RU2036539C1 - Submersible cell with water-salt electrolyte - Google Patents

Abstract

FIELD: conversion of chemical energy into electric energy. SUBSTANCE: cell has metal anode and cathode. Cathode is stainless steel carrier covered with thin layer of cobalt or activated charcoal-based catalyst. The latter can be made of cobalt or cobalt-nickel spinel at cobalt-to-nickel molar ratio exceeding 1, or of mixture of activated charcoal and polyvinyl chloride at charcoal- to-binder ratio within 1:4 and 1:2. EFFECT: enhanced reliability and operating characteristics of cell. 3 cl, 9 dwg

Description

 The invention relates to galvanic cells, in particular to submersible cells with a water-salt electrolyte, for example, sea water.

 A device is known as described in US Pat. No. 3,401,063. Here, a seawater-based battery is considered consisting of an annular basket containing metal wool serving as an anode of an element and a cylindrical metal anode located in a central cavity, its main feature being the ability to generate electricity for several years. Another important feature of this electrochemical cell is the ability to economically generate electricity in terms of costs per kilowatt-hour and watt-hour per kilogram. Using magnesium as the material for the anode and steel fiber as the material for the cathode, the device provides for a long time the generation of output voltages in the range 0.35-0.7 V.

 The main disadvantage regarding the output voltage produced by the known element is the corrosion of the cathode material. In addition to limiting the generation of output voltage, corrosion on steel fiber can cause the destruction of the cathode material during the life of the element or when kept in a humid atmosphere.

 A careful selection of the quality of the cathode material can eliminate the main disadvantages inherent in a battery using seawater. These disadvantages can be eliminated by the use of stainless steel cathodes specified in USSR patent N 559307. This improved device is not subjected to corrosion during storage or during operation. The mentioned USSR patent indicates that the output voltage of the element is approximately 0.9 V.

 However, with careful selection of the quality of the cathode material made of stainless steel and the creation of an optimal element design, this improved device should be able to produce output voltages up to 1.8 V. This would probably make it possible to increase the energy density of the element by two to three times.

 One example of a stainless steel quality that meets the requirements, that is, a quality in which stainless steel exhibits electrochemical passivity with respect to anodic corrosion or allows a very low level of corrosion when operating a battery with seawater, is the quality commonly designated by AlSI 316 by the American Iron Institute and steel. However, any other quality of stainless steel, given that stainless steel is defined as a glandular material containing more than 10% by weight of chromium and at least 50% by weight of iron, can in principle provide advantages over the device of US Pat. No. 3,401,063 .

 A device is also known according to US patent N 4522897, in which the metal anode is contained, the metal cathode is made of sintered stainless steel fibers coated with a catalyst, selected from the group of Pt, Pd, Pu, Ni and their alloys. The cathode is located coaxially around the rod anode.

 However, the known indicated improved devices, when immersed in natural sea water, show the worst quality of work in the initial period after exposure to them with sea water. After the initial period, the quality of the device’s work improves due to the formation of a biological film on the surface of the stainless steel cathode, a film that is active as a catalyst that serves to reduce oxygen. The duration of the initial period is usually from one week to one month, depending on several factors, the most important of which are the cathodic current density and the flow rate of water. In this initial period, the chemical current source will behave worse in terms of loadability and voltage generation compared to the same source after the formation of a biologically active film.

The cell voltage in this initial period largely depends on the current density at the cathode. At very small cathodic loads, for example 3 mA / m ^{2 of} cathode area, the cell voltage is approximately 1.2 V and after the initial period rises to approximately 1.7 V. At moderate loads of 50 mA / m ² the cell voltage is of the order of 0.7 V in the initial period, but very much depends on the speed of the water flow, and the voltage of the element after a month of exposure is 1.4-1.65 V, depending on the design of the element and the speed of the water flow. At higher loads, the initial voltage of the element will be even less than 0.7 V. At the same time, the duration of the initial period increases with increasing load, and if the load is too large, the element will not reach this higher level of work quality.

 Obtaining lower performance characteristics during the initial period of operation of the aforementioned improved known devices, when they are used in natural seawater, may result in the device being unable to provide sufficient energy to the equipment that is to be supplied with power during this period. Another consequence may be that in cases where the duration of use of the device is less than the specified initial period, the device should be increased in weight and volume in order to compensate for the worst performance to such an extent that its use is practically unprofitable due to limitations systems related to weight, volume or costs.

