Metallic CuCo2S4 nanosheets of atomic thickness as efficient bifunctional electrocatalysts for portable, flexible Zn-air batteries

Abstract

Optimized catalysts show great potential for renewable energy storage and conversion. Herein, we report metallic CuCo₂S₄ nanosheets (NSs) of atomic thickness as efficient bifunctional electrocatalysts for use in portable, flexible Zn-air batteries. The metallic CuCo₂S₄ NSs of atomic thickness with 4-atom-thick to 6-atom-thick layers are confirmed by temperature-dependent electrical resistance measurements and atomic force microscopy. Furthermore, extended X-ray absorption fine structure spectroscopy confirms that CuCo₂S₄ NSs with sulfur vacancies can further increase the OER activity. Due to high electrical conductivity and ultrathin nanosheet structure with abundant defects, CuCo₂S₄ NSs exhibit excellent reversible oxygen catalytic performance with an overpotential of 287 mV (at j = 10 mA cm⁻²) for the oxygen evolution reaction (OER) and an onset potential of 0.90 V for the oxygen reduction reaction (ORR). Additionally, the portable, flexible Zn-air battery using CuCo₂S₄ NSs as the air-cathode displays a high open circuit voltage and strong rechargeable capacity for 18 h. The present study highlights the importance of designing metallic catalysts having atomic thickness with surface defects for highly efficient and stable renewable energy storage and conversion.