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Electrochemistry is the science of studying the phenomenon of charged interfaces formed by two types of conductors and the changes that occur on them.

Electrical and chemical reaction interactions can be accomplished by batteries or by high-voltage electrostatic discharge (eg, oxygen is converted to ozone by a silent discharge tube), which is collectively referred to as electrochemistry, which is a branch of electrochemistry called discharge chemistry.

Because of the special name of discharge chemistry, electrochemistry is often referred to as “the science of batteries.”

Electrochemistry has now formed a number of branches such as synthetic electrochemistry, quantum electrochemistry, semiconductor electrochemistry, organic conductor electrochemistry, spectroelectrochemistry, and bioelectrochemistry.

Electrochemistry

Electrochemistry has been widely used in chemical, metallurgical, mechanical, electronic, aerospace, aerospace, light industry, instrumentation, medicine, materials, energy, metal corrosion and protection, environmental science and other scientific and technological fields.

Research topics of great concern in the world, such as energy, materials, environmental protection, life sciences, etc., are associated with electrochemistry in a variety of ways.

Primary Battery

The primary battery utilizes the difference in metallicity between the two electrodes to generate a potential difference, thereby causing the flow of electrons to generate electric current.

Also known as a non-battery battery, it is a kind of electrochemical battery, and its electrochemical reaction cannot be reversed, that is, the only chemical can be used. It can be converted into electrical energy. Simply put, it cannot re-storage power, as opposed to the battery.

A primary battery is a device that converts chemical energy into electrical energy. Therefore, by definition, ordinary dry batteries and fuel cells can be called primary batteries.

Chloralkali

 

The basic conditions for the formation of the primary battery:

  1. Two different inert metal (i.e., one is the active metal one is not), the one metal or graphite (Pt and graphite electrodes are inert, i.e., does not itself electronic gains and losses) like an inert electrode Insert into the electrolyte solution.
  2. Insert the wire into the electrolyte solution to form a closed loop.
  3. A spontaneous redox reaction occurs.

Primary battery working principle

The primary battery generates an oxidation reaction and a reduction reaction which are spontaneously carried out by a redox reaction on the negative electrode and the positive electrode of the primary battery, respectively, thereby generating an electric current in an external circuit.

Judging the electrode of the primary battery:

Negative electrode: one pole of electron flow, one pole of oxidation reaction; one pole of the active metal.

Positive electrode: a pole into which electrons flow, one pole where a reduction reaction occurs, a pole of a relatively inactive metal or other conductors.

In the primary battery, the external circuit is electronically conductive, and the electrolyte solution is ionically conductive.

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Determination of the primary battery:

(1) First analyze whether there is an external circuit, there is an external power supply for the electrolytic cell, and no external power supply may be the primary battery; then according to the formation conditions of the primary battery analysis and judgment, mainly “four look”: look at the electrode – two extreme Conductor and there is a difference inactivity (the electrode of the fuel cell is generally an inert electrode), see the solution – the two poles are inserted into the solution; look at the loop – form a closed loop or direct contact between the two poles; see the essence – with or without redox reaction.

(2) Multiple pools are connected, but when there is no external power supply, the pool with the most difference in the vitality of the two poles is the primary battery, and the other pools can be regarded as the electrolytic pool.

Cell

An electrolytic cell is a device that converts electrical energy into chemical energy.

Electrolysis is a process in which an electric current is passed through an electrolyte solution (or a molten electrolyte) to cause a redox reaction at the anodes and cathodes.

cell

Conditions for the occurrence of an electrolytic reaction:

1 Connect DC power supply

2 Yin and yang electrode cathode: connected to the negative pole of the power supply as the cathode

Anode: connected to the positive pole of the power supply as the anode

3 The two poles are in the electrolyte solution or molten electrolyte

4 Two electrodes form a closed-loop

Energy conversion during electrolysis (device characteristics):

Cathode: Must not participate in the reaction is not necessarily an inert electrode

Anode: Not necessarily involved in the reaction, not necessarily an inert electrode

Electrolysis Results:

New material generation on both poles

Writing of the electrode reaction equation for the electrolytic cell:

Anode: Active metal – electrode electron loss (except for Au, Pt, Ir) inert electrode – anion electron loss in solution

Note: electron loss ability: active metal (except Pt Au)>S2->I->Br->Cl->OH->oxygenate (NO3 ->SO4 2-)>F-

Cathode: Cations in the solution

Note: The electron ability: Ag+>Hg2+>Fe3+>Cu2+>H+(acid)>Pb2+>Sn2+>Fe2+>Zn2+>H2O(water)>Al3+>Mg2+>Na+>Ca2+>K+ (ie, the reverse of the active metal sequence table) )

Correspondence: Anode connected to the positive pole of the power supply, cathode connected to the negative pole of the power supply.

Regularity: Before the aluminum (containing aluminum) ions are not discharged, after the hydrogen (acid), the ions are discharged first, and the hydrogen (acid) before the aluminum is observed.

