NL1017632C1 - Mixed oxide material with high electron conductivity, used in production of electrode for electrochemical cell, does not contain metals from platinum group - Google Patents

Abstract

A mixed oxide material with high electron conductivity does not contain metals from platinum group. A mixed oxide material with a high electron conductivity has an empirical formula of ABOy. y = not equal to 3; A = sodium (Na), potassium (K), rubidium (Rb), calcium (Ca), barium (Ba), lanthanum (La), praseodymium (Pr), strontium (Sr), cerium (Ce), niobium (Nb), lead (Pb), neodymium (Nd), samarium (Sm), and/or gadolinium (Gd), and B is copper (Cu), magnesium (Mg), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), niobium, molybdenum (Mo), tungsten (W), and/or zirconium (Zr). A and B cannot both be Nb, and compound SrVO2.5 is excluded. Independent claims are also included for: (A) a method for producing an electrode for an electrochemical cell, comprising: (a) forming a cohesive layer of a mixed oxide on a substrate by applying a mixture of the above mixed oxide material, binder(s) and solvent(s), (b) removing the solvent, and optionally (c) heat treatment; and (B) an electrochemical cell comprising at least two electrodes and an electrolyte.

Description

Brief indication: Electrode for an electrochemical cell

The present invention relates to an electrode for an electrochemical cell. Electrochemical cell electrode is here understood to mean, in the broadest sense, the use of an electrode in combination with an electrolyte and other electrodes. That is, the invention relates to electrodes for electrochemical conversion and storage of electricity as they occur in electrochemical capacitors, also referred to as super-capacitors or ultra-capacitors, batteries, in particular also rechargeable batteries of the alkaline type or the alkaline type. metal / air type, fuel cells such as the polymer electrolyte fuel cell, electrolysis devices and sensors.

An electrochemical capacitor (or super-capacitor or ultra-capacitor) is a device in which electricity can be stored and subsequently withdrawn, in particular with a high power density (in W / kg and W / l), by using of electric double layer capacity and / or so-called pseudo-capacity which is linked to Faraday processes such as redox reactions or intercalation processes. Applications include the (short-term) storage and / or delivery of peak powers and the reduction of "duty cycles" of batteries, such as that occurs in, for example, battery or hybrid or fuel cell vehicles, installations or equipment that ensure central or local electricity networks or power supplies, and in electronic or portable equipment such as laptops and mobile phones. Such an electrochemical capacitor has two electrodes, an anode and a cathode, to which electrons are released and received, respectively. Furthermore, the capacitor contains an electrolyte, for example an aqueous or an organic solution, and a separator, and the whole can be built into a metal or plastic housing. At least one of the two electrodes can now be an electrode according to the invention. The charge, positive at one electrode and negative at the other, is stored in the electric double layer capacity at the interface of electrode and electrolyte, in the pseudo-capacity resulting from highly reversible rebox responses or intercalation processes at this interface or in the bulk of the electrode material, or in a combination of double layer and pseudo-capacity. Important properties here are the specific capacity (in pF / cm2) which is determined by the nature of the electrode material and the electrolyte used, the specific surface area of the electrode material (in cm2 / g) and the effective capacity resulting therefrom in (F / g). Furthermore, the nature of the electrolyte is important for the allowable potentials on the electrodes. These determine, in the case of pseudo-capacitance together with the effective potential region around the Nernst equilibrium potentials of the related reactions or processes, the operational voltage range of the capacitor which should preferably be as large as possible. The composition and the microstructure of the electrode materials, the microstructure of the separator and the composition of the electrolyte also determine, but not only, the internal resistance Ri (in Ω) of the capacitor, which should preferably be as low as possible. The quantities described also determine, but not only, the energy density of the capacitor (in Wh / kg and Wh / 1) and the power density (in W / kg and W / l). For known technologies, these are typically several Wh / kg and several thousand W / kg, respectively. For the energy E (in J) and the power P (in W) of the capacitor with capacitance C (in F) and charged to the voltage V (in V), the approximate E = CV2 / 2 and P = V2 / 4Ri.

