Process for making semipermeable polymers with ion exchange and ion conductive capabilities on an electrically conductive substrate

The process for preparation of semipermeable polymer layers with ion-exchanging and ion-conducting capabilities comprises the steps of making and depositing a polymer layer in situ by electrochemical polymerization on an electrically conductive substrate and subsequently cross-linking, by heating or irradiating. The electrochemically formed polymer layers are built up of poly(oxyphenylene) or poly(naphthylene) chains, in which the aromatic units contain the ion-exchanging and ion-conducting groups. These polymer layers are suitable for use as a semipermeable membrane in an electrode/membrane unit, as a selective layer or as a component of a selective layer of potentiometric and amperometric sensors and as a solid polymer electrolyte in electrochemical cells.

BACKGROUND OF THE INVENTION 
The present invention relates to a semipermeable polymer layer, which is 
semipermeable to charge carriers and/or permeable to neutral species, and 
more particularly to a process of its manufacture in front of or overlying 
an electrically conductive substrate, and its use and application. 
Placing the semipermeable polymer layer as a membrane in front of an 
electrically conductive substrate is generally known. The determinant 
membrane behavior to separate charge carriers or/and to be permeable to 
neutral species is governed by its structure and different driving forces 
involved in use of the membrane. An incorporation of ion exchanging and 
ion-conducting components into an individual polymer chain of the membrane 
allows for selecting a chemical species to be separated from other 
species; the permeability of the polymer layer further limits passage of 
the species through the membrane to only one kid of charge carried by the 
species. The incorporated ion-exchanging and ion-conducting components 
which are carrying a charge themselves are known as fixed sites. For each 
charge of the fixed sites, there is a corresponding counterion, which is 
present in the membrane. The separation capability of the membrane is 
based on the exchange or counterions with ions of the same polarity 
present in the solution (adjacent the membrane containing the species to 
be "separated"). Simultaneously, the exchange of co-ions of the same 
polarity as the fixed sites is prohibited. Therefore the passage of the 
co-ions through the membrane is suppressed. 
It is desirable that such polymer layers be made pinhole free, chemically 
inert and show high mechanical stability. Furthermore, the permeation and 
the exchange procedure or species should be carried out with high 
selectivity and high velocity. 
The application of polymer layers of prior art showing ion exchange and ion 
conducting properties of a membrane is based on two distinct manufacturing 
steps: 
1. The preparation of an ion exchange resin. 
The ion exchange resin is made by chemical polymerization or 
polycondensation. Such procedures provide a direct incorporation of ionic 
groups (fixed sites) into the polymer. When chemical mixed polymerization 
of styrene and divinylbenzene is used, a successively applied chemical 
introduction of ionic groups is required (F. Helfferich; Ionenaustauscher, 
Verlag Chemie, Weinheim, 1959). 
2. The crocessino of the ion exchange resin to a semipermeable membrane. 
The processing is carried out either by dissolving in an appropriate 
solvent only the ion-exchange resin or a mixture of the ion exchange resin 
and a binder (referred to as matrix --i.e. polystyrene, polyvinylchloride 
or polyethylene). The membrane is mechanically attached to the 
electrically conductive substrate by cast coating procedures, i.e., 
dip-coating or spring-coating processes. After the solvent evaporation, 
the polymer remains on the substrate and can subsequently be used as a 
membrane. Such membranes currently used are made, e.g., of Nafion, a 
perfluorinated polymer, containing sulfonic groups (Wilson A. d., Prosser 
H. J. (Eds.); Developments in Ionic Polymers, Elsevier; Vol 2, London, 
1983). They are capable of exchanging cations. 
