Multi-stability modulating of alkaline-earth metal doped LaCoO3 for rechargeable Zn-air batteries

Abstract

• Alkaline earth mental doped LaCoO 3 (Be, Mg, Ca, Sr, and Ba) with controlled Co 3+ electron spin state and Co-O covalency band. • 2.5 at.% Ca doped LaCoO 3 exhibits remarkable bifunctional ORR/OER stability without any deterioration after multiple electrocatalytic cycling operation. • Doping Ca atoms coupling with oxygen vacancy significantly decreases the energy barrier of LaCoO 3 with the lower theoretical overpotential (0.49 V). • The corresponding rechargeable ZnABs exhibit excellent discharging/charging durability (220 h) and higher specific capacity (793.0 mAh g −1 ). The realization of prominent and permanent electrocatalytic oxygen reduction/evolution reaction activities in perovskites is an intensively demanding and daunting challenge. Herein, a series of LaCoO 3 doped by alkaline earth metal (Ca) with controlled Co 3+ electron spin state and created oxygen vacancies are designed to enhance their super stable bifunctional electrocatalytic activities. Experiments demonstrate that Ca-doped LaCoO 3 exhibits remarkable bifunctional ORR/OER activity with lower potential gap (ΔE=0.89 V), excellent multi-durability in onset overpotential and current density without any deterioration after long-term OER/ORR cycling operations under the same conditions, which is beneficial for the discharging/charging durability (220 h) of rechargeable Zn-air batteries. Density functional theory calculations demonstrate that the intermediate spin state stabilized Co 3+ active sites near oxygen vacancies sufficiently optimize the binding strength between oxygen-related intermediates and the Ca-doped LaCoO 3 surface, simultaneously accelerate the surface charge transfer during electrocatalytic process, giving rise to the low theoretical overpotential (0.49 V) for the formation of OH*. This finding provides a promising strategy for substantially increasing the bifunctional electrocatalytic activity and stability of perovskite oxides.