Known are, inter alia, electrochemical capacitors with electrodes that have activated carbon as their most important component and which mainly use electric double-layer capacities. It is important that the activated carbon forms a porous structure with a high surface area accessible to the electrolyte to form the highest possible capacity, and with the highest possible conductivity for electrons to achieve the lowest possible resistance and as much electrode material as possible. to utilize. In this way the highest energy and power densities are obtained which is required for most applications. Carbon electrodes which mainly utilize double layer capacity can be used as an anode and as a cathode; symmetrical capacitors can be made in this way. Carbon electrodes can be used in combination with a - 3-water electrolyte, where the permissible capacitor voltage is a maximum of approx. 1.2 V and a low internal resistance is obtained, or in combination with an organic electrolyte where the maximum voltage is approx. 2.4 V V is but in general a less low internal resistance can be obtained.

For many applications, but in particular for use in vehicles, a higher energy density is desirable than is known in the prior art when using carbon electrodes. Particularly for this pursuit of higher energy density, the use of pseudo-capacity is useful, since it generally results in much higher specific values than with double-layer capacity. The use of ruthenium oxide RuO 2 and hydrated ruthenium oxide RuO 2 .xH 2 O is known, inter alia from U.S. Pat. Nos. 5,550,706, 5,851,506, 5,875,092 and 6,025,020. These compounds, in combination with aqueous electrolytes such as, for example, KOH solutions, have a high effective capacity in F / g based on redox reactions and can be used as an anode and as a cathode. They also have good electrical conductivity. Disadvantages of these compounds when used in (symmetrical) electrochemical capacitors are the limited operational voltage range and the very high cost of material of the desired purity. A lot of research is being done into alternative pseudo-capacity materials that can meet these drawbacks while still enabling the desired higher capacity and energy density.

It is generally assumed in the prior art that the use of compounds with noble metal elements, such as, for example, noble metal oxides, is necessary to obtain sufficiently high storage capacity, or sufficiently high conversion speed or catalytic activity of the electrode, and a sufficiently high electrical conductivity.

However, it will be understood that the costs of such connections are high. It has therefore been proposed to reduce the amount of noble metal in such compounds by using compositions consisting partly of inexpensive, non-noble metals. Known are compounds with the pyrochlore structure such as Pb2 Ru2 O7 (U.S. Pat. No. 5,841,627), perovskites A (Bi-xCx) 03 with 0 <x <1 and B from the series Pt, Ru, Ir, Rh and Pd (German patent specification). THE

1 - 4 - 196 40 926), - CaRuO 3 - x and LaNiO 3 etcetera. These compounds contain expensive (semi) noble metal elements, or are not oxygen deficient (or both). For the first category, it appears that, based on the capacity or activity obtained per quantity of (semi) precious metal 5, hardly any cost reduction is achieved. For the second category, the capacity or activity obtained per gram is so low that no improvement with respect to the carbon materials is achieved.

Furthermore, the use of metal hydroxides has been proposed, which can pass into metal oxy-hydroxides, such as in particular Ni (OH) 2.

This connection is attractive because of the low costs, the high specific capacity and the favorable potential range, but it has a low and charge-dependent conductivity. The reversible charge / discharge reaction at an electrode of this material in an alkaline electrolyte can be represented by