The transport of species to be separated through the membrane is a 
kinetically slow process. Therefore, the permeation of the species through 
the polymer layer is dependent upon the thickness of the layer. This fact 
makes the layer thickness an important variable for the permeation rate, 
which up to now could be exploited only in a limited way by applying 
casting techniques of prior art. Furthermore, the thickness of membrane 
layers manufactured by techniques of prior art is strongly dependent on 
the nature of the electrode surface to be coated. For example, using non 
pretreated and consequently rough substrate surfaces, the cast layers 
exhibit a relatively broad thickness range of at least 0.05 mmm to 0.1 mm 
due to the conditions of their preparation. Consequently, the fabrication 
of uniform membranes of thicknesses lower than that mentioned above is not 
feasible. A polished and consequently very smooth surface of the substrate 
enables the fabrication of uniform layers of thickness of about 200 nm. 
However, in that case, the thickness of the membrane is dependent upon the 
nature of the required solvent which is used for the processing of the 
precursor materials. 
With decreasing layer thickness of the polymer the possibility of creating 
pores and cracks increases. The polymer layer thus loses its unique and 
advantageous membrane property of separating charges of the permeating 
species. It is known that the membrane diffusion coefficients of species 
to be separated by such polymer-coated electrodes are lowered by a 
magnitude of three to four orders of magnitude when compared to those in 
the electrolyte solution. Therefore, the hitherto process for making a 
semipermeable polymer on the electroactive surface of the substrate yields 
a product with limited application and usefulness. (Espenscheid M. W., 
Ghatak-Roy A. R., Moore III R. B. et al., J. Chem. Soc., Faraday Trans. 1, 
82 (1986) 1051-70.) 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of our invention to provide a process of 
manufacturing, on conducting surfaces, a semipermeable polymer layer with 
ion exchange and ion conducting capabilities, which preferentially leads 
to thinner polymer layers (with thicknesses in submicrometer range) and 
which allows for a high exchange rate of species to be separated. The 
advantages of the procedure particularly are that the preparation of the 
polymer which exhibits ion-exchanging and ion-conducting properties is 
carried out in one processing step with high productivity, 
reproducibility, all of which is independent of the nature of the 
substrate surface upon which the polymer layer is disposed. The polymer 
layers are developed to provide a pinhole free membrane. 
In keeping with this object and with others which will become apparent 
hereinafter, our process comprises the steps of making a semipermeable 
polymer from an electrolyte bath by electrochemical polymerization of 
OH-containing aromatic monomers with acidic or basic functionalized groups 
or alternatively by copolymerization or mixed polymerization of said 
aromatic monomers with noncross-linkable or cross-linkable OH-containing 
monomers, respectively. The polymer is then deposited in situ on the 
electrically conductive substrate and subsequently cross-linked. The 
OH-containing aromatic monomers are selected from the groups of phenols or 
of naphthols. 
Several embodiments of our invention are possible. The polymer layer can be 
built up from a cation-exchanging monomer which has an aromatic 
OH-containing group containing acidic functionalized groups at the ortho-, 
meta- or para-position thereof. Advantageously, the acidic functionalized 
groups are carboxy, sulfonic, phosphinic or phosphonic groups. 
Alternatively, the polymer layer can be built up from an ion-exchanging 
monomer which has an aromatic OH-containing group containing basic 
functionalized groups at the ortho-, meta- or paraposition thereof. 
Advantageously, the basic functionalized groups are primary, secondary, 
tertiary amines, or quaternary ammonium compounds containing the same or 
different aliphatic groups having one to four carbon atoms. However, the 
basic functionalized groups of the aromatic monomer from which the polymer 
is built are linked to the OH-containing monomer by an aliphatic alkylene 
chain having one to five carbon atoms. 
In one embodiment of the invention the polymer can be built up by mixed 
polymerization or copolymerization of OH-containing monomers mentioned 
above with cross-linkable OH-containing aromatic monomer. Advantageously, 
this noncross-linkable monomer contains at least one aliphatic group with 
two to seven carbon atoms. Advantageously, the electrochemical preparation 
and deposition occurs on an electrically conductive substrate, which is 
connected to an electrical source to form an anode. In the process 
according to our invention the thickness of the polymer layer is 
controlled by the charge, which is consumed during the electrochemical 
polymerization, to achieve a thickness of 50 nanometers to 500 
micrometers. The electrolyte solution may contain an adherence promoting 
agent. The cross-linking of the polymer layer may be achieved by heating 
or by irradiating. 
