What Is an Electrode Line?

A component of an electronic or electrical device or device that is used as the two terminals of a current in a conductive medium (solid, gas, vacuum, or electrolyte solution). The pole of the input current is called anode or positive electrode, and the pole of current is called cathode or negative electrode. There are various types of electrodes, such as cathode, anode, welding electrode, electric furnace electrode, etc. ^[1]

In a battery, an electrode generally refers to a position where a redox reaction occurs with an electrolyte solution. There are positive and negative electrodes. Generally, the positive electrode is the cathode, which gains electrons and undergoes a reduction reaction. The negative electrode is the anode, which loses electrons and undergoes an oxidation reaction. The electrode can be a metal or a non-metal, as long as it can exchange electrons with the electrolyte solution, it becomes an electrode.

Chinese name: electrode
Foreign name: electrode
Presenter: Faraday

Presentation time: 1834
Applied discipline: physical
Scope of application: Electricity

Introduction to electrode physics

Electrode definition

The concept of electrode was put forward by M. Faraday in 1834 after conducting system electrolysis experiments. The original intention was only to refer to the metal rods that make up the battery and inserted in the electro-hydraulic. A component of a battery, which consists of a series of phases in contact with each other. One end is an electronic conductora metal (including graphite) or a semiconductor, and the other end must be an ionic conductoran electrolyte (herein it refers to an electrolyte solution, referred to as "electrolyte "Or" electro-hydraulic "). The electrode with the simplest structure should include two phases and a phase interface, namely [metal | electro-hydraulic]. The electrodes defined above are also called "half cells". ^[2]

Electrode designation

The nomenclature is very complicated, some are named according to the metal part of the electrode, such as copper electrode, platinum electrode, etc .; some are named based on the characteristic substances in the active redox pair of the electrode, such as calomel electrode, hydrogen electrode; Nomenclature, such as mercury drop electrodes, turntable electrodes; some are named according to the function of the electrode. These names, such as reference electrode, sodium ion selective electrode (see ion selective electrode), are all conventional. ^[2]

Electrode symbol

Usually the battery is marked with a "+" symbol, which is the positive electrode, and the other end is marked with a "-" symbol, which is the negative electrode. At the same time, only the positive electrode has a "+" on the battery, and the negative electrode does not. Color can also indicate positive and negative: red for positive, black for negative. ^[2]

Electrode expression

The method of expressing electrodes in books and publications is very inconsistent. The method adopted here is: write down the phases in series, and each phase interface is indicated by an isolation line. For example, the copper electrode is written as Cu | CuSO4 (1M, aqueous solution) or Cu | Cu; the calomel electrode is written as Hg |

electrode Hg2Cl2 | Cl; Passive iron electrode in aqueous solution can be written as Fe | Fe3O4 | Fe2O3 | aqueous solution.

The electrode block diagram expresses each phase of the electrode with separated squares, which is convenient to indicate the reaction at the interface of each phase and helps to understand the actual process that occurs on the electrode (Figure 1). ^[2]

Electrode physical type

Electrode reversible electrode

The potential (potential) of any metal in contact with the electrolyte is the most important characteristic of the electrode.

electrode If there is a fast electronic exchange of a single redox pair at the electrode interface, that is, there is a single electrode reaction with a large exchange current (see transition overpotential), this electrode can quickly establish electrochemical equilibrium, which is called reversible electrode. The potential energy of the reversible electrode remains stable for a long period of time, has a large anti-interference ability, and can be accurately measured. It is an essential component of a reversible battery, and it is the core component of a potentiometric measurement device, which has important practical significance. There are the following types of reversible electrodes:

Metal electrodes, such as copper electrodes (Figure 2), are characterized by redox couples that can migrate across the phase interface.

