Oxygen-Vacancy-Reinforced Titanium Dioxide@Graphene/Carbon Nanotubes n-p Heterojunction for High Rate Photo-Assisted Li-O2 Battery

Abstract

Photo-assisted Li-O 2 batteries have gained popularity due to their utilization of solar power to improve performance. However, challenges persist in synergizing the photocathode’s hierarchically porous structure with the catalytic activity of the active material. Herein, we used the direct ink writing technique to fabricate a freestanding 3D printed hierarchically porous structure cathode. Meanwhile, a p-n heterojunction is created in oxygen vacancy-rich rutile titanium dioxide/reduced graphene oxide/carbon nanotubes (Ov-TiO 2 @rGO/CNTs) through a freeze-drying and annealing strategy. The titanium dioxide contains abundant oxygen vacancies, which strengthen the electrostatic attraction with the graphene oxide and create unsaturated coordination sites. Upon annealing, the graphene oxide removes the oxygenated functional group and bonds covalently with O V -TiO 2 . The interaction between Ov-TiO 2 and rGO through Ti-C bonds creates a channel that facilitates charge transfer, thereby enhancing the rate capability and cyclability of the battery. Even at a high current density of 0.5 mA cm −2 under illumination, the 3D printed Ov-TiO 2 @rGO/CNTs photocathode delivers a discharge capacity of 17.43 mAh cm −2 and stable cycling for 400 h. The excellent performance is attributed to the efficient photocatalytic catalytic sites, fast electronic/ionic pathways, and Li 2 O 2 storage space of the freestanding photocathode. This design strategy shows promise for future energy applications.