Our invention also comprises the use of the polymer layer either as a 
semipermeable membrane within an electrode/membrane unit, as a selective 
layer or as component of a selective layer for potentiometric and 
amperometric sensors, which are made according to the above-described 
procedure. Our process also allows the use of the polymer layer as a solid 
polymer electrolyte. 
In the process according to our invention the formation of the polymer 
layers is carried out electrochemically in an electrolytic bath and 
results in development of very thin and pinhole free layers with uniform 
layer thickness which are in situ deposited on the electrically conductive 
substrate connected as an anode. In keeping with the above polymer layer, 
the presence of OH-containing aromatic units which bear basic or acidic 
functionalized groups in the polymer matrix provides the membrane with 
charge-selective ion exchange and ion conducting capabilities. The 
concentration of the basic and acidic functionalized groups is controlled 
by the portion of OH-containing, noncross-linkable aromatic units. 
Furthermore, the cross-linking degree in the polymer layer is determined 
by the portion of OH-containing, cross-linkable aromatic units. This leads 
to an optimization of the semipermeable polymer layer as to its 
selectivity to species to be separated. 
The use of an OH-containing aromatic monomer which does not bear any basic 
or acidic functionalized substituents for the production of a permeable 
polymer film is described in the Literature in Anal. Chem. (1987), pp. 
1758-1761. The polymer film used exhibits a permeability to small ions, 
especially H.sup.+, Fe.sup.2+ and Br. It is reported, that the 
permeability is exclusively dependent upon the size of the Stokes radii of 
the species. Thereafter, the species discrimination concerning their 
charge has not been considered. Because this is a different discriminating 
mechanism compared to that which our invention is based on, it could not 
be expected that the use of OH-containing aromatic monomers which bear 
acidic and basic functionalized groups will result in a preparation of a 
polymer film exhibiting charge-selective and semipermeable ion-exchange 
capabilities.

DETAILED DESCRIPTION OF THE INVENTION 
The polymer layers used according to our invention are built-up of 
poly(oxyphenylene) or poly(naphthylene) chains, both phenylene and 
naphtylene units, respectively, bearing ion-exchanging and ion-conducting 
acidic or basic functionalized groups in ortho-, meta-, or para-position. 
Acidic functionalized groups suitable for the preparation of a 
cation-exchanging and cation-conducting membrane are the carboxy (--COOH), 
sulfonic, (--SO.sub.3 H), phosphinic and phosphon groups, advantageously 
carboxy or sulfonic groups. The suitable cation-exchanging monomers may be 
4-hydroxyhenzenesulfonic acid, 3-hydroxyhenzoic acid, 
4,5-dihydroxynaphthaline-2, 7-disulfonic acid. 
The basic functionalized groups suitable for the preparation of an 
anion-exchanging and anion-conducting membrane are primary (--NH.sub.2):, 
secondary (--NHR.sub.1), tertiary amines (--NR.sub.1 R.sub.2), and 
quaternary ammonium compounds (--NR.sub.1 R.sub.2 R.sub.3), which are 
connected to the OH-containing aromatic group by aliphatic alkylene groups 
having one to five carbon atoms, advantageously one to two carbon atoms. 
The saturated aliphatic groups R.sub.1, R.sub.2, and R.sub.3 of the amines 
or ammonium units can be the same or different. The saturated aliphatic 
groups have a length of from one to four carbon atoms, advantageously one 
to two carbon atoms. Advantageously the anion-exchanging monomers may be 
trimethyl-[2-[4-hydroxyphenylene) ethyl ammonium chloride and 
N1N-dimothyl-3-(4-hydroxyphenylene)-ethyl amine. 