Redox electrodes, such as Pt | Fe, Fe electrode (Figure 3), Pt | Mn, MnO , H electrode, etc. Its redox couple cannot migrate across the electrode phase interface. The platinum Pt of the electrode only means that the electrode metal is inert. It only provides a place for electron exchange. Any inert metal can be used in practical applications.

electrode The gas electrode is a redox electrode when one of the components of the redox pair is a gas (Figure 4), such as a hydrogen electrode (Pt | H2 | H), a chlorine electrode (Pt | Cl2 | Cl), etc. In order to accelerate the balance, platinum black needs to be plated with platinum black to increase the surface area and perform electrocatalysis.

electrode

Insoluble salt electrode, a component of the redox couple is insoluble salt or other solid phase. Therefore, it contains three phases and two interfaces (Figure 1). There is a single rapid transition process at each phase interface, such as a calomel electrode (Hg | Hg2Cl2 | Cl) and a mercury oxide electrode (Hg | HgO | OH). In the calomel electrode, the dissolution balance of calomel and the electrolyte is completely controlled by the higher concentration of Cl in the electro-hydraulic, and the exchange rate of Cl at the Hg2Cl2 | electro-hydraulic interface is also very fast, so its electrode potential is very stable. It is the most commonly used reference electrode, and some books refer to this type of electrode as the second type.

electrode Membrane electrode A device that measures the activity of specific ions in an electro-hydraulic device using the potential of a membrane for a single type of ion or the ion exchange equilibrium established between the membrane surface and the electrolyte (Figure 5), such as glass electrodes, ion-selective electrodes .

Chemically modified electrodes use adsorption, coating, polymerization, chemical reactions and other methods to attach active groups and catalytic substances to the surface of electrode metals (including graphite and semiconductors), so that they have strong characteristic functions. This is a new development of electrode preparation methods since the 1970s.

Single electrode and multiple electrodes If there is only one type of electrode reaction at the metal-electro-hydraulic interface of the electrode, this is a single electrode; if there is more than one electrode reaction, it is a multiple electrode. For example, there may be two kinds of electrode reactions on a zinc electrode (Zn | ZnSO4 aqueous solution):

Zn Zn + 2e

2H + 2e H2

electrode However, due to the high overpotential of hydrogen on zinc metal, the reaction rate is too small and the reaction rate is dominant. The above zinc electrode is considered as a single electrode and is a typical reversible electrode. When less pure zinc is immersed in sulfuric acid, the reaction rates of rhenium and osmium are fast, so the [Zn | H2SO4] electrode is a double electrode, and its static potential can be based on the polarization curve and polarization of the reaction rhenium and osmium. To judge by law. Metal corrosion systems are often double electrodes. Multiple electrodes cannot be reversible

In practical applications, the electrode under study is called the working electrode W, and it is also called the indicator electrode in electrochemical analysis. Its potential can be measured by a two-electrode measuring cell composed of a reference electrode R. When the working electrode needs to be polarized, another auxiliary electrode (or corresponding electrode, represented by C) is used to form a three-electrode measurement battery system (Figure 6) to provide an adjustable current. At this time, in order to reduce the error of the ohmic potential drop ( IR ) in the electro-hydraulic measurement of the working electrode potential, a capillary tube should be used at the connection between the reference electrode and the electrolyte, which is as close as possible to the working electrode, which is called a Lugin capillary tube.

Electrode spark machine electrode

Spark machine electrodes, also known as copper males, are also indispensable in spark machining.

electrode During spark machining, the electrodes and the workpiece are connected to the two poles of a pulse power source, respectively. The spark voltage is generated by the pulse voltage applied to the electrodes and the workpiece. The instantaneous temperature of the discharge can be as high as more than 10,000 degrees Celsius, and the high temperature makes the surface of the workpiece partially vaporize or melt.

Immediately after the next pulse voltage, a spark discharge is generated between the electrode and the workpiece, and the above process is repeated.

Through countless repeated pulse discharges, a shape corresponding to the shape of the electrode is finally processed. Therefore, as long as the shape of the electrode is changed, various complicated profiles can be processed.

In spark machining, the role of the electrode is to convey processing pulses and to remove the workpiece with minimal loss of the electrode itself. Common electrode materials include copper, graphite, copper tungsten alloy, silver tungsten alloy, steel, brass, cast iron, and so on.

Electrode cerium tungsten electrode

It is a tungsten electrode product made by adding rare earth cerium oxide to the tungsten base through powder metallurgy and calendar grinding and polishing. It is the earliest non-radioactive tungsten electrode product produced in China. Arc performance, smaller arc current. Therefore, it is often used for welding of pipes, stainless steel products and small precision parts. Under low-current DC conditions or electrode diameters below 2.0mm, cerium-tungsten electrodes are the preferred alternative to thorium-tungsten electrodes.

