Correlating the crystal structure and facet of indium oxides with their activities for CO₂ electroreduction

Constructing structure-function relationships is critical for the rational design and development of efficient catalysts for CO₂ electroreduction reaction (CO₂RR). In₂O₃ is well-known for its specific ability to produce formic acid. However, how the crystal phase and surface affect the CO₂RR activity is still unclear, making it difficult to further improve the intrinsic activity and screen for the most active structure. In this work, cubic and hexagonal In₂O₃ with different stable surfaces ((111) and (110) for cubic, (120) and (104) for hexagonal) are investigated for CO₂RR. Theoretical results demonstrate that the adsorption of reactants on cubic In₂O₃ is stronger than that on hexagonal In₂O₃, with the cubic (111) surface being the most active for CO₂RR. In experiments, synthesized cubic In₂O₃ nanosheets with predominantly exposed (111) surfaces exhibited a high HCOO^- Faradaic efficiency (87.5%) and HCOO^- current density (-16.7 mA cm^-2) at -0.9 V vs RHE. In addition, an aqueous Zn-CO₂ battery based on a cubic In₂O₃ cathode was assembled. Our work correlates the phases and surfaces with the CO₂RR activity, and provides a fundamental understanding of the structure-function relationship of In₂O₃, thereby contributing to further improvements in its CO₂RR activity. Moreover, the results provide a principle for the directional preparation of materials with optimal phases and surfaces for efficient electrocatalysis.