Description of hydrogen and oxygen fuel cells

The positive reaction formula is:

If the electrolyte solution is an acid solution

The negative reaction formula is:

The positive reaction formula is:

The total reaction equation is:

In alkali solution, the content of OHˉ is extremely high, so H+ generated at the negative electrode will directly combine with OHˉ to form water, while OHˉ generated at the positive electrode will exist in the form of ions due to the lack of H+ combination. The opposite is true for acidic solutions.

Composition structure;

A type of fuel cell using hydrogen as fuel and oxygen as oxidizer. Hydrogen and oxygen from the outside through the pipeline into the battery for electrochemical reaction and output electricity. The theoretical specific energy of the hydrogen - oxygen fuel cell is 3600 watt - hour/kg. The working voltage of a single battery is generally 0.8 ~ 0.97 volts, and in order to meet the working voltage required by the load, dozens of single batteries are often connected into a battery pack.

In order to maintain the normal operation of the battery, it is necessary to continue to supply hydrogen and oxygen, and timely exclusion of reaction products (water) and waste heat. The battery pack is composed of the following parts: ① Hydrogen and oxygen supply system: the hydrogen and oxygen carried by the spacecraft are stored in supercritical liquid, which can reduce the volume of the tank and solve the problem of the separation of gas and liquid under weightless conditions, but the storage tank is required to have good adiabatic performance, low temperature resistance and high pressure resistance (6 mpa for oxygen tank and 3 ~ 3.5 mpa for hydrogen tank). ② Drainage subsystem: there are two main ways of dynamic drainage and static drainage. The former circulates hydrogen with water vapor to the cooling device to condense the water vapor into water for separation; The latter relies on porous fiber braided materials (such as wicks) to adsorb the condensed water, also known as wick drainage. The water discharged from the battery pack can be purified for astronauts to drink or use as coolant. ③ Heat removal subsystem: The battery pack circulates through the coolant (such as glycol solution) to bring the waste heat to the radiator and discharge it outward to maintain the temperature range of the battery pack to work normally. (4) Automatic control subsystem: including the control and adjustment of the working pressure, temperature, drainage and exhaust, voltage, safety and coolant circulation of the battery pack. The measured parameters are transmitted to the display in the astronaut's cockpit or sent back to the ground by telemetry equipment. When the battery string is faulty, the system automatically switches to the backup battery string.

Battery classification:

According to the cell structure and working mode, hydrogen and oxygen fuel cells can be divided into three categories: ionic membrane, bacon type and asbestos membrane.

① Ionic membrane hydrogen oxygen fuel cell: acid fuel cell with cation exchange membrane as electrolyte, modern use of perfluorosulfonic acid membrane. When the battery is discharged, water is generated at the oxygen electrode and sucked out through the wick. This kind of battery works at room temperature, has compact structure and light weight, but the internal resistance of ion exchange film is large and the discharge current density is small.

② Bacon type fuel cell: alkaline battery. The hydrogen and oxygen electrodes are both double-layer porous nickel electrodes (the inner and outer layers have different pore sizes), and platinum is used as catalyst. The electrolyte is a caustic potassium solution of 80% to 85%, which is solid at room temperature and liquid at the operating temperature of the battery (204 to 260°C). This battery has a high energy utilization rate, but it consumes a lot of power, and it takes a long time to start and stop (24 hours to start, 17 hours to stop).

③ Asbestos film fuel cell: also an alkaline battery. The hydrogen electrode is made of porous nickel plate plus platinum and palladium catalyst, and the oxygen electrode is a porous silver electrode. The two electrodes are sandwiched with an asbestos film containing 35% caustic potassium solution, and then a fluted nickel plate is pressed on the two electrode plates as a flow collector to form a gas chamber and package into a single battery. Water is generated on one side of the hydrogen electrode during discharge, which can be discharged by circulating hydrogen or by static drainage. The battery has a start-up time of only 15 minutes and can be stopped instantaneously.

Main features:

1. The product is water, clean and environmentally friendly;

2. Easy to continue to pass hydrogen and oxygen, generating continuous current;

3. High energy conversion rate, more than 80%(ordinary combustion energy conversion rate of more than 30%);

4. Can be combined as a fuel cell power station, less waste emissions, low noise, green power station. [2]

Application field:

As a promising new power source, hydrogen and oxygen fuel cells have many applications:

1, large-scale power generation