Hierarchical Carbon Nanocage-Enabled Electron Buffering to Indium Oxide for Efficient CO₂ Hydrogenation to Methanol

The hydrogenation of CO₂ to methanol over In₂O₃-based catalysts is highly sensitive to the concentration of surface oxygen vacancies (O_v). While increasing the O_v concentration can enhance the catalytic performance, it also increases the risk of over-reduction during CO₂ hydrogenation, leading to a trade-off between activity and stability. Here, we demonstrate that hierarchical carbon nanocages (hCNCs) act as effective "electron buffering agents" for In₂O₃, mitigating this trade-off and thereby enhancing the methanol yield, with nitrogen doping of hCNCs further amplifying this effect. Detailed investigations reveal that hCNCs donate electrons to O_v-deficient In₂O₃ to promote O_v formation, while also extracting electrons from O_v-rich In₂O_3-<i>x</i>, preventing over-reduction to metallic In. As a result, In₂O₃ supported on hCNCs maintains a consistently high O_v concentration, enhancing both the catalytic activity and stability. This work highlights the promising potential of hCNCs in the hydrogenation of CO₂ to methanol and stimulates interest in their exploitation for other redox catalytic processes.