 When using ordinary sea water, i.e. water containing sodium chloride or potassium chloride with an undetermined number of other components, or artificial sea water, for example, according to DIN 50010, the formation of a catalyst active biofilm does not occur. This means that when using this type of electrolyte, a known chemical current source will show poor performance even after it has been exposed to the electrolyte for a time longer than the aforementioned initial period.

 The aim of the invention is to create a device with the ability to supply the rated power from the moment of exposure to almost any form of salt water, a significant improvement in the performance of galvanic cells with stainless steel cathodes during their operation in the initial period, providing the possibility of using a chemical current source in ordinary salt water or in artificial sea water, improving the operating characteristics of an element, increasing the reliability of a chemical current source both in the initial period and follows it and ensuring the possibility of using one and the same element several times and each time for a short or long period.

 This is achieved by the fact that the submersible element with a water-salt electrolyte contains a metal anode and a metal cathode, which is a stainless steel substrate coated with a thin layer of a catalyst that restores oxygen dissolved in water, using a catalyst based on cobalt or activated carbon. The catalyst is applied to the surface of the cathode base of stainless steel, while the catalyst has the features listed below.

 First, the catalysts that form the basis of the invention have the ability to stimulate the reduction of oxygen dissolved in salt water. The specified stimulation of oxygen reduction leads to an increase in the voltage of the galvanic cell at a given current load and also contributes to an increase in load when there is no catalytic active biofilm.

 Secondly, the catalysts have chemical and electrochemical stability in the environment and in the conditions that they experience on themselves during the operation of the galvanic cell.

 Thirdly, the catalysts are mechanically stable and adhere firmly to the substrate without being subjected to repulsion, bubble blistering, or any other type of separation between the catalyst layer and the substrate during normal operation of the element or during manipulation of it.

 In addition, the catalysts do not contain any precious metals and do not require expensive manufacturing processes, which would contribute to a significant increase in the cost of the cathode.

 The catalysts do not contain toxic materials that would otherwise reduce the ability of the cathode to form the aforementioned catalytic active biofilm on its surface. This means that the catalysts that form the basis of the invention do not cause performance degradation during operation after an initial period.

 The introduction of these catalysts, in principle, makes the operation of the galvanic cell independent of the formation of a catalytic active biofilm, although if the biofilm is removed from the surface or if the cell operates in artificial sea water, a slight deterioration in the cell’s performance is observed.

 The preferred substrate on which the catalyst is applied should have a very high degree of corrosion resistance, since very high electrochemical potentials are applied to the cathode. Corrosion of the substrate would lead to a decrease in the cell voltage due to an increase in the local cathodic current density, since the total cathodic current density is the sum of the current densities taking into account the external load and the corrosion current density. One type of stainless steel alloy with sufficient corrosion resistance to be suitable as a support for the present catalysts contains approximately 17% Cr, 12% Ni and 2.5 Mo and is usually referred to as AlSI 316. However, for this purpose also other molybdenum-containing stainless steel alloys are also suitable. One of the preferred catalysts contains cobalt in the form of cobalt spinel or cobalt oxide as an active component of the catalyst.

 In addition to nickel, cobalt can also be replaced by other metal elements to obtain a spinel structure with greater catalytic activity to reduce oxygen dissolved in salt water than that obtained with a bare surface of a stainless steel base. Examples of such elements, which in combination with cobalt can create spinel structures, are iron and aluminum. In addition to the aforementioned, other elements can also be introduced to some extent in the cobalt spinel structure, while the preferred properties of the invention will be preserved.

 Another preferred catalyst contains materials commonly referred to as activated carbon, used as an active catalytic agent. This catalyst is created by mixing activated carbon with a binder containing a volatile solvent or a two-component binder, for example, one that is commonly called epoxy. After mixing, the mixture is applied to a substrate and kept at room temperature or at slightly elevated temperatures until the mixture hardens.

 One preferred type of binder contains polyvinyl chloride (PVC) diluted in organic solvents. One binder of this type is manufactured under the name "Tangit" by the company "Henkel A. G.".

