Fuel cell types
Depending on the electrolyte use types, fuel cells can be divided into several varieties.
1. Alkaline Fuel Cell (AFC)
This fuel cell is used as an electrolyte in KOH. Oxygen reduction in alkali electrolytes is faster than the kinetics of acid electrolytes and the use of non-metallic electro catalysts makes AFC economical. However, it does not allow the presence of acidic impurities such as CO2 in the environment due to emission rate.
Alkali systems work very well at room temperature and have the highest voltage efficiency among all other fuel systems. In addition, the AFC has a long operating life, as it can adapt well with many materials.
The AFC are reliable systems and are able to achieve relatively high power in small volume. The power densities vary between 100-200 mW/cm ². Costs are tried to be delivered to the 50/100 $/kw for the transport sector.
2. Phosphoric Acid Fuel Cell (PAFC)
In this fuel cell where phosphoric acid is used in electrolytically, the relative clean fuels (such as natural gas, LPG) or the gas from the aerator are cleaned. It focuses on two applications closest to the market. These are power plants and cogenaration units. It is necessary to use a soy metal electro catalyst in PAFC. Despite this disadvantage, phosphoric acid provides excellent thermal, chemical and electrochemical stability as an electrolyte. Furthermore, Pafcs are very advantageous for the utilization of waste heat.
PAFC systems are the most developed systems in the applications on Earth. They are mostly used to produce electricity in places such as apartments, malls, etc. Pafcs are commercially available in the form of a 24 V electric generator, from 250 W to 200 KW. The investment cost is $287/kw in a 200 KW PKC system that uses gas as fuel.
Pafcs can work best at a fixed output level. With a hybrid system, it performs better if the high power requirement required by acceleration is met with other tools. The most beautiful applications of PAFCS will be in heavy duty vehicles or locomotives.
3. Solid Oxide Fuel Cells (SOFC)
SOFCs are solid fuel batteries. Most of the cell materials consist of special ceramics and nickel. Operating temperature is around 1000 º C. As fuel is combined with CO, hydrogen is used and as a reaction product, water vapor and CO2 are emerging.
Sofc are places where both electricity and heat can be used as a cogeneration unit. A steam turbine can be combined with steam to be obtained even with 1000 º C. Thus, total system efficiency can reach up to 50-55%. The currently calculated investment costs are $1500/KW.
4. Proton Exchange Membrane Fuel Cell (PEMFC)
"PEMDC" was invented by General Electric in the early 1960s. It is referred to as a solid polymer electrolytic fuel cell. In this type of fuel cells, the membranes can be used to pass protons (hydrogen ions).
The PEM fuel cell is composed of a solid electrolyte with protons, such as perphorlu sulphuric acid polymers, pressed between two electrons coated with platinum. It creates a gas column between the electrolyte anode and cathode, enabling the transport of the correct hydrogen ions in the anode cathode. Polymer electrolytes consist of gas diffusion ducts found in gas electrodes. At the same time, these channels are also the task of gathering the electrical current. The operating temperature of the pems is at very low temperatures, such as 80-90 º C, and the operating pressures are between 1-8 atm pressures. These types of fuel cells can work with hydrogen and oxygen at a certain rate of moisture.
PEMs have a high power density of 350 mW/cm ² and are currently commercially available in the 100-500 W power range. Investment costs are also ranged from 5000-13000. With the decline in membrane and catalyst costs and in case of serial production, these costs will be 10-20 fold down.
High power intensity, fast and quick starter and variable power output conform to the PEMs available in the transportation area.
5. Melt carbonated fuel cell (MCFC)
The MCFC operates at a temperature of 600-650 º C and is one of the second generation fuel batteries developed recently. In Anotta CO2, rich gas product and H2O production is provided, and CO2 is sent to be mixed with the air entering the Catota.
Due to the high operating temperature of the MCFC, it can be used for valuable waste heat, process temperature and cogenaration purposes. Its most important advantages are directly used in the cell in the anode chamber for the conversion of its own waste heat from desulfurization to Hydrojene. The targeted investment cost for MCFC is at a level of $1000/KW.