Enriching Nano-Heterointerfaces in Proton Conducting TiO-SrTiO@TiO Yolk-Shell Electrolyte for Low-Temperature Solid Oxide Fuel Cells.

A challenging task in solid oxide fuel cells (SOFCs) is seeking for an alternative electrolyte, enabling high ionic conduction at relatively low operating temperatures, i.e., 300-600 °C. Proton-conducting candidates, in particular, hold a significant promise due to their low transport activation energy to deliver protons. Here, a unique hierarchical TiO-SrTiO@TiO structure is developed inside an intercalated TiO-SrTiO core as "yolk" decorating densely packed flake TiO as shell, creating plentiful nano-heterointerfaces with a continuous TiO and SrTiO "in-house" interfaces, as well the interfaces between TiO-SrTiO yolk and TiO shell. It exhibits a reduced activation energy, down to 0.225 eV, and an unexpectedly high proton conductivity at low temperature, e.g., 0.084 S cm at 550 °C, confirmed by experimentally H/D isotope method and proton-filtrating membrane measurement. Raman mapping technique identifies the presence of hydrogenated HO─Sr bonds, providing further evidence for proton conduction. And its interfacial conduction is comparatively analyzed with a directly-mixing TiO-SrTiO composite electrolyte. Consequently, a single fuel cell based on the TiO-SrTiO@TiO heterogeneous electrolyte delivers a good peak power density of 799.7 mW cm at 550 °C. These findings highlight a dexterous nano-heterointerface design strategy of highly proton-conductive electrolytes at reduced operating temperatures for SOFC technology.