Ni (OH) 2 + 0H “O NiOOH + H2 O + e, where Ni (OH) 2 conducts poorly and NiOOH shows a significant electrical conductivity, provided that it is in the correct phase (the β phase). These limitations in electrical conductivity necessitate the use of additives, such as, for example, graphite, and the use of conductive matrices, such as, for example, metal foams or metal mats, to enclose the material with additive. This limits the useful electrode thickness and entails additional costs, weight and volume. This also makes the manufacture of electrodes more complicated and more expensive. The occurrence of Ni (OH) 2 in more phases (α, β, γ) limits the allowable operational conditions for the electrode to those conditions where the desired β phase is stable. Furthermore, Ni (OH) 2 electrode can only be used as an anode, so that symmetrical capacitors cannot be made and, for example, a carbon counter electrode is needed. This limits the improvements in capacity and energy density that are achievable compared to the symmetrical carbon capacitor. Ni (OH) 2, but in particular the nickel component and optionally the nickel required for the preparation, are also attributed adverse environmental and health properties. As a result, requirements and regulations regarding processing and processing apply, which entail additional costs. This also applies restrictions on applicability, for example, to those applications and markets for which collection and / or reuse is arranged.

A (rechargeable) battery is a known device. Electricity can be stored in it and then extracted again, in particular with high energy density (in Wh / kg and Wh / 1), by making use of electrochemical conversion from electrical energy to chemical energy and vice versa. The construction of such batteries corresponds to the construction of electrochemical capacitors described earlier, although the construction and operation may differ. Known are, inter alia, (rechargeable) batteries of the nickel-cadmium type, nickel-zinc, and nickel-iron, of the nickel-hydrogen type, of the nickel-metal hydride type, and of the metal / air type such as iron / air, zinc / air, aluminum / air and lithium / air. At least one of the two electrodes of such batteries can now be profitably replaced by an electrode according to the invention. The nickel electrodes, the cadmium electrode and the air electrodes in particular, but not only, are eligible for this.

NiCd, NiZn, NiFe, NiH2 and NiMH (rechargeable) batteries are known, among which the "nickel electrode" consists of the same Ni (OH) 2 compound and has the same effect as indicated above for electrochemical capacitors. The same disadvantages also apply as a result of the limitations in electrical conductivity and the same problems with regard to the environment and health.

Also known are batteries of the type Fe / air, Zn / air, Al / air and Li / air, wherein during discharge at the air electrode oxygen is consumed by electrochemical reduction; such batteries are "mechanically recharged" by renewal of the anode. It is also known that bi-directional air electrodes which, in addition to reducing oxygen, can also evolve oxygen in the reverse process and thereby make electrically rechargeable metal / air batteries possible. Hitherto known compounds only allow moderate performance due to limited conductivity and catalytic activity, and are often expensive.

It is the object of the present invention to provide a high performance electrode which does not have the above disadvantages, that is, is inexpensive to manufacture, has no limitations on useful thickness, and has no environmental problems. .

It now appears that this object can be achieved at an electrode for an electrochemical cell by a compound comprising a perovskite of the type ΑΒ03_δ where precisely δ ^ 0, wherein A comprises a metal selected from the group Na, K, Rb, Ca, Ba, La, Pr, Sr, Ce, Nb, Pb, Nd, Sm and Gd, and B comprises a metal selected from the group Cu, Mg, Ti, V, Cr, Mn, Fe, Co, Nb, Mo, W and or Zr, and wherein no metal from the group Pt, Ru, Ir, Rh, Ni and Pd is present. Surprisingly, it has been found that when such a perovskite of the type ΑΒ03.δ is used in which no (semi) noble metals are present, nor nickel is present, and in which a particular choice is made between - 0.2 and - 0.05 or between + 0.05 and + 0.7 particularly good storage capacity (in F / g or Ah / kg), or conversion speed or catalytic activity is obtained and also a high electrical conductivity (in S / cm) . It has also surprisingly been found that the utilization of the electrode material comprising such a connection is practically independent of the electrode thickness. Such a property is completely unknown in the prior art. It should be understood that perovskites of the type ΑΒ03_δ are also understood to mean perovskites of the type or AlA2B03-5 or ΑΒ1Β203-δ or A1A2B1B203_6 with δ Φ 0 and δ in particular within the values specified above. Examples are Sm0.5Sr0.5CoO3-25 δ, Ndo.5Sr0.5Co03_5 and Nd0., S0.6Co.8Feo.203-5, but the invention is not limited thereto.

