DE1496217A1 - Fuel elements for aqueous electrolytes - Google Patents

Description

Oipl.-lng.nipl.oec.publ. ·. DIETRICH LEWINSKY PATENT ADVOCATE MlKku -PmIm. Aams-BwMiier-Slrri · 2iJ ^TeWon18139 February 27, 1964

74 - L / W

Societe Generale de Constructions Bleotriques et Meoanlques (ALSTHOM), Paris 16, avenue Kleber 16 (France)

"Fuel elements for aqueous electrolysis"

French priority dated March 1, 1963 from the French Patent application No. 2389 (Beifort)

There are numerous. Types of fuel elements known for aqueous electrolytes, which operate at low temperatures » and use oxygen and a fuel, usually hydrogen, directly. These elements generally have a electrode fed with the fuel, which oxidizes itself electrochemically by losing electrons, and one with Oxygen-fed electrode that electrochemically reduces itself by accepting electrons, these electrodes both are in contact with the same electrolyte as they are separates and the solution of an acid, a base or a * "Most of the time, because of the very poor reaction kinetics of the oxygen in an acidic environment, one is concentrated" Base solution used. But this basic environment is not necessarily that which is responsible for the oxidation of the fuel would be cheapest. In addition, in the case of carbon-containing fuels being turned, there is often an increasing formation of carbon «or formic acid» salts in the basic solution.

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From round the electrochemical kinetics one could for the Select the reduction of oxygen and, for the oxidation of the fuel, electrolysis with different pH values. A Element that actually has an electrolyte with a certain pH for the electrode of the fuel and another electrolyte with a different pH for the electrode of the oxygen would use, there would have to be one between the two electrolytes Have a partition that prevents diffusion between the two « but has only a low electrical resistance. A separation of the two half-elements with a simple porous Diaphragm either does not prevent rapid diffusion,

which leads to the neutralization of the two electrolytes, or resistance, sits too high / fuel elements of the mentioned redox Type that operate at low temperature with aqueous electrolyte, do not use the direct electrochemical reduction of oxygen and the direct electrochemical oxidation of the fuel, but use etween-Redoxsysteine. These redox systems, which are each dissolved in an electrolyte, go electrochemically from one degree of oxidation to the other within the element and are chemically returned to the initial state outside the element. The latter takes place under the influence of the oxygen or the fuel, while the electrolyte circulates between the element, where it flows to an electrode, and the regenerator.

The redox system, which serves as an intermediate system for the oxygen, is reduced electrochemically in the element

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an electrode, where electrons are withdrawn from it, and will then re-oxidized by oxygen in the regenerator outside the element. The redox system, which serves as an intermediate system for the fuel, is electrochemically oxidized in the element at another electrode by electrons flow in, and is then reduced again in a regenerator outside the element by the fuel.

The two systems must work quickly and reversibly. The Redcx element has at least one electrode around which the Carrier electrolyte of one redox system flows, an electrode, around which the carrier electrolyte of the other Redcx system flows, and a diaphragm dividing the element into two parts and separates the two carrier electrolytes from one another. This diaphragm is intended to allow diffusion between the two redox systems and thus prevent their mixing, but only have ... a low electrical resistance.

By the way, every redox system should have an oleic weight potential in the vicinity of the oxygen and the fuel have, under the respective environmental conditions, a maximum of free enthalpy of oxidation in the form of electrical energy of the fuel through the oxygen.

As is well known, the gleiehgewloht potential of the changes System oxygen - water (or ions of water) with the pH of the electrolyte. Under conditions of normal temperature and normal pressure and in relation to a normal hydrogen electrode, it follows the line: 909820/1028

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E ₁ (volts) - 1.23 ~ 0.058 ₁

The redox system that is chosen as the intermediate system for the oxygen »should have an equilibrium potential as close as possible to E ₁ , but somewhat lower.

