Proton transport enhancement by octahedral distortion and built-in electric field at the PMN–TiO2 heterointerface†

Abstract

Mixed ion–electron conductor-based electrolytes have shown great promise in solid oxide fuel cells (SOFCs), demonstrating attractive performance at low temperatures (<600 °C) due to their multi-interface conduction and interfacial effects. In this study, a new electrolyte composed of a PrMn_0.5Ni_0.5O_3−δ (PMN) perovskite and TiO₂ semiconductor in the form of a heterostructure was developed and evaluated in SOFCs. First-principles calculations identified the octahedral distortion and charge transfer at the PMN–TiO₂ interface in the heterostructure. It was found that doping and the heterostructure played important roles in facilitating proton transport in the PMN–TiO₂ electrolyte. Material characterization revealed that PMN–TiO₂ formed a bulk heterostructure with sufficient heterointerfaces, leading to enriched oxygen vacancies. The PMN–TiO₂ composite with a mass ratio of 9 : 1 achieved a total conductivity of 0.46 S cm⁻¹ at 550 °C. The 9PMN–1TiO₂ electrolyte-based SOFC demonstrated a promising peak power density of 235 mW cm⁻² at 450 °C. Measurements using KPFM, UPS, and UV-vis spectroscopy confirmed the presence of a built-in electric field (BIEF) in the 9PMN–1TiO₂ electrolyte, which enhanced ionic conduction. These findings indicate a novel electrolyte material and an optimized approach for improving SOFC performance.