Free‐Standing Air Cathodes Based on 3D Hierarchically Porous Carbon Membranes: Kinetic Overpotential of Continuous Macropores in Li‐O2 Batteries

Free‐standing macroporous air electrodes with enhanced interfacial contact, rapid mass transport, and tailored deposition space for large amounts of Li₂O₂ are essential for improving the rate performance of Li‐O₂ batteries. An ordered mesoporous carbon membrane with continuous macroporous channels was prepared by inversely topological transformation from ZnO nanorod array. Utilized as a free‐standing air cathode for Li‐O₂ battery, the hierarchically porous carbon membrane shows superior rate performance. However, the increased cross‐sectional area of the continuous macropores on the cathode surface leads to a kinetic overpotential with large voltage hysteresis and linear voltage variation against Butler–Volmer behavior. The kinetics were investigated based on the rate‐determining step of second electron transfer accompanied by migration of Li⁺ in solid or quasi‐solid intermediates. These discoveries shed light on the design of the air cathode for Li‐O₂ batteries with high‐rate performance.