DE2304380B2 - Electrodes with a Delafossit surface - Google Patents

Description

For numerous electrochemical reactions, such as the electrolysis of brines, hydrochloric acid and sulfates, electroplating, electrolytic extraction, electrolytic production of metal powders, electrolytic cleaning, electrolytic pickling and electrochemical generation -> n electrical power, non-consumable anodes are required. Graphite anodes have heretofore been used for such purposes, particularly for the electrolysis of brines and the electrolysis of hydrochloric acid. More recently, electrodes have been developed for such processes which have a suitable electrically conductive base or substrate and an electrocatalytic coating thereon. Typically, these electrocatalytic coatings form the platinum group metals, such as. B. platinum, osmium, iridium, ruthenium, palladium and rhodium and their oxides.

From DE-OS 18 16 820 electrodes are known in which the electrocatalytic coating with a inorganic glaze is combined. The disadvantage is that it makes some of the active The electrode surface is blocked and the electrodes are less efficient.

DD-PS 77 963 describes electrodes with surfaces made of oxides of the platinum metal group. These surfaces have a low electrical conductivity and are not yet sufficient with the usual loads resistant to chemical attack.

The object of the present invention was to avoid the disadvantages of the known electrodes and to create an anode that has a low chlorine overvoltage and below even at high current densities Resists chemical attack for long periods of time in operating conditions.

It has now been found that a particularly suitable anode for carrying out electrochemical Reactions is obtained when a delafossite surface is placed on a suitable electrically conductive substrate or base is applied. Delafossite are oxides of high electrical conductivity from the stoichiometric being in this formula A is platinum or palladium. B is typically chromium, cobalt, or rhodium.

The present invention relates to an anode with a chlorine overvoltage of less than 0.33 volts at a current density of 53.82 amperes per dm ² , which is characterized by an electrical

ίο conductive carrier made of a rectifier metal or Graphite with a coating thereon, which consists essentially of Delafossit, whereby one as delafossite the platinum-cobalt-delafossite, the palladium-cobalt-delafossite, the palladium-chromium-delafossite or the paliadium-rhodium-delafossite is used.

Delafossite also include non-stoichiometric Compounds that are isostructural with the stoichiometric Delafossites. A suitable electric conductive substrate is an electrically conductive substrate that is essentially not covered by the Electrolytes are attacked.

As already stated, the anodes according to the invention have a delafossite surface on an electrically conductive substrate. The delafossite has a unique crystal structure which _{is similar to that of the natural micral delafossite (CuFeO 2} ), the small differences in the crystal structure being due to the slightly different radii the ions are due.

Delafossite produce particularly satisfactory electrode materials because they combine high electrical conductivity, which is comparable to that of metals, with high resistance to chemical attack, which is comparable to that of refractory metal oxides. So is z. B. the electrical conductivity of compressed powders of platinum and palladium delafossite on the order of about 10 ³ to 10 * (ohm-centimeter) - '. Such platinum and palladium delafosites are also resistant to attack by strong acids, such as aqua regia at 70 ° C and also to nascent chlorine.

The Delafossite are a family of oxides made from two or more metals, the oxide having a rhomboid structure with a hexagonal crystal habit similar to _{that of the mineral Delafossite CuFeO 2.} Delafossite can also be characterized by the fact that their crystals have a space group of 166, a Shoenflies group of Z> L

'"a full standard symbol of Ri- (R. - 3, two over

m) and an international symbol of Rs _m (R, slash 3, m). Such oxides and their crystallography have been described repeatedly in the literature.

-, -) As a general rule, the Delafossite are further characterized by the fact that the Α-ions, which the Copper in the mineral delafossite have an effective ionic radius equal to that of two oxygen coordinations corresponds to, d. that is, that the effective lonenra-

M) are in the range from 0.45 to 0.68 angstroms. in the In the case of platinum and palladium delafossite, which are particularly good electrical conductors, the Α ions are effective ion radii in the range from 0.58 to 0.61 angstroms. the B ions, which are the iron ions in the mineral delafossite

to have an ionic radius that corresponds to one corresponds to octahedral coordination, d. that is, the effective atomic radii range from about 0.50 to are approximately 1.05 angstrom units. The one used here

The term "effective ionic radius" includes the equivalent Expression "crystal ionic radius".

CT P rewi 11, RD S ha η η ο η and DB R ο ge rs, Chemistry of Noble Metall Oxides, Inorganic Chemistry, Vol. 10 (1971), report that the synthetic platinum, cobalt delafossite (PtCoO ₂ ) has the delafossite type crystallographic structure. Both the stoichiometric and the non-stoichiometric platinum-cobalt delafosites are particularly suitable for use in the electrodes according to the invention.

The delafossite crystal structure and the relations between the platinum-cobalt-delafossite, the palladium-delafossite and the mineral-delafossite (CuFeO2) explained in more detail by referring to the figures The figures show the following:

F j g. Figure 1 is a graphical representation of the X-ray diffraction values _{found in the literature for the mineral delafossite (CuFeO 2} ) presented in Table I;

F i g. Figure 2 is a graph of the X-ray diffraction values reported _{in the literature for platinum-cobalt-delafossite (PtCoO 2} ) and summarized in Table λ;

F i g. 3 is a graph of the X-ray diffraction values reported in the literature for palladium-cobalt delafossite oxide (PdCoO ₂ ) and summarized in Table 3;

F i g. Fig. 4 is a graph of the x-ray diffraction values reported in the literature for palladium-chromium-jo delafossite (PdCrO ₂ ) and summarized in Table 4;

F i g. 5 is a graph of the X-ray diffraction values reported in the literature for palladium-rhodium-delafossite (PdRhO ₂ ) and summarized in Table 5.

The F i g. 1 to 5, which reproduce the values given in the literature and summarized in Tables 1 to 5, are plotted on the same scale as the abscissa and have a common ordinate. The abscissa indicates l / lo, the specified ratio of the intensity of the reflected beam to the incident beam. The ordinate d indicates the specified distance between the planes, calculated from the Bragg equation, which will be explained in more detail here.

Fig. 1 was based on the values of Salier and Thompson, Phys. Rev. Volume 44, page 644 (1935) reported in A.S.T.M X-Ray Powder Diffraction File 12 - 752, and reproduced in table t. The> n F i g. 2.3, 4 and 5 were based on the values of R.D. Shannon et al., Inorganic Chemistry, Volume 1C, pages 713, 717 op cit., And here in Tables 2, 3, 4 and 5 reproduced, created.

F i g. 6 is an X-ray diffraction of palladium-η cobalt delafossite (PdCoO ₂ ) prepared for use as an electrode material in Example 1;

Figure 7 is an X-ray diffraction of platinum-cobalt delafossite (Pto.eCoo, 80 ₂ ) prepared for use as an electrode material in Example 2; *O

8 is an X-ray diffraction of platinum-cobalt delafossite (Pto5Coo, 7330 ₂ ) prepared for use as an electrode material in Example 3.

The crystallographic units of platinum and palladium delafssite give a unique family of X-ray diffractions represented by peaks at "a" spacings from 5.90 / 2 to 6.0229 Angstroms, 2.9728 to 3.0137 Angstroms, a doublet with a Distance between peaks from 0.06 to 0.07 Angstroms with the first peak at 2.4260 to 2.3609 Angstroms and the second peak of the doublet at 2.5384 to 2.5141 Angstroms, a peak at 2.1460 to 2 , 2643 Angstroms and another peak at 1.6483 to 1.7104 Angstroms. For the mineral delafossite only values of 2 θ degrees in excess of about 30 ° are known, ie for d distances of less than 2.86 angstroms. The mineral delafossite (CuFeO ₂ ) has the doublel: at 2.58 and 2.508 Angstroms and on the peaks at 2.23B and 1.658 Angstroms. The differences in the results of X-ray diffraction between the individual members of the delafossite family are due to the slightly different cation radii.

