Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/28—Electrolytic cell components
  • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
  • G01N27/302—Electrodes, e.g. test electrodes; Half-cells pH sensitive, e.g. quinhydron, antimony or hydrogen electrodes

Definitions

• the present invention relates to a hydrogen electrode in rod form, particularly for use as a reference electrode in electrochemical measurements or as a pH measuring electrode, which contains the hydrogen supply in the form of a hydrogen development cell according to DE-PS 35 32 335 and integrates it during operation in provides a sufficient amount for the respective mode of operation.
• the hydrogen electrode is of central importance in electrochemical measurement technology. This is indicated by the so-called pH value, which is the negative value of the hydrogen ion exponent. It is obtained by logically decading the reciprocal of the concentration (or the activity) of the hydrogen ions in a solution. This is the most frequently used parameter for the characterization of aqueous solutions.
• the measurement is generally carried out by immersing a platinum-coated platinum sheet in the solution and washing it with hydrogen. It then represents the one voltage pole of a measuring cell, the other pole of which is a similar or different reference electrode in a standard solution with a known pH value, which is galvanically connected to the solution to be determined via an electrolyte key.
• the hydrogen electrode is an unloaded reference electrode in electrochemical measurement cells.
• the hydrogen-washed platinum electrode is immersed in a so-called Luggin capillary, the opening of which is located directly in front of the test electrode.
• the unloaded reference forms with it a galvanic element, the changes in voltage of which can be attributed solely to the changes in the potential of the test electrode during current passage or other changing test conditions.
• Hydrogen electrodes have the major disadvantage that they require a hydrogen source in the form of a compressed gas bottle with valves and hoses. This makes them unwieldy and expensive. A new type of supply technology would make the use considerably easier.
• the rod electrode according to the present invention It consists of three essential parts: a preferably replaceable hydrogen electrode, a hydrogen tube and an exchangeable hydrogen development cell as the source of hydrogen. The arrangement of the apparatus and the mode of operation of the invention are explained as follows in the two figures 1 and 2.
• the hydrogen electrode (1) consists of a placed platinum wire, which is located in the mouth of a tapered hydrogen tube (3).
• the other end of the hydrogen tube is screwed, inserted or glued gas-tight into the actual gas cell container (7).
• This preferably cylindrical gas cell container (7) holds the hydrogen development cell (9) according to DE-PS 35 32 335. It contains zinc powder or zinc gel and potassium hydroxide together with the so-called hydrogen development electrode.
• a catalyst layer bound with PTFE is rolled into a metal mesh and has a fine-pored PTFE film on the side facing away from the zinc. kidney.
• the zinc electrode and the hydrogen development electrode are located in a housing which is usually composed of two mutually insulated metal parts, one of which is connected to the zinc electrode and the other to the hydrogen development electrode in an electron-conducting manner.
• the housing part containing the hydrogen development electrode corresponds to the interior of the gas pipe (3) via at least one bore.
• the bore can be sealed by a sticker which, when the cell is in operation, exposes the hole due to the top pressure.
• the gas cell container (7) is closed by the screwed-on or plugged-on cover (10), which can take over several functions. After it has been closed, it expediently exerts pressure on the cell (9) by means of elastic spring elements (not shown), so that the cell (9) by means of the annular seal (8) via the hole in the cell housing part with the gas pipe ( 3) corresponds. These spring elements can be the electronic contacts (12) and (13) that contact the two housing parts.
• the cover (10) expediently carries a fixed or variable electrical resistance (11) in series with an on-off switch to which the contacts (12) and (13) are connected. This can be, for example, a potentiometer (11) with an "off position". Instead of the cover, this electrical switching and current control circuit can also be permanently connected to the gas cell container (7).
• the metal wire is guided from the hydrogen electrode, if possible within the hydrogen tube or embedded in its jacket, to the gas cell container, where it ends in a contact screw accessible from the outside or in a single-pole socket shown in Fig. 3.
• Platinum electrodes are particularly suitable for use in acidic media because they also resist all oxidizing acids.
• many other metals of the 8th group of the periodic table of the elements, their alloys or electron-conductive solid bodies metallized therewith are also suitable, provided they have the catalytic abilities for chemisorptively cleaving the hydrogen molecule. This applies, for example, to palladium and iridium, but also to activated carbon, which is metalized (catalyzed) with these metals.
• nickel is a very effective hydrogen catalyst, especially in the form of Raney nickel.
• This is a powdery material which is obtained from a nickel / aluminum alloy by extracting the aluminum with an alkali metal hydroxide solution.
