Pr/Ba cation-disordered perovskite Pr2/3Ba1/3CoO3-δ as a new bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions

Electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) play an important role in renewable energy source technologies, typically including metal-air batteries, fuel cells and water splitting devices. Therefore, the development of bifunctional catalysts for OER and ORR is of great importance to enhance the performance of these devices. Herein, we present a Pr/Ba cation-disordered perovskite Pr2/3Ba1/3CoO3-delta, as a novel bifunctional catalyst for OER and ORR. Here delta is the content of oxygen vacancies. Rietveld refinement of the X-ray powder diffraction data of Pr2/3Ba1/3CoO2.98 was successfully performed by a single phase with an orthorhombic Pnma Pr/Ba cation-disordered perovskite-type structure. The bond valence sum of Co cation, 3.11 and thermogravimetric measurements suggested the coexistence of Co3+, Co4+, Pr3+ and Pr4+ cations in the bulk Pr2/3Ba1/3CoO2.98. The X-ray photoemission spectroscopy of Pr2/3Ba1/3CoO2.98 indicated the coexistence of these four cations at the sample surface, which would improve the electrocatalysis. The electrical conductivity sigma of Pr/Ba cation-disordered perovskite Pr2/3Ba1/3CoO3-delta was higher than that of Pr/Ba cation-ordered layered perovskite PrBaCo2O6-delta. The sigma of Pr2/3Ba1/3CoO3-delta and PrBaCo2O6-delta decreased with an increase of temperature. The concentration of oxygen vacancies delta of Pr2/3Ba1/3CoO3-delta increased with increasing temperature. Electrochemical measurements of the Pr/Ba cation-disordered perovskite Pr2/3Ba1/3CoO2.98 indicated higher OER and ORR catalytic activities, compared to the Pr/Ba cation-ordered layered perovskite PrBaCo2O6-delta. The Pr2/3Ba1/3CoO2.98 exhibited higher bifunctional electrocatalytic activities compared with many bifunctional catalysts in the literature. These results highlight the Pr/Ba cation-disordered perovskite-type Pr2/3Ba1/3CoO3-delta as a promising bifunctional catalyst for renewable energy applications. (C) 2018 The Ceramic Society of Japan. All rights reserved.