What is the working principle of fuel cells and hydrogen energy vehicles?

The so-called hydrogen energy source does not mean that there is a large amount of hydrogen on the earth, which can be “exploited” for use as an energy source. Instead, water can be decomposed by light to produce hydrogen instead of oil and electricity.

Hydrogen has many advantages as an energy source. Hydrogen can be produced by photolysis, and the water reserves are large and relatively low. Hydrogen fuel is produced after combustion, which is a harmless and very clean energy source. Hydrogen is less than the power loss in storage and transportation, and the heat of combustion of hydrogen is high. The heat generated by burning 1 kilogram of hydrogen is equivalent to the calorific value of 3 kilograms of gasoline or 4.5 kilograms of coke. However, in applications, the storage and transportation of hydrogen and the use of solar energy to decompose water to produce hydrogen have been the bottleneck restricting the development of hydrogen energy.

Let's talk about fuel cells. It is an energy conversion device that directly converts chemical energy in fuel into electrical energy. From the outside, there are positive and negative electrodes and electrolytes, like a battery, but in essence it cannot "storage electricity," but a small "power plant". There are many types of fuel cells. After years of exploration, the most promising for automobiles is the proton exchange membrane fuel cell. Its working principle is: sending hydrogen to the negative electrode, through the action of the catalyst (platinum), two electrons in the hydrogen atom are separated. These two electrons generate current through an external circuit under the attraction of the positive electrode. Hydrogen ions (protons) that lose electrons can pass through the proton exchange membrane (the solid electrolyte), recombining with the oxygen atoms and electrons into water at the positive electrode. Since oxygen can be obtained from the air, as long as hydrogen is continuously supplied to the negative electrode and water (steam) is taken away in time, the fuel cell can continuously supply electric energy.

At present, the use of hydrogen energy is mainly hydrogen fuel cells. The distinguishing feature of the electric car is that it does not have a bulky battery load and that the mileage does not have the power to drive the car. Therefore, hydrogen fuel cells can be said to be an excellent driving force. A car powered by this kind of power is called a zero-pollution hydrogen-powered car.

The fuel cell is a power generation device that directly converts the chemical energy of fuel and electrolyte into electrical energy. It is also the fourth power generation device after thermal power, hydropower, andspecial power. It is a high-tech development field that is highly valued by developed countries today.

Hydrogen-oxygen fuel cell uses hydrogen as fuel as reducing agent and oxygen as oxidant

Hydrogen oxygen fuel cell

The battery that converts chemical energy into electrical energy through the combustion reaction of the fuel works in the same way as the primary battery.

When the oxyhydrogen fuel cell operates, hydrogen is supplied to the hydrogen electrode while oxygen is supplied to the oxygen electrode. Hydrogen and oxygen form water through the electrolyte under the action of a catalyst on the electrode. At this time, there is excess electrons on the hydrogen electrode and negatively charged, and the oxygen electrode is positively charged due to lack of electrons. This process similar to combustion can be carried out continuously after the circuit is switched on.

During operation, fuel (hydrogen) is supplied to the negative electrode, and oxidant (oxygen) is supplied to the positive electrode. Hydrogen is decomposed into positive ions H+ and electrons e- by the action of a catalyst on the negative electrode. Hydrogen ions enter the electrolyte, and electrons move along the external circuit to the positive electrode. The electrical load is connected to an external circuit. On the positive electrode, oxygen and the hydrogen ions in the electrolyte absorb the electrons reaching the positive electrode to form water. This is the reverse of the electrolytic reaction of water.

A oxyhydrogen fuel cell does not require a device that stores all of the reducing agent and oxidant in the battery.

The reactants of the oxyhydrogen fuel cell are all outside the battery. It is only a container for providing a reaction.

Both hydrogen and oxygen can be supplied from outside the battery.

A fuel cell is a chemical battery that uses the energy released by a chemical reaction of a substance to directly convert it into electrical energy. From this point of view, it is similar to other chemical batteries such as zinc-manganese dry batteries, lead batteries, and the like. However, it requires continuous supply of reactive materials - fuel and oxidant - which is not the same as other common chemical batteries. Since it converts the energy released by the chemical reaction into electrical energy, it is called a fuel cell.

Specifically, a fuel cell is a "generator" that utilizes the reverse reaction of electrolysis of water. It consists of a positive electrode, a negative electrode and an electrolyte plate sandwiched between the positive and negative electrodes. Initially, electrolyte plates were formed by infiltration of electrolyte into porous plates, and in 2013, they were developed to use solid electrolytes directly.

During operation, fuel (hydrogen) is supplied to the negative electrode, and an oxidant (air, which acts as oxygen) is supplied to the positive electrode. Hydrogen is decomposed in the negative electrode into positive ions H+ and electrons e-. When hydrogen ions enter the electrolyte, the electrons move along the external circuit to the positive electrode. The electrical load is connected to an external circuit. On the positive electrode, oxygen in the air and hydrogen ions in the electrolyte absorb electrons reaching the positive electrode to form water. This is the reverse of the electrolytic reaction of water. In this process, water can be reused, and the principle of power generation is similar to that of solar cells that can be used at night.

The electrode material of the fuel cell is generally an inert electrode and has strong catalytic activity, such as a platinum electrode, an activated carbon electrode, and the like.

With this principle, the fuel cell can continuously transmit electricity to the outside during operation, so it can also be called a "generator."

In general, writing the chemical reaction equation of a fuel cell requires a high degree of attention to the acidity and alkalinity of the electrolyte. The electrode reaction occurring on the positive and negative electrodes is not isolated, and it is often closely related to the electrolyte solution. For example, hydrogen-oxygen fuel cells are available in both acid and basic forms:

If the electrolyte solution is an alkali or a salt solution

A type of fuel cell uses hydrogen as a fuel and oxygen as an oxidant. Hydrogen and oxygen are externally supplied to the battery through a pipe for electrochemical reaction and output electrical energy. The theoretical specific energy of an oxyhydrogen fuel cell is 3,600watt-hours/kg. The operating voltage of the single cell is generally 0.8 to 0.97 volts. In order to meet the operating voltage required for the load, dozens of single cells are often connected in series to form a battery pack.

In order to maintain the normal operation of the battery, hydrogen and oxygen must be continuously supplied, and the reaction product (water) and waste heat should be eliminated in time. The battery pack consists of the following parts: 1 Hydrogen and oxygen supply subsystem: The hydrogen and oxygen carried by the spacecraft are stored in supercritical liquid, which can reduce the volume of the tank and solve the separation problem of gas and liquid under weightless conditions, but requires the tank to be insulated. Good performance, low temperature resistance, high pressure resistance (6MPa for oxygen tank and 3 to 3.5MPa for hydrogen tank). 2 Drainage Subsystem: There are two main modes: dynamic drainage and static drainage. The former circulates hydrogen with water vapor to a cooling device to condense the water vapor into water for separation; the latter relies on a porous fiber woven material (such as a wick) to adsorb the condensed water, which is also called wick drainage. The water discharged from the battery pack is purified for use by astronauts or as a coolant. 3 Row heat separation system: The battery pack circulates through a coolant (such as aqueous glycol solution) to discharge the waste water to the radiator to maintain the temperature range in which the battery pack operates normally. 4 Automatic Control Subsystem: including battery pack operating pressure, temperature, drainage and exhaust, voltage, safety and coolant circulation control and regulation. The measured parameters are transmitted to the display of the astronaut cockpit or sent back to the ground by the telemetry device. When the battery pack fails, it automatically switches to the backup battery pack.

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