Solid Oxide Fuel Cell Research

Today we finished our research on solid oxide fuel cell systems.

Summary

A Solid Oxide Fuel Cell (SOFC) is a type of fuel cell that uses a solid electrolyte as opposed to a liquid or molten electrolyte that other fuel cells use. A lot of development has focused on these types of fuel cells because they are able to handle a wide variety of fuels and do so with a high efficiency (40-60% unassisted, up to 70% in a pressurized hybrid system). However, high efficiency and fuel adaptability are not the only benefits to SOFCs. They are reliable, clean, nearly pollution-free, and have little to no noise pollution since there are little moving parts.

The solid fuel cell

SOFCs are totally solid fuel cells. The anode, cathode, and electrolyte are solid and in order for the cell to function properly, it has to run at high temperatures (600 - 1000°C). Most SOFCs use yttria-stabilized zirconia (YSZ) as an electrolyte because of its low thermal expansion coefficient.

Electrodes:

Anode:

Similarly, the anode has to meet the same requirements as the cathode for electrical conductivity, thermal expansion compatibility and porosity. Most development with the anodes has been focused on nickel because of its abundance and affordability. However, the thermal expansion of nickel (13.3×10^-6/C compared with 10×10^-6/C for YSZ) is too high to pair it in pure form with YSZ. To fix this, a composite of nickel and YSZ, Ni-YSZ, is commonly used.

Cathode

Because of the high temperature, platinum catalysts aren’t necessary to carry the reaction through. SOFCs use lanthanum maganite (LaMnO₃), typically doped with strontium (Sr) to give a compound called LSM (La_1-xSr_xMnO₃). This material has a similar thermal expansion coefficient to YSZ ( ~10.0×10^-6/C) which means the material won’t change the surface are the hydrogen can bond to very much, as it gets hot.

Advantages:

The advantages of a solid oxide fuel cell are obvious. It can use a wide variety of fuels due to the high temperature that it operates at, its high electrical efficiency (35-45%), and the durability of the parts (the electrolyte, anode, and cathode specifically).

Disadvantages:

The fact that SOFCs operate at such a high temperature provides an issue. This much heat is hard to contain and utilize. Another issue is that this fuel cell takes a long time to warm up to 600°C which is the temperature it needs to reach to be efficient. Another problem is using nickel as an anode. Nickel catalyzes some hydrocarbons into lead, which can build up and clog entrances for hydrogen to catalyze.