For the mineral delafossite (CuFeO ₂ ), the values of the X-ray diffraction are given in Table 1 and in FIG. 1 or are shown graphically. The results of X-ray diffraction on delafossites of metals of the platinum group are shown in tunnels 2 to 5 and the graphs in FIG. 2 to 5 reproduced. It is pointed out once again that the values for Tables 1 to 5 and the graphic representations 1 to 5 are taken from the literature. The figures are idealized and show family relationships and trends. From the F i g. 1 to 5 does not reveal any keynote or irregularity that normally occurs in X-ray examinations.

Samples of the delafossite powder are used when observing and recording X-ray examinations Subjected to x-rays from a copper target. The methods for such an investigation are in the chapter of the book by Klug and Alexander, X-Ray Diffraction Procedures, John Wiley & Sons, Inc., New York (1954), pages 235-318. especially pages 270 to 318, and at N e w f i e I d X-Ray Diffraction Methods, John Wiley & Sons, Inc. New York (1966), pp. 177-207.

Like Klug and Alexander and also N e w f i e I d indicate, X-rays at a wavelength of 1.5405 Angstrom units are directed to a To hit the sample of the powder to be examined. The X-rays are diffracted by a sample. the Diffracted X-rays are particularly intense at certain angles (Θ), which leads to the formation of Peaks in the leaves of the diffractometer or of lines in diffraction photographs.

Diffraction values are used in the X-ray examination obtained using a diffractometer which has a direct reading in 2θ. The value (180 ° min- 2 Θ) is the angle between the incident ray and major. reflected beam.

Table 1 shows the diffraction values of the X-ray analysis for the ivlineral delafossite (CuFeO ₂ ). Particularly noteworthy is the doublet at 2.58 and 2.508 Angstroms and the peaks at 2.238 and 1.658 Angstroms.

For the diffraction values of the X-ray examination of powdery delafossites of metals of the platinum group, some similarities can be established. First, a particularly strong peak can be observed at a value of "d" about 5.9072 to 6.0229. It can then be seen in FIGS. 2 to 5 that there is a strong doublet, the peaks being separated from one another by about 0.06 to about 0.07 Angstroms with larger separations of the peaks and larger differences in intensities in delafossiites of the platinum group larger elementary

cells and closely spaced peaks and of nearly equal intensity for delafossite of the platinum group with a more compact unit cell.

For the platinum-cobalt delafossite (PtCoOz) the peaks of the doublet are at 2.4260 and 2.3609 angstroms. For palladium-cobalt delafossite (PdCoO ₂ ), the two peaks of the doublet are around 2.4272 and 2.3616 angstroms, whereas for palladium-chromium delafossite the two peaks are 2.5065 and 2.4375 angstroms and for palladium -Rhodium delafossite (PdRhOj) the two peaks are around 2.5884 and 2.5141 Angstroms. Also noteworthy is the increasing difference in intensity between the two members of the doublet in the progression from the Delafossites with the more compact to those with the less compact elementary cells. The first peak of the doublet corresponds to a distance between the levels of about 2.42 Angstroms (PtCoO?) To about 2.58 Angstroms (PdRhO ₂ ). whereas the second peak corresponds to a distance between the planes of about 2.36 Angstroms (PtCoO ₂ ) to about 2.51 Angstroms (PdRhOj).

There is also a strong peak at about 2.1460 to about 2.2644 Angstroms. This peak is about 2.14 Angstroms for the more compact unit cell of platinum-cobalt-delafossite, at a distance of 2.1448 angstroms for palladium-cobalt-delafossite (PdCoO ₂ ), at a distance of 2.2088 for palladium-chromium -Delafossite (PdCrO ₂ ) and at 2.26 Angstrom for the slightly less compact unit cell of platinum-rhodium-delafossite (PtRhO ₂ ).

Also of interest is a faint doublet in the 2.0185 and 1.9814 Angstrom range with intensities of 0.30 to 0.40 for the more compact platinum-cobalt delafossite. As the unit cell increases in size, this particular doublet becomes more spread out and less intense. For the only slightly less compact palladium-cobalt delafossite, the doublet occurs at "d" spacings of 2.0165 and 1.9715 Angstroms. where the weaker of the two members has an intensity of c [\\ a 0.15. For the palladium-chrome delafossite (PdCrO ₂ ), the weaker of the two members of the doublet has an intensity of about 0.02 and the doublet occurs at 2.0753 and 2.0089 angstroms, respectively. For the even less compact palladium-rhodium-delafossite (PdRhO ₂ ), the terms of the doublet occur at 2.1198 and 2.0088 angstroms. both having intensities less than 0.05.

For the more compact crystals of the delafossite of the platinum group, there is a peak at about 1.76 to 1.81 angstroms. This peak is for platinum-cobalt delafossite (PtCoO ₂ ) at about 1.7655 and has an intensity of about 030. For the palladium-cobalt delafossite, the peak is observed and has a distance of the planes of about 1.7616 angstroms an intensity of about 030. For the slightly less compact palladium-chromium delafossite (PdCrO ₂ ), the peak occurs at about 1.8084 angstroms and has an intensity of less than 0.05.

Table 1

X-ray examination of a
Powder of copper-iron delafossite
(CuFeO ₂ )

2.86
2.58

35
18th

(I. / 7ii / 'A. i / k 2.508 100 90 45 2.238 25th 100 90 2.083 6th 70 80 1.902 9 90 100 1.658 35 70 85 1.512 40 30th 15th 1.434 20th 40 50 1,336 18th 30th 30th 1,295 12th 60 85 1.253 IO 20th 35 1,184 6th 40 70 I. 19th IO 30th 65 1.108 6th 15th 15th 1.040 18th 10 15th 0.984 16 30th 65 0.965 it) Table 2 one X-ray examination from Palladium-Cobalt Powder Platinum-Cobalt-Delafossite (PtCoO ₂ ) Delafossite (PdCoO ₂ ) <l d 5.9450 2.9072 2.9728 2.9559 2.4260 2.4272 2.3609 2.3616 2.1460 2.1448 2.0185 2.0165 1.9814 1.9713 1.7655 1.7616 1.6483 1.6445 1.4856 1.4788 1.4415 1.4373 1.4135 1.4149 1.3751 13762 1.3513 1.3474 1.2764 1.2762 Table 3 X-ray examination

Table 4

X-ray examination of a
Palladium-Chromium-Delafossite (PdCrO ₂ ) powder

d /// "

6.0229 20th 1 / I ₀ 3.0137 65 5 2.5065 30th 90 2.4375 KK) 10 2.2088 40 100 2.0753 2 95 2.0089 10 5 , 8084 5 2 , 6864 30th 85 , 5074 5 15th I 41-ί - \ t C
I J 70 , 4614 20th 85 , 3791 2 80 1.3151 15th 60 Table 5 X-ray examination of Pal ladium-rhodium-delafossite (PdRhOj) d 6.0209 3.0130 2.5884 2.5141 2.2644 2.1198 2.0088 1.7104 1.5071 1.4874 1.5106 1.3503 1.2945

are both less than I and, for example, about 0.070 to 1.00 can be. Such delafosites can also be used to good effect in the invention.

