B-site doping effects of NdBa0.75Ca0.25Co2O5+δ double perovskite catalysts for oxygen evolution and reduction reactions

Abstract

As bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), we introduce an economical, particularly active, stable, and completely noble-metal-free catalyst based on CaO-doped NdBaCo₂O_5+δ with the aim of exploiting its high catalytic activity for the oxygen electrode. Further, the electrochemical performances of the NdBa_0.75Ca_0.25Co₂O_5+δ catalyst are improved by doping transition-metal oxides (Fe²⁺, Ni²⁺, Cu²⁺, and Mn²⁺) into the B-sites of double perovskite oxides, facilitating the movement of electrons and oxygen-ions through oxygen vacancies. Among these, NdBa_0.75Ca_0.25Co_1.5Fe_0.5O_5+δ (NBCCFe) shows the highest electrocatalytic oxygen electrode activity for the OER and ORR, and NBCCFe thus is hybridized with nitrogen-reduced graphene oxide (N-rGO) to further improve its catalytic activity with excellent durability. Hybridization of NBCCFe with N-rGO further boosts bifunctional oxygen electrode activity (0.761 V) with better durability, which surpasses those of Pt/C (0.815 V) and Ir/C (0.768 V) catalysts. A rechargeable lithium–air battery assembled with the NBCCFe/N-rGO catalyst exhibits remarkably improved discharge capacity, reduced charge overpotential and an extended cycle life, corroborating the excellent bifunctional catalytic activity of NBCCFe/N-rGO. The NBCCFe/N-rGO catalyst also displays the most improved polarization during both discharge and charge, further confirming the highest bifunctional catalytic activity of NBCCFe/N-rGO.