Furthermore, it has surprisingly been found that the above stated objective in an electrode for an electrochemical cell can also be achieved by a connection comprising a brown-millerite ABO (2.5 - ξ) wherein ξ * 0, and A and B are selected from the groups indicated above. A high capacity, or conversion speed or catalytic activity, and a good electrical conductivity can occur in particular for values of ξ between - 0.2 and -0.05 or between + 0.05 and + 0.3. An example of such a connection 35 is SrCoO (2.5 - ξ), but the invention is not limited to this.

It should be understood that an electrode can comprise more than one of the perovskites and / or brown millerites in question.

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By applying these compounds, it is possible to obtain electrodes with desired properties at low material costs and via a simple manufacturing process. Furthermore, the invention makes it possible to use electrodes up to large thicknesses in a useful manner, without the need for additions of additional materials or components, for example for electrical conduction or current collection. Preferably, such electrodes have considerable porosity to increase the effective surface with the electrolyte. Such an electrode preferably consists at least near the surface of a porous structure which consists of at least 30% and preferably more than 70% of one or more of the above compounds. It has surprisingly been found in an electrochemical capacitor that such electrodes have a high pseudo-capacitance. For example, when used as an anode in an asymmetric electrochemical capacitor with a carbon cathode and with KOH electrolyte, a high electrode capacity was found which, given the effective surface, cannot be attributed to double layer capacity. A high capacity of the total cell was also found, with a low internal resistance, a conveniently located Nernst equilibrium potential E0 and a favorable usable voltage range. This results in high energy and power densities for the cell. Individual measurements demonstrated high electrical conductivity for electrode connections according to the invention. A comparison with the properties of electrodes known from the prior art is given in Table 1. In particular, the electrical conductivity is of the same high level as that of Pb2 Ru2 O7 and the capacitance in pF / cm2 of the same high level as that of Ni (0 H) 2. In addition to the expensive ruthenium, an electrode according to the invention can also, but not necessarily, avoid the heavy lead.

Table 1. Comparison of properties between electrodes * according to the state of the art and a Smo.5Sr0.5CoO3 -5 electrode * according to the invention. C is capacity; σ is electrical conductivity, A 35 is effective surface. Maximum voltage V and maximum voltage drop Δ V apply to the entire cell.

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Self-Active Ru02.xH2 O Pb2 Ru2 O7 SrRuO3 Ni (OH) Sm0.sSro5 CoO3-0 shelf coal 2 C (pF / cm 2) 10 ... 40. . . · 60 2200 2600 A (m2 / g) <1200 120 10 ... 150 70 100 <5 (0) C (F / g) <100 <720 72 20 ... 200 2200> 130 <°> σ (S / cm) <1. . 500 ... . > 700 V (V) 1.2 1.3 .. 1.2 1.6 1.6 Δ V (V) 1.0 1.0 0, 9 0.7 0, 8 1.2 K Euro / kg ) 2.25 (1) 3000 <2) ... 1000 (2) ...> 3000 (2) 6 ... 10 <5) 20 (2) ... 1200 (6) 500013> 23,000 (4) > *) as a working electrode in a super capacitor with carbon versus electrode and KOH electrolyte.

(0)> 2600 F / g with> 100 m2 / g 5 (1) purchase price on a 1000 kg basis (2) raw material price (3) purchase price on a 25 kg basis and depending on purity (4) chemically pure and based on 5 grams ( 5) based on NiO raw material price for> 1000 kg 10 (6) purchase price of a one-off batch of 1 kg

In addition to one or more of the above compounds according to the invention, the electrodes may also, but not necessarily, contain a binder to form a coherent structure. Such a structure can, but does not have to, be arranged in a matrix. Also, but not necessarily, the electrodes may have undergone heat treatment or calcination treatment or sintering treatment.