The metal ion represented by A in the formula can be any monovalent metal ion with an effective ionic radius of about 0.45 Angstrom units to about 0.68 Angstrom units. Such monovalent ions are palladium (Pd ⁺ ) with an effective ionic radius of about 0.59 angstroms and platinum (Pt ⁺ ) with an effective ionic radius of about 0.60 angstroms. Two or more such monovalent cations can also exist in the same delafossite crystal. The preferred delafosites are those in which the monovalent cation has an effective ionic radius of about 0.58 to 0.61 angstroms, such as. B. Palladium (+ 1) and platinum (+ 1).

The cation represented by B in the formula is most commonly chromium, cobalt and rhodium. B is typically a trivalent cation with an effective ionic radius of about 0.50 Angstroms to about 1.05 Angstroms, and most often about 0.50 Angstroms to about 0.89 Angstroms. The preferred trivalent cations are those with an effective ionic radius of about 0.50 to about 0.70 Angstroms, such as. B. Cobalt (Co ³ +) with an effective ion radius of about 0.52 Angstrom, chromium (Cr ³ +) with an effective ion radius of 0.62 Angstrom and rhodium (Rh ³ +) with an effective ion radius of about 0.70 Angstrom.

The platinum delafossite close the stoichiometric oxygen bond of platinum and cobalt with the Delafossite structure (PtCoO2) and also the non-stoichiometric Oxygen compounds of platinum and cobalt with the delafossite structure. Such non-stoichiometric Delafossite have the formula

Finally, with regard to the X-ray examinations, a peak of medium intensity at around 1.6453 to around 1.7104 Angstroms should be pointed out. This peak has an intensity of about 030 for palladium-chromium delafossite and of about 0.85 for palladium-cobalt-delafossite (PdCoO ₂ ) and palladium-rhodium delafossite (PdRhO ₂ ). It is 1.6453 angstroms for platinum-cobalt delafossite (PtCoCh ^ at about 1.6445 angstroms for palladium-cobalt delafossite, about 1.6864 angstroms for palladium-chromium delafossite and about 1.7104 angstroms for palladium -Rhodium DelafossiL

The chemical nature of the Delafossite will now be discussed again. The delafossite are oxides or oxy compounds of two or more metals and are generally as follows formula

SUBSCRIPTION ₂

When considering this formula, it must be taken into account that non-stoichiometric compounds which have defects in their structures can also be used according to the invention. Such non-stoichiometric delafosites with errors in their structure have the formula A _x ByO ₂ , where either χ or y or Pt.

Co, Q ₂

I I - I, *

where η has a value between 0.5 and 0.8.

As additional components in the Delafossi

th, especially in the platinum delafossites, small amounts of other metal ions occur, e.g. B.

Ions of scandium, titanium, vanadium, chromium, manganese, iron, cobalt or nickel. If so, the Deiafossit following formula:

Pt, Co, MO ₂

where χ is about 0.70 to 1.00, y is about 0.70 to 1.00 and ζ is less than 0.11 Typically ζ is about 0.004 to about 0.11, and M is Sc, Ti, V, Cr, Mn, Fe, Co or Ni.

The platinum-cobalt delafossite used as the electrode surface particularly useful in accordance with this invention has the formula

Pi Co, Q ₂

I + π I - n__ ■ *

~~ T ~ 3

in which π has a value from about 0.50 to about OJS .
Palladium delafossite, which is particularly suitable as an electrode surface, correspond to the formula

PdMO ₂

where M is cobalt, chromium, rhodium or a mixture thereof. Examples of particularly suitable palladium delafossites are palladium-cobalt delafossite (PdCoO ₂ ), palladium-chromium delafossite (PdCrO ₂ ), palladium-rhodium delafossite (PdRhO ₂ ).

The anodes according to the invention provide in most cases, an electrically conductive substrate or base member with a Delafossitoberfläche. In one such embodiment of the invention is the delafossite in direct contact with the base member and the ^r> electrolyte.

Also, the platinum and palladium delafossite used to put an electrically conductive coating on the electrically conductive base or to form a substrate, the delafossite surface being a further outer coating of a suitable electrocatalytic material, such as. B. has a spinel, such as this z. B. in US-PS 37 11 382 disclosed is. Instead of the spinel, a perovskite or a perovskite bronze can be used, such as this z. B. in r> the previous DE-OS 22 10 065 is disclosed. Alternatively, as an outer coating over the Other electrocatalytic materials are required can be used, such as Ruthenate, Rut'ienide, Rhodite, Rhodateu. like

It is also possible to arrange a porous layer of an essentially non-reactive material such as titanium dioxide, vanadium oxide, tantalum oxide, tungsten oxide, niobium oxide, hafnium oxide, zirconium oxide, silicon dioxide 2 ^r > and the like between the delafossite surface and the electrolyte. Such external coatings improve the mechanical resistance of the Delafossit surface even further. In addition, the porous outer coatings form a large surface for catalytic reactions of the products formed on the electrode or the starting materials. These outer oxide coatings are preferably formed "in situ", as will be explained in more detail later.

Different fabrics can be mixed with the Delafossit materials. So you can z. B. conductive j-, Materials such as perovskites, perovskite bronzes, platinum group metals, platinum group oxides, and mixed carbides, nitrides, oxides and borides, which are resistant to the electrolyte, in mixture use with the Delafossit. Such materials may be present for a better one Conductivity or reactivity. Alternative materials are the oxides of titanium, tantalum, Niobium, hafnium, tungsten, aluminum, vanadium, silicon and other film-forming metals. These too Additives improve the shelf life of the Delafossite. To bind the delafossite particles to the substrate, Any oxides that are formed "in situ" during surface fabrication can be used and which are essentially non-reactive with the electrolyte.

Although the anodes with a delafossite coating according to the invention also include an electrode made entirely of delafossite, such electrodes will not normally be used for economic reasons. Therefore, anodes according to the invention are preferred which have a delafossite surface or coating on a suitable electrically conductive substrate. The delafossite surface can be only 8 angstroms thick. For practical reasons, however, a delafossite surface is used which has a thickness or thickness of at least 1.52 microns, with thicknesses of at least 3.81 to 5.08 microns being preferred. The Delafossitoberflächen need not be more than about 635 to 7.62 & microns. While a delafossite coating thicker than 7.62 microns, such as 2032 microns, can be used without any adverse effects being observed, no further benefit is obtained from using such thick coatings.

A "suitable electrically conductive substrate or base" means a substrate with a electrical resistivity within the economic limits meant with this substrate also still essentially non-reactive with the electrolyte and the products of electrolysis should be. In the electrolysis of brines, for. B. does not use a suitable electrically conductive substrate Solutions of sodium hydroxide or sodium chloride do not react and also do not react with wetting chlorine to be attacked.

Suitable electrically conductive substrates are / .. B. Rectifier valve metals. The rectifier details are those metals that form an oxide film under anodic conditions. To the rectifier metals belong e.g. B. titanium, tantalum, niobium, hafnium, tungsten, aluminum, zirconium, vanadium and their alloys. In In most cases, for economic reasons, titanium or titanium alloys are used as the substrate for the base member of the electrodes used in this invention. However, other materials can also be used can be used, such as graphite or carbon. One can also laminate a rectifier metal with a use less expensive metal, such as iron or steel, with a delafossite coating on the rectifier metal.

Alternatively, titanium hydride or another electrically conductive, anodically stable hydride can be used as electrically conductive substrate can be used in the electrode of this invention. Such a hydride can be the sole component of the substrate or it can be in the form of a flat structure on the other material rest.

Alternatively, the hydride can be a hydride surface of a metal, e.g. B. a titanium substrate with a Titanium hydride layer between the metallic substrate and the delafossite surface.