 The weight ratio between the amounts of dry activated carbon and PVC in the binder should be such that the catalyst has a good ability to reduce the amount of oxygen in salt water and at the same time good mechanical adhesion to the substrate, as well as sufficient mechanical resistance for long-term use in a galvanic cell. The range of ratios that ensure the satisfaction of all these requirements is 1: 4-1: 2.

 Both of these catalysts satisfy the specified requirements and ensure the achievement of the above objectives.

 In FIG. Figure 1 shows an example of an immersion cell containing a stainless steel cathode, not involving the use of a prefabricated catalyst together with a magnesium anode and using natural sea water as an electrolyte (Fig. 1 shows the relationship between cell voltage and time at constant current output); in FIG. 2 is a graph of the results of the first two experiments, similar to those shown in FIG. 1, in which in this case cathodes are used with a cobalt-containing catalyst deposited on the surface of the cathode substrate of stainless steel; in FIG. 3 is a graph of experimental results similar to those shown in FIG. 1 and 2, but in this case they use a catalyst containing activated carbon deposited on a stainless steel substrate; in FIG. 4-9, three possible designs of a submersible element using cathode catalysts constituting the basis of the present invention are given.

 To further clarify the invention, the following examples are presented below.

 PRI me R 1. Used an immersion element consisting of a cylindrical magnesium anode and a stainless steel cathode, consisting of eight parallel square plates, each of which has a circular opening in the center for the input of the Central anode. The intermediate distance between the plates was 15 mm, and each plate was 0.5 mm x 0.5 mm in size and 1 mm thick. The diameter of the central hole is 0.2 m. The cathode plates were mechanically fixed using four parallel stainless steel rods that were welded to each corner of the plates and which passed through all the plates. At the end of these rods, two end plates of insulating material were mounted to secure the anode. The diameter of the anode was 0.14 m and the length was approximately 0.2 m. Corresponding electrical connections were made to the metal anode and cathode.

 In addition to magnesium, the anode material included approximately 6% aluminum and 3% zinc as the main constituents.

 The cathode was made of an alloy of stainless steel type 254 MO and manufactured by the Swedish company "Avesta A.B" This alloy contains approximately 20% Cr, 18% Ni and 6% Mo as the main components, except for Fe. In this experiment, stainless steel cathodes did not cast any pretreatment.

The described primary current source was immersed in natural sea water so that the parallel cathode plates were oriented vertically and the axis of the cylindrical anode extended horizontally in the water. The sea water had a temperature of 8-12 ^{° C,} and its flow rate was approximately 1 cm / s. The cell was under a constant current load of 50 mA / m ² of cathode area and the corresponding voltage was periodically recorded at the cell terminals.

FIG. 1 shows the voltage of the immersion element in the first 90 days of operation. During the first 20 days, the cell voltage was low, i.e. approximately 0.7 V at a specific load of 50 mA / m ² . After 20 days, the cell voltage increased to about 1.4 V, and after the next 20 days to about 1.7 V. The increase in cell voltage, which was observed 20 days later, was due to the presence of an active biological film formed on the cathode surface, about than stated in the description above. The reason for this two-step increase in cell voltage is unknown.

 During the first 20 days, this element gave out power that is less than half the power received at the output after 40 days of operation at a given cathode current density. In addition, loading during this period is significantly less than after the initial period.

 EXAMPLE 2. A chemical current source was prepared similar to that shown in Example 1, but characterized in that the cathode plates were pretreated in order to increase catalytic activity to reduce oxygen dissolved in sea water during the initial period of operation of the cell.

The pretreatment consisted of applying a thin layer of cobalt nitrate diluted in isopropyl alcohol, after thoroughly cleaning the surface of the cathode. The cobalt concentration in this mixture was 0.2 mol per 1 liter. After drying the cathode plates were placed in an oven at about 400 ^{° C} and held therein for 1 hour. The ambient atmosphere in the furnace during the heat treatment time was air.

The element was placed under experimental conditions similar to those of Example 1. FIG. 2 shows the cell voltage in the first 40 days of operation at a specific constant cathodic current load of 50 mA / m ² . As seen in FIG. 2, the cell voltage was initially approximately 1.5 V, compare with a voltage of 0.7 V for the known device shown in Example 1. After a week of operation, the cell voltage rose from 1.5 V to 1.77 V. The cell voltage remained at that level for 7 months. after which the experiment was completed.

