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

Abstract

Atomic substitutions at the tetrahedral site (ATd ) could theoretically achieve an efficient optimization of the charge at the octahedral site (BOh ) through the ATd -O-BOh 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 gZn -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.