Medium-entropy perovskite Pr0.4Ba0.2Ca0.2La0.2Co0.2Fe0.8O3 as a promising bifunctional electrocatalyst for electrochemical energy conversion device.

[Display omitted] • A novel medium-entropy perovskite is prepared and used as semiconductors. • (R-)PBCLCF enhances electrochemical oxidation and reduction activity. • Co nanocatalysts are in situ exsolved from the perovskite oxides. • Redox kinetics of medium-entropy perovskite for HOR and ORR are studied. • The single cell with (R-)PBCLCF showcases remarkable reversible performance. Reversible solid oxide cells (R-SOCs) are considered to be a promising energy conversion device that can achieve efficient conversion between fuel and electrical energy. However, there are still significant challenges in developing a promising bifunctional electrocatalyst as an electrode material for R-SOC devices. Here, a medium-entropy perovskite Pr 0.4 Ba 0.2 Ca 0.2 La 0.2 Co 0.2 Fe 0.8 O 3 (PBCLCF) is designed to enhance the electrochemical oxidation and reduction activity. Under hydrogen atmosphere, cobalt metals are in situ exsolved from the perovskite structure, accompanied by partial phase transformation (denoted as R-PBCLCF). Characterizations show that PBCLCF and R-PBCLCF can increase the concentration of oxygen vacancies, thereby enhancing oxygen migration ability. Combined with electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis, the medium-entropy PBCLCF exhibits better oxygen reduction reaction (ORR) activity and R-PBCLCF shows better hydrogen oxidation reaction (HOR) activity. Furthermore, the oxygen dissociation is identified as the rate-determining step (RDS) in the ORR process, whereas the HOR process is dominated by the hydrogen adsorption and dissociation. The single cell with (R-)PBCLCF showcases remarkable reversible performance. When O 2 is employed as the oxidant and H 2 as the fuel, this cell achieves a maximum power density of 468.1 mW cm−2 in solid oxide fuel cell (SOFC) mode at 700 °C. Moreover, when O 2 is employed as the oxidant and humidified H 2 (30 %H 2 O) as the fuel, the current density of the cell in solid oxide electrolysis cell (SOEC) mode is −647.3 mA cm−2 at 1.3 V and 700 °C. [ABSTRACT FROM AUTHOR]