The high operating temperature of the SOFC permits direct operation on hydrocarbon fuels by either electrochemical oxidation or reforming within the fuel cell (internal reforming). The direct electrochemical oxidation reaction of hydrocarbons at the SOFC anode can be described as follows (using methane as an example):
CH4+4O2−=CO2+2H2O+8e−
The key issue in the direct oxidation of hydrocarbons at the Ni/YSZ anode is carbon deposition.
Internal reforming involves conversion of hydrocarbons to hydrogen (and carbon monoxide) followed by electrochemical reactions:
CH4+H2O=3H2+CO
CH4+2H2O=4H2+CO2
followed by
H2+O2−=H2O+2e−
CO+O2−=CO2+2e−