In a preferred embodiment of the invention, a layer of an electrically conductive material, which has a better conductivity than the delafossite and is resistant to the electrolyte, is arranged between the delafossite and the substrate. Such an intermediate layer may be formed from a platinum group metal such as e.g. B. of metallic ruthenium, rhodium, palladium, osmium, iridium, platinum or their alloys. Particularly suitable alloys for this purpose are, for. B. platinum-palladium alloys, especially those containing about 3 to about 15 wt .-% platinum, also platinum-iridium alloys, especially those containing about 2 to about 50 wt .-% iridium. Alternatively, such an intermediate layer may be an oxide of a platinum group metal such as e.g. B. ruthen oxide (RuO ₂ ), rhodium _{oxide (Rh 2} O ₃ ), palladium oxide (PdO ₂ ), osmium oxide (OsO ₂ ), iridium oxide (Ir ₂ O ₃ ), platinum oxide (PtP ₂ ) or mixtures thereof. Such mixtures can include mixtures of platinum oxide and palladium oxide containing from about 3 to about 15 weight percent platinum oxide or platinum oxide and iridium oxide mixtures containing from about 2 to about 50 weight percent iridium oxide. In connection with the metals of the platinum group or their oxides, oxides of other metals can also be used, such as the oxides of titanium, zirconium, hafnium, vanadium, niobium, tantalum, tungsten and aluminum. When such conflicts

layers are present, they usually have a thickness of about 0.51 to about 3.05 microns, with thicknesses of about 1.52 to 3.05 microns being preferred. The intermediate layers can also be Hünner and, for example, only 0.13 microns thick if they are applied evenly so that they result in a pore-free coating. It is also possible also to use thicker intermediate layers, but this is not associated with any significant advantage.

If, in the case of an anode with a delafossite surface on a substrate, the substrate reacts with the delafossil to form an electrically insulating barrier after prolonged operating times at high current densities, a layer of a less reactive material that is more resistant to the electrolyte can be placed between the substrate and the delafossite the substrate. Less reactive materials are understood to mean materials which do not form an electrically insulating barrier or which contribute to the formation of such a barrier when they are arranged between the delafossite and the substrate. Such less reactive materials can be the noble metals already mentioned or their oxides. Alternatively, platinum-cobalt Delafossit (PtCoO ₂₎ may, palladium-chromium Oelafossit (PdCrO ₂₎ palladium-rhodium Delafossit (PdRhO ₂₎ are used, or to be less reactive materials to form an intermediate layer between a palladium-cobalt Delafossit (PdCoO ₂ ) coating and a titanium substrate. When such interlayers are used, they typically have a thickness of 0.51 to 3.05 microns, with thicknesses of 1.52 to 3.05 microns being preferred. If the intermediate layers are applied evenly and are pore-free, they can also be thinner, e.g. B. 0.13 microns thick. Thicker coatings are also possible.

The anodes with Delafossit surfaces according to the invention can be used for any electrochemical process with a non-consumable electrode. By "non-consumable" is meant that the electrode is not dissolved by the electrolyte and is not redeposited on the opposite electrode. The electrodes according to the invention can, for. B. for the electrolysis of brines, sulphates, hydrochloric acid. Phosphates and the like can be used. Alternatively, the electrodes are useful in processes in which cations are deposited on a cathode, such as e.g. B. in the electrolytic extraction of metals, electrolytic refining, electroplating, electrophoresis, electrolytic cleaning and electrolytic pickling. Copper, nickel, iron, manganese, brass, bronze, cadmium, gold, indium, silver, tin, zinc, cobalt, chromium and similar metals can be electroplated onto cathodes from appropriate solutions. Alternatively, metal powder can be prepared by depositing cationic release on a suitable cathode using the anodes of this invention. The electrodes of the invention can also be used for the electrolytic cleaning of aqueous solutions, sodium phosphate, sodium carbonate and the like. Furthermore, the electrolytic pickling of suitable materials, which are cathodic with respect to the anodes according to the invention, can be used to oxidize organic compounds electrolytically. So you can z. B. carry out the electrolytic oxidation of propylene to propylene oxide or propylene glycol with the electrodes of this invention. In addition, metal structures such as hulls can be cathodically protected using the anodes of this invention.
In addition, the anode of this invention can be used in fuel cells. When using the electrode with the Delafossit coating in fuel cells, these electrodes will be permeable to the flow of the electrolyte. Such electrolyte permeability can be achieved by an electrically conductive porous substrate having a delafossite material deposited thereon, or by dispersion of delafossite particles in a suitable inert medium, or by other methods known in the art.

ι ϊ The anodes according to the invention can be produced by synthesizing the delafossite and subsequently on a suitable electrically conductive substrate or Carrier applies. Delafossite can be made by oxidation at low temperatures and high pressures, such as

z. B. by a hydrothermal reaction. They can also be carried out by oxidation at high temperatures and high pressures Solid reactions and oxidation at low temperatures and low pressures in one

:> Get oxidizing flux. Alternatively it is possible to delafossite at low pressure and low temperatures in an anion exchange reaction to manufacture.

Delafossite useful in the present invention can e.g. B. by the procedures outlined in the following references are described: R.D. Shannon et al .. Chemistry of Noble Metal Oxides, 1. Syntheses and Properties of ABO: Delafossite Compounds, Inorganic Chemistry, Volume 10.

i-, page 713 (1971): US-PS 34 98 931: US-PS 35 14 414 and U.S. Patent 3,414,371.

Hydrothermal syntheses of Delafossite are carried out at relatively low temperature under oxidizing conditions carried out. The hydrothermal method can e.g. be used to produce platinum-cobalt delafossites. the copper delafossite and tier silver delafossite can be used. The method calls for heating of two oxides in water in a v, closed inert tube, such as B a platinum or gold tube (with

4> high pressure, e.g. B. about 3000 atmospheres and a temperature of about 500 to 700 ⁼ C for about 24 hours).

The platinum, palladium delafossite can be at relative low pressures and low temperatures in one

-, o reaction produced by an exchange characterized by ions and the formation of a solid or molten salt as a by-product is. This method uses the halide of platinum, palladium and the oxide of the second metal reacted to form delafossite and a halide * of the second metal. Alternatively, it can Halide or the metal and the halide of the first metal and a lithium oxide compound of the second metal (such as lithium chromate, lithium cobate or lithium rhodate) with the formation of delafossite and Lithium halide are implemented.

The Anioner.austauschreaktion is conducted in an evacuated sealed silica tube at a temperature of about 5Ou to about 800 C ^c.

o5 The halide salts obtained as a by-product are after the formation of the Delafossit through expenses, z. B. removed with water If metallic Platinum or palladium remains or if the chloride

of the precious metal remains, these residues become by leaching with a suitable solvent, such as. B. hydrobromic acid or aqua regia, removed.

Delafossite can also be made by diffusing finely powdered mixed oxides at high temperatures. The platinum and palladium delafossite require a temperature above 700 ^° C. and a pressure of about 3000 atmospheres in order to obtain the delafossite through a reaction in the solid state.

The delafossite produced by one of these methods can either be used as such for an electrode can be used or preferably serve as a surface or coating of an electrode made of a suitable base or substrate material.

In the "egel" is the electrically conductive base or Substrate material a rectifier metal such as titanium. Such a substrate can be in the form of a flat, plate-like structure or it can also be in the form of a perforated plate or an expanded one Have latticework. Alternatively, it can be in the form of fine wires, rods, or other shapes, such forms the outflow of the gases formed from the volume between the anode and the cathode in spaces behind the anode.

