Advances in waste-derived nano-catalysts for zinc–air batteries: Enhancing OER efficiency and sustainability in energy storage

Zinc–air batteries (ZABs) are increasingly recognized as advanced energy storage systems due to their elevated energy density, inherent safety characteristics, and reliance on materials that are abundant in the earth's crust. Nevertheless, their extensive implementation is impeded by the kinetic limitations associated with the oxygen evolution reaction (OER), which is commonly facilitated by rare and costly noble metals such as platinum and iridium. To address this obstacle, recent advancements have been focused on the development of economical and highly efficient electrocatalysts sourced from industrial, electronic, and biomass waste materials. This review provides a comprehensive examination of the synthesis methodologies, structural optimization techniques, and electrochemical performance of nano-catalysts derived from waste, specifically designed for ZAB applications. These catalysts, produced through processes including pyrolysis, hydrothermal synthesis, and the incorporation of heteroatoms, have exhibited a reduction of up to 50 mV in OER overpotential, an enhancement in battery cycle longevity exceeding 40 %, and a decrease in production expenses of up to 50–70 % compared to noble-metal-based alternatives. Lifecycle assessment (LCA) findings reveal a 35 % reduction in CO₂ emissions and a 90 % recyclability rate, which bolsters their sustainability credentials. Furthermore, the incorporation of artificial intelligence (AI) for optimizing catalysts and the application of neutral electrolytes (e.g., ZnSO₄) to enhance system compatibility are examined as prospective avenues for further exploration. The review concludes with an analysis of scalability challenges, regulatory considerations, and potential future research directions. By integrating waste valorization strategies with principles of the circular economy and objectives for green energy, this work highlights the transformative potential of waste-derived catalysts in decarbonizing and democratizing energy storage technologies.