Tuning polyoxometalate composites with carbonaceous materials towards oxygen bifunctional activity

Abstract

Oxygen electrochemistry plays an imperative role in renewable energy systems. Development of non-precious metals and efficient bifunctional catalysts for the oxygen reduction reaction and oxygen evolution reaction (ORR & OER) is highly demanded for metal–air batteries. Herein, a conjugate of tetra-cobalt sandwich polyoxometalate [Co₄(H₂O)₂(PW₉O₃₄)₂]¹⁰⁻ (CoPOM) and polyvinyl butyl imidazolium (PVIM) (PVIM–CoPOM) supported on carbonaceous materials was explored as an oxygen bifunctional catalyst in alkaline media. The PVIM–CoPOM/NCNT composite is highly active towards ORR and OER. The novel composite exhibits a low overpotential (η_j10) of 0.28 V vs. RHE for OER, outperforming the state-of-the-art RuO₂ catalyst (0.35 V), and a comparable ORR activity to Pt/C with similar overall oxygen electrode activity to the benchmark precious metal catalyst. A conventional Zn–air battery with the PVIM–CoPOM/NCNT air cathode shows high energy density and a low charge–discharge potential gap.