Electrode lanthanum tungsten electrode

It is an improved variety launched by European countries in the 1980s in the hope of replacing thorium tungsten products. Once introduced, it has attracted much attention and is very popular in the international welding industry for its excellent welding performance, especially sought after by the European Welding Academy for this reason. The export volume of lanthanum tungsten electrode is second only to thorium tungsten, and its recognition in the domestic market is not high. Its characteristics are that the conductive performance is closest to 2% thorium tungsten electrode, the durable current is high, and the loss rate is the smallest.

Electrode Tungsten Electrode

It is the earliest used rare earth tungsten electrode, and it is also the tungsten electrode with the best welding performance so far. Therefore, the tungsten electrode market share of this species is the highest in the world. Radioactive contamination has occurred, so European and American countries restrict the production of this type of electrode, but because of its excellent welding performance, its use is not restricted.

Electrode Yttrium Tungsten Electrode

When welding, the arc beam is slender, with a large degree of compression, and its penetration depth is the largest at medium and large currents. Mainly used in military industry and aerospace industry.

Electrode zirconium tungsten electrode

It is an electrode variety developed to improve the disadvantages of pure tungsten electrodes that are easy to melt themselves and pollute the workpiece under high load welding conditions. The biggest feature of this electrode is that under the condition of high load current, the end of this electrode can be kept in a spherical shape. It reduces the phenomenon of tungsten infiltration and has good corrosion resistance.

Electrode pure tungsten electrode

Pure tungsten electrode is the earliest electrode used in argon arc welding. However, under DC welding conditions, the electrode is prone to no arc or unstable maintenance. Adding rare earth oxide can greatly improve this situation. Therefore, pure tungsten electrode Only as a welding electrode under AC conditions or as a resistance welding electrode.

Pure tungsten electrodes are most widely used under AC welding. It is generally used for welding aluminum, and magnesium alloy (AC) is generally used under alternating current.

Electrode physical source

Electrodes in galvanic cells

Electrodes are an essential part of galvanic cells. A device that uses a spontaneous redox reaction to generate a current is called a primary battery. A primary battery must consist of two basic parts: two electrodes and an electrolyte solution. An electrode that gives an oxidation reaction to an electron, such as the Zn electrode in a Daniel battery (shown in the upper right of the figure), is called a negative electrode because of its lower potential; and a pole that accepts an electron to undergo a reduction reaction, such as The Cu electrode is called a positive electrode because of its higher potential.

Electrodes can be classified into three types based on the state of the materials that make up the electrodes. The first type of electrodes are metal and gas electrodes, such as zinc and copper electrodes in Daniel cells, and standard hydrogen electrodes; the second type of electrodes are metal-metal insoluble salt electrodes and metal-metal insoluble oxide electrodes, such as Ag-AgCl electrode. The third type of electrode is a redox electrode (any electrode is a redox electrode, and the redox electrode referred to here refers to the substances that participate in the electrode reaction are all in the same solution), such as electrodes composed of Fe3 + and Fe2 + solutions.

Electrodes in an electrode cell

An electrode is a conductor during which the current enters or leaves the electrolyte during electrolysis. The electrolysis process is a redox reaction at the electrode phase interface.

The electrode is divided into a cathode and an anode. The anode connected to the positive electrode of the power supply is an anode, and an oxidation reaction occurs on the anode; the anode connected to the negative electrode of the power supply is a cathode, and a reduction reaction occurs on the cathode.

There are many types of electrolytic materials. Carbon electrodes are commonly used. In addition, metals such as titanium can also be used as electrodes. In electroplating, the metal containing the plated metal is often used as the anode, and the product to be plated is used as the cathode.

Electrodes in Medicine

The device that takes the ECG signal from the body is called an electrode. It is an essential part of the ECG lead. The material used to make the electrode should be resistant to polarization, low impedance, and long life. Therefore, metal silver is generally used as the material for electrode production. Electrodes can be divided into three types: plate electrodes, adsorption electrodes, and pacing electrodes. The plate electrode is mainly used for standard leads and pressurized unipolar limb leads, about 4cm × 5cm. Since the lead must be attached to the limb, a device that is close to the electrode plate is needed. The adsorption electrode is mainly used as the detection electrode of the unipolar lead, with a diameter of less than 3cm, a circular shape, and a suction cup that enables the electrode to closely adhere to the chest wall. It is very convenient to use. A pacing electrode is an electrode connected to a pacing catheter. ^[3]