US1442238A - Electrolytic apparatus - Google Patents

Description

Jan. 16, 1923.

A. K. SMITH.

ELECTROLYTIC APPARATUS.

FILED JULY 29.192.

'IIIII II'IIIIII/II,

Base Meta! Nickd-ke. M2101 5 Adhereni Coafinq Containing The Oxide 01' Hydrox'ndn of Nickd or Cobdt.

INVENTOR.

ATTORNEY.

Patented Jan. 16, 1923.

. UNITED STATES PATENT OFFICE.

ALBERT KELVIN SMITH, or CLEVELAND, OHIO.

ELECTROLYTIC APPARATUS.

Application filed July 29, 1922. Serial No..578,498.

To all whom it may concern:

Be it known that I, ALBERT KELvIN SMITH, a citizen of the United States, residing at Cleveland, in the county of Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in Electro- 1s gaseous, there is a phenomenon known as over-voltage, cons1st1ng of the excess in voltage required to produce the actual evolution of the gases over that which is theoretically necessitated by thermodynamic require ments. At any voltage above the theoretical decomposition value there will'be produced a collection of decomposition products at the surfaces of the electrodes, but owing to this over-voltage condition there will be no material evolution of the same in gaseous form until the impressed voltagerises to a definitely higher amount which depends upon the nature of the solution, the concentration of the solution, the nature of the electrodes, the surface condition of the electrodes, the temperature of the solution, and the current density. The consequences of this over-voltage are a waste of power, which 15 the most expensive single item in the operation of most electrolytic processes, and the production of local heat which it is sometimes inconvenient to dissipate.

Thus in the electrolytic production of oxygen and hydrogen, whatever be the nature of the electrolyte, the hydrogen is evolved at the cathode andtbe oxygen at the anode tial be employed. Ordinarily the best results are obtained with an electrolyte of potassium hydroxide for the reasons that its corrosive effect upon the electrodes is less than that of acids and the solution offers a minimum of electric resistance. Such an electrolyte enables the employment of nickel- (or'nickel-like) electrodes but these have the disadvantage of a high over-voltage, which, with customary current densities and electrolyte concentrations, ordinarily necessitate a potential of from 2% to 2% volts, whereas the theoretical decomposition potential is only about 1% volts. This is equivalent to a power loss of from 45 to 50 per cent, which is not only a serious item in it- Self but which tends to cause boiling and steaming and requires dissipation by cooling water. Likewise in the case of an alkalichlorine cell wherein hydrogen is evolved at the cathode, the same phenomenon ofovervoltage appears at this point; and similarly in every process wherein a part of the reaction consists of the decomposition of water 'or the evolution of one or both ofthe gases of which water iscomposed.

It is well known that the electrode material which offers the least over-voltage with respect to hydrogen is a plate of ,platinum covered with platinum-black, but this is prohibitively expensive'Ifor commercial use. It has also been discovered that a coating of platinum-black when applied to the surface of some less noble metal such as nickel will serve nearly as well, and that nickel-black can be used in place of platinum-black with a very great advantage over the naked nickel electrode (I refer to the application of Albert W. Smith filed November 8, 1920, Serial No. 422,638). I have discovered, however, that there are certain non-metallic, electrically-conducting, substances which can be employed as a coating upon the electrodes with a very great decrease in the over-voltage both of the oxygen and hydro gen; that these substances can be formed in situ on the surfaces of the electrodes with a minimum of labor and expense; that they are highly satisfactory as regards permanency either in the operating or in the waiting condition of the apparatus; and that their electrolytic performance equally rivals that of platinized platinum.

My improved electrodes are characterized by the possession of an adherent coating providing that a current of suflicient potenconsisting of or containing the oxide or hydroxide-of nickel or cobalt, which can either be pure or mixed with other substances such as finely divided metallic nickel or cobalt.

It is necessary that this coating be closely and firmly adherent and in order to secure this condition I preferably form the same in situ. One of the best methods I have so far discovered of producing this coating is as follows: The electrode is immersed in an ammoniacal solution of nickel-nitrate made for example by dissolving 7 5 parts of nickelnitrate crystals in 1500 parts of water and adding 400 parts concentrated ammoniumhydroxide solution (sp. g. 0.90). This electrode is now made a cathode for a short period, say one to ten minutes, at room temperature, with a current density of from .nickel seems to vary with the concentration, temperature, and current density. The current is now reversed for about l;th the effective time of the first deposit; that is to say if the voltage is maintained constant I find that a period of %th affords the best result, although at a lower potential the reversal can continue for a longer period. This causes the coating to become denser and more adherent and incidentally darker in color. The only reason for limiting the time of reversal is that if maintained toolong the first deposition will be finally redissolved.

