High-Entropy Oxides: A New Frontier in Photocatalytic CO 2 Hydrogenation.

Herein, we investigate the potential of nanostructured high-entropy oxides (HEOs) for photocatalytic CO 2 hydrogenation, a process with significant implications for environmental sustainability and energy production. Several cerium-oxide-based rare-earth HEOs with fluorite structures were prepared for UV-light driven photocatalytic CO 2 hydrogenation toward valuable fuels and petrochemical precursors. The cationic composition profoundly influences the selectivity and activity of the HEOs, where the Ce 0.2 Zr 0.2 La 0.2 Nd 0.2 Sm 0.2 O 2-δ catalyst showed outstanding CO 2 activation (14.4 mol CO kg cat -1 h -1 and 1.27 mol CH 3 OH kg cat -1 h -1 ) and high methanol and CO selectivity (7.84% CH 3 OH and 89.26% CO) under ambient conditions with 4 times better performance in comparison to pristine CeO 2 . Systematic tests showed the effect of a high-entropy system compared to midentropy oxides. XPS, in situ DRIFTS, as well as DFT calculation elucidate the synergistic impact of Ce, Zr, La, Nd, and Sm, resulting in an optimal Ce 3+ /Ce 4+ ratio. The observed formate-routed mechanism and a surface with high affinity to CO 2 reduction offer insights into the photocatalytic enhancement. While our findings lay a solid foundation, further research is needed to optimize these catalysts and expand their applications.