The same applies to fuel. For example, follows at Hydrogen is the equilibrium potential of the system hydrogen - water (or ions of water) under conditions of normal temperature and normal pressure unfl in relation to the Normal - hydrogen electrode with changing pH of the electrolyte the relationship:

E ₂ (volts) - 0.00 τ'0.058 PH ₂

The redox system, which is chosen as the intermediate system for the hydrogen, should have an equilibrium potential as close as possible to E ₂ , but somewhat higher.

When the pH of the electrolyte In the two half-elements is the same, E. and Eg are not independent. which consumes hydrogen and oxygen then gives you:

H ₁ ■ « Ii ^ + 1.25 (volts;)

The equilibrium weight potentials of the two redox elements are therefore no longer independent. If the probability of finding a redox system that corresponds to all points of weight is small istf so the probability of finding two of them is the due to the condition that different equilibrium potentials are compared with one another, much less. One has

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By the way, until now on electrolysis of strong acids and stronger Bases limited. In this way, not only the difference between the equilibrium potentials becomes »but even more so its absolute Set altitude and leads to exploration of only a very limited range of redox systems.

In fact, the equilibrium potential of numerous redox systems changes according to a Hegel that _{differs from O 4} 058 pH (and often does not change at all even in a certain pH range) * It will be possible for a large number of such soluble, faster and reversible systems to choose a pH value so that its equilibrium potential at this pH is close to E. It is also possible for a large number of such soluble, faster and reversible systems

its »to choose a pH value so that its Gleiohgewlohtspotentia.l is in the vicinity of E ₂ . The redox element can therefore be built up in such a way that one selects a redox system from the first and the second group, both of which use an electrolyte with a suitable pH. But the diaphragm "that separates the two electrolytes of such an element" is intended to prevent diffusion between the two electrolytes and thus their neutralization of an optimal element with electrolytes of the same pH value is the same in both half-elements (e.g. 1.23 V for the element under normal conditions that uses hydrogen and oxygen.

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The invention asked a special separator for

and ^ which works under defined conditions. These Device allows * different pH values in both Using half-elements opposes the diffusion between the two with an increased resistance *, on the other hand, hardly inhibits the Migration of certain ions present and allows it * one theoretical electromotive force to maintain «the same is the one who would have an element »the same Starting materials using only one electrolyte consumed. The invention thus represents an additional structural variant. For setting up fuel elements with aqueous electrolytes in general and especially for Redoxel ducks by using the two in this case Makes redox systems partially or completely independent of each other »

According to the invention, this separating device consists of a combination of one or more ion exchange membranes and certain electrolyte solutions that are designed in such a way that the number of cations transported except H ^{+ is} either zero or only very low compared to those of the cationic membranes and the number of transported anions other than OH "is either zero or only very low compared to that of OH" in the anionic membranes.

Ion exchanger membranes have already been used in fuel elements * mainly as Slekfcrolvte in solid form or as 909820/1028

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Diaphragms that are designed to allow only the passage of ions, but not that of neutral molecules »In the case of redox elements, these diaphragms serve to» prevent the diffusion of the constituents of the redox system. In the device according to the invention, the ion exchangers also exercise their already known functions, but their ability to selectively permeate ions and the resulting membrane potentials are added.

It is known that when a membrane (selective or not) is placed between two solutions, the. contain several types of ions in different concentrations, a potential E _M = E ₀ ~ E ₁ develops between the surfaces of the membrane, which is calculated

Solution (2)

• ^ - / 2; Ii ^{d L} ° e ^a ] i Z ₁

'Solution (1)

in which R has the Gaslconstante »T is the absolute temperature, F is the Faraday" see ZaIiX and a ^ _y ^ t, and Z _± oils activity, the transport number and the value (as algebraic value) of the ion i represent..

