Hydrothermal integration of carbon nanotube (CNT) into NiCo oxysulfide electrocatalysts for improved rechargeable zinc–air battery performance

Abstract

Zinc-air batteries (ZABs) represent a promising alternative energy storage solution owing to their elevated energy density, superior safety, and economic nature. This research explores a one-step hydrothermal synthesis of oxygen-incorporated, defect-rich spinel-type (Ni,Co)₃(O,S)₄₋ᵧ, facilitated by a trimetallic Co–Mn–Ni precursor system and in situ CNT integration. XRD and Raman analyses confirmed that the predominant crystal structure was the spinel-type NiCo₂S₄ phase. Nonetheless, EDS and XPS analyses indicated partial oxygen substitution within the sulfide lattice, associated with the molecular configuration of (Ni, Co)₃(O, S)₄ for the mixed spinel-type and oxygen-substituted (Ni, Co)₃S₄. Elemental studies verified that the Mn precursor failed to integrate into the compounds due to its diminished reactivity under moderate hydrothermal conditions; however, its participation in synthesis significantly enhanced catalytic activity by interfering with the precipitation step. The integration of carbon nanotubes did not influence the crystal structure but significantly enhanced electrical conductivity and interfacial charge transport. However, electrochemical evaluations revealed that CMN-S-CNT-10, which incorporated 10 mg of CNT, exhibits superior electrode performance, with a discharge power density of 126.9 mW/cm², specific capacity of 820 mAh/g_Zn, and extremely high energy density of 966 mWh/g_Zn. It exhibits remarkable stability, as evidenced by a 60-h long-term cycling test, during which the charge-discharge voltage gap increased only 0.09 V, indicating exceptional structural stability after incorporating CNTs. This research presents a distinct synthesis strategy that combines defect engineering, oxygen incorporation, and CNT integration in a single step, offering markedly enhanced electrochemical performance of rechargeable ZABs.