When using a titanium link as a substrate material you can prepare this titanium member for its use as an electrode by having the Deposits the Delafossit coating, degreasing and then etching. Degreasing can be done by any known method, e.g. B. using detergents, abrasives or organic degreasing agents. Then the degreased titanium substrate can be etched with hydrofluoric acid, hydrochloric acid, or similar materials. The etching is used to remove the naturally occurring oxide film and through it to replace a thin film of hydride.

The delafossite can be applied to the etched titanium surface in various ways. So can one z. B. a slurry of delafossite in a solvent such as ethanol, butanol, benzyl alcohol, Produce phenol, benzene, cumene and the like. Such a slurry can be applied to the titanium surface, e.g. B. Apply with a paintbrush or a brush. After each spread, heat is applied to decompose or volatilize the solvent. The slurry can additionally contain finely divided materials such as silicon, titanium, zirconium, hafnium, vanadium, niobium, tantalum, Molybdenum, tungsten, or other materials that are capable of being "in situ" during the process of Evaporation or decomposition of the solvent to form an oxide. Usually used as such finely divided material uses a chloride, such as. B. titanium trichloride.

Alternatively, you can make a slurry from Delafossi !, a metal, an organic one Solvents such as ethanol. Butanol, benzyl alcohol, phenol, benzene, cumene, polyene and the like, and one Silica compound or a metal compound which is soluble or in the organic solvent is dispersible, e.g. B. a resinate. Such a slurry can be painted onto the titanium be, where z. B. about 4 to about 8 spreads used and heated after each spread to the decompose or volatilize organic components. Alternatively, for the application of the Delafossits can be used on the substrate but also other methods, such as joining by pressing sen or cathodic electrophoresis.

In the above procedures for the overcoat of the titanium substrate with the delafossite was the use of a titanium or a silicon compound indicated, but such connections are for there! Function of the electrode is not required. the Oxidation products of such compounds as

ίο z. B. titanium dioxide or silicon dioxide, however, confer the delafossite surface has an additional physical Strength and durability Alternatively, oxides of zirconium, hafnium, vanadium, niobium, tantalum can be used Molybdenum or tungsten on the surface of the dei

is electrode can be produced "in situ" in order to obtain the To improve the resistance and durability of the electrode surface.

The invention is explained in more detail in the following examples.

example 1

One is made of a titanium substrate, a coating of a palladium-cobalt delafossii (PdCoO ₂ ) and one between the titanium and the Delafossit inlaid layer of metallic platir existing electrode.

The delafossite is made from 2.6642 g of palladium chloride (PdCl ₂ ) and 2382 g of cobalt oxide in such a way that the chloride and the oxide are thoroughly ground, ir

fills cm ίο a 2 hour air sucked empty quartz tube ¹ a outer diameter of 10 mm and a length before and 12.7 in 1 hour at 110 ° C heated after which closes the quartz tube. Then HEATER the sealed quartz tube to 850 ⁰ C, it keeps Ii Minutes at this temperature, the Temperatui can then ^{drop to 700 °} C. and the heating continues at this temperature for 65 hours. One scrapes there; resulting product from the quartz wall, grind it thoroughly, wash it twice at 25 ° C with 200 m Water, then with acetone and dry it. You get 2.4 g of a gray metallic product with a particle size in the range from 0.03 to 0.5 and from 1 to 1 Micron.

This powder is examined by X-ray scattering)

in a Philips diffractometer. For the X-ray roar a voltage of 35 kilovolts and an amperage of 15 milliamperes are used for the detector Voltage of 1265 volts. One uses the Strahlunj of a copper target and works with a divergence diaphragm of Γ, a beam diaphragm of 0.1524 mm an aperture of 1 °. The detector is left with a time constant of 2 seconds at 2Θ = 2 ° pn Minute and the test specimen at 2Θ = Γ per minute rotate. The un <in the following table (6) are obtained measured values shown in FIG.

Table 6

5.925
4,572
3.448
2.957
2.566
2,440
2.362

40
5
5

90

10

60

100

continuation

2.252 2.148 1.759 1.646 1,480 1.438 1.415 1,350 1.325 1.277 1.273

40

10

50

10

20th

30th

20th 20th

A titanium strip 14.6 cm long, 9.5 mm wide and thick 3.175 mm with a under the trademark »Comet« commercially available household cleaning agents containing abrasives, rinsing it in distilled water, dipping it for one minute in 1% hydrofluoric acid and then for 23 hours in 12 'η hydrochloric acid of 27 "C.

A solution of 10 g of a platinum resinate of the Engelhard type "0-5X" containing 73% by weight of platinum calculated as the metal in 9 g of toluene is prepared and applies this solution in three layers to the etched titanium strip. Each time after applying the In the first two layers, the strip is heated at a rate of 50 ° C to 500 "C in 5 minutes and keep it at this temperature for 10 minutes. After applying the third layer, heat the Strips at a speed of 50 ° C in 5 minutes to a temperature of 550 ° C. Also at this temperature is kept for 10 minutes.

It is made from 0.5 g of palladium-cobalt delafossite (PdCoCb), 1 g of a _{4.5% strength by weight titanium solution prepared by adding 3.4 g of titanium chloride (TiCl 3} ) to 20 g of ethanol, and 1.0 g of ethanol produced a sludge and applied six coats of this with a brush to the strip of Tiian as described. After each coating, the strip is heated to 100 ° C. and held at this temperature for 30 minutes. After the last coat has been applied, the strip is heated in vacuo at a rate of 100 ° C. in 10 minutes to 400 ° C., after which it is held at this temperature for 40 minutes.

After applying the last layer, test the electrode in a beaker chlorate cell. The chlorate cell used is a 500 ml beaker which contains a saturated saline solution and in which the platinum-coated titanium cathode is located at a distance of 9.5 mm from the anode through a Teflon spacer. The electrolysis is carried out at a current density of 53.82 amperes per dm ² and a cell voltage of 3.5 volts. At a current density of 53.82 amperes per dm ² , the cell has a chlorine overvoltage of 0.08 volts.

The anode is placed in a laboratory chlorine diaphragm cell. The cell has an iron mesh cathode which is 9.5 mm away from the anode and separated from it by asbestos paper. The electrolysis of a saline solution containing 315 g of NaCl per liter is carried out at a current density of 53.82 amperes per dm ² and a temperature of about 90.degree. The cell initially has a voltage of 3.64 volts and a chlorine overvoltage of 0.08 volts. To an electrolysis time of 816 hours it has a Voltage of 3.92 volts and a chlorine overvoltage of 033 volts.

Example 2

An electrode is produced from a titanium substrate and the Delafossite PtasCoasCh as a coating layer.

The delafossite is exhibited by an anion exchange

Platinum chloride, cobalt oxide (CoO) and cobalt oxide (Co ₃ O ₄ ). The cobalt oxides are used in the form of a _{mixture consisting of 0 ^ 048 g Co 3} O ₄ and 0.1274 g CoO. They are in the form of a powder with a grain size of less than 325 mesh. One pounds the powder mixture in a mortar to even greater fineness is poured into a quartz tube of an outer diameter of 10 mm and a length of 10.16 cm, sucks this evacuated, it closes, it is heated au- ^r 700 ° C and keeps it 25 Hours at this temperature. Man receives one from a black powder and light blue Mixed phase consisting of crystals. You grind this material, fill it into another quartz tube, suck it up 3 Evacuated for hours, heated to 710 ° C, held at this temperature for 18 hours, and then another 15 Hours at a temperature between 700 and 710 ° C, the quartz tube cools down and removes the material from it. You crush it in a mortar, put it in a 150 ml beaker and add 100 ml of water. Man filtered the resulting sludge at 25 ° C through a

jo sintered glass filter funnel. The insoluble The residue is washed twice with 25 ml of water and then with acetone. You get a gray-black Solid which, as described in Example 1, is examined by X-ray scattering. An X-ray is obtained diagram with the in Table 7 and F i g. 7 shown Readings.

