Relationship between Electrochemical Properties and Electrolyte Partial Conductivities of Proton-Conducting Ceramic Fuel Cells

Abstract

Proton ceramic fuel cells (PCFCs) have attracted attentions because of the high potential to enhance the electrical efficiency of SOFCs, in which proton-conducting ceramic is used as electrolyte instead of the yttria-stabilized zirconia (YSZ) which is the most common electrolyte material of SOFCs. In previous study, we measured the P O2 dependence of total electrical conductivities of the proton-conducting solid oxides, BaZr0.1Ce0.7Y0.1X0.1O3- d (X = Ga, Sc, In, Yb, Gd), which were divided into partial conductivities of the respective charge-carriers, such as electron, ion, and hole, by using the difference in P O2dependence of the charge-carriers. In this study, we have investigated the electrochemical properties of the PCFCs with the various partial conductivities in the electrolytes. The electrochemical properties were found to have large dependences on operation condition. When ASR and external current density were given constant values of 0.383 ohm cm2 and 0.25 A cm-2, respectively, an influence of the dopant species on the electrical efficiencies η xwas found to have the following sequential order: η x=SC > η x=In > η x=Ga > η x=Y > η x=Gd When the external current density was given as a variable, increasing the external current density will result in the increase of the voltage drop and the decrease of a ratio of leakage current to external current. This suggests that according to the partial conductivities the external current density has an optimum value maximizing the electrical efficiency. Acknowledgements This research is supported by The Japan Science and Technology Agency (JST) through its “Center of Innovation Science and Technology based Radical Innovation and Entrepreneurship Program (COI Program)."