In situ growth of vertically aligned FeCoOOH-nanosheets/nanoflowers on Fe, N co-doped 3D-porous carbon as efficient bifunctional electrocatalysts for rechargeable zinc–O2 batteries

Abstract

Rational design of cost effective, highly active and robust bifunctional electrocatalysts for the oxygen evolution and reduction reactions (OER/ORR) is crucial for rechargeable metal–air batteries. Encapsulating and supporting transition-metal nanomaterials for the OER in and on porous carbon-based catalysts for the ORR are the two main routes for the construction of bifunctional OER/ORR catalysts. However, none of the above two strategies has achieved simultaneous maximum exposure of OER and ORR active sites, while maintaining high catalytic stability. In this study, it is demonstrated that transition-metal oxide nanosheets/nanoflowers in situ vertically grown on Fe, N co-doped 3D-porous carbon (FeCoOOH-NS/NF⊥3D-FeNC) can achieve the simultaneous maximum exposure of both OER and ORR active centers. Benefiting from this unique vertical growth structure, the FeCoOOH-NF⊥3D-FeNC catalyst demonstrates an outstanding half wave potential of 855 mV for the ORR and a low overpotential of only 230 mV at a current density of 10 mA cm⁻² for the OER, ranking it among the most active non-noble metal bifunctional OER/ORR catalysts reported in the literature. Remarkably, when being employed as an O₂ electrode in primary and rechargeable zinc–O₂ batteries, FeCoOOH-NF⊥3D-FeNC presents a higher power density of 220 mW cm⁻² than that of Pt/C + IrO₂ (190 mW cm⁻²) as well as excellent cycling durability.