Table 7

I / Io

5,901 3.292 2.968 2,428 2,364 2.146 2.077 2.020 1,979 1.764 1.648 1,549 1.445 1.441 1.414 1.374 1,350 1.321 1.277

90 10 100 30 70 40

10 80 10 40

60 20 10

5 10

5 10

A titanium strip 14.6 cm long, 9.5 mm wide and thick 3.175 mm with the household cleaning agent »Comet«, etches it for 5 minutes in a 2 percent volume Hydrofluoric acid solution and then 22 hours at 27 ° C in 12N hydrochloric acid.

0.25 g of the above-described platinum-cobalt delafossite (PtOiCo ₀₃ O ₂ ), 0.5 g of a 4.2% by weight solution of titanium chloride (TiCl ₃ ) in ethanol and 0.5 g of ethanol are used Mud and applied five coats to the titanium strip with a brush. After each of the coatings 1 to 4 by heating the strip to 100 ⁰ C, keeping it for 30 minutes after the application of the last coating by heating the strip in a vacuum tube then to 500 ⁰ C. In this temperature is maintained him 30 minutes.

The electrode is first tested in a beaker cell. A 400 ml beaker is used as the beaker cell. This contains the anode to be tested and a platinum-coated titanium cathode, 9.5 mm away from it through a Teflon spacer. A saturated saline solution is used as the electrolyte, which contains 315 g of saline per liter. After 18 hours, the electrode shows a voltage of 3.15 volts with a current density of 26.91 amps per dm ² and a voltage of 3.8 volts with a current density of 53.82 amps per dm ² . At a current density of 53.82 amperes per dm ² , the voltage against a calomel electrode is 1.12 volts and the chlorine overvoltage is 0.06 volts

The electrode is then placed in a laboratory chlorine diaphragm cell. The cell contains an iron mesh cathode which is located at a distance of 9.5 mm from the anode and is kept separated from it by asbestos paper. At a current density of 5J.82 amperes per dm ² and a temperature of the electrolyte of 90 ⁰ C h ^ *. the cell initially had a voltage of 3.58 volts and a chlorine overvoltage of 0.06 volts. After a Betrrb of 104 days, the cell has a voltage of 3.70 volts and a residual chlorine is voltage of 0.08 volts.

Example 3

An electrode is produced from a titanium substrate and the Delafossite PtO ₅ Co _{0 I 33} O _{2 as a coating layer.}

The platinum-cobalt delafossite is produced by the anion exchange process in such a way that 5.322 g of platinum chloride (PtCl ₂ ), 1.9622 g of cobalt oxide (CO3O4) and 0.882 g of cobalt oxide (CoO) are milled to a grain size of less than 325 Chop up the mesh, mix it, pour the mixture into a quartz tube with an outer diameter of 12 mm and a length of 12.7 cm, vacuum the tube at 25 ° C for 2 hours and at 125 ° C for 16 hours and then seal it - .0 . The tube containing the powder is then heated to 700 ^° C., kept at this temperature for 70 hours, and then rapidly cooled to room temperature, whereupon it is opened. Its contents consist of a gray metallic solid, solid blue γ, crystals and a green solid. Comminuting the total product by grinding to a particle size of less than 325 mesh, the crushed product filled into a second quartz tube of an outer diameter of 12 mm and a length of 12.7 cm, _b n sucks the tube 1 hour at 25 ° C and 3 hours at 135 ° C, seal it, heat it to 700 ° C and keep it at this temperature for 47 hours. Then cool it down to room temperature and open it. It contains blue and green crystals at its cooled ₆ ^r > end and also a gray metallic solid. Comminuting the gray metallic solid to a particle size of less than 325 mesh, washed twice at 25 ° C with 25 ml distilled water and then twice with acetone and dried at 70 ⁰ C. Thereafter, the powder is kept for 16 hours at 25 ° C under Vacuum. The light gray crystalline metallic substance obtained is examined by X-ray spectroscopy in the manner described in Example 1. The X-ray diagram is shown in FIG. 8 It is, apart from only minor differences, essentially identical to the X-ray _{diagram known from the literature of Delafossit Pt 03} CoQ ₈ O _2.

The titanium strip is etched as described in Example 1 and carried on it from a sludge composed of 0.25 g of platinum-cobalt delafossite, 0.50 g of a titanium resinate solution containing 4.2% by weight of titanium, calculated as the metal, 0.19 g of toluene and 0.06 g of phenol consists of five coating layers. Heating the layers 1 to 4 at a rate of 50 ⁰ C in 10 minutes to 425 ° C, and the fifth layer is also at a rate of 50 ⁰ C in 10 minutes to 500 ⁰ C. All layers is maintained for 10 minutes at their respective Maximum temperature.

The electrode obtained is tested in the manner described in Example 1 in a beaker chlorine cell. At a current density of 53.82 amps per dm ² and a temperature of the electrolyte of 60 ⁰ C, the cell has a chlorine overvoltage of 0.07 volts, and against a calomel electrode, an electrode voltage of 1,125VoIt.

The anode is then placed in a laboratory Chiordiaphra? Mazelle of the type described in Example 1 and the electrolysis is also carried out as described in Example 1 at a current density of 53.82 amperes per dm ² . The cell initially has a voltage of 3.65 volts and a chlorine overvoltage of 0.07 volts. After 744 hours of electrolysis, the cell has a voltage of 3.85 volts and a chlorine overvoltage of 0.28 volts.

Example 4

An electrode is produced from a titanium substrate and the palladium-rhodium delafossite (PdRhO _{2) as a coating layer.} The delafossite to set ₍₂ LiRhO) metallic palladium and palladium chloride (PdCl ₂₎ following the anion exchange process from Lithiumrhodanat. The lithium rhodanate (LiRhO ₂ ) is obtained from rhodium oxide (Rh ₂ O ₃ ) and lithium carbonate (Li ₂ CO ₃ ). Rhodium oxide (Rh ₂ O ₃₎ is obtained, when heated in an air stream to rhodium chloride (RhCl ₃ · 3 H ₂ O) for 42 hours at 790 ⁰ C. To produce lithium rhodate, the rhodium oxide is ground, 1.0367 g of it is mixed with 0.3660 g of lithium carbonate (Li ₂ CO ₃ ), the powder mixture is placed in an alundum bowl, heated to 1040 ^° C. and held there for 66 hours Temperature, the product obtained is comminuted to a grain size of less than 325 meshes and checked by X-ray spectroscopy. The X-ray diagram obtained is essentially identical to the X-ray diagram known from the literature on lithium manganate (LiMnO _2).

The Delafossit is prepared by mixing _{1.0817 g of lithium rhodanate (LiRhO 2} ), 0.4068 g of metallic palladium and 0.6672 g of palladium chloride (PdCl ₂ ), the mixture is comminuted by grinding, and the powder is transferred to a quartz tube an outer diameter of 9 mm and fills a length of 12.7 cm, the pipe sucks I hour at 25 ° C and 3 hours at 110 ⁰ C deflated, the tube closes, heated to 79O ° C and 75 hours at this temperature holds.

The product obtained is ground, placed in a second quartz tube with an outer diameter of 9 mm and a length of 12.7 cm, the tube is vacuumed, heated to 180 ^° C., kept at this temperature for 18 hours, and closed , heats it to 775 ° C and keeps it at that temperature for 48 hours. The product obtained is washed four times with distilled water and once with acetone.

