Innovative Air Cathode with Ni-Doped Cobalt Sulfide in Highly Ordered Macroporous Carbon Matrix for Rechargeable...

To realize the practical application of rechargeable Zn-Air batteries (ZABs), it is imperative to develop a non-noble metal-based electrocatalyst with high electrochemical performance for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Ni-doped Co₉S₈ nanoparticles dispersed on an inverse opal-structured N, S co-doped carbon matrix (IO─Ni_xCo_9-xS₈@NSC) as a bifunctional electrocatalyst is presented. The unique 3D porous structure, arranged in an inverse opal pattern, provides a large active surface area. Also, the conductive carbon substrate ensures the homogeneous dispersion of Ni_xCo_9-xS₈ nanocrystals, preventing aggregation and increasing the exposure of active sites. The introduction of heteroatom dopants into the Co₉S₈ structure generates defect sites and enhances surface polarity, thereby improving electrocatalytic performance in alkaline solutions. Consequently, the IO─Ni_xCo_9-xS₈@NSC shows excellent bifunctional activity with a high half-wave potential of 0.926 V for ORR and a low overpotential of 289 mV at 10 mA cm^-2 for OER. Moreover, the rechargeable ZAB assembled with prepared electrocatalyst exhibits a higher specific capacity (768 mAh g_Zn ^-1), peak power density (180.2 mW cm^-2), and outstanding stability (over 160 h) compared to precious metal-based electrocatalyst.