ^" .

An aqueous solution contains some amount of inorganic salt to prevent, as a result of dissociation, excessive unfolding of macromolecules of polyelectrolytes and to maintain the preferential conformation of macromolecules in the form of a coil. For ions to which this salt dissociates into water, membrane 6 is permeable.

The implementation of the invention

Consider the mechanism of occurrence in the Element, shown in the drawing, the emf associated with the Donnan effect and the internal PKK of type I conductors.

At the cathode, as a result of the dissociation of polyelectrolyte 7 and diffusion into the solution, beyond the coil of the macromolecule of polyelectrolyte, small K ⁺ counterions, near the surface of the inner part 3 of the composite electrode, an increased concentration of positive ions occurs. The positive charge arising near the surface of the composite electrode 3 is not compensated by negatively charged macroions, i.e. macromolecules that have lost some of their small counter-ions as a result of dissociation and diffusion, because due to their size, macroions are farther from the electrode surface. This well-known phenomenon, consisting in the occurrence of a potential difference between the macro-ion of a polyelectrolyte and the solution surrounding it, is called the Donnan effect, and the corresponding potential difference is called the Donnan potential. Thus, the boundary layer of the solution, which is in direct contact with the electrode surface, has a positive charge. As a result of electrostatic induction, a negative charge arises from the conduction electrons on the surface of the electrode adjacent to the solution. Those. at the interface between the surface of the electrode and the solution, a double electric layer appears.

Similarly, at the anode, as a result of the dissociation of polyelectrolyte 8 and diffusion into the solution, beyond the coil of the macromolecule of polyelectrolyte, small counter-ions A ~, an increased concentration of negative ions occurs near the surface of the inner part 4 of the composite electrode. The negative charge arising near the surface of the composite electrode 4 is not compensated by positively charged macroions, i.e. macromolecules that have lost some of their small counter-ions as a result of dissociation and diffusion, because due to their size, macroions are farther from the electrode surface. Thus, the boundary layer of the solution, which is in direct contact with the surface of the electrode, has a negative charge. As a result of electrostatic induction, a positive charge appears on the surface of the electrode adjacent to the solution. Those. at the interface between the surface of the electrode and the solution there is a double electric layer.

On membrane 6, as a result of diffusion of small counter-ions K ⁺ into the anode space, and small counter-ions A ^“ in the cathode space, a double electric layer also appears in accordance with the Donnan effect. Moreover, a positive charge is acquired by a layer of solution bordering the membrane b from the anode space, and a negative charge acquires a layer of solution bordering the membrane 6 from the side of the cathode space, i.e. a field appears on the membrane 6 that accelerates positive ions from the anode space to the cathode, and negates flax from the cathode - to the anode.

At the junction of the inner 3 and outer 1 parts of the composite electrode, an internal CRP arises due to the diffusion of electrons from part 3, made of intercalated graphite donor impurity, into part 1, made of ordinary graphite. A double electric layer appears between the contacting surfaces, with the surface of part 3 being positively charged, and part 1 being negative. Here we consider only the internal CRP associated with the difference in the contacting substances of the concentrations of conduction electrons.

Similarly, at the junction of the inner 4 and outer 2 parts of the composite electrode, an internal КРП arises, due to the diffusion of electrons from part 2, made of ordinary graphite, into part 4, made of intercalated acceptor impurity of graphite. Between the contacting surfaces there is a double electric layer, and the surface of part 2 is positively charged, and part 4 - negative. Here we also consider only the internal CRP, which is related to the difference in the concentrations of conduction electrons from the contacting substances.

Summing up all the potential jumps described above, concentrated in double electric layers at the interfaces between the phases, from the outer part 1 to the outer part 2 of the composite electrodes, we obtain a certain, though small, but non-zero value. Let's call it additional emf. and we denote by E _ext .

Everywhere in the text, including the claims, the dimensions of ions and molecules (generally any particles in a solution) mean the sizes of their solvation shells, on which the dynamic and geometric characteristics of particles in a solution substantially depend.

In the considered example of the implementation of the Element, the internal parts 3 and 4 of the composite electrodes are made of activated carbon, i.e. a material having, among other qualities, a very large surface area. A large surface area of the electrodes is needed, in particular, in order to achieve a practically significant increase in the efficiency of the Element associated with the use of the Donnan potential arising at the interface between the surfaces of the electrodes and the solution.

Undoubtedly, other factors contribute to the appearance and parameters of the electrical double layer at the boundaries between the surfaces of the electrodes and the solution, in addition to the Donnan effect.

One of these factors is the specific adsorption of solution ions on the surfaces of the electrodes, which can lead to a decrease or increase in the double potential jump electrical layer. /TO. Fetter "Electrochemical Kinetics", translated from German with the author's additions for the Russian edition edited by Corr. USSR Academy of Sciences prof. Kolotyrkina Ya.M., publishing house "KHIMIYA" Moscow 1967. - 856 p, p. 102 /

In the claims, we did not reflect the possibility of using specific adsorption to increase the jumps of the potentials of double electric layers between the surfaces of the electrodes and the solution and, as a consequence, the possibility of increasing E _add , although such an increase can be achieved by appropriate selection of materials of electrodes and electrolytes.

