High-Entropy Oxides: A New Frontier in Photocatalytic CO₂ Hydrogenation

Abstract

Herein, we investigate the potential of nanostructured high-entropy oxides (HEOs) for photocatalytic CO₂ 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 CO₂ hydrogenation toward valuable fuels and petrochemical precursors. The cationic composition profoundly influences the selectivity and activity of the HEOs, where the Ce_0.2Zr_0.2La_0.2Nd_0.2Sm_0.2O_2-δ catalyst showed outstanding CO₂ activation (14.4 mol_CO kg_cat^-1 h^-1 and 1.27 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>mol</mml:mi><mml:mrow><mml:msub><mml:mrow><mml:mi>CH</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:mi>OH</mml:mi></mml:mrow></mml:msub></mml:math> kg_cat^-1 h^-1) and high methanol and CO selectivity (7.84% CH₃OH and 89.26% CO) under ambient conditions with 4 times better performance in comparison to pristine CeO₂. Systematic tests showed the effect of a high-entropy system compared to midentropy oxides. XPS, <i>in situ</i> DRIFTS, as well as DFT calculation elucidate the synergistic impact of Ce, Zr, La, Nd, and Sm, resulting in an optimal Ce³⁺/Ce⁴⁺ ratio. The observed formate-routed mechanism and a surface with high affinity to CO₂ 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.