A Carbon-Free and Free-Standing Cathode From Mixed-Phase TiO 2 for Photo-Assisted Li-CO 2 Battery.

Li-CO 2 battery provides a new strategy to simultaneously solve the problems of energy storage and greenhouse effect. However, the severe polarization of CO 2 reduction and CO 2 evolution reaction impede the practical application. Herein, anodic TiO 2 nanotube arrays are first introduced as carbon-free and free-standing cathode for photo-assisted Li-CO 2 battery, and the photo-assisted charge and discharge mechanism is first clarified from the perspective of photocatalysis. Mixed-phase TiO 2 exhibits a long cycling life of 580 h (52 cycles) at 0.025 mA cm -2 and delivers a high discharge specific capacity of 3001 µAh cm -2 under UV illumination. The charge voltage dramatically reduces from 4.53 to 3.03 V under UV illumination. The improvement of photo-assisted Li-CO 2 battery performance relies on the synergistic effect of the hierarchical porous structure, strong UV absorption, efficient separation, and transfer of photo-generated electrons and holes at hetero-phase junction, and the facilitation of photo-generated electrons and holes on CO 2 reduction and CO 2 evolution reaction. This work can provide useful guidance for designing efficient photocathode for photo-assisted Li-CO 2 battery and other metal-air batteries.