Bifunctional electrocatalysts for Zn-air batteries: A comprehensive review of design optimization and in-situ characterization

Rechargeable Zinc-Air Batteries (ZABs) stand out for their superior energy density, safety, cost-effectiveness, and environmental sustainability, making them a promising energy storage solution. Their performance depends on the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air electrode but is hindered by sluggish kinetics, limited bifunctionality, precious metal dependence, and corrosion. This review explores cutting-edge bifunctional electrocatalysts, focusing on strategies that enhance ORR and OER activity. It critically examines ZAB fundamentals, reaction mechanisms, and innovations in catalyst design-optimizing micro/nanoarchitectures, electronic structures, binding energies, and surface properties to improve activity, selectivity, and durability. A detailed analysis of electronic, geometric, and synergistic effects at a microscopic scale sheds light on catalytic performance enhancement. In situ characterization techniques are emphasized to unravel electrode-electrolyte interfacial dynamics, surface reconstruction, and mechanistic pathways. Finally, key challenges and future research directions are outlined, driving the next generation of high-performance ZABs.