The polymerization of the ion-exchanging monomers is carried out 
electrochemically. During that process, the polymer layers with a linear 
or nonlinear structure are formed. The position of the functionalized 
groups on the aromatic part of the chain determinates the structure of the 
polymer. The polymer layers as manufactured exhibit by themselves 
ion-exchanging and ion-conducting capabilities without any addition of 
comonomers. Several embodiments of our invention are possible. 
The selectivity of the resulting semipermeable polymer to the exchangeable 
species can be optimized in situ during the electrochemical formation of 
the polymer layer. That optimization can be attained by addition of 
aromatic, noncross-linkable OH-containing comonomers to the electrolytic 
bath besides the ion-exchanging monomers. The noncross-linkable comonomers 
have to have at least one aliphatic group with two to seven carbon atoms, 
advantageously up to four carbon atoms, which is present at the ortho-, 
meta-, or paraposition, preferably at the ortho-position in order to build 
up a linear polymer structure. Monomers like o-cresol, 2-ethylphenol, 
2-isopropylphenol can be used as comonomers besides the ion-exchanging 
monomers. The comonomers can be added to the electrolytic bath up to a 
proportion of 84 Mol % relative to the total monomer concentration. 
The permeability of the resulting semipermeable polymer layer to the 
exchangeable species can also be optimized in situ during the 
electrochemical deposition of the polymer layer. The optimization can be 
attained by addition of aromatic, cross-linkable OH-containing comonomers 
to the electrolytic bath besides the ion-exchanging monomers. 
Advantageously the aromatic group of the comonomer has an aliphatic group 
with up to seven carbon atoms, advantageously up to four carbon atoms. 
This aliphatic group is advantageously unsaturated. A suitable, 
unsaturated aliphatic group has the length of from two to seven, 
advantageously two to four carbon atoms, and is advantageously a vinyl or 
allyl group. An appropriate comonomer may be the 2-allylphenol. 
Advantageously the aliphatic group of the comonomer is placed in the 
ortho-position. The aromatic, cross-linkable OH-containing comonomers can 
be added besides the ion-exchanging monomers up to a proportion of 50 Mol 
% relative to the total monomer concentration to the electrolytic bath. 
In examples 3 and 4 (to be discussed hereafter), it is illustrated, that 
the diffusion coefficient, which is a measure of the permeability for 
species to be separated, can be controlled. That control is attained by 
adjustment of the concentration of the cross-linkable OH-containing 
aromatic component in the monomer solution. The cross-linkable 
OH-containing aromatic component used was 2-allylphenol. Hence, the 
diffusion coefficient within the membrane decreases with an increasing 
concentration of the cross-linking component. 
The electrochemical deposition of ion-selective polymer layers occurs in 
acidic or in basic media. The electrochemical deposition of 
cation-selective polymer layers is performed by anodic oxidation of the 
monomers at the substrate, advantageously in aqueous alkaline media. The 
electrolyte solution contains an amine besides the monomer in order to 
suppress the passivation of the electrode surface. Advantageously the 
amine is a primary amine with an aliphatic group. The aliphatic group is 
advantageously an alkyl group with one to ten carbon atoms, which can be 
unsaturated. Suitable amines include the allylamine and propylamine. 
The electrochemical deposition of anion-selective polymer layers occurs by 
anodic oxidation of the monomers at the substrate, advantageously in 
aqueous acidic media. The electrolyte solution used contains, besides the 
monomer, an acid and salt of the acid which suppress the passivation of 
the electrode surface. Advantageously the acid is a dicarbonic acid and 
the salt is a diammonium compound of the dicarbonic acid. Suitable 
compounds include the oxalic acid and diammonium oxalate for the formation 
of the polymer layers. Advantageously a water-alcohol mixture is used, 
which has a mixture ratio of 1:10 to 10:1 by volume, advantageously 1:5 to 
5:1 by volume. An aliphatic alcohol of low molecular weight is 
advantageously utilized. 