A titanium strip 143 cm long, 9.5 mm wide and 3.175 mm thick is cleaned and etched as described in Example 1 and four layers of a sludge made from 0.2 g of palladium-rhodium delafossite (PdRhO ₂ ) are painted on it, 0.4 g of a titanium resinate containing 4.2% by weight of titanium, 0.05 g of phenol and 0.15 g of toluene, with a brush. After each of the coatings 1 to 3 by heating the strip at a rate of 50 ⁰ C in 10 minutes at 45O ⁰ C, followed by keeping it for 10 minutes at this temperature. After applying the last layer, heating it, also at a rate of 50 ° C in 10 minutes, to 500 ⁰ C. In this temperature is maintained the strip i0 minutes.

The electrode produced in this way is tested as an anode as described in a beaker chlorate cell. At a current density of 53.82 amps per dm ² and a temperature of the electrolyte of 60 ⁰ C, the electrode is a chlorine overvoltage of 0.07 volts.

The anode is placed in a laboratory chlorine diaphragm cell of the type described in Example 1 and the electrolysis is carried out as described in Example 1 at a current density of 53.82 amperes per dm ² . At the beginning the cell has a voltage of 3.69 volts and a chlorine overvoltage of 0.07 volts. After 1320 hours of electrolysis, the cell has a voltage of 3.71 volts and a chlorine overvoltage of 0.15 volts.

Example 5

An electrode is produced from a titanium substrate and the palladium chromium delafossite (PdCrO _{2) as a coating layer.} Delafossit is made from palladium metal, palladium chloride and lithium chromate using the anion exchange process. Lithium chromate is obtained by reacting lithium carbonate (Li ₂ COj) with chromium oxide (Cr ₂ Oj). For this purpose, a mixture of 3.6945 g of lithium carbonate (Li ₂ COj) and 7.6010 g of chromium oxide (Cr ₂ O ₃ ) is ground, the powder is placed in an alundum bowl and heated in it for 4 hours at 330 ° C. and 12 hours to 930 ⁰ C. it grinds the erhai'.ene product, then heated 23 hours at 93O ⁰ C, zermahit it again and heated in 23 hours 1040 ⁰ C. it zermahli the dark green product obtained and analyzed it, as in example 1 described, by X-ray spectroscopy. According to its X-ray diagram, it has the same crystal form as LiM _n O ₂ .

A powder with a particle size of less than 325 mesh is prepared from 1.8190 g of lithium chromate (LiCrO ₂ ), 1.0670 g of palladium metal and 1.776 tg of palladium chloride (PdCl ₂ ) by grinding, and the powder mixture is placed in a quartz tube with an outer diameter 10 mm and a length of 12.7 cm, the pipe sucks for 16 hours at 130 ⁰ C deflated, it closes heated in 46 hours 800 ° C and cools it. The product obtained is ground up, filled into a second quartz tube with an outer diameter of 10 mm and a length of 12.7 cm, the quartz tube is vacuumed at 130 ^° C. for 5 hours, closed and heated to 800 ^° C. for 64 hours , which means that it is heated to 800 ° C for a total of 110 hours.

The product obtained is ground to a grain size of less than 325 meshes, and it is washed 25 "C with distilled water, then washes it twice more with acetone at 25 ° C and dries it.

One cleans and etches a Tixan strip 14.6 cm long, 94 mm wide and one Thickness of 3.175 mm to that described in Example 1

ίο wise.

A solution of 10 g of a platinum resinate of the Engelhard i> 0-5X «type containing 7.5% by weight of platinum as metal is prepared in 9 g of toluene, so that the solution is 3.9% by weight, calculated as metal Platinum contains and applies four coatings to the titanium strip from this solution. ^{The strip is heated to 40O 0} C in 5 minutes after the application of the coatings 1 to 3 at a rate of 5 ° C. and after the application of the fourth

Coating, at a rate of 50 ° C in 10 minutes, to 500 ⁰ C and holds it in each case 10 minutes at the respective maximum temperature.

0.2 g of palladium-chromium delafossite (PdCrO ₂ ), 0.4 g of a titanium resinate containing 4.2% by weight of titanium, 0.05 g of phenol and 0.16 g of toluene are prepared Mud and then apply four layers of coating to the titanium strip with a brush. Heating the electrode in each case after the application of the coatings 1 to 3 at a rate of 50 ⁰ C in 10 minutes to 450 ⁰ C and after application of the last coating, also at a rate of 50 ⁰ C in 10 minutes, to 500 ° C and keeps it in any case for 10 minutes at the respective maximum temperature.

The electrode is then tested as an anode in a beaker chlorate cell as described in Example 1. At a current density of 53.82 amps per dm ² , the anode has 0.05 volts.

Example 6

A titanium substrate is used, a layer of platinum applied to it, a further layer of platinum-cobalt delafossite (PtOaCOn ₁₈ O ₂ ) and a layer of porous material covering this layer

4ι titanium dioxide ago an electrode.

The platinum-cobalt delafossite is produced by reacting platinum chloride (PtCl ₂ ) with cobalt (II + III) oxide (Co ₁ O ₄ ) and cobalt (II) oxide (CoO) that 7 , 9842 g of platinum chloride (PtCl ₂ ), 3.6123 g

- Pound n cobalt (II + III) oxide (Co ₃ O ₄ ) and 1.1241g cobalt (II) oxide (CoO) in a mortar to a powder with a core size of less than 325 mesh and mixes the powder into a quartz tube with an outer diameter of 10 mm and a length of 12.7 cm

v, and heated in a vacuum to 130 ⁰ C for 18 hours, whereupon the tube is closed.

The closed quartz tube is heated to 700 ^° C. for 46 hours, the product formed is taken out of the quartz tube, it is ground, and it is put into a second one

w) quartz tube mm from an outer diameter of 10 and a length of 12.7 cm, the tube is heated in a vacuum for 8 hours to 130 ° C, verschüeOt it and then heated it 64 hours at 700 ⁰ C.

The resulting product is taken out of the tube

_b 5 out, it is washed five times at 25 ° C with distilled water, then washed twice at 25 ° C with acetone, it is dried in an air stream at 70 ⁰ C pounds it in a mortar to a grain size of less than 325

Mesh and crush it further by using it in a commercial hammer mill for an hour treated with a hammer made of boron carbide.

After examination with an electron microscope, the material obtained has grain sizes im Range between 0.02 and 7.5 microns. The grain size distribution lies within two different size ranges. The main grain sizes are between 0.02 and 0.3 microns and between 1.5 and 6.0 microns. In the area of fine particles is the mean grain size 0.1 micron, in the range of larger particles it is 2.5 microns.

A 14.6 cm long, 9.5 mm wide and 3.175 mm thick titanium strip is cleaned and etched, as described in Example I, and eight layers of 0.25 g of Delafossite Pt0.eCon.sO2, 0.12 g titanium tetrachloride (TiCl ₄ ) in butanol. 0.75 g of butanol and 0.15 g of phenol on existing sludge.

k " _r ,,, r. ηχ, Ι

Speed from 50 ⁰ C to 425 "C in 5 minutes.

A sludge is then made from titanium tetrachloride (TiCU) in butanol. who, billed as metal. 2.25% by weight titanium contains and spreads this sludge in four layers on the delafossite surface of the titanium strip. Heating the strip in each case after the application of the coatings 1 to 3 20 minutes 1 IOC and after 10 minutes 425 ⁰ C. After application of the last coating heating it 20 minutes 11O ¹⁵ C and 15 minutes at 500 ⁰ C.

