Engineering Asymmetric Bimetallic CoM (M = Ni, Fe, Mn, Cu) Nanoparticles Encapsulated in Freestanding Wood-Derived Carbon Electrodes for Enhanced ORR Kinetics in Zinc-Air Batteries

The electrochemical reduction of oxygen is pivotal for advancing emerging energy technologies. Precise control over morphology and electronic structure is essential for enhancing catalytic activity and stability in the oxygen reduction reaction (ORR). In this study, a freestanding carbon electrode is developed by in-situ growth of carbon nanotube (CNT)-encapsulated bimetallic CoM (M = Ni, Fe, Mn, Cu) nanoparticles (NPs) within a hierarchical carbonized wood matrix (CoM@NWCC). The hierarchically porous architecture of the electrode promotes efficient mass transfer during the ORR. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analyses revealed that incorporating metals such as Ni, Fe, Mn, and Cu modulates the electronic structure of Co, specifically adjusting the distance between the d-band center (E_d) and the Fermi level (E_F), thus optimizing ORR kinetics. Among these, CoNi@NWCC, with its asymmetric electronic configuration, achieves an optimal balance between OH^* and OOH^* adsorption, significantly enhancing catalytic performance. This study demonstrates the potential of band structure engineering to precisely tailor catalyst properties, offering a cost-effective and high-performance solution for zinc-air batteries (ZABs) suitable for large-scale deployment.