Solid oxide fuel cells (SOFC) generate energy power by diffusion of O2- anions through an electronically insulating membrane (electrolyte). In principle, any fuel that combines with oxygen can be used in a SOFC to generate electricity. Since SOFCs operate at high temperatures where catalytic-combustion rates are significant, direct oxidation of the fuel is possible at the anode : CnH2n+2 + (3n+1) O2- → (n+1) H2O + 2(3n+1)e- + n CO2
In most of SOFCs, the anode is a ceramic-metallic (CERMET) composite. The ceramic compound is frequently the same as that used as electrolyte and Ni plays the role of electron conductor. The primary problem with direct oxidation of hydrocarbons on a Ni-cermet anode is that Ni catalyses the cracking reaction yielding carbonaceous species on the anode. The aim of our work is to develop an anode stable toward carbon formation for SOFCs running on natural gas directly.
Requirements for Fuel Electrode (anode)
- Chemical stability in reducing environment of the fuel,
- Electronically conducting,
- Adherent to the electrolyte,
- Interconnected porosity,
- Able to reform and/or directly oxidize natural gas.
Development of an anode material, 18,7%-vol. Ni/BaIn0.3Ti0.7O2.85 cermet, for SOFC application with natural gaz
By creating disorder within an ordered arrangement of oxygen vacancies :
- a good Ni dispersion (dark grey) in Ba2In0.6Ti1.4O5.70.3 oxide (light grey ) and 40% of open porosity (black) (Fig.1)
- a metallic behavior and a good electronic conductivity (Fig. 2) : σ = 100 S.cm-1 at 700 °C
- a resistance towards cracking of natural gas (Fig. 3) by means of a specific treatment
|Fig. 1 : SEM of Ni/BaIn0.3Ti0.7O2.85 cermet
||Fig. 2 : conductivity of Ni/BaIn0.3Ti0.7O2.85 cermet|
Fig. 3 : Under natural gas at 700°C the anode is destroyed.
A protection treatment was developed to avoid cracking of hydrocarbons