Semiconducting Metal–Organic Polymer Nanosheets for a Photoinvolved Li–O2 Battery under Visible Light

Abstract

Li–O 2 batteries are considered the ultimate energy storage technology for their potential to store large amounts of electrical energy in a cost-effective and simple platform. Large overpotentials for the formation and oxidation of Li 2 O 2 during discharging and charging have thus far confined this technology to a scientific curiosity. Herein, we consider the role of catalytic intervention in the reversibility of the cathode reactions and find that semiconducting metal–organic polymer nanosheets composed of cobalt-tetramino-benzoquinone (Co-TABQ) function as a bifunctional catalyst that facilitates the kinetics of the cathode reactions under visible light. Upon discharging, we report that O 2 is first adsorbed on the Co atoms of Co-TABQ and accepts electrons under illumination from the d z 2 and d xz orbitals of Co atoms in the π 2p * orbitals, which facilitates reduction to LiO 2 . The LiO 2 is further shown to undergo a second reduction to the discharge product of Li 2 O 2 . In the reverse charge, the holes generated in the d z 2 orbitals of Co are mobilized under the action of the applied voltage to enable the fast decomposition of Li 2 O 2 to O 2 and Li + . Under illumination, the Li–O 2 battery exhibits respective discharge and charge voltages of 3.12 and 3.32 V for a round-trip efficiency of 94.0%. Our findings imply that the orbital interaction of metal ions with ligands in Co-TABQ nanosheets dictates the light harvesting and oxygen electrocatalysis for the Li–O 2 battery.