If the membrane is cationic and of high selectivity, ie practically impermeable to anions, the relevant values for the anions In in the expression of E _{n are} negligible. The environment surrounding the membrane continues to exist

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apart from H ⁺ only contains those cations which cannot diffuse through the membrane, be it because they are too large or from another orund, the potential goes back to the

| 2L

- | 2L Log - ^ - [| t] - - 0.058 (PH ₂ - PH ₁ ) volts

If the membrane is anionic and of high selectivity, i. is practically impermeable to cations »the relevant values for the K & t & ons in the expression for E ^ are negligible. If the environment surrounding the membrane continues apart from OH "only contains such anions" which cannot diffuse through the Heabrän "be it" that they are too large are or for some other reason, so that goes. Potential goes back to the equation

0 * 058 (PH ₂ -

If several anionic and cationic membranes are connected

) ■ · ■

so that each of them works under conditions to be defined, it is easy to see that the potential difference between the solutions surrounding this compound will correspond to the

B ₁₄ «0.058 (pH ₂ - PH ₁ ) VoIt

Between membranes operating under the conditions defined above, the diffusion of solutions 1 and 2 is very low if the selectivity is high (it becomes zero »

■ ■ * in if the selectivity is 100g, what / some special

BAJj-

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actually occurs), pas real potential of the membrane becomes all the closer to his theore derived above " table value !! «gen * The higher the selectivity.

There are currently numerous types of anionic and cationic exchanger membranes available · »which have a high Have ion selectivity and the passage of! Your one, offer only a slight resistance to valuable ions.

The example of the element hydrogen - oxygen shows that the theoretical electromotive force of the element of direct oxidation - reduction with two electrolytes and a separating device according to the invention remains the same as that of a single electrolyte. If one considers an element "which directly consumes hydrogen and oxygen and has two electrolytes with different pH, of which the one in contact with the electrode for oxygen" and the other in contact with the electrode for hydrogen "with these electrolytes are separated by one or more Ioneimratauscheriaeratoranen and hold such connections ^ that the number of transported cations except E " ⁵ " is equal to zero or is »low compared to that of Ef * in ^ eder kafcionic membrane and the number of anions transported other than OH""Equal to zero or very low compared to that of OH * in every anionic membrane, then under conditions of normal temperature and normal pressure and in relation to the Korjaal -Ihydrogenelectroö © the equilibrium potential of the system oxygen - water (or ions of water)

9 0 9 8 2 0/1 Ö 2 8 bad 0ί ^: .: · 3!: - ί &.

E ₁ (volt) »1.25 - 0.058 PH ₁ - 1 0 -

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and that of the system hydrogen - water (or ions of water)

E ₂ (volts) = 0.00-0.0158 PH ₂
Then the potential difference between the surfaces of the separator is:

E _M (volts) - 0.058 (PH ₁ - PH ₂ )
The theoretical electromotive force of the element is thus:

E * E ₁ - Eg Ψ Ej ^ = 1.25 volts
this is the same as with only one electrolyte «

► One can also show, as an example of the element oxygen - hydrogen, that the theoretical electromotive force of a redox elemite with two electrolytes and a separating device according to the invention remains the same as that with only one electrolyte Contains? H in each half-element, these electrolytes being separated from one another by one or more ion exchange membranes and containing such compounds that the number of cations transported except. H ⁺ equal to zero or very low compared to that of H ⁺ in each cationic membrane and the number of anions transported other than 0H ^{r are} equal to zero or very low compared to that of OH "in each anionic membrane, so every redox system has to be under theoretical conditions Equal weight potential that is equal

to the system H ₀ - mass (or ions of water) and 0_ «water ο * 2 2

"O. (or ions of water).

_a Under conditions of normal temperature and normal pressure

iv> and in B @ EUg on the normal hydrogen electrode, the equation

weight »potential of the redox system * that as an intermediate - ^ ""..'■

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serves the oxygen «so:

E ₁ (volt) «1.25 - 0.058 PH ₁

and the redox system, which serves as an intermediate system for the hydrogen:

E ₂ (volts) »0.00 - 0.058 PH ₂

The potential difference between the surfaces of the separator is therefore:

E ₁₄ (volt) - 0.058 (PH ₁ - PH ₂ )

This results in the theoretical electromotive force of the element as:

E = E ₁ - E ₂ + E _M »1.2? volt

this is the same as the theoretical of a redox element, whose two electrolytes have the same pH.