Electrolysis of four types of electrolysis type

1 Electrolyzed Water Type (strong alkali, oxoacid, active metal oxyacid salt), pH is determined by the acidity and alkalinity of the solution, the solution is alkaline, the pH is increased, and the solution is acidic. The pH is reduced, the solution is neutral and the pH is unchanged. Recovery of the electrolyte solution – add an appropriate amount of water.

2 Electrolytic Electrolyte Type (oxygen acid, an inactive metal anoxate), the pH of the anaerobic acid becomes large, and the pH of the inactive metal is not changed. Recovery of the electrolyte solution – add an appropriate amount of electrolyte.

3 Hydrogenated Base Type (active metal hypochlorite), the pH becomes larger. Recovering the electrolyte solution – adding the same acid as the anion.

4 Oxygenated Acid Type (oxyacid salt of inactive metal), the pH becomes small. Recovery of the electrolyte solution – the addition of the same base or oxide as the cation.

Electrochemistry History

In 1663, the German physicist Otto von Guericke created the first generator, which was quieted by friction in the machine.

Electricity. This generator puts a huge sulfur ball into a glass ball and fixes it on a shaft. By rotating the crankshaft to rotate the ball, a static spark is generated when a pad rubs against the rotating ball. This sphere can be disassembled and can be used as a source of electrical testing.

In 1781, Charles Augustin Coulomb (Charles-Augustin de Coulomb) in the process of trying to study the charge made by the British scientist Joseph Priestley repulsion rule of law in the development of electrostatic attraction.

In 1791, Galvani published the “animal electricity” phenomenon in which metal can shrink the muscles of frog legs, which is generally considered to be the origin of electrochemistry. 1799 Volta on the basis of the work of Galvani invented the “stack” with a different metal composition of the film holder wet paper, i.e. so-called modern ” voltaic pile.” This is the prototype of chemical power. Prior to the invention of DC motors, various chemical power sources were the only power sources that provided constant current. The discovery of Faraday ‘s law of electrolysis in 1834 laid a quantitative basis for electrochemistry.

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In the second half of the 19th century, the work of Helmholtz and Gibbs gave the battery “power” (now called ” electromotive force “) with a clear thermodynamic meaning; in 1889, Nernst derived the participating electrode with thermodynamics. The relationship between the concentration of the reaction substance and the potential of the electrode, namely the famous Nernst formula, in 1923, Debye and Huckel proposed the electrostatic theory of the dilute solution of strong electrolytes, which greatly promoted the theoretical discussion and experimental methods of electrochemistry.

After the 1940s, the application and development of electrochemical transient technology, the combination of electrochemical methods and optics and surface technology, enabled people to study fast and complex electrode reactions, providing information on the molecules at the electrode interface. Electrochemistry has always been a relatively active sub-discipline in physical chemistry. Its development and mutual development of solid physics, catalysis, life sciences, and other disciplines promote each other.

Material Protection

According to the principle of electrochemical corrosion, a material protection technique that changes the potential of a metal by the inflow of an external current, thereby reducing the corrosion rate of the metal.

Surgery. According to the trend of metal potential fluctuation, electrochemical protection is divided into two types: Cathodic Protection and Anode Protection.

1 cathodic protection

Cathodic protection is achieved by reducing the metal potential for protection purposes. Cathodic protection has an applied current method and a sacrificial anode method depending on the source of the protection current.

The impressed current method is to provide protection current by an external DC power source, the negative pole of the power supply is connected to the protection object, the positive pole is connected to the auxiliary anode, and the current loop is formed by the electrolyte environment.

electrochemistry

The sacrificial anode method relies on the metal ( sacrificial anode ) whose potential is negative to protect the object to provide protection current, and the protection object is directly connected to the sacrificial anode to form a protection current loop in the electrolyte environment. Cathodic protection is mainly used to prevent metal corrosion in neutral media such as soil and seawater.

2 anode protection

It is called anodic protection by increasing the potential of passive metal to make it passive. Anode protection uses an anodic polarization current to stabilize the metal in a passive state.

Its protection system is similar to an impressed current cathodic protection system, except that the polarization current is in the opposite direction. Only corrosion systems with activation-passivation transitions can use anode protection techniques, such as concentrated sulfuric acid storage tanks, ammonia storage tanks, and the like.

Separation Method

The method of separating metal ions and organic molecules in a solution by electrochemical means is divided into four categories:

Electrolytic separation method for controlling potential

When two or more metal ions are present in the solution, if their reduction potentials are similar, they will be reduced and precipitated during electrolysis, failing to achieve the purpose of separation. As for the choice of potential, depending on the experimental conditions, when the method is applied, the concentration of ions to be electrolyzed cannot exceed the concentration of ions that are first electrolyzed.

Mercury cathode electrolysis separation

When H□ is reduced on the mercury cathode, there is a large overvoltage, so some easily removed metal ions can be separated in the acidic solution so that some heavy metals (such as copper, lead, cadmium, zinc) are deposited on the mercury cathode. On top, amalgam is formed while retaining a small number of ions that are not easily reduced, such as alkali metals, alkaline earth metals, aluminum, iron, nickel, chromium, titanium, vanadium, tungsten, silicon, and the like.

Internal electrolysis separation

In an acidic solution, an internal electrolytic cell can be formed by utilizing the difference in metal oxidation-reduction potential, electrolysis can be performed without applying an external voltage.

