Detailed explanation of the basics of hydrogen and oxygen fuel cells

What is a hydrogen-oxygen fuel cell?

Fuel cells are a new power source with great development prospects. They generally use hydrogen, carbon, methanol, borohydride, coal gas or natural gas as fuel, as the negative electrode, and oxygen in the air as the positive electrode. The main difference from ordinary batteries is that the active substances of ordinary batteries are placed in advance, so the battery capacity depends on the amount of active substances stored; while the active substances (fuel and oxidant) of fuel cells are continuously input while reacting, so this type of battery is actually just an energy conversion device. This type of battery has the advantages of high conversion efficiency, large capacity, high specific energy, wide power range, and no need to charge, but due to high cost and complex system, it is limited to some special uses, such as spacecraft, submarines, military, TV relay stations, lighthouses and buoys.

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

1. Ion membrane hydrogen and oxygen fuel cell: an acidic fuel cell using a cation exchange membrane as the electrolyte. Modern technology uses a perfluorosulfonic acid membrane. When the battery is discharged, water is generated at the oxygen electrode and is sucked out through the wick. This type of battery works at room temperature, has a compact structure, and is lightweight, but the internal resistance of the ion exchange membrane is large and the discharge current density is low.

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

3. Asbestos membrane fuel cell: also an alkaline battery. The hydrogen electrode is made of a porous nickel sheet with platinum and palladium catalysts, and the oxygen electrode is a porous silver electrode. The two electrodes are sandwiched with an asbestos membrane containing 35% caustic potash solution, and then a grooved nickel sheet is pressed tightly on the two plates as a current collector to form a gas chamber and encapsulate it into a single cell. When discharging, water is generated on one side of the hydrogen electrode, which can be discharged by circulating hydrogen or by static drainage. The start-up time of this battery is only 15 minutes, and it can be shut down instantly. It is more environmentally friendly than lithium iron phosphate batteries.

The principle of hydrogen-oxygen fuel cells

When working, 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- under the action of the catalyst on the negative electrode. The hydrogen ions enter the electrolyte, while the electrons move to the positive electrode along the external circuit. The load that uses electricity is connected to the external circuit. At the positive electrode, oxygen and hydrogen ions in the electrolyte absorb the electrons that reach the positive electrode to form water. This is the reverse process of the electrolysis reaction of water.

Advantages of hydrogen-oxygen fuel cells

1. Clean and environmentally friendly, the product is water;

2. It is easy to continuously pass hydrogen and oxygen to generate continuous current;

3. The energy conversion rate is high, exceeding 80% (the energy conversion rate of ordinary combustion is more than 30%);

4. It can be combined into a fuel cell power station, which has less waste emissions, low noise, and is a green power station.

Application of hydrogen and oxygen fuel cells

As a new power source with great development prospects, hydrogen and oxygen fuel cells have many application areas:

1. Power generation from large power stations

2. Portable power bank

3. Emergency power supply

4. Home power supply

5. Aircraft, cars, warships