Advantageously the electrolyte solution contains an adhesion promoting 
agent, which promotes the adherence of the formed polymer to the 
electrolyte surface. Suitable adhesion promoting agents are the ethylene 
glycol monobutyl ether or ethylene glycol monomethyl ether. The adhesion 
promoting agent can be used up to a proportion of one to ten vol % of the 
electrolyte solution. Advantageously, the electrochemical oxidation occurs 
preferentially potentiostatically by applying a triangular voltage sweep 
in the range of 0 to 6 Volts, or advantageously within the potential range 
of 0 to 2 Volts vs. saturated calomel electrode (reference) by applying a 
scan rate of 0.5 to 200 mV/s, advantageously 5 to 100 mV/s. The 
electrochemical deposition is processed at 20.degree. to 50.degree. C., 
especially at room temperature. 
The thickness of the polymer layer is controlled during the electrochemical 
deposition by means of the charge consumed in the anodic polymerization 
reaction. For the charge control during the formation of the polymer on 
the electrode, a theoretical columbic efficiency of 4F/Mol per 
OH-containing aromatic monomer is assumed. After the electrochemical 
deposition of the firmly adhering polymer layer to the substrate, the 
layer must be cross-linked by the unsaturated groups present in the film 
by heating or irradiation. Advantageously, a thermal treatment, i.e., 
heating at 60.degree. to 150.degree. C., preferably at 80.degree. to 
150.degree. C. is performed. A suitable temperature may be easily 
determined by conducting suitable simple experiments with a given polymer 
layer. An irradiation treatment with UV-radiation is also possible. 
The thickness of the membrane is in the range of 50 nanometers to 500 
micrometers, advantageously from 100 nanometers to 10 micrometers, 
preferably in the range of 100 nanometers to 1 micrometers. It has been 
found that membranes with a layer thickness in this range provides the 
desired cation- and anion-exchanging capabilities and a high permeability 
to the species to be separated. The diffusion coefficients of the species 
to be separated within the prepared membrane is slightly lower than those 
present in the electrolyte. Therefore, the substrate coated with the 
membrane of our invention can be used in such processes, in which 
substrates coated by the techniques of prior art (i.e., dip-coating 
process) cannot be employed hitherto due to the extremely low permeability 
of the species within the membrane. 
According to one advantageous use of our invention, the polymer layers can 
be applied as charge-selective and cation-and anion-conducting membranes 
in an electrode/membrane unit. An electrode, which electroactive area is 
equipped with a charge-selective and cation- or anion-conducting polymer 
layer, can be employed to charge-exchanging composite electrode or used in 
electrochemical processes or in electrochemical devices 
(Bogenschutz/Krusenmark; Elektrochemische Bauelemente; Verlag Chemie, 
Weinheim, 1976). 
According to another advantageous use of our invention, the polymer layer 
can be employed as a selective layer or as a component of a selective 
layer of electrodes, which are used as potentiometric or amperometric 
sensors (Cammann, Das Arbeiten mit ionenselektiven Elektroden; 
Springer-Verlag, Berlin, 1977; J. Janata, The Principles of Chemical 
Sensors, Plenum Press, New York, 1989). 
According to still another advantageous use of our invention the polymer 
layers can be used as solid polymer electrolyte, which are employed in 
electrolytic cell to separate the anolyte compartment from the catolyte 
compartment of the cell or to eliminate interfering reactions during the 
electrochemical processes. 
Our invention is illustrated in more detail by the following examples: 
Example 1 
A cation-exchanging and cation-conducting membrane was polymerized and 
deposited on the electroactive area of electrical conducting substrates. 
As electrode materials, nobel metals (i.e., platinum or gold) or composite 
materials, (i.e., carbon-polyethylene, or carbon fiber with a diameter of 
8 micrometer) were employed. The following electrolyte solution was used: 
______________________________________ 
0.23 Mol/1 
3-Hydroxybenzoic acid 
0.4 Mol/1 
Allylamine 
0.2 Mol/1 
Cellosolve (Ethylenglycol monobuthylether) 
______________________________________ 
This was dissolved in Methanol and Water 1:1 (volume proportions). 
