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

Single-atom catalysts (SACs) exhibit high catalytic activities in many systems including metal-air batteries. However, the fundamental catalytic mechanism of SACs during charge/discharge process are still unclear. Herein, we report a real time imaging of the microscopic evolution of the single-atom Co/reduced graphene oxide (SA-Co/rGO) in Na-O2 nanobatteries via in situ environmental transmission electron microscope. Clearly, Na2O2 spheres were formed on the surface of SA-Co/rGO scaffold during discharge, which can be easily decomposed during charge. In contrast, the formation and decomposition of Na2O2 on bare rGO without SACs were very sluggish. Moreover, coin cell Na-O2 battery with SA-Co/rGO air cathode also displays superior performance than bare rGO cathode. DFT calculations reveal that significant electron transfer occurs between O2 and single atom Co, and isolated Co species can adopt a range of local coordination environments and oxidation states, 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.