Figure 1 shows results of measurements on 20 electrochemical capacitors with a carbon electrode and, respectively, a Ni (OH) 2 (represented by Δ) electrode known from the prior art and a Sm0.5Sro.5Co03-5 electrode ( represented by O) according to the present invention. In the Ni (0H) 2 electrode, graphite was added in different percentages to improve the electrical conductivity, while in the Sm0.5Sr0.5CoO3-5 electrode no addition was used. It is clear that the electrode according to the invention can be used to greater thicknesses without loss of effective capacity. It is thus possible to utilize electrodes according to the invention to greater thicknesses without the use of additives, such as, for example, graphite, or conductive matrices, such as, for example, metal foams. This makes cells and stacks of cells possible with less inactive material and therefore with higher energy and power density. Due to the high conductivity it is also possible to use a matrix which conducts less well than, for example, a metal foam, for example a matrix of a conductive plastic or a conductive polymer, and with which reductions in weight and costs are also achieved. It is also possible to form independent, relatively thick electrode layers, for example by printing, printing, casting or dipping, whether or not on other (electrical or electronic) components, and which have a high capacity and do not use expensive precious metal elements.

All this does not alter the fact that electrodes according to the invention can also be made as thin layers, for example by printing, printing, casting, dipping, painting or spraying, and applied.

The electrodes according to the invention are not limited in their design and application to asymmetrical capacitors or to capacitors according to the construction described; they can also be used profitably in symmetrical electrochemical condensers, in batteries and in fuel cells, reversible fuel cells, electrolysis devices and sensors. For example, an electrode comprising one or more compounds according to the invention can replace the known Ni (OH) 2 electrode in an alkaline battery, for example a NiCd or NiMH battery. For this purpose, the composition of the electrode according to the invention is then chosen such that the capacitance lies precisely in the potential range desired for the battery.

An electrode according to the invention is characterized by a specific oxygen stoichiometry, i.e. a specific value interval for δ and or ξ, and by the total or complete avoidance of noble metal elements, in particular ruthenium and irridium, by a high pseudo-capacity (of the same level as with Ni (OH) 2) and or high catalytic activity and or high conversion speed, due to a high electrical conductivity (of the same -10 level as with Pb2Ru207) practically independent of the charge state or polarization, due to a large stability due to the absence of undesired phases and due to a favorable voltage range. In an electrode according to the invention, the use of environmentally harmful elements, such as nickel and lead, occurring in electrodes according to the prior art can also be avoided. As a result of the properties mentioned, an electrode according to the invention, compared to what is known in the prior art, can be cheaper, have a higher round-trip efficiency, in particular at higher currents, can be manufactured more easily, used in the in the form of a thin layer or thick layer, and may or may not be enclosed in a matrix which may also consist of a light, cheap and moderately conductive plastic. In this way, an electrode according to the invention also permits concepts other than those known in the art for capacitors, super capacitors, batteries, fuel cells, electrolysers and sensors. For example, it is now possible to print the electrode as a layer on another component and in this way add a function to that component. That component can for instance be part of a photovoltaic solar cell or an electro-chrome window.

The present invention will be described in more detail below with reference to a number of examples.

Example 1 Electrode according to the invention manufactured by applying a layer of suspension, ink or paste to a substrate. The substrate can be, for example, a metal foil or a plastic foil. The suspension, ink or paste comprises one or more compounds according to the invention, a solvent and possibly auxiliaries such as dispersants, surfactants, wetting agents and the like. The compounds according to the invention can be added in the form of a powder with a high specific surface area. The suspension, ink or paste can optionally also contain a binder. Application is by means of lubrication, painting, spraying, dipping, printing, casting, sludge casting, rolling or rolling. After application, the layer can first be dried, with solvent and auxiliaries wholly or partially extracted. A heat treatment, calcination or sintering can optionally be used, after drying, or as a substitute for drying. Subsequently, the substrate with the layer, which can have characteristic thicknesses between approximately 2 μκι and approximately 1000 μιη, and which can be between approximately 5% and approximately 40% porous, is used in a super-capacitor or battery.

