Cation-Tuning Induced d-Band Center Modulation on Co-Based Spinel Oxide for Oxygen Reduction/Evolution Reaction

Atomic substitutions at the tetrahedral site (A_Td ) could theoretically achieve an efficient optimization of the charge at the octahedral site (B_Oh ) through the A_Td -O-B_Oh interactions in the spinel oxides (AB₂ O₄ ). Despite substantial progress having been made, the precise control and adjustment of the spinel oxides are still challenging owing to the complexity of their crystal structure. In this work, we demonstrate a simple solvent method to tailor the structures of spinel oxides and use the spinel oxide composites (ACo₂ O₄ /NCNTs, A=Mn, Co, Ni, Cu, Zn) for oxygen electrocatalysis. The optimized MnCo₂ O₄ /NCNTs exhibit high activity and excellent durability for oxygen reduction/evolution reactions. Remarkably, the rechargeable liquid Zn-air battery equipped with a MnCo₂ O₄ /NCNTs cathode affords a specific capacity of 827 mAh g_Zn ^-1 with a high power density of 74.63 mW cm^-2 and no voltage degradation after 300 cycles at a high charging-discharging rate (5 mA cm^-2 ). The density functional theory (DFT) calculations reveal that the substitution could regulate the ratio of Co³⁺ /Co²⁺ and thereby lead to the modulation of the electronic structure accompanied with the movement of the d-band center. The tetrahedral and octahedral sites interact through the Mn-O-Co, and the Co³⁺ _Oh of MnCo₂ O₄ with the optimal charge structure allows a more suitable binding interaction between the active center and the oxygenated species, resulting in superior oxygen electrocatalytic performance.