The Role of the A-Site Cation on the Bifunctional Electrocatalytic Activities of Ln0.5Sr0.5CoO3-δ (Ln = La, Pr and Sm) for Rechargeable Zinc-Air Batteries

Developing efficient bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is crucial for the large-scale application of rechargeable zinc-air batteries. Perovskite oxides are attractive candidates as bifunctional electrocatalysts. Herein, Ln(0.5)Sr(0.5)CoO(3-delta) (Ln = La, Pr and Sm) was prepared by the sol-gel method and evaluated as bifunctional electrocatalysts for both ORR and OER. Compare with La0.5Sr0.5CoO3-delta (LSC) and Sm0.5Sr0.5CoO3-delta (SSC), Pr0.5Sr0.5CoO3-delta (PSC) demonstrated the enhanced catalytic activity towards ORR with the limiting current density of 4.19 mA cm(-2) at 0.40 V vs. RHE and OER with the potential of 1.75 V vs. RHE at 10 mA cm(-2) as well as the Tafel slope of 105 mV dec(-1). The higher Co3+/Co2+ ratio in PSC played an essential part in boosting the bifunctional electrocatalytic activities for ORR and OER. For demonstration, rechargeable zinc-air batteries with PSC as the air electrode displayed the maximum power density of 72 mW cm(-2), the low charge-discharge voltage gap (1.01 V) at 10 mA cm(-2) over 80 cycles and outstanding cycling stability. This work highlights the importance of A-site cations of the perovskite oxide as a valid strategy to improve ORR and OER activities.