The current is now reversed again so as to make the electrode under formation a cathode, whereupon a second oxide layer is deposited upon the first layer and this in turn is hardened and compacted by a succeeding reversal. This process is repeated until a deposit of the desired thickness is obtained. I find that about four repetitions of the process produces a very satisfactory coatmg.

The electrode is now ready for use and can be employed in the usual manner in all cases wherein the decomposition of water or the evolution of either of the waterforming gases is effected with an alkaline electrolyte; as in the production of oxygen and hydrogen for commercial purposes, the cathode compartment of alkali-chlorine cells, and similar situations. It can either be used immediately or stored and shipped without deterioration. Not only is this coating firmly adherent, but it is electrically conducting, sufficiently porous to afford a large working surface, and exhibits such a catalytic character as greatly to reduce the over-voltage either for hydrogen ,when used as a cathode or for oxygen when used as an anode. When employed in an alkaline electrolyte it appears to be proof even against the anode reaction, but it cannot be used in acid media.

It would appear that the beneficial operation of my improved electrode for the purpose stated is due primarily to the presence of various oxides of nickel (or nickellik metal), but the exact nature and composition of this coating is not important and perhaps not ascertainable. It contains less oxygen than Ni 0 and more oxygen than NiO, although the resenceof at least some proportion of Ni 3 can be demonstrated. It is also impossible to determine with accuracy whether these oxides are present in the hydrated or dehydrated form, and this indeed may vary to some extent depending upon whet-her the electrode is dried between formation and use. This point appears to have no practical importance to the operation of the apparatus, although it is believed that ordinarily at least a part of the active substance is in hydrated form. Likewise the presence or absence of metallic nickel inthe coating appears to be immaterial inasmuch as its proportion is generally very small and its inclusion in the larger volume of oxide blankets any effect it might otherwise exhibit.

In the drawing accompanying and forming a part of this application I have shown in unconventionalized form a pair of electrodes embodying my improvements, those shown in Fig. 1 being of base metal plated with nickel-like metal, and those shown in Fig. 2 beingof homogenized internal structure. In either case they are provided with a smooth superficial coating containing an admixture of finely divided metallic nickel as shown in the above description. It will be understood that these electrodes may be made of any desired shape and size required b v the design of the apparatus, and employed in any desired number; also that one electrode containing my improvements can be used in company with an electrode of any other material or formation dependent upon the work in view.

By the employment of my improved electrodes for anode purposes in a caustic potash solution as employed in commercial oxygen production I have been able to reduce the over-voltage by about 0.2 volt from that exhibited by the usual nickel electrode, and by its employment for cathode purposes in a similar solution as employed for oxygen production I have been able to produce approximately the same economy. This amounts to a total power saving of approximately 20 per-cent when employed for both terminals. Cobalt exhibits much the same effe ct as nickel although the saving is slighter. Owing to the well known relationship between the nickel and cobalt I have included the two substances in my claims under the expression nickel-like. Also by the word oxide or oxides I mean to designate the hydrated oxide com ounds equally with the anhydrous forms 0? the same. It will be noted that I have not specified the metal of which the electrodes are made. Preferably I make the same superficially of nickel which may take the form either of a cast or rolled nickel plate, although the same may be made of some baser metal like iron or copper plated therewith. However Ido not restrict myself to this inasmuch as my improved coating can be plated directly upon some baser metal, nor do I limit myself in any other way except as specifically recited in the claims hereto annexed.

Having thus described my invention what I claim is:

1. Apparatus for the purpose described comprising,.in combination, a pair of electrodes consisting at least superficially of nickel-like metals having their faces covered with a porous, adherent, conductive coating consisting essentially of a mixture of nickel- ]ike oxides.

2. Apparatus for the purpose described comprising an electrode of nickel-like metal covered with a porous, adherent, conductive coating containing a mixture of nickel-like oxides.

3. An electrode for reducing the over-voltage of the decomposition products of water characterized by having a superficial covering containing the oxides of a nickel-like metal.

4. An electrode for the purpose stated having an adherent coating of oxides of nickel.

5. The herein described process of forming an electrode which contains the steps of subjecting a metallic plate to electrolysis in an aminoniacal nickel nitrate solution and slowly alternating the direction of current flow, while maintaining cathode conditions at said electrode during a larger proportion of the time than anode conditions.

6. An electrode for the low-voltage evolution of water-forming gases from alkaline electrolytes consisting of an electrically conducting support coated with a porous, adherent, catalytic layer containingthe oxides of nickel-like metals.

In testimony whereof, I hereunto aflix my signature.

ALBERT KELVIN SMITH.

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