Electrochemical Impedance Spectroscopy of High-Efficiency Hydrogen Membrane Fuel Cells Based on Sputter-Deposited BaCe 0.8 Y 0.2 O 3−δ Thin Films

A hydrogen membrane fuel cell (HMFC) consisting of a Pd solid anode, 1 μm thick BaCe 0.8 Y 0.2 O 3−δ thin-film electrolyte, and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 cathode was examined. A single-phase BaCe 0.8 Y 0.2 O 3−δ thin film was successfully deposited by radio frequency cosputtering with BaCe 0.8 Y 0.2 O 3 and Ce 0.9 Y 0.1 O 2 double targets, as checked by X-ray diffraction, transmission electron microscopy, and wavelength dispersive X-ray analysis. The maximum power density reached 1.05 W cm –2 at 600 °C, and this value was higher than the champion data of the recently reported proton-conducting ceramic fuel cells (PCFCs). Electrochemical impedance analysis was performed to characterize the anode and cathode polarization behavior. The impedance responses of HMFC were explicable with an equivalent circuit built by a series connection of cathode charge-transfer elements and anode mass-transfer elements. The contribution of the mass transfer in Pd bulk was found to be relatively small in comparison to cathode polarization and ohmic loss in normal fuel cell atmosphere. Moreover, the cathodic charge-transfer resistance of HMFC was found to be 25 times smaller than those of the recent PCFC systems. The current results demonstrated that the HMFC retained relatively large gas–proton–electron triple-boundary zones near the interface between the BaCe 0.8 Y 0.2 O 3−δ electrolyte and porous La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 –δ cathode.