In this study, an efficient bifunctional electrocatalyst for oxygen reduction and evolution reactions (ORR and OER) was synthetized. The catalyst comprised small-size CoMn2O4 spinel on multi-walled carbon nanotubes (CNT), interface-engineered to introduce defects and nitrogen heteroatoms, and was compared with CoMn2O4 on Vulcan carbon without surface modification. X-ray diffraction analysis confirmed the tetragonal structure with similar crystallite sizes (10–12 nm) on both carbon supports, which was validated by transmission electron microscopy (TEM). The spinel-based catalysts exhibited good activity for oxygen reactions, exhibiting a 4e − pathway for ORR on both supports, with a slightly improved in onset potentials for the supported-on N-CNT, additionally, CoMn2O4/N-CNT demonstrated superior durability, retaining 90–100% of initial current for ORR and OER, while CoMn2O4/C retained 82% and 17%. This effect on stability was corroborated by the Zinc-air battery tests, since, the CoMn2O4/N-CNT was the only catalyst that completed the 260 cycles (around of 72 h), even, the noble catalysts were only able to complete 190 cycles. Additionally, the nanocomposite demonstrated an impressive 910 mA·h/g specific capacity at 5 mA cm−2 discharge rate, surpassing CoMn2O4/C (400 mA·h/g). These findings highlight the potential of the interface-engineered nanomaterial for energy storage, offering a substantial cycling capacity boost.