3D architecture double perovskite NdBa0.5Sr0.5Co1.5Fe0.5O5+δ embedded hollow-net Co3O4 bifunctional electrocatalysts coupled with N-doped CNT and reduced graphene oxide for oxygen electrode reactions

Double perovskites have received great attention as low-cost, highly active, and stable bifunctional electrocatalysts in electrochemical water electrolysis. However, perovskite-based catalysts still have limitations in performances due to their low surface area and electrical conductivity. Herein, double perovskite (NdBa0.5Sr0.5Co1.5Fe0.5O5+δ, NBSCF) is synthesized and embedded into porous, hollow nanostructured Co3O4, showing excellent activity for OER. Synergistic effect between hollow-net Co3O4 and NBSCF is demonstrated by considerably increased BET surface area (1.2 → 65.1 m2‧g−1) and high ratio of multivalent Co oxidation state (Co3+/Co2+ and Co3+/Co4+), leading to high performance of Co3O4/NBSCF for OER and ORR. Furthermore, hybridization of Co3O4/NBSCF compound in 3D architectures with conductive polyaniline and N-doped carbon nanotube/reduced graphene oxides (NCNT/NrGO) further boosts oxygen electrode activity (0.80 V) in alkaline media because of improved electrical conductivity and mass transport of oxygen species. In particular, NCNT/NrGO-Co3O4/NBSCF-PANI (NNCNP) hybrid catalysts show 0.80 V at near half-wave potential (−3 mA‧cm−2) and 1.60 V at 10 mA‧cm−2 for ORR and OER, respectively, indicating excellent intrinsic OER/ORR kinetics of NNCNP. In addition, after 1,000th voltammetric cycle testing for OER and 10,000th cycle testing for ORR, the least performance decay is observed among synthesized catalysts, demonstrating that NNCNP is an efficient bifunctional electrocatalyst for overall water splitting.