 An increase in the cell voltage after the first week of operation shows that the catalyst, which forms the basis of the invention, does not inhibit the formation of an active biofilm on the cathode surface. Indeed, the duration of the initial period was apparently reduced by introducing the attached catalyst. Indeed, the duration of the initial period was apparently reduced by introducing the attached catalyst.

 In addition, loading was increased significantly with the introduction of a cobalt spinel type catalyst. If the above film were destroyed, then there would be a slight deterioration in performance, corresponding to a decrease in the cell voltage from approximately 1.7 to 1.5 V.

 The power at the output of the galvanic cell in the initial period increased approximately two times with the introduction of a cobalt spinel type catalyst.

PRI me R 3. Another experiment was carried out using a galvanic cell of identical design and with pre-treatment of the cathode specified in example 2, except that they used a specific cathode current load of 100 mA / m ² , all other conditions experiment were identical to the conditions specified in example 2. As can be seen from FIG. 2, the cell voltage is in the same state as in the previous experiment. The voltage of the element during the entire experiment was somewhat lower due to the higher current load. However, even with such a high cathodic load, the cell voltage in the initial period was approximately 1.45 V, which was two to three times higher than the voltage that would be expected from a comparable known device. This illustrates the improvement in performance both from the point of view of obtaining the cell voltage, ensuring loadability, output power, and from the point of view of ensuring reliability in the initial period, which is a direct result of the application of the invention.

PRI me R 4. In water containing 0.5 mol of sodium chloride, three stainless steel plates of type 254 S MO were tested. A first plate treated with catalyst according to the pretreatment specified in Examples 2 and 3. The second plate was catalyzed by applying a thin layer of a mixture of cobalt nitrate and nickel nitrate diluted in isopropyl alcohol, followed by carrying out a heat treatment ^at 400 ° C for 1 hour The molar ratio of cobalt nitrate to nickel nitrate was 2: 1. The third plate was a non-catalyzed plate.

The plates were tested in an electromechanical cell using a magnesium counter electrode. The electrolyte was circulated in the cell using a peristaltic pump. The electrolyte temperature was approximately 20 ^° C. The open area of the cathode plates was 3.5 cm ² . The plates were tested potentiostatically. The corresponding element currents were recorded.

1, элемент с катодным катализатором типа кобальто-никелевой шпинели как элемент

2 и элемент без катализатора как элемент

3.The table shows the cell voltage and the corresponding currents of three different electromechanical elements. The measurement was carried out 20 hours after exposure to electrolyte. An element with a cathode catalyst of the cobalt spinel type is designated as an element

1, an element with a cathode catalyst of the cobalt-nickel spinel type as an element

2 and an element without a catalyst as an element

3.

 The performance of the three chemical current sources using cobalt spinel, cobalt-nickel spinel and the third source respectively do not use a catalyst at all.

 As can be seen from the table, the cell current, 20 hours after the start of exposure to the cell with salt water, has higher values for both cells with catalyzed cathodes compared to a cell without a catalyst.

 PRI me R 5. In this example, the chemical current element working with sea water is identical in design to the elements in examples 2 and 3, but in this case a cathode catalyst containing active carbon as an active component was used.

 The catalyst in this experiment was obtained by applying a thin layer of a mixture of activated carbon and a binder of polyvinyl chloride on a carefully cleaned stainless steel substrate. The mixture consisted of one part (by weight) of Norit SX Ultra activated carbon manufactured by Norit activated Carbons, Holland and two parts of a Tangit type polyvinyl chloride binder. Methylene dichloride was additionally added to this mixture to give it a viscosity that allowed the mixture to be applied to a stainless steel substrate. In this experiment, up to ten parts of methylene dichloride (by weight) were introduced for each part of a mixture of coal and polyvinyl chloride.

After applying the catalytic material to the surface of the substrate, the material was cured by evaporation of volatile ingredients at 60 ^about C.

The element was immersed in natural seawater and subjected to the same experimental conditions as in Example 3, i.e. applied specific cathodic current load equal to 100 mA / m ² .

