In situ TEM visualization of single atom catalysis in solid-state Na-O2 nanobatteries†

Abstract

Single-atom catalysts (SACs) exhibit high catalytic activities in many systems including metal-air batteries. However, the fundamental catalytic mechanism of SACs during the charge/discharge process is still unclear. Herein, we report a real-time imaging of the microscopic evolution of single-atom Co/reduced graphene oxide (SA-Co/rGO) in Na-O2 nanobatteries via an in situ environmental transmission electron microscope. Clearly, Na2O2 spheres were formed on the surface of the SA-Co/rGO scaffold during discharging, which can be easily decomposed during charging. In contrast, the formation and decomposition of Na2O2 on bare rGO without SACs were very sluggish. Moreover, a coin cell Na-O2 battery with an SA-Co/rGO air cathode also displays superior performance to a bare rGO cathode. DFT calculations reveal that the local coordination environment (Co + 4N) played a key role in tuning the charge density and oxidation states of the isolated Co active sites, thus activating O2 molecules and facilitating the oxygen reduction reaction/oxygen evolution reaction processes. This study suggests that SA-Co/rGO may be a promising catalyst for enhancing the performance of Na-O2 batteries.