3.16.2 Solid Oxide Fuel Cells (SOFC)

• SOFCs are useful as electrochemical conversion devices in which oxidation of fuel leads to production of electricity.
  

• Schematic of such a device is shown in Figure 3.10 where two electrodes, anode and cathode, are separated by an electrolyte e.g. CSZ (cubic stabilized zirconia with 8-10 mol% Y₂O₃).
  

• This device can usually work with an efficiency of ~60% at 1000 (^oC) with an output power of 100 kWh.
  

• The device can be used in a wide range of oxygen partial pressures (~1 atm to 10^-20 atm) and can work at temperatures between 700-1000(^oC) with areal resistance of ∼ 15μΩm^-2 .
  

• Anode material is typically porous Ni and cathode is a porous p-type semiconducting oxide such as La_1-x Sr_x MnO_3+y .
  

• One needs to connect many of these devices together to obtain substantial power and for that purpose, interconnects are used which are typically made of Ca, Mg or Sr doped LaCrO₃ or stainless steel depending upon the operation temperature.
  

  Figure 3.10 Schematic of (a) a SOFC device and (b) operation of a SOFC device

  
  In case of H₂ and CO gases as fuels, the following reactions take place at two electrodes, as shown in Figure 3.10.

Anode/Electrolyte Interface Reaction:

	and

Reaction at the Cathode/Electrolyte Interface

Overall reactions that occur are:

It must be noted that high ionic conduction through the electrolyte is required to minimize the resistive losses.