In this way, for example, a 1 cm 2 electrode according to the invention was made as follows. An amount of 1 g of Sm0.5Sro.5CoO3 -5 powder with a low effective surface area <5.0 m2 / g was placed in 1.5 ml of solution consisting of 4 Μ KOH electrolyte and 0.1% wt surfactant. A homogeneous suspension of this was obtained by stirring for 24 hours, part of which was then applied to a 50 µm thick nickel foil (the current collector). The whole was dried at 80 ° C for 4 hours so as to obtain a 1 cm 2 electrode - current collector laminate, the electrode layer being approximately 15 µ thick. This laminate was applied in a Teflon cell housing together with a separator and a counter-electrode of activated carbon. Both electrodes were supplied with approximately 50 μΐ electrolyte, after which the cell housing was sealed. Two stainless steel pins ensure the contact of the power collectors to the outside of the cell. The internal resistance ESR of the super capacitor thus obtained was measured by impedance spectroscopy. Charging and discharging cycles were then performed, cyclic voltamograms were recorded and charging and discharging cycles were again performed at current densities up to 500 mA per gram of Sm0.5Sr0.5CoC> 3-5 and between cell voltages 0 and 1.8 V. Figure 2 shows see the results of a cell with another platinum reference electrode in the separator. The potential curve of the electrode during charging and discharging with a current of 0.25 A / g results in an effective capacity for the connection according to the invention of> 130 F / g.

Example 2

Electrode manufactured by applying a suspension, ink or paste in a matrix. The matrix can be a metal foam, or a metal mat, metal mesh, polymer foam, polymer mesh, or other porous structure. The suspension, ink or paste comprises one or more perovskite and / or brown-millerite compounds according to the invention, and may further contain components as described in Example 1. The perovskite and / or brown-millerite compounds can be added in the form of a powder with a high surface area. The application of the suspension, ink or paste can take place according to the methods described in Example 1. After application, the steps as in example 1 can follow. Typical thicknesses of the formed electrode structure will now be between approximately 100 µm and approximately 1500 µm.

In this way, for example, a 1 cm 2 electrode according to the invention was made as follows. An amount of 1 g of Smo.5Sr0.5CoO3.5 powder with a low effective surface area <4.0 m2 / g was placed in 1.5 ml of solution consisting of 4 Μ KOH electrolyte and 0.1% wt surfactant. A homogeneous suspension of this was obtained by stirring for 24 hours, which was pressed into a 900 μm thick nickel metal foam. The filled foam was then dried at 80 ° C for 12 hours. In the same way as in Example 1, a super capacitor cell was made with this and experiments were done. Figure 3 shows the results of a cell in which another platinum reference electrode was provided in the separator. The potential curve of the electrode during charging and discharging with a current of 0.37 A / g results in an effective capacity for the connection according to the invention of> 120 F / g.

20

Example 3

Electrode manufactured by applying a layer of suspension, ink or paste to a substrate. The suspension, ink or paste comprises one or more perovskite and / or brown-millerite compounds according to the invention, a solvent and possibly auxiliaries such as dispersants, surfactants, wetting agents and the like. The perovskite and / or brown-millerite compounds can be added in the form of a powder with a high specific surface area. The suspension, ink or paste can optionally also contain a binder. The substrate is a smooth surface. The suspension is distributed over the surface by lubrication, painting, printing or pouring and is dried. The tape formed is then removed from the smooth surface as an independent electrode layer. For use in a capacitor, battery, fuel cell, electrolyser or sensor, heat treatments, calcination or sintering may also be applied to the tape.

