Three-Dimensional-Order Macroporous AB₂O₄ Spinels (A, B =Co and Mn) as Electrodes in Zn-Air Batteries

In this work, atomically substituted three-dimensionally ordered macroporous (3DOM) spinels based on Co and Mn (MnCo₂O₄ and CoMn₂O₄) were synthetized and used as cathodic electrocatalysts in a primary Zn-air battery. Scanning/transmission electron microscopy images show a 3DOM structure for both materials. Skeleton sizes of 114.4 and 140.8 nm and surface areas of 65.3 and 74.6 m² g^-1 were found for MnCo₂O₄ and CoMn₂O₄, respectively. The increase in surface area and higher presence of Mn³⁺ and Mn⁴⁺ species in the CoMn₂O₄ 3DOM material improved battery performance with a maximum power density of 101.6 mW cm^-2 and a specific capacity of 1440 mA h g^-1, which shows the highest battery performance reported to date using similar spinel materials. The stability performance of the electrocatalyst was evaluated in half-cell and battery cell systems, showing the higher durability of CoMn₂O₄, which was related to its better capability to perform the electrocatalytic process as adsorption, electron transfer, and desorption. It was found through density functional theory calculations that the CoMn₂O₄ spinel has a higher density of states in the Fermi level vicinity and better conductivity. Finally, the unique shape of 3DOM spinels promoted a high interaction between electroactive species and catalytic sites, making them suitable for oxygen reduction reaction applications.