Bi-functionality of samarium- and praseodymium-based perovskite catalysts for oxygen reduction and oxygen evolution reactions in alkaline medium

Abstract

The present study ellucidates bi-functional catalytic activity of the graphene-supported praseodymium (PrNixCo1-xO3-δ) and samarium (SmNixCo1-xO3-δ) perovskites towards oxygen evolution and oxygen reduction reactions in alkaline solutions. The perovskites with varied Ni and Co content (of x = 0.1, 0.5, and 0.9) were synthesized via sol-gel glycine-nitrite combustion followed by heat-treated at 700, 900 and 1200 °C. The cubic perovskite phase of PrNixCo1-xO3-δ was stabilized at x = 0.1, 0.5 in the entire temperature range (of 700 °C–1200 °C), while the perovskite phase of SmNixCo1-xO3-δ (x = 0.1, 0.5) was observed only at lower temperatures (of 700 and 900 °C). Consequently, changes in structural properties resulted in superior oxygen evolution reaction (OER) electrochemical activity in comparison to the state-of-the-art IrO2. Among the Sm-based perovskites, SmNi0.1Co0.9O3-δ (700 °C) demonstrated OER mass activity of 495 mA/mg and the highest oxygen reduction reaction (ORR) activity of 95 mA/cm2·mg. For Pr-based perovskites, the highest electrocatalytic activity toward OER and ORR was observed for PrNi0.1Co0.9O3-δ (900 °C) resulting in 60 mA/mg for ORR and 680 mA/mg for OER which is 50% higher than the mass activity of the state-of-the-art IrO2 catalyst. The overall performance of the composites is discussed in terms of graphene support interactions, Co and Ni redox processes, relative concentration of oxygen-vacancy sites and OER/ORR bi-functionality.