Unveiling the key factor for the phase reconstruction and exsolved metallic particle distribution in perovskites

Abstract

The exsolution of transition metals in perovskite oxides has been actively researched for intelligent catalyst design in energy-related applications. To significantly increase the amount of exsolved particles, the complete phase reconstruction from simple perovskite to Ruddlesden-Popper (R-P) perovskite is greatly desirable. However, a comprehensive understanding of key parameters affecting the phase reconstruction to R-P perovskite is still unexplored. Herein, the oxygen vacancy formation energies (Evf-O) from PrO and TO2 in Pr0.5(Ba/Sr)0.5TO3-δ (T = Mn, Fe, Co, and Ni) are proposed as the important factor in determining the type of phase reconstruction in perovskites. Furthermore, using in-situ temperature & environment-controlled X-ray diffraction measurements, we mapped out the phase diagram and found the optimum ‘x’ range required for the complete phase reconstruction to R-P perovskite (x ≥ 0.3) in Pr0.5Ba0.5-xSrxFeO3-δ (PBSF) system. Among PBSF, the (Pr0.5Ba0.2Sr0.3)2FeO4+δ – Fe metal (R-PBSF30) has the smallest size of exsolved Fe metal particles when the phase reconstruction occurs from simple perovskite under reducing condition. The exsolved nano-Fe metal particles exhibited high particle density and are well-distributed on the perovskite surface, showing great catalytic activity in fuel cell mode (1.23 W cm-2 at 800 oC) and high syngas production by co-electrolysis of CO2 and H2O (–1.62 A cm-2 at 1.5 V, 800 oC).