DE19728772C1 - Water electrolysis hydrogen cell shut down by termination of electrical supply - Google Patents

Abstract

In a process to operate an electrolysis assembly used for the production of hydrogen from water, an electric current passes between electrodes and through the water. If the generation of hydrogen is interrupted, the supply of electricity to electrodes is terminated, and the water oxygen content is reduced by blowing nitrogen into the water.

Description

The invention relates to a method for operating an electrical system lysis device and an electrolysis device for generating hydrogen with one through the electrolysis room performed water cycle.

Such electrolysis devices for generating water normally run in continuous operation. If you are in the inter middle operation, e.g. B. in coupling to be operated with a solar field, conventional Systems who provide the electrodes with a protective potential to counteract corrosion on them. This means, that a polarization voltage is present during downtimes the electrodes must be applied, which is usually 1.3 volts per cell.

This application of voltage to the electrodes during breastfeeding Service life of the electrolysis device brings problems in the technical implementation with it and worsens the overall System energy balance clearly.

From US-A-5,013,617 it is known during downtime electrodes diluted with nitrogen in the electrodes Cathode area and nitrogen in the anode area of a cell bring in. From the description it appears that this on ei ner cell with phosphoric acid as the electrolyte takes place in the Oxygen in the cathode area and oxygen in the anode area a hydrogen-rich gas stream separated hydrogen becomes. The supply of nitrogen to the water released  is done to prevent the formation of nickel tetracarbonyl on the To prevent catalyst. The acid diluted with nitrogen Substance serves to provide an acceptable level of protection at the cathode al of about 0.8 volts.

Such a cell is also disclosed in US-A-5,419,978 wrote, following the above Steps on the natural gas like desulfurized methane Anodes are applied to passivate them, i. H. a mi nimal electrode potential of the anode during downtimes to reach.

If gases are present within a cell, as in the case above The current state of the art is a change in the charge ten gas flow relatively easy to carry out, which is the case with electronics Lysis device according to the preamble, in which water is internal half of the cell, not easily accessible is.

Finally, from DE-U-91 15 337 an electrolysis Device known in which in hydrogen and oxygen water to be separated apart from potassium hydroxide, poorly conductive gas is added to reduce the stray currents. Because of that achievable reduction in stray currents becomes the efficiency of the Electrolysis device increased.

The object of the invention is therefore a method for operation an electrolysis device and an electrolysis device to generate hydrogen with one through the electroly to further develop the water cycle passed through it in such a way that the application of a protective potential to avoid Corrosion in the area of the electrodes during downtimes the electrolysis device is no longer required.

This object is achieved in that at egg interruption of hydrogen production, the electrodes span  be switched free and that the oxygen content of the im Electrolysis room water is reduced.

The electrolysis device according to the invention stands out from that means for interrupting the electroly water circulation leading through it.

The advantages of the invention are essentially that no protective po even when the electrolysis device is at a standstill tential more must be created to prevent corrosion of the elec avoid treading. In addition to the lower construct tive effort in particular to a significant improvement in Total energy balance.

Advantageous further developments of the method according to the invention and the device according to the invention result from the Un claims.

It is e.g. For example, in the context of the invention that to reduce the Oxygen content of a gas other than oxygen in the Electrolysis room water is injected. This will preferably nitrogen.

Another preferred method of reducing oxygen content is the electrolyte, preferably just before the interruption of hydrogen production can no longer be proven not to circulate anymore. This leads to an acid material depletion near the electrodes.

It is particularly preferred to combine both methods binieren.

As a means of interrupting the water cycle is preferred a second water cycle with oxygen gas-free water water provided. In other words, it is not a gaseous one Oxygen absorbed in the water.  

The invention can be further developed in that the elec trolyte circuit into an anolyte and a catholyte circuit is divided.

According to the invention it is provided that the negative electrode is a Metal hydrogen electrode is.

An exemplary embodiment of the invention is described below described in a drawing.

It shows Fig. 1 shows the course of the cell voltage (as OCV) as a function of time at different conditions.

The invention is based on the knowledge that the electrode po potential can be maintained if during standstill there is no oxygen in the electrolyte.

It was used in the scope of the invention in the context of laboratory tests found that the cell voltage after one hour of electroly operation and then switching off within minutes collapsed when the electrolyte is agitated by stirring was or oxygen was stirred into the electrolyte was brought.

On the other hand, it could be shown that a cell voltage of at least 1.3 volts after one hour of electrolysis and then keep it switched off for several hours if the electrolyte was not moved (and consequently oxygen depletion near the electrodes of the electrolyte) or if nitrogen was added to the Electrolyte was injected.

As can be seen from Fig. 1, the following experimental series was carried out. First curve 1 was recorded, in which the electrolyte was stirred. Shortly after switching off the electrolysis device at time 0, the electrode potential drops sharply and falls below the value of 1.3 volts after about 15 minutes.

By contrast, without stirring the electrolyte, only a very slight drop in the electrode potential can be observed, as curve 2 shows. After 180 minutes, i.e. three hours of standstill of the electrolysis cell, there is an electrode potential of approximately 1.3 volts.

The effect of a nitrogen supply expelling the oxygen bound in the water can be read from curve 3 . Here, although stirring was carried out as in curve 1 , the profile of the electrode potential is only slightly above curve 2 .

Curve 4 finally shows a cross-test, with oxygen being added with stirring and an even faster drop in the electrode potential to even lower values than in curve 1 can be observed.

From this series of measurements it can be concluded that the electrodes potential is best preserved if the electrolyte is possible is moved as little as possible and additionally the oxygen is out is driven out of the electrolyte, for example by a Nitrogen addition.

In practice, for example, these conditions may result from this can be achieved by vorese a second electrolyte circuit hen is in which there is an oxygen gas-free electrolyte. Of further it makes sense to check the electrolyte during standstill not to circulate times anymore, but the upheaval already to finish shortly before the shutdown process.

Claims (10)

1. A method of operating an electrolysis device for generating hydrogen with a water circuit carried out through the electrolysis room, characterized in that the electrodes are switched off when the hydrogen production is interrupted and that the oxygen content of the water in the electrolysis room is reduced . 2. The method according to claim 1, characterized, that the oxygen content by blowing another gas as oxygen into the water in the electrolysis room is induced. 3. The method according to claim 2, characterized, that nitrogen in the water in the electrolysis room is blown in. 4. The method according to any one of the preceding claims, characterized, that the oxygen content of what is in the electrolysis room Water is reduced by not moving the water. 5. The method according to claim 4, characterized, that the movement of the water shortly before the interruption of the Hydrogen production is stopped.   6. Electrolysis device for performing the method according to at least one of claims 1 to 5, wherein the electro lyse device through the electrolysis room led water cycle, characterized, that means to interrupt the out through the electrolysis room performing water cycle are available. 7. Electrolysis device according to claim 6, characterized, that a second water cycle with oxygen gas-free water is provided. 8. Electrolysis device according to claim 7, characterized, that the water of the second water cycle ent nitrogen gas holds. 9. Electrolysis device according to one of claims 6 to 8, characterized, that the electrolyte circuit into an anolyte and a Katho lytkreislauf is divided. 10. Electrolysis device according to one of claims 6 to 9, characterized, that the negative electrode is a metal hydrogen electrode is.