 FIG. 3 shows the cell voltage as a function of the cell operating time, similar to that shown in FIG. 2. The element behaves in the same way as the elements in the two previous examples, where the case of preliminary deposition of the catalyst layer on the cathode surface is indicated. However, there is a slight decrease in performance compared to the case when using a catalyst such as cobalt spinel, although this may be due to less optimized pre-treatment before using activated carbon catalyst.

 In FIG. 4 and 5 schematically show one embodiment of the invention (Fig. 4 shows a section A-A in Fig. 5, and Fig. 5 shows a section B-B in Fig. 4). Between two stainless steel gratings 1 and 2, a cathode 3 is placed, consisting of a stainless steel fiber with a catalyst, as described above, and inside this cathode 3, anode 6 located coaxially is supported by insulating means 4. The power output from the element is carried out via cable 7, which by means of connecting clamps 8 and 9 is connected to the cathode 3 and the anode 6. Positions 10 and 11 indicate the suspension means by which the element can be vertically mounted in sea water.

 The use of the invention is not limited to its use for an element of one particular design, for example, involving the use of catalyzed stainless steel fiber as a cathode material. There is a wide range of possible ways of assembling an element working with sea water, involving the use of a catalyzed cathode material, which forms the basis of the invention and allows to obtain advantages in comparison with known devices.

 To illustrate this, in FIG. 6 and 7 schematically show one alternative element design. In FIG. 6 shows a section BB in FIG. 7, and in FIG. 7 shows a partial section along the line G-G in FIG. 6. In this case, the element consists of a central cylindrical metal anode 12, which may be a magnesium alloy, an aluminum alloy, a zinc alloy or a lithium alloy, i.e. any metal of the galvanic series that is electronegative with respect to stainless steel.

 The cathode 13 in FIG. 6 and 7 consists of a plurality of parallel-mounted stainless steel plates 14 having a catalytic active layer with the characteristics indicated above. In the center of each plate, which can be rectangular or round, there is an opening 15 for receiving a metal anode 12. Each plate is attached to two or more rods 16, preferably made of the same material as the cathode plates 14 so as to ensure reliable electrical contact between the plates 14 and the rods 16. The cathode is electrically connected by contact means 17. At the end ends of the anode-cathode assembly, there are two end plates 18 and 19 made from a material that is electrical insulating, which ensures mechanical safety of the use of the anode-cathode structure. At one end of the anode there are devices that make it possible to remove current from the anode 12. Fasteners are indicated by 20 and 21.

 In FIG. 8 and 9 show an alternative method of creating a plate-cathode plate working with seawater 22. FIG. 8 shows a section DD in FIG. 9, and in FIG. 9 shows a section EE in FIG. 8. A plurality of catalyzed stainless steel plates or sheets 25 are mounted radially with respect to the rod anode 24 in the cell. Between the end plates 26 and 27, cathode plates 25 are installed and all these components are assembled into a single structure using rods 28 and 23. Supporting devices and electrical connections are not shown.

 The above constructions of the working submersible element should be considered only as examples illustrating three possible options for assembling parts of the element and are presented only in order to clarify the invention, and not in order to limit its scope. Although the use of stainless steel fiber and plates as a catalytic substrate for the cathode and magnesium alloys as the material for the anode is considered to be preferable, nevertheless, in order to improve the performance of a chemical current source compared to known devices, it is possible to use metals in other combinations. Therefore, it is understood that some modifications, changes and replacements may be allowed in the design of the device if they do not fall outside the scope of the invention. Cathode plates, for example, can be perforated metal plates.

Claims (3)

 1. SUBMERSION ELEMENT WITH A WATER-SALT ELECTROLYTE, containing a metal anode and a metal cathode, which is a stainless steel substrate coated with a thin layer of a catalyst that reduces oxygen dissolved in water, characterized in that a catalyst based on cobalt or activated carbon is used.  2. The element according to claim 1, characterized in that the catalyst used is cobalt spinel, or cobalt-nickel spinel with a molar ratio of cobalt to nickel of more than 1.  3. The element according to claim 1, characterized in that the catalyst is a mixture of activated carbon and polyvinyl chloride as a binder with a ratio between coal and binder in the range from 1 4 to 1 2.

Images