The construction of the separator and the condition of the two Electrolytes, the general definition of which has already been given, are explained in more detail by means of a few examples.

It should first be remembered that an aqueous electrolyte should meet two conditions here: It should be a conductor, and its pH should be buffered * If it consists of the concentrated solution of a strong acid or a strong base, these two conditions are met at the same time. If, on the other hand, if you want to use an electrolyte whose pH is neither strongly acidic nor strongly basic, you have to set it to the Buffer desired pH, which is done in different catfish can. The examples are limited to those cases in which

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“This buffering is achieved by means of mixtures of buffer solutions will. It is known that a buffer mixture consists of a mixture of equivalent amounts of an appropriate acid and base, both of which

defined in the Brönsted * sense. :

The buffer mixes considered here are »theirs Base and acid molecules with a higher molecular weight are "big enough" not to be able to pass through the membranes; the The indurability of a membrane is evidently not an » multiple function of the molecular weight of the particle »but depends on numerous factors» such as the physical Structure and chemical nature of the membrane «the chemical Nature "the form, the value of the particle" etc .; very numerous organic systems are useful »all of them Cover the pH range. These non-diffusible particles are marked with the letter K.

Two types of buffer mixtures are unterseheidem 2sää! £ JLL When the acid of the buffer a cation R ⁺ ( "lie corresponding base, then another cation or a neutral particle that can be ROH review) is" they arose in Fojrtn of Salt RX of a strong acid HX (X ^r - SO ·, * "*, Cl", NOj »etc.). Following Ttilchenarten are in the solution then orhanden in appreciable concentrations \: R ⁺ »ROH, X ~.

Type 2; If the base of the buffer is an anion R "(the corresponding acid is then another" anion or a neutral 'particle "that can be written RH), it turns into

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In the form of a base MR of a strong base MOH (H ⁺ => Na ⁺ , K *, etc.) · The following types of particles are then present in the solution in noticeable concentrations: R "*, RH, M ⁺ .

The following examples show that the separation device can be carried out with pH buffering of one and the other electrolyte: with strong acid, strong base or a Buffer mix of one type or the other.

example 1

The two buffers are of type 1 Electrolyte 1 cationic membrane electrolyte 2

R ⁺ RAW

x '

R ¹ OH

In the borderline case, in which one milieu is strongly acidic, becomes the buffer is replaced by a strong acid HX ':

Electrolyte 1 cationic membrane electrolyte 2

R "*

H ⁴

.1'

RAW

(Incidentally, X 'can also be a large anion). As bases ROH and R ¹ OH, compounds such as lauryl-pyridiniura-hydroxides, cetyl-pyrldinium-hydroxide, hexamethyl-tetramine, polyvinylpyridine * larigkettige can serve as bases. quaternary amines, etc. The membranes "ASAHI * type CSO and CMQ", the membranes "AMP" can be used as catlonisohe membranes.

type C-60 and C-IOJ-C etc.

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Example 2

The two buffers are of type II: electrolyte 1 anionic membrane M * R **

RH

In the borderline case _s in which the; an environment is strongly basic, the buffer is replaced by a strong base M'OH: electrolyte 1 anionic © membrane. Electrolyte 2

Electrolyte 2

M '+ R ^1-

R ¹ H

tr R "" RH

OH*

(Incidentally, M '"*" can be a large cation here). As acids BH and B * H, compounds such as polystyrene _{sulfonic acid, naphthalene sulfonic acid 5} citric acid, conyl naphthalene sulfonic acid * long-chain sulfonic and carboxylic acids, etc. can be used as anionic membranes, for example the membranes "kShEl" type ASG and AMG * the membranes "AMP" type iU60 Tjnd Ä-104 B etc..