For example, to remove trace copper from a large amount of lead, Cu is reduced first than Pb in a sulfuric acid solution, so the lead plate can be used as an electrode and connected to the platinum electrode to form an internal electrolytic cell, which generates a spontaneous electromotive force derived from Pb. Oxidation and reduction of Cu.

This electromotive force allows the reaction to proceed until the current approaches zero, and the internal electrolytic cell is no longer active. Internal electrolysis can separate a small amount of easily reducible metal ions. The disadvantage is that the electrolysis is slow, so the application is not wide.

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Electrodialysis

Ions or charged particles in the liquid can migrate under the influence of an electric field. Due to the nature of the ions, the rate of migration is also different, and the direction of positive and negative charges is also different. When a DC voltage is applied to the two poles of the battery, some organic mixture can be separated.

For example, in clinical experiments, this method is commonly used to study proteins. The sample is placed on a carrier. After the electric field is applied, the charged particles migrate along with the carrier to the oppositely charged electrodes. Because they move at different rates, they can be separated.

The serum protein is divided into five parts. The improved experimental technique allows the concentration of concentrated spots to be around 25 microns, followed by electrodialysis to separate the serum proteins into twenty distinct parts.

Analysis

A chemical analysis method based on the electrochemical properties of a solution. The electrochemical analysis was first introduced by the German chemist C. Winkler in the field of analysis in the 19th century. The instrumental analysis began in 1922 with the Czech chemist J. Halovsky establishing the polarographic method.

The basis of the electrochemical analysis is the electrochemical reaction that takes place in the electrochemical cell. The electrochemical cell consists of an electrolyte solution and two electrodes immersed therein, the two electrodes being connected by an external circuit.

Electrolysis

A redox reaction occurs on the two electrodes, and electrons flow from one electrode to the other through an external circuit connecting the two electrodes.

The relationship between the electrochemical properties of the solution (such as electrode potential, current, conductance, charge, etc.) and the chemical or physical properties of the test substance (such as the chemical composition of the electrolyte solution, the concentration, the ratio of the oxidation state to the reduced state, etc.) The concentration of the substance to be measured is converted into an electrical parameter to be measured.

According to the International Federation of Pure and Applied Chemistry, electrochemical analysis is divided into three categories:

1 neither the electric double layer nor the electrode reaction, including conductance analysis, high-frequency titration, etc.

2 relates to an electric double layer but does not involve an electrode reaction, such as an analytical method for determining the concentration by measuring surface tension or illegally pulling the impedance.

3 relates to an electrode reaction, is divided into two categories: one is the electrolysis current is zero, such as potentiometric titration, another electrolytic current is not equal to 0, including timing potential method, chronoamperometry, anodic stripping voltammetry, alternating current polarography, single-scan polarography, square wave polarography, coulometric analysis, etc.

Electrochemistry Applications

Among the many branches of physical chemistry, electrochemistry is the only discipline based on large industries. Its application is divided into the following aspects:

1 Electrolytic industry, wherein the chlor-alkali industry is the inorganic basic industry after synthetic ammonia and sulfuric acid, and the intermediate monomer adiponitrile of nylon 66 is synthesized by electrolysis; aluminum and sodium For the smelting of light metals, the refining of copper and zinc is also the use of electrolysis.

2 The mechanical industry should use electroplating, electropolishing, electrophoretic painting to complete the surface finishing of the parts.

3 Environmental protection can be removed by electrodialysis Cyanide ion, chromium ion, and other pollutants.

4 Chemical power supply.

5 Metal corrosion prevention problem, most metal corrosion is an electrochemical corrosion problem.

6 Many life phenomena such as muscle movement, nerve information transmission involve electrochemical mechanism; Various electrochemical analysis methods developed using the principle of electrochemistry have become an indispensable means of laboratory and industrial monitoring.

Electrochemical Protection

The oil-field oil-water separator separates important equipment such as gas (upper), crude oil (middle), and water (lower, which accounts for half of the separator). However, the internal structure of the separator is complicated. The average water content of the oil well in the later stage of oilfield development is about 85%. Therefore, more than half of the bottom part of the separator is in the separated sewage medium, and the corrosion problem is very serious.
In the past, the sacrificial anode cathodic protection method was generally applied to the inner wall of the separator, but the inner wall temperature of the separator was high, the composition of the inner wall deposited water was complicated, and the water quality may be acidic or alkaline.

Therefore, the sacrificial anode protection period is short, and it is generally consumed in less than half a year. Sacrificial anode protection also has a protection dead angle. On the other hand, the sacrificial anode cathodic protection potential cannot be measured, the protection current cannot be adjusted, and the length of the protection period cannot be predicted.
An applied current cathodic protection method for the inner wall of the oil-water separator. A titanium-based tubular mixed metal oxide anode is used as an auxiliary anode fixed on a support having a certain height in the aqueous phase at the bottom of the separator, and a silver/silver chloride reference electrode or a high-purity zinc reference electrode is used. The method is convenient to install, has a long service life (up to 10 years), uniform protection potential, and adjustable protection current output.