Proton transport enhanced by octahedral distortion and built-in electric field in PMN-TiO2 heterointerface

Abstract

Mixed ion-electron conductor based electrolytes have shown great promise in solid oxide fuel cells (SOFCs) with attractive performance at low temperatures (<600 °C), due to their multi-interface conduction and interfacial effects. In this study, a new electrolyte made of PrMn_0.5Ni_0.5O_3-δ (PMN) perovskite and TiO₂ semiconductor in a form of heterostructure is developed and evaluated in SOFCs. First-principles calculations identify the octahedral distortion and charge transfer of PMN-TiO₂ interface in heterostructure. It is found the doping and heterostructure play the important roles in resulting in the proton transport in the PMN-TiO₂ electrolyte. Material characterization reveals that the PMN-TiO₂ forms a bulk-heterostructure with sufficient heterointerface, which produces enriched oxygen vacancies. The PMN-TiO₂ composite with mass ratio 9:1 realizes a total conductivity of 0.46 S cm^-1 at 550 °C. The 9PMN-1TiO₂ electrolyte-based SOFC demonstrates a promising peak power density of 235 mW cm^-2 at 450 °C. Measurements of KPFM, UPS, and UV-vis spectra confirm the built-in electric field (BIEF) in the 9PMN-1TiO₂ electrolyte, which is beneficial to the enhancement of ionic conduction. These findings indicate a new electrolyte material and optimizing approach for SOFCs performance.