Enriching Nano‐Heterointerfaces in Proton Conducting TiO2‐SrTiO3@TiO2 Yolk–Shell Electrolyte for Low‐Temperature Solid Oxide Fuel Cells

Abstract

AbstractA 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 TiO2‐SrTiO3@TiO2 structure is developed inside an intercalated TiO2‐SrTiO3 core as “yolk” decorating densely packed flake TiO2 as shell, creating plentiful nano‐heterointerfaces with a continuous TiO2 and SrTiO3 “in‐house” interfaces, as well the interfaces between TiO2‐SrTiO3 yolk and TiO2 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−1 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 TiO2‐SrTiO3 composite electrolyte. Consequently, a single fuel cell based on the TiO2‐SrTiO3@TiO2 heterogeneous electrolyte delivers a good peak power density of 799.7 mW cm−2 at 550 °C. These findings highlight a dexterous nano‐heterointerface design strategy of highly proton‐conductive electrolytes at reduced operating temperatures for SOFC technology.