The electrode produced in this way consists of a titanium substrate as a base, a coating layer made of platinum-cobalt-delafossite and an outer layer of titanium dioxide covering this. The electrode is placed in a beaker chlorate cell as an anode. At a current density of 53.82 amperes per dm ² , the anode has a voltage of 1.175 volts against a calomel electrode and a chlorine overvoltage of 0.12 volts.

Example 7

A titanium substrate is used as the base, a coating of platinum-cobalt-delafossite Pt0.eCo0.sO2 and an outer layer of titanium dioxide applied thereon to produce an electrode.

A 4.6 cm long, 9.5 mm wide and 3.175 mm thick titanium strip is cleaned in the manner described in Example 1, and it is applied from a sludge made of 0.5 g of the platinum-cobalt delafossite (PtOiCo ₀₈ O _2), 0.25g of titanium tetrachloride (TiCl), 0.75 g of but? iol and 0.15g phenol six coatings on and heats the strip after each coating first for 30 minutes 110 ° C and then 15 minutes at 400 ⁰ C.

A solution of titanium tetrachloride containing, calculated on the metal, 2.1% by weight of titanium is prepared in Butanol and uses this solution to apply four coatings to the delafossite surface of the electrode. After every of coatings 1 to 3, the electrode is heated first to 110 ° C. for 20 minutes and then to 425 ° C. for 10 minutes. After the fourth coat, it is first heated to 110 ° C for 20 minutes and then to 500 ° C for 15 minutes.

The electrode consisting of the titanium substrate, a coating of platinum-cobalt delafossite and an outer coating of porous titanium dioxide is tested as described in Example 1 as an anode in a beaker-chlorate cell. At a current density of 53.82 amperes per dm ² , the anode has a voltage of 1.160 volts against a calomel electrode and a chlorine overvoltage of 0.10 volts.

The anode is placed in a laboratory chlorine diaphragm cell of the type described in Example 1 and the electrolysis according to Example 1 is carried out at a current density of 53.82 amperes per dm ² . The cell initially has a voltage of 374 volts and a chlorine overvoltage of 0.10 volts. After 74 days of electrolysis, the cell has a voltage of 3.94 volts and a chlorine overvoltage of 0.17 volts.

Example 8

With a titanium substrate as a base, a coating of platinum-cobalt-delafossite (Pt ₀ * Coo.s02)

ι. and one between the substrate and the delafossite over / ug Inlaid layer of ruthenium dioxide (RuO)) produces an electrode.

You degrease, clean and etch a 14.6 cm long, 9.5 niüi wide and 3,175 γππρ itarkrn titanium tires

JIi the manner described in Example 1 and then spreads five layers of a 1.5 g of Ruthcniumtrichlorid (RuCh-3H ₂ O) in 9 g of ethanol containing sludge with a brush. The strip is dried on the for 10 minutes after each of the first four coats

r. Air and then heats it to 300 ° C for 10 minutes with a supply of air. It also dries the last coating next 10 minutes in the air, but then heated it Minul 45 'η supply of air to 450 ⁰ C.

It is made from 0.5 g of the platinum-cobalt delafossite

in (Pl0.eCo0.nO2) according to Example 6. 1.0 g of a metal calculated 4.2 wt .-% titanium containing solution of titanium tetrachloride (TiCU) in Butarcl, 0.2 g phenol and a drop of nonylphenoxypolyoxyethylene ethanol and put on six coatings

r> the strip on. After each coating you heat the Strip first at 110 "C for 20 minutes and then at 400" C for 15 minutes.

The strip is then coated with a layer of a titanium 2.1% by weight, calculated as metal

χι containing solution of titanium tetrachloride (TiCU) in butanol and heated it first to HO ⁰ C for 20 minutes and then to 500 ° C for 15 minutes. The electrode obtained by this method has a uniform gray appearance.

1-, The electrode is tested in the manner described in Example 1 as an anode in a beaker chlorate cell. At a current density of 53.82 amps per dm ² , the anode has a voltage of 1.147 volts against a calomel electrode and a chlorine surge

iii voltage of 0.09 volts.

The electrode is then inserted as an anode laboratory chlorine diaphragm cell of the type described in Example 1 and conducts the electrolysis as in Example 1 described at a current density of 5332

Amps per dm ² . The cell initially has a voltage of 3.60 volts and a chlorine overvoltage of 0.09 volts. After electrolysis for 936 hours, the cell has a voltage of 3.72 volts and a chlorine overvoltage of 0.07 volts

Example 9

It is made with a titanium substrate as a base, a coating made of the palladium-cobalt-Delafossil (PdCoO2) and a layer of ruthenium inserted between the substrate and the delafossite coating dioxide (RUO2) produces an electrode.

You degrease, clean and etch a 14.6 cm long 9.5 mm wide and 3.175 mm thick titanium strips aui

in the manner described in Example 1, and sweeps it, with a brush four layers of 1.5 g of ruthenium trichloride (RuCIj ■ 3 H ₂ O) in 9 g ethanol containing ·.! Mud up. Dry the strip of any of the first three coatings 10 minutes in air and then heating it in an air-open furnace to a temperature of 300 ⁰ C, at which it is h'-Mt 10 minutes. Dry the strip after the fourth coating is also 10 minutes in the air, but then heating it in an air-open oven at 450 ⁰ C and holding it for 45 minutes at this temperature.

It is made from 0.2 g of the palladium-cobalt Delafossil (PdCoOi) according to Example I, 0.4 g of one as metal calculated 4.2% by weight of titanium-containing titanium resinate, 0.15 g of toluene and 0.05 g of phenol produced a slurry uses it to apply six coatings to the titanium strip. Heat the after each of the first five coats Strip at a speed of 50 "C in 5 miniilrn: inf 475T 'Narh Hrm Ipf7lpn llhpryng prl.im one the strip at a speed of 50 C in

5 minutes to a temperature of 500 ° C, at which one holds it for 15 minutes.

The electrode consisting of a titanium substrate, a coating of the palladium-cobalt delafossite and a ruthenium dioxide layer interposed between the substrate and the delafossite coating is inserted as an anode in a beaker chlorate cell according to Example 1. At a current density of 53.82 amperes per dm ² , the anode has a voltage of 1.141 volts against a calomel electrode and a chlorine overvoltage of 0.08 volts.

The anode is placed in a chlorine diaphragm cell of the dimensions customary in the laboratory and the electrolysis is carried out according to Example 1 at a current density of 53.82 amperes per dm ² . The cell initially has a voltage of 3.48 volts and a chlorine overvoltage of 0.08 volts. After a duration of the electrolysis of 576 hours, the cell has a SInanniincr vrtn λ 4Q VnIt linH fMnp PhlnriiKorcnannnno -r ~ ■ -c ■ --- -. ■ -. ~ .. _ .., - ....... ~ -........ _u ...., f ~ · ···· £

of 0.07 VcIt.

llier / u 4 lihill /.cichiiunccn

Claims (3)

see formula claims: ABO2 1. Anode with a chlorine overvoltage of less than 0.33 volts at a current density of 53.82 amps per dm ³ , characterized by an electrically conductive carrier made of a rectifier metal or graphite with a coating thereon which consists essentially of delafossite, wherein the platinum-cobalt-delafossite, the palladium-cobalt-delafossite, the palladium-chromium-delafossite or the palladium-rhodium-delafossite are used as delafossite 2. Anode according to claim 1, characterized by one between the carrier and the delafossite surface located intermediate layer, which essentially consists of ruthenium, rhodium, palladium, platinum, Osmium, iridium or their alloys or ruthenium oxide, rhodium oxide, palladium oxide, Platinum oxide, osmium oxide, iridium oxide or mixtures of which consists 3. Anode according to claims 1 or 2, characterized in that the carrier consists of titanium.