The electrochemical polymerization was performed potentiostatically by 
applying a triangular voltage sweep in the range of 0 to 1 Volt vs. 
saturated calomel electrode at room temperature. After a single triangular 
sweep with a start and final potential of 0 Volt vs. saturated calomel 
electrode, the polymer layer deposited on the electrodes was heated in an 
oven at 80.degree. C. for approximately 15 to 30 minutes in order to 
remove possibly remaining electrolyte. The polymer layer formed has a 
layer thickness of approximately 0.8 micrometers and exhibits 
cation-exchanging and cation-conducting behavior. Anions, like 
Fe(CN).sub.6.sup.3 - or J-, were totally screened out by the semipermeable 
membrane. Consequently, these coated electrodes did not show any 
electrochemical activity to the above-mentioned anions. The neutral 
species could be detected. 
Example 2 
Again a cation-exchanging and cation-conducting membrane was polymerized 
and deposited on the electroactive area of electrical conducting 
substrates. As electrode materials, the metals mentioned in example 1 were 
employed. The following electrolyte solution was used: 
This was dissolved in Methanol and Water 1:1 (volume proportions). 
The electrochemical polymerization was performed according to example 1. 
Afterwards, the polymer layer deposited on the electrodes was heated in an 
oven at 80.degree. to 100.degree. C. for approximately 15 to 30 minutes in 
order to crosslink the polymer and to remove electrolyte which possibly 
remained. The polymer layer formed has a layer thickness of approximately 
0.5 micrometers and exhibits cation-exchanging and cation-conducting 
behavior. As described in example 1 anions, like Fe(CN).sub.6.sup.3- or 
J.sup.-, were totally screened out by the semipermeable membrane. No 
electrochemical activity of the anions could be detected by using these 
coated electrodes. In comparison to an uncoated electrode and to the 
electrodes coated according to example 1, the selectivity to large 
cations, like Ru(NH.sub.3).sub.6.sup.3+, could be improved. An increase of 
diffusion limiting current for the reduction of Ru(NH.sub.3).sub.6.sup.3+ 
dissolved in solutions could be observed. For small cations, i.e., 
Fe.sup.2+, the accumulation effect was not observed. 
Example 3 
Again a cation-exchanging and cation-conducting membrane was polymerized 
and deposited on the electroactive area of electrical conducting 
substrates. As electrode materials, the metals mentioned in example 1 were 
employed. The following electrolyte solution was used: 
______________________________________ 
0.23 Mol/1 
4-Hydroxybenzenesulfonic acid 
0.003 Mol/1 
2-Allylphenol 
0.03 Mol/1 
Allylamine 
0.2 Mol/1 
Cellosolve (Ethylenglycol monobuthylether) 
______________________________________ 
This was dissolved in Methanol and Water 1:1 (volume proportions). 
The electrochemical polymerization and the following heat treatment were 
performed according to example 2. The polymer layer formed has a layer 
thickness of approximately 0.15 micrometers and exhibits cation-exchanging 
and cation-conducting behavior. Also in this example, electrochemically 
active anions do not reach the electrode surface. They could not be 
detected amperometrically, although, the layer thickness was reduced to 
approximately 70% when compared to those given in example 1 and 2. The 
diffusion coefficient of Ru(NH.sub.3).sub.6.sup.3+ within the membrane 
was determined to D.sub.o =4.4 10.sup.-6 cm.sup.2 /s. This value is only 
slightly lower than that of Ru(NH.sub.3).sub.6.sup.3+ in solution 
(D.sub.o =5.5 10.sup.-6 cm.sup.2 /s). 
