Influence of Local Atomic Structure and Chemistry on Proton Conductivity and Electrical Leakage in Proton-Conducting Oxides

Electrolyte materials in solid-oxide electrolyzer cells (SOECs) require high, purely ionic conductivity to maximize their efficiency for hydrogen production. However, the most widely used electrolytes in proton-conducting SOECs exhibit non-negligible electrical leakage, usually arising from acceptor doping. As a result, it is desirable to identify and design materials that possess high protonic conductivity with minimal electrical leakage. Here, we use DFT calculations to identify candidate oxides to this end. First, we explore the structural considerations, such as coordination environments, bond lengths, and interlayer spacing that underlie ionic and electrical conductivity. Next, we present results for two candidate proton-conducting oxides, Ba₂ScAlO₅ and Ba₇Nb₄MoO₂₀, hexagonal perovskites with properties amenable to use as efficient electrolytes. We present experimental analysis of their structure and conductivity to support our computational work. Our results provide physical insights into the ionic and electronic conductivity of novel proton conducting oxides. Additionally, we offer guidance for the design and development of superior proton-conducting electrolytes based on a holistic consideration of local atomic structure and chemistry.

This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.