• Hydrogen electrode bodies can be produced therefrom by powder metallurgical manufacturing processes. Such methods are described in the book by E. Justi and A. Winsel, Fuel Cell Fuel Cells, Steiner-Verlag, Wiesbaden 1962 and the patents cited therein.
• electrodes suitable for this purpose are also produced from the catalyst powders by intensive mixing with PTFE powder in very fast-running knife mills and rolling the powder mixture into a metal mesh made of nickel, silver, gold or even titanium.
• Such electrodes are also preferred to be provided on one side with a fine-pored, hydrophobic PTFE layer which faces the reacting gas and keeps the three-phase boundary electrode / electrolyte / gas stable.
• Such electrode structures are described in EP-PS 144 002 (1983). However, it can be advantageous to improve the storage capacity by using so-called hydride storage alloys in addition to Raney nickel, DE-OS 37 02 138 (1987).
• Fig. 2 shows how to integrate such a porous hydrogen electrode into the stick electrode according to the invention.
• (1) denotes the electrode body, which is screwed onto the end of the hydrogen tube (3) by means of the union holder (4). In between is an electrical contact disk (2) which is connected to the contact screw (5) by the contact wire.
• the hydrogen tube (3) above the electrode (1) can be provided with a very thin hole which is immersed in the electrolyte of the measuring cell. With its capillary pressure, this then acts like a pressure relief valve. In most cases, however, it is sufficient to adjust the hydrogen supply in such a way that a small bubble occasionally escapes from the gas pipe opening via the electrode (1) into the electrolyte.
• the gas cell (9) is inserted into the holder (7) without the paper sticker on the gas outlet opening.
• a large gas cell stream is then switched on, with which the atmospheric oxygen in the gas tube is first consumed by the gas cell (9).
• electrolyte is sucked into the hydrogen tube through the opening.
• the strong hydrogen evolution starts, which blows the hydrogen tube (3) freely.
• continuous measurements over 1 year can also be carried out.
• the proper function can be checked by measuring the working voltage at contacts (12) and (13) of less than 0.4 V.
• the contacts (12) and (13) are also kept accessible from the outside.
• Ralf Wendtland claims a "method for the continuous pH value measurement of liquids with a hydrogen diffusion electrode with a coarse-pore working layer and fine-pored applied on both sides Cover layers whose coarse-pore catalyst layer is filled with hydrogen gas, characterized in that the hydrogen diffusion electrode arranged between two electrolyte spaces is constantly flushed with the measuring liquid by means of a pressure difference between these spaces, so that the hydrogen pressure is constant in the process maintained and the pH of this liquid is determined in a known manner by measuring the potential of the electrode.
• a corresponding procedure for pore purging of hydrogen electrodes of the hydrophobic type can be found in DBP 1,496,247 from 1965 (inventor: Prof. Dr. August Winsel).
• the delivery of the measuring liquid can be made particularly simple with the help of the pressure energy of the hydrogen developed in the gas cell.
• a reference solution as a measurement solution, for example a buffer solution, Fig.4.
• the movement of the measuring liquid from an integrated storage vessel (14) through the pores of the hydrogen electrode can also take place with the help of the integrated hydrogen development cell, which not only supplies the hydrogen gas for the measuring process, but also the necessary delivery energy for the measuring solution. Since the measuring solution is saturated with the hydrogen gas due to the long contact time, the gas dissolved in the measuring solution is sufficient to provide the measuring current in the hydrogen electrode in the case of a high-resistance measuring arrangement.
• Fig.4 gives an example of this procedure according to the invention in accordance with CH-PS 394.640.
• the stopper of the storage vessel (14) is designated. If you want to bring the hydrogen gas from the gas cell (9) to the hydrogen electrode (1) in parallel and independently of the measurement solution, you can connect both with one or more PTFE capillaries or with a porous sintered strip of PTFE into which the measurement solution cannot penetrate from container (14) because of the non-wettability. In general, the measurement solution and hydrogen gas can be guided side by side by combining wettable (wick) and non-wettable porous structures.
• REPLACEMENT LEAF immersed and a second in a reference solution, which is galvanically connected to the measurement solution in a known manner via an electrolyte key.
• the voltage between the two is proportional to the difference between the pH values of the measuring solution and the reference solution.
• Dissolved oxygen in the measuring solution is reduced at the hydrogen electrode; this corresponds to an anodic load on the hydrogen electrode.

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• 1991
  • 1991-04-19 DE DE19914112784 patent/DE4112784C1/de not_active Expired - Lifetime
• 1992
  • 1992-03-18 EP EP19920906655 patent/EP0536346A1/de not_active Withdrawn
  • 1992-03-18 WO PCT/EP1992/000597 patent/WO1992018858A1/de not_active Application Discontinuation

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