ALKALINE FUEL CELL (AFC)

Alkaline Fuel Cell (AFC) using an electrolyte solution (KOH) or alkaline solution. Operating temperature between 150 °C - 200 °C using hydrogen fuel and pure oxygen and free of CO_2. Because impurities can cause side reactions and CO₂ reacts with the electrolyte to form a precipitate carbonate will seal the surface of the catalyst and inhibit the reaction at the surface of the anode and cathode. Alkaline fuel cell (AFC) has been used as a source of power for spacecraft since 1960.

Alkaline systems operate well at room temperature, yield the highest voltage (at comparable current densities) of all fuel cell systems, and cell and electrodes can be built from low-cost carbon and plastics. Because of a good compatibility with many construction materials AFCs can achieve a long operating life

Complete reaction can be seen as below:

Anode reaction:

2H₂ + 4OH^- à 4H₂O + 4e^-

Cathode reaction:

O₂ + 2H₂O + 4e^- à 4OH^-

The overall reaction: 

2H₂ + O₂ à 2H₂O

Started working mechanism of the reaction of water and oxygen at the cathode generates hydroxyl ions (OH^-)^. Hydroxyl ions through the electrolyte transferred to the anode side. On the anode side hydrogen reacts with hydroxyl ions produce water and liberate electrons. Electrons generated at the anode side out of the system and used as electric power and then back to the cathode. On the cathode side the electrons react with oxygen. To more clearly below show the mechanism of action (AFC): 

Figure 1.

AFC structure

The AFCs for remote applications (space, undersea, military) are not strongly constrained by cost. On the other hand, the consumer and industrial markets require the development of low-cost components to successfully compete with alternative technologies. Much of the recent interest in AFCs for mobile and stationary terrestrial applications has addressed the development of low-cost cell components.