Example 3

The buffers are different
Electrolyte 1 cationic membrane, anionic «membrane electrolyte

M ⁺ R ^f "

ROH R ¹ H

As acids R ¹ H * bases ROH and cationic and anionic membranes, for example, those mentioned in the preceding examples

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th connections and membranes are used.

The connection between the two membranes can be a direct one. You can also fill one with liquid In between, they leave either the solution of a strong acid RH with a large anion or the solution of a strong base Must be RAW with large cation.

Here, too, if the electrolyte 1 should be strongly acidic, the buffer is replaced by a strong acid HX; likewise, if the electrolyte 2 should be strongly basic, the buffer replaced by a strong base MOH. If these two borderline cases are brought about at the same time, one has: electrolyte 1 cationic membrane anionic membrane electrolyte

H " ¹

M ⁺

OH

If a strong acid with a large anion is used, the cationic membrane can be lost. If you use a strong base with a large cation, the anionic membrane can be omitted. If you use a strong one at the same time Acid with a large aeolon and a strong base with a large cation, in this way a single membrane can be used, which can be of either type. In this latter case

diffusion is practically zero,
co

JJJ The conductivity of the electrolytes is essentially determined by

ο "," j. ·. · ■

^. the small mobile ions X and M secured when using the buffer mixtures considered ο; in the case of a strong acid or a strong base, all ions present contribute to the conductivity, if it is a base with a small

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Cation and an acid with a small anion, and almost only the ions H * and OH *, if it is a Särace with a large anion and a base with a large cation. The conductivity can be increased if necessary, by, in the case of an electrolyte, with a buffer of the Type 1 is a Sals RX of a strong acid with a small anion and a weak base with a large cation, and in the case of an electrolyte with a type 2 buffer, a salt MR of a strong acid with a large anion and a strong base with a small cation adds. Of course, the acids, bases, buffers and salts chosen should be electrochemical under the working conditions be indifferent *.

In the case of redox elements, they should be the electrolyte added redox systems leave them in their generally defined composition, which is easy to do if the Redox systems are otherwise suitable, i.e. if they are not ; can diffuse through the diaphragm «Man vird for the selection of such suitable redox systems all the different properties of ion exchange membranes can be used, e.g. compared to the components of the redox systems. (Especially the organic redox systems, by the way most of them, have very often high molecular weight particles that cannot penetrate the ion exchange membrane @ n). Naturally must use the redox systems with all others in the solutions existing components are compatible

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If a fuel element is equipped with a separating device according to the invention, the oxidation of the water * substance or one of the redox systems charges the corresponding electrolyte with positive xons, while the reduction of oxygen or another redox system charges the corresponding electrolyte with negative ions Wanderungestrom, the electric neutral! did usr * Lööiwßen restore searches, done in LCIT $ .on ± sQhsa Koipbranea by the H ⁺ "ion and the anionisahen membranes through the OH" ions ,, ions, which dig respective membranes offer me little resistance.

The above examples are only intended to show that there are many possibilities, different ones. Use pH value® in the two half- elements according to the invention. One can also "brew" all Herkiaale of selectivity and specificity of Mem, which not only relate to the type of ions; For example, certain cationic (or anionic) membranes become less permeable to even small cations (or anions) when their valency increases. All the different properties of ion exchange membranes can be used to advantage _? to & A £ the various solutions yeiae the electrolyte hersustellen taking into account the general definition of the separation device.

In certain cases, in the case of the elements themselves, one of the two electrolytes can simply come from the Maabran itself; consist «if the separating device only consists of ₄ or one of the

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two membranes "if it comprises two. Sine kationiaehe Hern bran in the H ^ form (or an anionic membrane in the OH " • Shape) itself represents an electrolytic environment by definition.

It is also to be noted in the case of R © dox <3l © ra © nten that it is possible is * a dual redox system only for one electrode to use »while the other electrode is directly oxygen or consumes fuel. In this case, the electrolyte. " which is in contact with this latter electrode, simply consist of the membrane itself, if there is only one, or from the membrane which is closest to the electrode if the diaphragm has several membranes.

