Electrochemical performance and anode reaction process for Ca doped Sr2Fe1·5Mo0·5O6-δ as electrodes for symmetrical solid oxide fuel cells

Ca doped Sr2Fe1·5Mo0·5O6-δ (SFM) is investigated as a novel electrode for symmetrical solid oxide fuel cells. CaxSr2-xFe1.5Mo0.5O6-δ (Cax-SFM) maintains the perovskite phase under both oxidizing and reducing atmospheres when the doping content x ≤ 0.50. The Ca doping significantly improves the conductivity, from 39.9 S cm−1 for SFM to 55.7 S cm−1 for Ca0.25-SFM, and 93.1 S cm−1 for Ca0.5-SFM at 800 °C in hydrogen atmospheres. The Ca0.25-SFM based symmetrical cell exhibits peak power densities of 709, 480, and 392 mW cm−2 at 800 °C when hydrogen, the syngas, and carbon monoxide are tested as the fuel, respectively. The interfacial polarization resistance for hydrogen oxidation reaction on Ca0.25-SFM anode is studied via a three-electrode system considering hydrogen concentration and temperature. The impedance spectroscopy demonstrates a decreasing polarization resistance with increasing hydrogen content and temperature, as well as a nearly constant polarization resistance under variation of the water-vapor content. The distribution of relaxation times analysis and reaction kinetics calculation confirms that the H2 dissociated adsorption process is the rate-limiting step. •Ca doping significantly improves the conductivity.•Ca doping increase the peak power density.•H2 dissociated adsorption is the rate-limiting step on Ca0.25-SFM surface.