We can broadly divide voltaic cells into chemical cells, which use a chemical reaction, and physical cells, which use solar or thermal energy. Chemical cells can further be divided into primary cells, which cannot be recharged, secondary cells, which can be recharged and repeatedly used, and fuel cells. Two types of physical cells are solar batteries and thermopiles.

Let's assume that a zinc plate and a copper plate, which are immersed in diluted sulfuric acid (H2SO4), are connected by a conductor. These two plates are called electrodes.

An ion is an atom or molecule that is charged to a positive or negative state. If it's positive, it's called a cation, and if it's negative, it's called an anion.

If zinc ions are produced there, the hydrogen, which has a weaker ionization tendency than zinc, unites with the electrons that moved to the copper plate and becomes hydrogen gas. The hydrogen gas is produced from the copper plate!

The electrolyte is absorbed in cotton or paper or made into a paste so that it is easy to handle.

Something called polarization acts to hinder the flow of electricity, which causes a drop in voltage to occur.

Aqueous hydrogen peroxide (H2O2) is used as an oxidizing agent in the electrolyte to oxidize the hydrogen gas and make water. This oxidizing agent is called a depolarizer. A depolarizer is also put into a dry cell, manganese dioxide (MnO2) and others are used.

A material that causes an electrochemical reaction is called an active material.

In technical terms, a chemical cell creates electricity through a reduction-oxidation (redox) reaction of the positive pole and negative pole.

Since it's dangerous to perform an actual analysis, I'll use a diagram for my explanation.

Interior of a manganese dry cell: A manganese dry cell battery consists of the positive pole compound, which is mixed manganese dioxide (MnO2) for the positive pole and a zinc chloride (ZnCl2) solution for the electrolyte, and a zinc (Zn) can, which is the outer negative pole material.

If a manganese dry cell is used continuously, the voltage is depleted quickly. But if you give it a little rest, the voltage is restored, and the current can flow again. Therefore, this type of battery is appropriate for a flashlight or a clock that operates with little electric power.

Interior of an alkaline dry cell: In an alkaline dry cell battery, manganese dioxide (MnO2) is used for the positive pole, zinc (Zn) powder for the negative pole, and potassium hydroxide (KOH), which is a strong base, for the electrolyte.

Since the alkaline dry cell is structured to contain a lot of manganese dioxide and zinc, it provides greater current and has a longer lifetime. Therefore, an alkaline dry cell is suitable for the power supply of a device that requires a large current, such as a motor.

The electrolysis of water is simply a means of producing oxygen and hydrogen by passing electricity through water.

Since pure water has a low conductivity, we'll add a substance such as sodium hydroxide (NaOH, caustic soda) in our experiment. This will speed up the decomposition process.

The decomposed hydrogen and oxygen will combine to produce electricity, water, and heat. This is the principle of a fuel cell.

The electron is sent out as electricity and the hydrogen ion moves to the anode. At the anode, the platinum (Pt) catalyst causes the hydrogen ion to react with the supplied oxygen, and water is produced.

There is no vibration or noise, and we can use a tool called a fuel reformer to extract the hydrogen that we need for the fuel from natural gas or methanol (CH3OH), and we can simply use oxygen from the atmosphere. If the waste heat is also used, it is very efficient, and since hydrogen fuel can be retrieved in various ways, resources can easily be guaranteed.

It looks like everybody wins!

We can even use common items that are close at hand.

If we just use a penny (copper) for the positive pole, a folded piece of aluminum foil for the negative pole, and insert a tissue that was soaked in salt water as the electrolyte between them, we have a battery!

If we stack a bunch of these sets together so they make a series circuit enough electric power will be produced for a small light-emitting diode (LED).

If we create a circuit by joining both ends of the two types of metal and let the junctions have different temperatures, current will flow. Let's see it in action. If we wrap a copper wire around an iron nail and heat one end of the nail with a flame, a small amount of electricity will flow. This phenomenon is called the Seebeck effect. A thermopile is a type of physical cell that uses this phenomenon.

The greater the temperature difference between the junctions, the greater the current that will flow. Current will continue to flow as long as there is a temperature difference.

The junctions of these two types of metals are called thermocouples.

If this is combined with an ammeter, it can also be used as a thermometer.

There is also a phenomenon that is the reverse of the Seebeck effect. If a DC current is connected to the thermocouples and current flows, the thermocouple at one side will absorb heat and the other one will generate heat. This is called the Peltier effect.

The heat-absorbing side of a Peltier device, which is a semiconductor device, is used in an appliance such as a small refrigerator that does not need a motor.

Phenomena such as the Seebeck effect or Peltier effect are collectively known as thermoelectric phenomena. (+Thomson effect)

I really learned a lot!