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Claims (12)

/ Ore - '. ~ ¹⁹ 'U96217 Patent claims: (1.) Separating device for burners working at low temperatures Material elements for * wiisrlga electrolytes, which directly consume the oxygen and the fuel, whereby an electrolyte with a certain pH is in contact with the oxygen electrode and another electrolyte with a different pH is in contact with the pulp electrode, and for fuel elements working at low temperatures for Aqueous electrolytes of the redox type with an electrolyte with a certain pH in one of the two half-elements and another electrolyte with a different pH in the other of the two half-elements, a separating device which offers increased resistance to the diffusion of the two electrolytes, but only a low one electrical resistance, the element retains a theoretical electromotive force equal to that which an element with only one electrolyte or with two electrolytes with the same pH would have, and thus represented an additional variable in the structure of the element which is particularly useful in the case of Redox elements 1st, since they are e whose two redox systeresis give partial or complete independence, characterized in that they consist of one or more analogous and cationic ion exchange membranes, which are composed of a liquid electrolyte lying in between ° are surrounded or separated, associated with such electrolyte ro solutions that adjoin each diaphragm dis that the number of ο. v. transported cations other than H equal to zero or only very low compared to that of H ⁺ in each cationic membrane and the number of transported cations other than OH * equal to zero or only very little compared to that of OH * in every anionic membrane is *; «. _p /, r, oR ^ t ^ 'AL ^ _n H96217 2. Separating device according to claim 1, characterized in that the electrolyte is the solution of a cationic membrane Buffer mixture with the desired pH is the acid (in the sense of «?. von Brönsted) is a cation that does not pass through the membrane can diffuse, the buffer in the form of the salt the corresponding base and a strong acid with a small mobile anion is present. yy. Separating device according to claim 1, characterized in that the electrolyte on a cationic membrane is a strong acid solution. ^. Separating device according to claim 1, characterized in that The electrolyte on a cationic membrane is the solution of a strong base with a cation that does not cross the membrane can diffuse through. 5. Separating device naoh claim 1 to 4, characterized in that that the electrical conductivity of the electrolyte on a cationic membrane is increased by adding a salt a strong acid with a small mobile anion and a strong base with a cation that does not cross the membrane can diffuse through. 6. Separation device according to claim 1, characterized in that the electrolyte on an anionic membrane is the solution of a buffer mixture with a pH value whose base (in the sense of Br ^ö nsted) is an anion which cannot diffuse through the membrane, wherein the buffer in the form of salt 909820/10 23 - 21 - the corresponding acid is present with a strong base with a small mobile cation. 7. Separating device according to claim 1, characterized in that the electrolyte on an anionic membrane is a solution of a strong base, 8. Separating device according to claim 1, characterized in that the electrolyte is the solution of an anionic membrane strong acid with an anion that cannot diffuse through the membrane. 9. Separating device according to claim 1 to 8, characterized in that that the electrical conductivity of the electrolyte on an anionic membrane is increased by adding a salt strong acid with an anion that cannot diffuse through the membrane and a strong base with small mobile cation. 10. Separating device according to claim 1 to 9, characterized in that that the anions and cations that are not just as thermal membranes can diffuse through, organic ones Are high molecular weight particles. 11. Separating device according to claim 1, characterized in that one of the two electrolytes of the element is an ion exchange membrane itself is. -. / ~ 22 « 9098 ^ 0/1028 H9621-7 12. T, nnvorrichtung to A _n demanding I ₁ characterized in 'that the organic into the electrolyte dissolved redox systems, their components are of such high molecular weight that they do not by the membranes lonenaustauschermem "can diffuse hinduoh. Separating device according to claim 1, characterized in that the redox element only uses an intermediate redox system for one electrode, while the other electrode consumes either the oxygen or the fuel directly. 909820/1028