Proton Conduction Properties of Bzcy and Szcy Perovskites Type Oxides; Addressing the Effect of Dopant Levels and Proton Content

Abstract

Electrochemical devices based on perovskites-type proton conducting oxides, are gaining wide interest as promising green technologies for hydrogen production and seperation. Interest in this class of materials stems from their lower activation energy for proton transport (typically 0.3-0.6 eV) relative to that for oxide ion conduction, thus making them suitable electrolyes for steam electrolysis cell operation at intermediate temperature. Despite the advances in proton-conducting electrolytes, their development still lag behind the oxygen-ion counterparts. The most prominent limitation being, conductivity, chemical stability, incomplete hydration of the electrolytes, as well as the grain boundary resistance. In the present contribution, starting from SrZr0.5Ce0.4Y0.1O3-δ, we examined the effects of Ba substitution for Sr and the doping level of Y on the lattice structure, electrical properties, proton content as well as chemical stability of the following compositions A(Zr5/9Ce4/9)1-x Y x O3- δ , (A= Ba, Sr and x=0.1, 0.2). Thermo-gravimetric analyses revealed almost similar proton concentration in both SZCY541 and SZCY(54)8/9-2 with a constant Zr/Ce fraction of 5:4. Both samples showed almost comparable proton conductivities in humidified 1% H2 hydrogen. BZCY(54)8/9-2 shows a maximum proton limit of 13.3 mol % compared to only 6.03 mol % for SZCY(54)8/9-2 and retained the highest proton conductivity of 1.44 × 10-2 Scm-1 in wet 1 % H2 at 600 oC (Fig. 1.) as well as excellent chemical stability under 80 % steam for 200 hours. Ba at A-site provides higher proton mobility than Sr. It is also evident from the data that the bulk and grain boundary contributions on the conductivity were strongly dependent on the A-site host, with the grain boundary response dominating the impedance spectra of the BZCY system relative to the SZCY. However the major difference in conductivity among the compositions originates mostly from the differences in proton concentration levels as well as the magnitude of the grain boundary contribution. This paper discusses these aspects based on experimental results as well as steam electrolysis using SZCY541 and BZCY(54)8/9-2 as electrolytes. Acknowledgement This work was supported by the Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier”(Funding agency: JST) and by World Premium International Research Center Initiative (WPI), MEXT Japan. Figure 1