A Carbon-Free and Free-Standing Cathode From Mixed-Phase TiO2 for Photo-Assisted Li-CO2 Battery.

Li-CO2 battery provides a new strategy to simultaneously solve the problems of energy storage and greenhouse effect. However, the severe polarization of CO2 reduction and CO2 evolution reaction impede the practical application. Herein, anodic TiO2 nanotube arrays are first introduced as carbon-free and free-standing cathode for photo-assisted Li-CO2 battery, and the photo-assisted charge and discharge mechanism is first clarified from the perspective of photocatalysis. Mixed-phase TiO2 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-CO2 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 CO2 reduction and CO2 evolution reaction. This work can provide useful guidance for designing efficient photocathode for photo-assisted Li-CO2 battery and other metal-air batteries.

Insight into the Growth Mechanism of Mixed Phase CZTS and the Photocatalytic Performance.

In this work, CZTS particles with a mixed phase of wurtzite and kesterite were synthesized by the solvothermal method. The time-dependent XRD patterns, Raman spectra, SEM, and EDS analysis were employed to study the growth mechanism of CZTS. The results revealed that the formation of CZTS started from the nucleation of monoclinic Cu7S4 seeds, followed by the successive incorporation of Zn2+ and Sn4+ ions. Additionally, the diffusion of Zn2+ into Cu7S4 crystal lattice is much faster than that of Sn4+. With increasing time, CZTS undergoes a phase transformation from metastable wurtzite to steady kesterite. The morphology of CZTS tends to change from spherical-like to flower-like architecture. The mixed-phase CZTS with a bandgap of 1.5 eV exhibited strong visible light absorption, good capability for photoelectric conversion, and suitable band alignment, which makes it capable to produce H2 production and degrade RhB under simulated solar illumination.