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Example 4

Electrode manufactured by applying a suspension, ink or paste comprising one or more compounds according to the invention, on a substrate or in a matrix, said substrate or matrix forming part of or becoming part of another component or device , such as a photovoltaic solar cell or electro-chrome window.

Example 5 One or more compounds according to the invention are packed in powder form in an envelope of porous plastic material, inert to the electrolyte to be used and electrically insulating. To close the envelope, powder material, envelope and a wire or strip of metal are compressed in such a way that contact occurs between the powder particles and between the wire or the strip and the powder. The structure created in this way is used as an electrode in an electro-chemical cell.

Through . the typical use of perovskites and / or brown millerites in the electrodes according to the invention, there are, compared to known materials and electrodes, many possibilities to influence the properties and to adapt them to specific application requirements.

Although the invention has been described above with reference to preferred embodiments, it is to be understood that after reading the above description, those skilled in the art will immediately come up with variants that are obvious and are within the scope of the invention. scope of the appended claims.

Claims (16)

An electrode for an electrochemical cell, comprising a perovskite of the type AB03-5 wherein δ is between approximately -0.2 and - 0.05 or between + 0.05 and approximately + 0.7 and wherein A comprises a metal selected from the group Na, K, Rb, Ca, Ba, La, Pr, 5 Sr, Ce, Nb, Pb, Nd, Sm and Gd, and B comprises a metal selected from the group Cu, Mg, Ti, V, Cr , Mn, Fe, Co, Nb, Mo, W and or Zr and wherein no metal from the group Pt, Ru, Ir, Rh, Ni and Pd is present. An electrode for an electrochemical cell, comprising a brown millerite of the type ΑΒ02) 5_ξ wherein ξ is between approximately - 0.2 and - 0.05 or between + 0.05 and approximately + 0.3 and wherein A comprises a metal selected from the group Na, K, Rb, Ca, Ba, La, Pr, Sr, Ce, Nb, Pb, Nd, Sm and Gd, and B comprises a metal selected from the group Cu, Mg, Ti, V , Cr, Mn, Fe, Co, Nb, Mo, W and or Zr and in which no metal from the group Pt, Ru, Ir, Rh, Ni and Pd is present. The electrode of claim 1 or claim 2, wherein A and or B comprises a metal doped with a further metal. The electrode of any one of the preceding claims, wherein A comprises SmxSr (1 x) with x between about 0.4 and about 0.6. The electrode of any one of the preceding claims, wherein A comprises NdxSr (i_x) with x between about 0.4 and about 0.6. The electrode of any one of the preceding claims, wherein B comprises Co. 30 The electrode of any one of the preceding claims, wherein B comprises Fe. An electrode according to any one of the preceding claims, wherein B Co (i-X) Fex comprises with x between about 0.2 and about 0.6. -15- An electrode according to any one of the preceding claims, comprising at least 30 wt. % of one or more of those perovskites and or brown millerites. 10. Method for manufacturing an electrode according to any of the preceding claims, comprising providing a substrate and applying a layer thereon comprising one or more of those perovskites and or brown millerites. 10 A method of manufacturing an electrode according to any of the preceding claims, comprising providing a matrix and applying therein one or more of those perovskites and or brown millerites. 15 A method of manufacturing an electrode according to any of the preceding claims, comprising fabricating an independent tape or structure comprising one or more of those perovskites and or brown millerites. 20 A method for manufacturing an electrode layer according to any of the preceding claims, comprising integrating said electrode layer into a component or device and comprising said perovskite. 25 An electrochemical cell comprising an electrode according to any one of the preceding claims, as well as an electrolyte and a further electrode. 15. An electrochemical cell according to claim 14, wherein said further electrode comprises a carbon electrode, or a RuO2 electrode, or a RuO2.xH2O electrode. 16. Electrochemical cell comprising two electrodes, each according to one of claims 1 to 13 and possibly different from each other, and an electrolyte.