Example 4 
Again a cation-exchanging and cation-conducting membrane was polymerized 
and deposited on the electroactive area of electrical conducting 
substrates. As electrode materials, the metals mentioned in example 1 were 
employed. The following electrolyte solution was used: 
______________________________________ 
0.23 Mol/1 
4-Hydroxybenzenesulfonic acid 
0.08 Mol/1 
2-Allylphenol 
0.03 Mol/1 
Allylamine 
0.2 Mol/1 
Cellosolve (Ethylenglycol monobuthylether) 
______________________________________ 
This was dissolved in Methanol and Water 1:1 (volume proportions). 
The electrochemical polymerization and the following heat treatment were 
performed according to example 2. The polymer layer formed has a layer 
thickness of approximately 0.1 micrometers and exhibits cation-exchanging 
and cation-conducting behavior. Electrochemically active anions could not 
be detected amperometrically. The diffusion coefficient of 
Ru(NH.sub.3).sub.6.sup.3+ within the membrane was determined to D.sub.o 
=2.3 10.sup.-6 cm.sup.2 /s. In comparison to example 3 the membrane 
permeability to the species to be separated was reduced by a factor of 
0.5. due to the increase of the cross-linking degree. 
Example 5 
An anion-exchanging and anion-conducting membrane was polymerized and 
deposited on the electroactive area of electrical conducting substrates. 
As electrode materials, the metals mentioned in example 1 were employed. 
The following electrolyte solution was used: 
______________________________________ 
0.23 Mol/1 
Trimethyl-[2-(4-hydroxyphenyl) ethyl] 
ammonium choloride 
0.003 Mol/1 
2-Allylphenol 
0.4 Mol/1 
Allylamine 
0.2 Mol/1 
Cellosolve (Ethylenglycol monobuthylether) 
______________________________________ 
This was dissolved in Methanol and Water 1:1 (volume proportions). 
The electrochemical polymerization was performed potentiostatically by 
applying a triangular voltage sweep in the range of 0 to 2 Volt vs. 
saturated calomel electrode at room temperature. After a single triangular 
sweep with a start and final potential of 0 Volt vs. saturated calomel 
electrode, the polymer layer deposited on the electrodes was heated in an 
oven at 80.degree. to 100.degree. C. for approximately 15 to 30 minutes in 
order to crosslink the polymer and to remove the electrolyte which 
possibly remained after deposition. The polymer layer formed has a layer 
thickness of approximately 0.3 micrometers and exhibits anion-exchanging 
and anion-conducting behavior. Cations, like Ru(NH.sub.3).sub.6.sup.3+, 
Ag.sup.+, or Fe.sup.2+ were totally screened out by the semipermeable 
membrane. They could not be detected potentiostatically using the 
electrodes coated according to our invention. 
Example 6 
Again an anion-exchanging and anion-conducting membrane was polymerized and 
deposited on the electroactive area of electrical conducting substrates. 
As electrode materials, the metals mentioned in example 1 were employed. 
The following electrolyte solution was used: 
______________________________________ 
0.23 Mol/1 
Ethyl-dimethyl-[2-(4-hydroxyphenyl) 
ethyl] ammonium chloride 
0.2 Mol/1 
Oxalic acid 
0.1 Mol/1 
Diammonium oxalate 
0.2 Mol/1 
Methylcellosolve (Ethylenglycol monomethylether) 
______________________________________ 
This was dissolved in Methanol and Water 1:1 (volume proportions). 
The electrochemical polymerization and the following heat treatment were 
performed according to example 5. The polymer layer formed has a layer 
thickness of approximately 0.3 micrometers and exhibits anion-exchanging 
and anion-conducting behavior like the membrane prepared according to 
example 5. However, as a result the diffusion coefficient of 
Fe(CN).sub.6.sup.3- within the membrane is increased by a factor of 2 in 
comparison to the above-mentioned membrane (example 5). 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
electrodes. 
While the invention has been illustrated and described as a coating of an 
electrically conducting substrate, a process for making it and a process 
for using it, it is not intended to be limited to the details shown, since 
various modifications and structural changes may be made without departing 
in any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of the prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.