Curtailing the Overpotential of Li–CO₂ Batteries with Shape-Controlled Cu₂O as Cathode: Effect of Illuminating the Cathode

Li–air batteries are limited to lab-scale research owing to the uninterrupted formation of discharge products. In the case of Li–CO₂ batteries, the increase in overpotential caused by Li₂CO₃ formation results in cell death. In this study, Cu₂O crystals having three different types of shapes (i.e., cubic, octahedral, and rhombic) were synthesized to compare their catalytic activity toward CO₂ reactions. The full-cycle and long-term stability test revealed that rhombohedral Cu₂O facilitates Li₂CO₃ decomposition more efficiently than that of cubic and octahedral Cu₂O. The cycle was extended to investigate the photocatalytic activity of the rhombic Cu₂O by illuminating the cell. The repeated cycles to 1 h showed a maximum overpotential of 1.5 V, which is 0.5 V lower than that of the cell without illumination. A postmortem analysis of the cell after dividing the cycles into segments demonstrated interesting results concerning the role of light and Cu₂O during the cell cycle.