Let us further consider examples of the operation of the Element in two modes: in the mode of the current source and in the mode of the electrolyzer.

As an example of the operation of an Element in current source mode, consider the concentration electrochemical element described below. Let small counterions K ⁺ represents a hydrogen ion H ⁺ and small counterions A ^"represent hydroxide ions ^OH", i.e. the cathode space is filled with polyacid, and the anode space is filled with polybase. In the cathode space, i.e. at the cathode, hydrogen is supplied under _a pressure P, and the anode compartment, i.e., to the anode, hydrogen is supplied under pressure P _a . Then we obtain a concentration electrochemical cell without transfer, since mixing polyacid and poliosnovaniya can not occur by reason of the smallness of the membrane pores 6 polyelectrolyte macromolecules 7 and 8, with a combination of two hydrogen electrodes, working at different pressures of gas P _{to the} cathode space and P _a in the anode compartment, wherein R _k is less than P _a At the anode 2, 4, the ionization of hydrogen will occur to a greater extent, than cathode 1, 3. Accordingly, at the cathode 1, 3 the discharge of H ⁺ ions will prevail. This process is reduced to the transfer of hydrogen molecules from a higher pressure to a lower one. The current in the load of such an Element, due to the difference in the activities of hydrogen on the electrodes and, in accordance with the Nernst equation, the difference in electrode potentials, will be increased due to the additional emf. E _dop , the mechanism of occurrence of which is described above. The increase will occur due to the fact that, firstly, when moving through an external circuit from the inside of the anode 4 to the inside of the cathode, 3 fields of double electric layers at the junction of the parts of composite electrodes 4, 2 and 1, 3 for electrons are accelerating; and secondly: when moving through the solution from the inside of the anode 4 to the inside of the cathode 3 fields of double electric layers at the interfaces between the surfaces of electrodes and electrolytes, as well as electrolytes of the cathode and anode spaces between them, are also accelerating for hydrogen ions H ⁺ . For the current source from the above example, this also means that the external hydrogen pressure used for the Element operation can be reduced, leaving the quantitative current output in the load at the same level if additional emf is used in the Element operation. E _add .

As an example of the operation of an Element in the electrolyzer mode, we consider water electrolysis. Suppose that, as in the example of the elements in the current source mode, small counterions K ⁺ are H ⁺ hydrogen ions and small counterions A ^"represent hydroxide ions ^OH" i.e. the cathode space is filled with polyacid, and the anode space is filled with polybase. Macroions in used polyelectrolytes should be more resistant to electrolysis than water molecules, for most polyelectrolytes used in practice, this condition is satisfied. When the Element electrodes are closed, an external circuit containing a voltage source and _external , plus to the anode, and minus to the cathode, current flows through the Element. In this case, an electrochemical reduction reaction of hydrogen ions will take place at the cathode, and an oxidation reaction of hydroxide ions to oxygen will take place at the anode. The current through the Element due to external voltage and _external will be increased due to the additional emf. E _dop , the mechanism of occurrence of which is described above. The increase will occur due to the fact that firstly: when moving through the external circuit from the inside of the anode 4 to the inside of the cathode, 3 fields of double electric layers at the junction of the parts of composite electrodes 4, 2 and 1, 3 for electrons are accelerating; and secondly: when moving through the solution from the inside of the anode 4 to the inside of the cathode 3 fields of double electric layers at the interfaces between the surfaces of electrodes and electrolytes, as well as electrolytes of the cathode and anode spaces between them, for hydrogen ions H ⁺ and hydroxide ions OH ^"are also accelerated. in the electrolysis process, it also means that the external supplied to the cell voltage can be reduced, leaving a quantitative yield of the electrolysis products depends in accordance with the law of Faraday current Jun h element at the same level, if the Element is involved additional emf

Thus, in the examples given above, the Element, having design features aimed at using the potential of Donnan and the internal PKK of type I conductors for more emf in the circuit, it allows to increase the efficiency of electrolysis processes and to obtain useful electric power in the load, which, all other things being equal, entails an increase in the efficiency of the Element.

Claims

ECONOMIC ELECTROCHEMICAL ELEMENT The claims

1. Electrochemical cell, characterized in that it has an electrode partially made of a material with hole conductivity, and uses an internal contact potential difference arising at the interface between conductors with different types of conductivity to obtain an additional electromotive force in the circuit.

2. Electrochemical cell, characterized in that it contains a semipermeable membrane and electrolytes that dissociate into positively and negatively charged ions, differing in size so that the membrane is permeable to small ions, but not permeable to large ions, and uses Donnan potentials arising at the interface phases, for more electromotive force in the circuit.