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

Hydrogen-oxygen fuel cells can be divided into three types according to the cell structure and working mode: ionic membrane, bacon membrane and asbestos membrane.

① Ion exchange membrane hydrogen-oxygen fuel cell: an acidic fuel cell with cation exchange membrane as electrolyte, and a perfluorosulfonic acid membrane was adopted in modern times. When the battery is discharged, water is generated at the oxygen electrode and sucked out through the core. This kind of battery works at room temperature, with compact structure and light weight, but the internal resistance of ion exchange membrane is large and the discharge current density is small.

② Bacon fuel cell: alkaline cell. Hydrogen and oxygen electrodes are both double-layer porous nickel electrodes (the inner and outer layers have different pore sizes), and platinum is added as catalyst. The electrolyte is 80% ~ 85% caustic potash solution, which is solid at room temperature and liquid at battery working temperature (204 ~ 260℃). This kind of battery has high energy utilization rate, but it consumes a lot of energy and has a long start-stop time (start 24 hours, stop 17 hours).

③ Asbestos membrane fuel cell: it is also an alkaline cell. The hydrogen electrode is made of porous nickel sheet with platinum and palladium catalysts, and the oxygen electrode is porous silver sheet. An asbestos film containing 35% caustic potash solution was sandwiched between the two electrodes, and then the slotted nickel sheet was pressed on the two plates as a current collector to form an air chamber and package it into a single battery. When discharging, the water generated at one side of the hydrogen electrode can be discharged by circulating hydrogen or static drainage. The start-up time of this battery is only 15 minutes, which can be stopped instantly. hydrogen oxygen fuel cell

The fuel cell converts the reaction product (water) of the battery into reactants (hydrogen and oxygen) through the electrolytic cell, and then uses it to generate electric energy, which consists of the fuel cell and the electrolytic cell. And can be used as an energy storage device of a high-power solar cell array power supply system. When there is sunshine, the solar array provides electric energy for the spacecraft load, and it is also used to electrolyze water to generate hydrogen and oxygen, thus storing some electric energy. When the spacecraft enters the shadow area, the solar cell cannot generate electricity or the power supply is insufficient, and the power supply is provided by this fuel cell.