Co/Co9S8 nanoparticles coupled with N,S-doped graphene-based mixed-dimensional heterostructures as bifunctional electrocatalysts for the overall oxygen electrode

Abstract

The design and preparation of highly efficient and durable electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is essential due to their applications in many green energy conversion devices, such as fuel cells and rechargeable metal–air batteries. Herein, we report a Co/Co₉S₈ composite catalyst, which is coupled with reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) via a combined hydrothermal reaction with a calcination method. Benefiting from the unique porous scaffold structures and synergistic interactions between rGO/MWCNT and Co/Co₉S₈, the electrocatalyst (Co/Co₉S₈/rGO/MWCNT-800) exhibits high electrochemical activity for the ORR, showing a four-electron oxygen reduction pathway with an onset potential of 0.946 V (vs. RHE) in alkaline medium. Meanwhile, the electrocatalyst shows high electrochemical stability, excellent selectivity and methanol tolerance over the commercial Pt/C. It also exhibits good overall oxygen electrode activity (ΔE = E_OER,10 − E_ORR,1/2 of 890 mV). The present work highlights a potential general strategy for developing carbon-based transition metal sulfide nanocomposites as cathodes with better performance in the ORR/OER.