Curtailing the Overpotential of Li–CO 2 Batteries with Shape‐Controlled Cu 2 O 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–CO 2 batteries, the increase in overpotential caused by Li 2 CO 3 formation results in cell death. In this study, Cu 2 O crystals having three different types of shapes (i.e., cubic, octahedral, and rhombic) were synthesized to compare their catalytic activity toward CO 2 reactions. The full‐cycle and long‐term stability test revealed that rhombohedral Cu 2 O facilitates Li 2 CO 3 decomposition more efficiently than that of cubic and octahedral Cu 2 O. The cycle was extended to investigate the photocatalytic activity of the rhombic Cu 2 O 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 Cu 2 O during the cell cycle.